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Arterial baroreceptor control of the circulation during forced dives in ducks (Anas Platyrhynchos var.) Smith, Frank Melvin 1987

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ARTERIAL BARORCEPTOR CONTROL OF THE CIRCULATION DURING FORCED DIVES IN DUCKS (ANAS PLATYRHYNCHOS v a r . ) by FRANK M. SMITH B. Sc., The U n i v e r s i t y o f B r i t i s h Columbia, 1976 M. Sc., The U n i v e r s i t y o f B r i t i s h Columbia, 1980  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES Department  o f Zoology  We a c c e p t t h i s t h e s i s as conforming to the required  standard  THE UNIVERSITY OF BRITISH COLUMBIA September 1987  © F r a n k M., Smith  I987  In  presenting  degree  this  at the  of  department publication  of  partial  British Columbia,  thesis by  for scholarly  his  this thesis  or  her  of  the  I agree  I further agree  purposes  may  representatives.  It  be is  requirements  for  an  Department of The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3  advanced  that the Library shall  make it  that permission  for extensive  granted  head  by the  understood  that  for financial gain shall not be allowed without  permission.  DE-6(3/81)  fulfilment  for reference and study.  this or  in  University of  freely available copying  thesis  of  my  copying  or  my written  ii ABSTRACT  When d a b b l i n g d u c k s a r e i n v o l u n t a r i l y arterial  v a s o c o n s t r i c t i o n produces a l a r g e i n c r e a s e i n t h e  peripheral decrease  resistance t o blood  i n output  i s maintained. pressure,  flow which i s balanced  of t h e heart,  Arterial  and a r t e r i a l  baroreceptors  and p r o v i d e t h e a f f e r e n t  baroreflex  f o r pressure  responses,  regulation.  diving,  involved i n the diving t o be  important to diving.  s t u d y was t o i n v e s t i g a t e t h e r o l e  baroreceptors  i n maintaining blood pressure  and i n t h e i n i t i a t i o n  blood  limbs of  of t h e c a r d i o v a s c u l a r responses  purpose of t h i s  pressure  systemic  The e f f e c t o r  and t h e b a r o r e c e p t o r s a r e l i k e l y  in the integration  arterial  sense  blood  by a  information t o the  t h e b a r o r e f l e x a r e t h e same as t h o s e  The  submerged,  of the during  and m a i n t e n a n c e o f t h e d i v i n g  responses. Baroreceptor v a r i o u s times  f u n c t i o n was s t u d i e d b y d i v i n g  after barodenervation,  and by  ducks a t  electrically  stimulating the central  end o f one b a r o r e c e p t o r n e r v e i n  baroreceptor-denervated  animals  baroreceptor  input before  Intact baroreceptor the  t o simulate a controlled  and d u r i n g  submersion.  i n n e r v a t i o n was n o t n e c e s s a r y f o r  development of p e r i p h e r a l v a s o c o n s t r i c t i o n ,  the b a r o r e c e p t o r s m o d i f i e d t h e c a r d i a c response  b u t l o s s of t o submersion  by i m p a i r i n g the v a g a l l y mediated b r a d y c a r d i a . e f f e c t of b a r o r e c e p t o r  nerve s t i m u l a t i o n on  r e s i s t a n c e d u r i n g d i v i n g , and heart  r a t e i n modulating blood  r a t e or blood  pressure  pressue.  d r i v e r e s u l t s from decreased blood  e a r l y i n the  oxygen and  i n p u t s may  the r e s u l t s of baroreflex  be at l e a s t p a r t l y  responsible  baroreflex effectiveness.  main c o n c l u s i o n  baroreceptors  increased  showed t h a t an i n t e r a c t i o n between chemoreceptor  and b a r o r e c e p t o r  The  dive.  Strong chemoreceptor  experiments t o determine the mechanism of  f o r reducing  peripheral  ineffective in altering  carbon d i o x i d e l e v e l s i n the d i v e , and  attenuation  no  the b a r o r e f l e x operated v i a the  L a t e r i n the d i v e , s t i m u l a t i o n was e i t h e r heart  There was  from t h i s work i s t h a t the  arterial  c o n t r i b u t e t o the d i v i n g responses through  modulation of h e a r t  r a t e , t o h e l p balance the f a l l  in cardiac  output a g a i n s t the baroreceptor-independent p e r i p h e r a l v a s o c o n s t r i c t i o n i n the f i r s t minute of f o r c e d  dives.  iv TABLE OF CONTENTS Abstract  i i  Table of Contents  iv  L i s t of Tables  v  L i s t of Figures  vi  Acknowledgements  viii  General Introduction Section  I.  1  C a r d i o v a s c u l a r Responses t o A o r t i c Nerve Stimulation During Diving i n Acutely B a r o d e n e r v a t e d Ducks Introduction Methods Results Discussion  Section  22 24 35 44  I I . C a r d i o v a s c u l a r Changes i n t h e T r a n s i t i o n from Acute t o Chronic Barodenervation Introduction Methods Results Discussion  Section  51 57 76 102  I I I . C a r d i o v a s c u l a r Responses t o D i v i n g i n the T r a n s i t i o n from Acute t o Chronic Barodenervation Introduction Methods Results Discussion  Section  IV. C a r d i o v a s c u l a r Responses t o A o r t i c Stimulation During Diving i n the T r a n s i t i o n from Acute t o Chronic Barodenervation  115 116 119 131 Nerve  Introduction Methods  138 143  Results Discussion  163 197  V  General  Discussion  205  Bibliography  238  Appendix  251  vi L I S T OF  T a b l e 1.  TABLES  E f f e c t s of continuous a o r t i c nerve s t i m u l a t i o n on c a r d i o v a s c u l a r v a r i a b l e s during d i v i n g i n acute barodenervates  37  T a b l e 2.  A r t e r i a l b l o o d gas t e n s i o n s and pH d u r i n g d i v i n g i n acute barodenervates  38  T a b l e 3.  E f f e c t s of i n t e r m i t t e n t s t i m u l a t i o n on c a r d i o v a s c u l a r v a r i a b l e s d u r i n g d i v i n g i n acute barodenervates  42  E f f e c t s o f i n t r a v e n o u s p h e n y l e p h r i n e on b l o o d p r e s s u r e and h e a r t r a t e b e f o r e and after barodenervation  77  T a b l e 5.  E f f e c t s o f b i l a t e r a l b a r o d e n e r v a t i o n on b l o o d g a s e s and pH d u r i n g d i v i n g  128  T a b l e 6.  E f f e c t s of b e t a - a d r e n e r g i c blockade on p r e d i v e and d i v e h e a r t r a t e i n i n t a c t and a c u t e l y b a r o d e n e r v a t e d d u c k s  130  A r t e r i a l b l o o d g a s e s and pH d u r i n g d i v i n g and r e c o v e r y i n u n i l a t e r a l and b i l a t e r a l barodenervates  175  A r t e r i a l b l o o d g a s e s and pH b e f o r e and d u r i n g oxygen d i v e s i n b a r o d e n e r v a t e d ducks  186  A r t e r i a l b l o o d g a s e s and pH d u r i n g a i r b r e a t h i n g and d u r i n g h y p o x i c h y p e r c a p n e a  193  T a b l e 4.  T a b l e 7.  T a b l e 8.  Table  9.  V l l  L I S T OF FIGURES Figure  Figure  Figure  Figure Figure  Figure  Figure  Figure  Figure Figure  Figure  1.  2.  3.  4. 5.  6.  7.  8.  9. 10.  11.  V e n t r a l view of a n t e r i o r thorax duck \  the large a r t e r i e s i n the of a female w h i t e P e k i n 26  Schematic diagram of t h e sympathetic g a n g l i o n c h a i n on t h e l e f t s i d e i n t h e p e l v i c r e g i o n o f t h e duck  70  A r t e r i a l blood pressure responses to p h e n y l e p h r i n e i n t h e same a n i m a l b e f o r e and a f t e r b i l a t e r a l b a r o d e n e r v a t i o n  79  Immediate e f f e c t s o f b i l a t e r a l b a r o d e n e r v a t i o n on c a r d i o v a s c u l a r v a r i a b l e s  82  Cardiovascular adaptations barodenervation  86  to  bilateral  E f f e c t s of sympathetic g a n g l i o n c h a i n s t i m u l a t i o n on h i n d l i m b v a s c u l a r resistance  92  Photographs of s e c t i o n s of the ischiatic a r t e r i e s f r o m a n o r m o t e n s i v e and a h y p e r t e n s i v e duck  95  R e l a t i o n s h i p between i n s i d e d i a m e t e r and w a l l c r o s s - s e c t i o n a l a r e a f o r h i n d l i m b a r t e r i e s i n i n t a c t and b a r o d e n e r v a t e d ducks  98  I n s i d e d i a m e t e r s and w a l l cross-sectional a r e a s f o r two r a n g e s o f h i n d l i m b a r t e r i e s  100  A r t e r i a l p r e s s u r e and h i n d l i m b b l o o d f l o w r e c o r d i n g s d u r i n g d i v i n g i n t h e same duck b e f o r e and a f t e r b a r o d e n e r v a t i o n  121  C a r d i o v a s c u l a r r e s p o n s e s d u r i n g d i v i n g and r e c o v e r y i n t h e t r a n s i t i o n from a c u t e t o chronic barodenervation  123 146  Figure  12.  M e d i a l view of the surrounding tissue  left aortic i n a duck  nerve  Figure  13.  Schematic view of the r e g i o n of the common c a r o t i d a r t e r y i n a d u c k  and left  158  viii Figure Figure  Figure  Figure  Figure  Figure Figure  14. 15.  16.  17.  18.  19. 20.  F i g u r e 21.  F i g u r e 22.  Figure  23.  Schematic of c a r o t i d body p e r f u s i o n apparatus  160  A r t e r i a l p r e s s u r e and h i n d l i m b b l o o d f l o w r e c o r d i n g s d u r i n g d i v i n g and a o r t i c nerve s t i m u l a t i o n i n a c u t e l y barodenervated duck  164  P r e s s u r e and f l o w r e c o r d i n g s d u r i n g d i v i n g and s t i m u l a t i o n i n c h r o n i c a l l y b a r o d e n e r v a t e d duck  167  C a r d i o v a s c u l a r r e s p o n s e s t o d i v i n g and a o r t i c nerve s t i m u l a t i o n i n the t r a n s i t i o n from acute t o c h r o n i c barodenervation  169  C a r d i a c and p e r i p h e r a l r e s i s t a n c e responses t o a o r t i c nerve s t i m u l a t i o n i n b a r o d e n e r v a t e d d u c k s b e f o r e and d u r i n g diving  181  Cardiovascular responses to a o r t i c s t i m u l a t i o n d u r i n g oxygen d i v e s .  188  nerve  Normalized blood pressure responses to a o r t i c n e r v e s t i m u l a t i o n i n n o r m o x i a and hypoxic hypercapnea  191  E f f e c t s of i s o l a t e d c a r o t i d body p e r f u s i o n w i t h v e n o u s b l o o d on a r t e r i a l p r e s s u r e response t o a o r t i c nerve s t i m u l a t i o n  195  E f f e c t o f b a r o d e n e r v a t i o n on t h e r e l a t i o n s h i p b e t w e e n mean a r t e r i a l and h e a r t r a t e a t r e s t  208  pressure  Comparison of t h e e f f e c t s of v a r i o u s m e t h o d s o f b a r o d e n e r v a t i o n on c a r d i o v a s c u l a r variables  F i g u r e A l . E l e c t r o d e s f o r s t i m u l a t i o n of the a o r t i c nerve i n ducks (Appendix)  227  left 253  ACKNOWLEDGEMENTS I am g r a t e f u l t o my s u p e r v i s o r , Dr. D a v i d R. J o n e s , f o r h i s p a t i e n c e and g u i d a n c e t h r o u g h o u t t h i s s t u d y , f o r h i s v a l u a b l e comments d u r i n g t h e p r e p a r a t i o n o f t h i s m a n u s c r i p t , and f o r h i s e f f o r t s i n s e c u r i n g me f i n a n c i a l s u p p o r t . I am i n d e b t e d t o t h e N a t i o n a l S c i e n c e s and E n g i n e e r i n g R e s e a r c h C o u n c i l o f C a n a d a and t o t h e B r i t i s h C o l u m b i a H e a r t F o u n d a t i o n f o r t h e i r s u p p o r t o f my r e s e a r c h p r o j e c t t h r o u g h g r a n t s t o Dr. J o n e s . I am g r a t e f u l t o t h e members o f my r e s e a r c h c o m m i t t e e , Dr. J . R. Ledsome, D r . W. K. M i l s o m , Dr. D. J . R a n d a l l and Dr. J . S t e e v e s f o r d i s c u s s i o n s o f my d a t a and f o r t h e i r a d v i c e d u r i n g t h e p r e p a r a t i o n o f my t h e s i s . I would a l s o l i k e t o t h a n k Dr. G. R. J . G a b b o t t f o r h i s r e n d e r i n g o f F i g u r e s 1, 2, 12, 13 and 14, and f o r d i s c u s s i o n o f my d a t a . I t h a n k Dr. W. V o g l f o r t h e u s e o f t h e e q u i p m e n t t o make t h e p h o t o g r a p h s i n F i g u r e 7. To my w i f e , S a r a h , I w i s h t o e x p r e s s my g r a t i t u d e f o r h e r h e l p and s u p p o r t t h r o u g h o u t t h i s study. I am t h a n k f u l t o t h e D e p a r t m e n t o f Z o o l o g y f o r s u p p o r t i n t h e f o r m o f T e a c h i n g A s s i s t a n t s h i p s d u r i n g my Ph. D. p r o g r a m . The e x p e r i m e n t s i n S e c t i o n I w e r e p e r f o r m e d i n c o l l a b o r a t i o n w i t h D. R. J o n e s and W. K. M i l s o m .  1  GENERAL  The  cardiovascular  submersion responses those  are which  organs,  without  the  the  oxygen.  skeletal  gut  muscle,  changes,  by  ensures  which  remain  which  buffers  thus  the  have  an  the  blood  adequate  more. is of  changes arms  pressure role  or  in  by  cannot  beds,  of  function while  as  skin,  face  of  these  during  diving,  those  organs  to  or  baroreflex,  pressure,  diving  operates  response,  and  baroreceptors,  the  to  peripheral  the  blood  it  %. ,  such  reflex,  or  reflex  80-90  nutrients  receptors,  during  redistribute  In  the  control  of  maintained  in  as  set  elevate  The b a r o s t a t i c  effector  important  fall  may  animals  which  vascular  supplies  short-term  arterial  may  pressure  perfused.  same  10  and  brain,  kidney  of  diving  integrated  output  and  in  output  peripheral  factor  arterial  which  through  a  an  and t h e  Cardiac in  of  cardiac  heart  vasoconstriction  resistance  adjustments  result  reduce  INTRODUCTION  circulation  may  during  diving. The  systemic  baroreflex,  is  the  systemic  vascular  response  to  the  walls  pressure as  of in  arterial  collective calibre  changes large the  in  central  correcting  name  for  and c a r d i a c  input  which  the  or  changes  output  sense  circulation. system  moderate  reflex,  in  the  in  occurring  from b a r o r e c e p t o r s ,  arteries,  a negative-feedback  rapidly  baroreceptor  located  arterial  displacements  of  intact blood  in  blood  The b a r o r e f l e x awake,  in  operates  animal, pressure  2  f r o m t h e c u r r e n t mean. sensory  nerve  endings  The b a r o r e c e p t o r s  themselves are  interleaved with the structural  elements of t h e a r t e r i a l  walls of the baroreceptor  zones.  When t h e v e s s e l w a l l s a r e s t r e t c h e d c i r c u m f e r e n t i a l l y , a rise  i n blood  pressure,  these  nerve  g e n e r a t i n g p o t e n t i a l s which t r i g g e r baroreceptor fibres  nerve  fibres  (Brown,  enter the brainstem  influence control  vascular tree  (Spyer,  where t h e y  1981).  at the baroreceptor  results  i n reflex  peripheral  of vaso-  and c a r d i o m o t o r responses Bert,  zones,  afferent their  neuron p o o l s  as b l o o d  flow.  effects  to a f a l l  pressure  Blood  which  rises,  and i n t h e  pressure  i s reversed  i n blood  i s thus  The d i r e c t i o n i nthe  pressure.  i n 1870, e s t a b l i s h e d t h e i m p o r t a n c e o f i n p r o l o n g i n g t h e underwater  e n d u r a n c e o f d i v e r s when he f o u n d pronounced b r a d y c a r d i a  obtained  i nthe  ultimately exert  before the disturbance.  c a r d i o v a s c u l a r adjustments  responses  These  by  An i n c r e a s e i n v e s s e l w a l l  r e s i s t a n c e t o blood  to the level  baroreflex  firing  reductions i n c a r d i a c output  restored  not.  1980).  respond  and t h e h y d r a u l i c r e s i s t a n c e o f t h e  stretch  did  impulse  on t h e v a s o m o t o r and c a r d i o m o t o r  c a r d i a c output  Paul  endings  due t o  t h a t ducks developed  a  d u r i n g f o r c e d s u b m e r s i o n and c h i c k e n s  The n e u r a l mechanisms s u b s e r v i n g t h e d i v i n g was n o t a d d r e s s e d  directly  a diving bradycardia  delimiting this  until  Huxley  i n decerebrate  (1913)  ducks,  thus  c a r d i a c r e f l e x pathway t o t h e b r a i n s t e m .  T h i s work was l a t e r  confirmed  and e x t e n d e d b y A n d e r s e n  3 (1963b), a l s o i n decerebrate  ducks.  That t h e vagus i s t h e  e f f e r e n t p a t h w a y f o r c a r d i a c r e t a r d a t i o n i n d i v i n g d u c k s was first  demonstrated by R i c h e t  (1899),  b l o c k i n g drug atropine t o prevent  who u s e d t h e c h o l i n e r g i c  bradycardia.  o b s e r v a t i o n has s i n c e been c o n f i r m e d , pharmacological  by vagotomy and  means, i n a l l o t h e r v e r t e b r a t e d i v e r s w h i c h  have been examined Some a u t h o r s  This  ( s e e B u t l e r a n d J o n e s , 1982 f o r summary).  have r e p o r t e d  a residual bradycardia  a t r o p i n i z a t i o n i n ducks ( H o l l e n b e r g  after  a n d U v n a s , 1963; F o l k o w ,  N i l s s o n and Yonce, 1967) and coypu (Folkow, L i s a n d e r and O b e r g , 1 9 7 1 ) w h i c h was e l i m i n a t e d i n d u c k s b y beta-adrenergic  b l o c k a d e (Folkow e t a l . , 1967).  engagement o f t h e s y m p a t h e t i c  sympathetic The  c a r d i a c nerves i n c o n t r o l of  t h e a v i a n h e a r t d u r i n g d i v i n g i s c o n t r o v e r s i a l , however, s i n c e t h e r e s u l t s o f Folkow e t a l . (1967) c o u l d n o t be confirmed there  by B u t l e r and Jones (1971).  On t h e o t h e r  hand,  i s no d o u b t t h a t t h e p e r i p h e r a l v a s o c o n s t r i c t i o n  accompanying submergence r e s u l t s from i n c r e a s e s i n sympathetic  v a s o c o n s t r i c t o r - f i b r etone,  pharmacological  as i n d i c a t e d by  s t u d i e s i n b i r d s ( D j o j o s u g i t o , F o l k o w and  Y o n c e , 1 9 6 9 ; K o b i n g e r a n d Oda, 1969; A n d e r s e n a n d B l i x , 1974; and  B u t l e r a n d J o n e s , 1971) a n d i n mammals ( F o l k o w e t a l . .  1971). The  s u b j e c t o f t h e a f f e r e n t pathways which e n t r a i n t h e  d i v i n g response has generated a great deal of controversy i n the years  s i n c e t h e w o r k o f B e r t a n d R i c h e t , w i t h much o f t h e  4  disagreement probably  stemming from s p e c i e s d i f f e r e n c e s .  i m p o r t a n c e of apnea i n t h e d i v i n g r e s p o n s e i n b i r d s recognized  B u t l e r and  not  l o c a t e d u n t i l A n d e r s e n ( 1 9 6 3 a , b)  J o n e s (1968) found,  i n d a b b l i n g ducks,  s t i m u l a t i o n o f r e c e p t o r s i n and c a v i t y and  internal  nasal  r e s p i r a t o r y passages of t h e head w i t h  t h a t a p n e a a l o n e was  produce b r a d y c a r d i a  and  that  around the n o s t r i l s ,  water i n i t i a t e d breath-holding.  Feigl  and  Folkow  (1963)  n o t enough, however,  to  i n d a b b l i n g d u c k s ; t h e r e must a l s o  subsequent r e d u c t i o n i n a r t e r i a l C02  was  by t h e e a r l y i n v e s t i g a t o r s , b u t t h e r e f l e x o g e n i c  z o n e f o r a p n e a was  concluded  The  o x y g e n t e n s i o n and  be  increased  t e n s i o n , s e n s e d by c h e m o r e c e p t o r s i n t h e b l o o d s t r e a m ,  the f u l l  e x p r e s s i o n of t h i s response.  B a m f o r d and  Jones  Hollenberg  denervate  and  and  by  Uvnas (1963) d e s c r i b e d e x p e r i m e n t s i n the c a r o t i d bodies  divided surgically  a possible arterial  that t h i s procedure prevented t h e y b e l i e v e d t h a t t h e y had  i n ducks  i n an a t t e m p t t o  chemoreceptor s i t e .  They f o u n d  most of t h e b r a d y c a r d i a ,  a l s o denervated  baroreceptors.  No  the authors  t e s t e d t h e i r denervates  had  confirmed  (1974).  which the t i s s u e s surrounding were l i g a t e d  T h i s was  for  i n d i c a t i o n was  but  arterial  g i v e n i n t h e i r work t h a t to confirm the  loss  of e i t h e r chemoreceptor or b a r o r e c e p t o r f u n c t i o n . Nevertheless,  l a t e r w o r k by J o n e s and  Purves  (1970)  e s t a b l i s h e d t h e r o l e of v a g a l l y i n n e r v a t e d c a r o t i d chemoreceptors i n producing  firmly body  f o r c e d - d i v e b r a d y c a r d i a i n ducks,  5  and in  this  was  heart  thus  c o n f i r m e d by  rate  due  to  during  altered  chemoreceptors, initiated and  by  narial Most  rate  as  because the to  early  during  These the  long  small  gas  the  of  the  to  the  measured  in  noted  diastolic predive; artery  in  to  that  of  the  also toe  peripheral  vasoconstriction  in  al.  must  Vasoconstriction during  c i r c u l a t i o n to  and Aakhus,  and J o n e s ,  pressure  in  Hollenberg  the  1971)  dive  and Uvnas  was  the  glottis  large of  (1942)  blood  1963;  variable  in  is  heart  pressure the  pressure  rate. during  dive  concluded off  diving. that  as  since  the  reported  these  heart  been and  Krog,  H o l l e n b e r g and Uvnas, of  from  large  (Johansen  maintenance  than  recorded  markedly during  closing  of  pressure  in  in  d i v i n g has  in  heart  appear  pressure  fall  fall  (1942) be  in  response,  maintain pressure  although  (1963)  change  a major component  seal,  f o r c i b l y - s u b m e r g e d ducks  Johansen  in  the  much s l o w e r  slowed.  Butler  the  the  of  1959;  is  breathing  and G r i n n e l l  found t h a t  I r v i n g et  on  measured  portions  in  fall  by p e r i p h e r a l  of  diving  is  decreased  results,  documented  the  and  rate  was  From t h e s e  the  of  have  periods  the  sensed  receptors  focused  easily  face  they  The  d a b b l i n g ducks  cessation  Scholander  the  (1972).  beak.  extent  workers  in  tensions,  reporting that,  well  authors  of  Irving,  diving,  occurred a  is  first  maintained  Sorensen  submersion  diving studies  index  rate  the  blood  and  trigeminally-mediated  response. be  forced  subsequent  region  an  Holm  1963;  blood  experiments.  increased  pressure  in  6 s h o r t d i v e s o f 1-2 m i n , w h i l e B u t l e r a n d J o n e s J o h a n s e n and A a k h u s ( 1 9 6 3 ) r e p o r t e d p r e s s u r e o f t h e same l e n g t h .  E l i a s s e n (1960),  change i n e i t h e r s y s t e m i c diving birds. pressure  ( 1 9 7 1 ) and  drops i n d i v e s  h o w e v e r , r e p o r t e d no  o r pulmonary a r t e r i a l p r e s s u r e s i n  McKean ( 1 9 8 2 ) a l s o r e p o r t e d m a i n t a i n e d  i n f o r c e - d i v e d b e a v e r and n u t r i a ,  t r a c e of abdominal a o r t i c blood pressure t h e r e was no c h a n g e i n p r e s s u r e  blood  a n d showed i n one  during a dive that  d u r i n g an e x t e n d e d  diastole  o f 23 s e c (McKean, 1982, F i g u r e 3 ) . Given  t h a t t h e d i v i n g r e s p o n s e e m p l o y s t h e same e f f e r e n t  pathways as t h e b a r o r e f l e x , i t i s r e a s o n a b l e a r t e r i a l baroreceptors  t o suppose t h a t  p l a y an a c t i v e r o l e i n g e n e r a t i n g a n d  maintaining c a r d i o v a s c u l a r adjustments t o d i v i n g . and  Aakhus (1963) c o n s i d e r e d t h i s h y p o t h e s i s  measured b l o o d p r e s s u r e  when  Johansen they  and h e a r t r a t e d u r i n g f o r c e d d i v e s ,  b u t p r o p o s e d t h a t , s i n c e t h e r e was no c o n s i s t e n t r i s e i n s y s t o l i c pressure experiments,  p r i o r t o t h e onset  a r t e r i a l baroreceptor  of bradycardia  i n their  s t i m u l a t i o n would n o t have  been s u f f i c i e n t t o b r i n g t h e b a r o r e f l e x i n t o p l a y and, t h e r e f o r e , t h e b r a d y c a r d i a was n o t b a r o r e f l e x - i n d u c e d . Hollenberg  a n d Uvnas ( 1 9 6 3 ) c o n s i d e r e d  p r e s u m e d chemo- a n d b a r o d e n e r v a t e d  that, i n their  ducks, t h e r e d u c t i o n i n  b r a d y c a r d i a was due t o e l i m i n a t i o n o f p e r i p h e r a l c h e m o r e c e p t o r i n p u t , and n o t t o l o s s o f t h e b a r o r e c e p t o r s . However, i t i s d o u b t f u l t h a t t h e i r e x p e r i m e n t a l did,  i n fact,  ablate baroreceptor  input.  procedure  7  Andersen  (1966),  in  adaptations  to  diving,  play  a  in  generating  that  the  role  baroreflex  pressure the  rises  methods  to  evaluate  in  ducks  central by  manoeuvers  baroreceptor  dive,  reflexes the  1967,  also  or a  seems  of  the  early-dive  been  Folkow et  will  the  not  in  vagotomized "the  the  animals, of  intense  the  for  the  resistance.  response,  was  these  effects  since  prevented  they  dive  blood  stated  cannot  that  lower  baroreceptor  (Folkow  of in  (and by  in  cardiac  et  and  al.,  baroreceptors  were  peripheral vasoconstriction hypertension)  of  K o b i n g e r and Oda  baroreceptors  also  vasoconstriction,  role  the  the  balance  which  implying a  dive  to  from  the  maintaining  submerged"  the  from  same p a p e r  balance the  input  rate  control  and  Neither  important in  into  in (1969)  secondary experiments thus  by  attempted  circulatory  heart  and  detectable  (1967)  volumes  kept  that  easily  to  if  peripheral  in  that  resistance  later  could  subtle  baroreceptors),  reflex  felt  therefore  drown  circulatory  r a p i d l y withdrawing blood  authors  prevent  to  al.  contributions  detectable  dive, to  speculated  importance which  in  p.359),  control  have  baroreceptors).  was  the  baroreceptors  response  the  However,  animal  not  in  (loading produced  of  bradycardia during diving,  (unloading  and p e r i p h e r a l  rate  the  same b l o o d  atropinized  heart  that  the  and t h e  pressure.  review  injecting  baroreceptors  in  might  available.  circulation  circulation  output  the  d u r i n g d i v i n g by  rapidly  the  suggested  may o p e r a t e  which  then  a thorough  in  possible  bretylium-induced  8  blockade still  driven  animals.  by  preventing In  not  the  the  produce  breathing  (1970)  chemo-  degree  generating  1972  for  the  paper,  cardiac  and  the  dive,  eliminated  Sorensen  small  (nodose in  nerve  to  by  that,  with  either  animal,  are  of  these  or  primary  The  did  and  In of  on  the  They b e l i e v e d  in  their their  distal  that  role  Purves  1972 combined  consisted  the  could  same  importance  which  leaving  the  nicotine  receptors  Jones  details  called  methods  stimulation  position  presented  branches  either  spontaneously  their  procedure,  that  authors  their  since  diving.  they  The  confirm  cyanide  the  stated  deafferentation  state  to  ganglion). what  (1970)  ducks.  did they  response  and b a r o d e n e r v a t i o n  baroreceptors  of  diving bradycardia.  chemoreceptors the  in  concurring with  chemo-  ganglion  hypertension  entirely  tests  reversed  Holm  all  untreated  baroreflex-  the  Sorensen  contended  paper,  cutting  nor  intact  chemoreceptors, that  and  chemoreceptors  paralyzed  a  the  a  beginning been  f r o m any  They a l s o  responsible in  to  bradycardia  in  and b a r o r e c e p t o r  a bradycardia in  or  the  have  as  animals,  1 min d i v e s  evidence  peripheral  authors,  Holm  barodenervation,  of  the  report,  present or  at  should  bradycardia in  denervation.  of  untreated  in  same  release,  vasoconstriction.  of  be  If,  peripheral  prevented  not  the  response  a brief  combined  not  nearly  vasoconstriction  cardiac  chemo-  norepinephrine  b r a d y c a r d i a occurred consequent  induced  did  peripheral  occurred to  control  this  of  of vagal  there  were  "carotid trifurcation"  9  (presumably  that  area  base  neck  in  of  the  thyroid  made  clear),  small  nerve  Sorensen the  nearby  body,  cranial  explored  diving  the  not  in  Butler  evidence  that  suggested  vasoconstriction developed  in  much more  than  baroreflex by  acted  % in to  line  of  the  area  the  (Jones  this  is  1,  ganglion. an  the  caudal  Figure  not  by  nodose  a  Holm  innervation  authors  of  the  and  of  ganglion,  the  latter  who  have  and P u r v e s ,  to  1970;  that,  had the  in  the  animals, the  the  (1974)  effects  in of  a  role  by  the  same  vagally  % in  amount blocked would  rise  the in  dive.  of animals  have  They proposed  pressure  in  that,  50  to  from  They found  pressure  dive.  reduce  rose  response  speculated  may h a v e  diving.  pressure  pressor  (1971)  baroreceptors  in  that  risen  as by  the  atropinized  outflow.  investigation  and Refsum  investigated  other  and Jones  l i m i t i n g vasomotor  This  is  at  artery  though  nodose  to  the  the  their  there  study  occurred  50  by  this  blood  untreated  to  glossopharyngeal:  adjustments  The  artery  1978).  ducks,  authors  that  the  and K i n g ,  ducks,  airway,  connection  in  atropinized  and t o  nearby  supported  anatomy  cardiovascular  Gautvik  a  IX,  the  rise  according to  a pharmacological  indirect  ducks  of  state  and  nerve  is  Abdel-Magied In  sections  also  gives  arteries,  innervated,  (1972)  contention  body  common c a r o t i d  which  branch from the  carotid  from  the  birds  and c a r o t i d  supplying  of  a  was study  further in  pursued by  ducks  alpha-blockade  in  with  which  Blix, they  10  phenoxybenzamine on t h e did  heart,  not  given  on  and  at  a dose  vagolytic  effects  dive,  degree  the  their  pressure  fell,  in  which  authors  concluded  peripheral  of,  presented deplete  by  the  further  authors  a  went  the  blood  lower  in so  animals  1974).  large  drop  of  the  far  heart  rise.  proposed  generating  the  in  dive.  also  of  say  that  unimportant  in  the  control  the  the  dive,  about  presented role  of  was  to reduced  of 20  sec  as  the and  the  chemoreceptors of  and  In  markedly  injection  a as  dive  was  the  and  rate.  diving bradycardia,  to  The  rises  occurred,  primary  as  to,  rate  This  the  blood  reserpine  intravenously  in  to  untreated  heart  When a b o l u s  administered  in  start  with  fibre  In  and  pressure  the  due  used.  secondary  b r a d y c a r d i a was  a pressure  evidence  relatively diving.  was  by  baroreceptors  to  in  peripheral vasoconstriction  dive,  accompanied  pressure  the  when  when  situation  at  vagus  heart  not  alpha-blockade  the  increases  activated  and B l i x ,  noradrenaline  to  blood  pretreating  the  agent  reduced  bradycardia is  catecholamines,  (Andersen  into  contrast  by  the  vasoconstrictor  pharmacological  vasoconstriction:  is  of  d u r i n g d i v i n g were  prevented  resistance  which  complete  of  Phenoxybenzamine  control  b r a d y c a r d i a was  that  actions  response.  vagal  produced  maintained  baroreflex in  affect  the  was  animals  consequence  of  cholinergic  diving  results  of  vasoconstriction  the  the  which  so  ducks  on  significantly  blockade,  the  both  responses  to  were forced  11  Arterial limb  of  baroreceptors the  rabbit.  1974),  nerve  which  causes  (White a  are  apnea,  has  a trigeminal  produces  a marked b r a d y c a r d i a and  absence degree  of of  response  carotid  in  neurones  to  the  not  pressure  was  facilitated  by  that,  to  generated operate  Jones in  baroreceptors,  the  by  (1973).  ducks,  there  located  one  loss  in  of  peripheral In  the  input,  the  half  of  the  of  the  the  resistance  or  White  al.  that  et the  besides  and  vagal  cardiac  baroreflex  which  the  in  walls  then  Such  ducks.  baroreceptors  only  motor  response  vasoconstriction.  He f i r s t is  rabbits,  lung  pressure.  during diving role  of  bradycardia in  the  al.,  inhalation,  the  the  the  et  In  in  proposed  smoke  the  activity  inhalation.  (1974)  in  diving  peripheral  smoke  contribution  the  roughly  although  to  White  increase  vasoconstrictor  approach to  taken  unequivocally  to  from  baroreceptor  to  either  input  cessation  arterial  reduced  rabbit,  also  rise  an  cardiac  inhalation  1973; to  the  trigeminal  aortic  response  may a l s o  A direct  in  and White  sympathetic  secondary  arterial  and  affect  in  directly,  continued  rise  responses  input  a mechanism  diving  a  sinus  and M c R i t c h i e  affecting  a  as  intact  does  trigeminal  made  the  pressure  (1974)  with  bradycardia is  baroreflex blood  well  by  in  component.  resulting  input  as  smoke  initiated  receptor  resistance,  to  resemblance  and t h e  along  implicated  and M c R i t c h i e ,  striking  also  been  responses  responses  and b e a r  response, smoke  circulatory  These  trigeminal  have  in  established one  set  of  of  the  ascending  12  aorta,  and  innervated  "depressor" poles  of  ducks, blood  the  there  1969;  was  cardiac  no  (Jones,  et  bilateral  Nonidez  ganglia.  function  Faris  SO d a y s  of  nodose  pressure  baroreflex  by  nerves  bilaterally  a l . .  after  surgery.  barodenervates sham-operated  animals  vasoconstriction  in  Jones  in  the  the  hind  in  denervates  to  animals  in  the  The l a r g e  dive  therefore  was  vasoconstriction, author  concluded  baroreceptors responsible to  from  dive  as  by  the  in  intact  baroreceptors  chemoreceptor-driven Angell carotid  James,  sinus  due  characteristics  to  rises  those  in  test  in  and  fell  Pickering, ducks  animals  in  SO-  intact  bed was,  in  as  seen  and of  however,  in  rate  in  the  that  a  in  of  The degree  heart  that  falling  in  as  that  workers  but  intact  in  the  dive.  in  The  the  had  suggested,  secondary  response  peripheral  response  blood  to  pressure  unloading as  a  develops.  and E i s n e r  baroreceptors  cut  a proportional increases  earlier  bradycardia  Daly  in  bradycardia  to  caudal  chronic  dives.  experiments  animals  the  were  the  these  half  fall  (the  barodenervated  extent  pressure  these  not,  the  than  matched  and b l o o d  were  for  less  peripheral vasoconstriction,  resistance of  not  Sleight  limb vascular  reduced  dive.  accepted  in  2 min f o r c e d  from  nerves  and d i v e d  same  nerves  drug-induced rises  (1973)  section,  to  to  (Smyth,  Bradycardia  developed  arising  a widely  mammals  nerve  aortic  When t h e s e response  1980).  aortic  the  (1935))  1973),  in  by  (1978)  seals  have  terrestrial  established similar  mammals.  that  discharge The  authors  13  attempted interval  to  determine  reflex  was  reflex  changed  of  beat-to-beat  the  during  injections, water.  in  was  catheters.  occurred  with  it  the  (and  p r o b a b l y a new  the  in  did the  with  such  simply limb  level  degree the of  the of  of  pressure is  there  barostatic  paper,  Angell in  reflex  since  is  a  of  it  the  greater  reflex is  James  carotid  of  reset  heart  give in  engagement  al.  of  the  increase  breathing,  sinuses  in  change  in  interval  The p r o b l e m a  clear  the of  submersion,  (1978)  in  well)  dive;  the  it  cardiac  when  the  manipulated a r t i f i c i a l l y . et  for  rate  as  cardiac  pressure  during  was  pressure  predive. not  of  except  sensitivity  in  with  authors  resistance  given  does  face  bradycardia  appeared to  at  blood  pressure  analysis  the  level  change  change  spontaneously  which the  a new  this  relationship  intact  since  peripheral  that  vasoconstriction  in  were  The c l o s e d - l o o p  regulation  that  experiments  animals  flooding  animals  of  phenylephrine  "closed-loop"  the  experiments,  same  the  shows  same  a  interval  an a n a l y s i s  of  of  as  the  blood  i n d u c e d by  p r o d u c e d a much l a r g e r  than  picture  arterial  around  barostasis.  their  dive  examined  diving seals,  operated  baroreceptor-cardiac dives  to  "gain"  baroreceptor-cardiac reflex  so  preserve  They  the  maintained blood pressure,  that  that  baroreceptor-cardiac  and a f t e r  since In  dive  to  during  intended  arterial  concluded  diving.  pressure  function,  the  and whether  interval  before,  This  baroreflex  reset,  during  elevations  whether  presented  In  results  anaesthetized  had been  isolated  from  a  14  the  c i r c u l a t i o n and  baroreceptors were  while  monitored the  pressure  to  carotid  relating  heart  as  sinus  effects  a  times  relating unclear or  blood  of  to  the  pressure  these  animals.  pressure dives  The a u t h o r s that  response  facilitated  during  baroreceptors  vasomotor  limbs  Millard  rate  half  in  This  conclusion  al.  injected ducks  slope  of  dive,  (1978)  the  to  is  using  the  same  also  than in  be  slope  not  of  the  in  both  the  the  dives, line  but  it  is  anaesthetized open-  baroreflex-heart in  be  heart  during  interval,  from  the  changing  could  repeated  performed  that  pressure  pressure  pulse  rate  seal,  cardiac  and  and  that  and  response. pressor  and  determine  an to  depressor  the  and d u r i n g  pressure-heart  opposite  blood  steeper  must  the  both  before  indicating  these  systemic  diving  to  diving  relationship  the  et  the  into  that  the  of  (1980)  intravenously heart  contribute  pressure  systemic  was  conclude  the  sinus  baroreflex-induced  in to  were  experiments  the  of  observed  closed-loop is  is, sinus  basis  the  indicating that,  p r o c e d u r e was  was  sinus  That  In  relating  pressure  carotid  on t h e  increase  whether  line  sac  sac  systemic  experiments).  the  sinus  When t h e  carotid  awake  and  rate  changes.  entirely  changes.  heart  peripheral resistance  altering  rate 10  rate  pressure  explained  to  slope  seal,  of  ramp a p p l i e d  ("open-loop"  experiments  non-diving  a pressure  rate  blood  i n h i b i t i o n of that  method  reached in  the  pressure-  diving, line  agents  was the  and  reduced  by  baroreflex.  by A n g e l l seal.  found  In  James another  15  study  involving  (1982)  estimated,  central that in  the  dive.  heart  It  is of  the  pressure  fact  through In the  Jones et  that  an  attempt  and West  al.  nerve  (1983,  in  these  be  to  acute  procedure  could  the  and  over that  groups  limb  in  the  applied  I)  tests  or  used  previous  10  response,  % to  stems  or  overall  the  2 min  surrounding  from other  limb  regulation further  and t h e  changes  during a  controversy  one  is  dive  of  of  the  complicated  dive  response  the  role  of  system  the  by  act  baroreceptors  during  preliminary experiments,  on  a more the  extensive  central the  cut  contralateral  baroreflex  different means  before  to  of  almost  altering certainly  aortic to  was  of  then diving  this  activation  baroreflex  circulatory  one  and d u r i n g  baroreflex the  Jones  implanted  vagus  nerve  The advantage  for  of  diving, and  study,  end  The b a r o r e c e p t o r  input  workers  than  diving  picture  methods  other  the  al.  systems.  in  the  same in  the  of  barodenervates. other  less  cardiovascular in  in  resistance  of  the  sectioned  engage  for  reexamine  (1978)  pressor by  to  series  index  baroreflex  barodenervation.  stimulated  was  on  effector  of  a participation  some  the  the  electrodes  ducks  complete  dive  itself; both  et  behaviour  and n o t  same  control  hind  that  the  the  stimulating  in  on  Jones  contributed  baroreceptors  baroreflex,  blood  of  ducks,  receptor  or  obvious  concentrating  in  rate  the  barodenervated  means  baroreceptors  role  the  by  and p e r i p h e r a l  either  the  acutely  in  the  mechanism  states;  the  baroreceptor did not  use  of  input  result  in  16  identical  inputs  under  different  the  during  recorded  Jones blood  vascular  total  the  and West pressure  rate  heart  limb vascular  increase  as  an  in  degree  blood of  (to  pressure,  reduction  cardiac  the  barodenervation reported Predive  by  Jones  pathways  before  and  reduction  rate in  parameters  control  of  during  were  the  the  In  400  after to  to  baroreflex  suggest  aortic  elevated beats  due  to  concurred with  contrary  to  per  reduction  dive  less  This  acute bradycardia  produced a  in  drop i n  is  (1980)  heart  These  ability  diving  reached  a  of  in  and led  the  baroreflex  ducks,  by A n g e l l  a  blood  rate  inhibited. for  in  identical  results the  ducks.  fall  resulting  on b o t h  reduced. the  of  in  dive  after  full  and  further  since  diving  to  min)  barodenervation.  nerve  effects  Millard  conclusion  a  due  Stimulation with  caused  that  circulation  their  provoked a  the  pressure.  dive  findings  the  of  behaviour  c h r o n i c a l l y barodenervated  significantly  to  the  in  the  denervates  response  contrast  mean b l o o d  investigators  the  (1983) hind  and p e r i p h e r a l r e s i s t a n c e ,  because  resistance  in  than  al  and m o n i t o r e d  was  apparently  in  et  dives.  Diving  unaffected  (1973)  stimulation  heart  pressure  was  of  pressure  resistance.  was  in  index  greater  bradycardia  rate,  during  blood  vasoconstriction  to  baroreflex  and Jones  and h e a r t  peripheral resistance  increased  both  (1978)  resistance  resting  the  nervous  cardiovascular conditions  barodenervates,  hind  central  diving.  Both  limb  to  James  Their but et  were al.  17  (1978)  on  the  basis  of  pharmacological  baroreceptor-stimulation The were  aortic  carried  heart  rate  nerve  out  in  had more  likely  that  this  of  the  combination  so  would  have  barodenervation the  loss  pointed  of  heart  in  one  vagus  removed  that  heart  rates  affect  in  (Jones, in  the  1973).  that  the  fully dive  of  and  would  the  but  (Jones,  portion  least  not  This  that  with  of  time  full  alone  did  not  produce  tested,  but  this  to  to  periphery. not  in  a  is  retain  taken  I)  elevated did  dive.  full  dive  dive  blood  due  to  a  vasoconstriction in  animals,  If  series  the  1982b)  diving  but  with  procedure  maintain  peripheral  of  cardiac  (1983  response  are  control  al.  barodenervated  the  the  animals  express  and J o n e s ,  response  cardiac  vasoconstrict response  vagal  develop  degree  of  and  have  ducks  Lillo  section,  et  ability  result  (1971)  barodenervated  1973;  the  is  and Jones  rate  the  It  of  heart  acutely the  Jones  which  result  in  lose  drop  to  in  the  probable  able  above  rate.  was  nerve  ipsilateral  be  3 animals  rate  solely  Butler  seems  animals  consequence  and not  input. of  a  outlined  intact  aortic  partly  used  it  heart  and  vagotomy  proportional  bradycardia,  in  at  in  preliminary tests,  Chronically  reduction  increase vagotomy  unilateral  the  pressure  from the  doubled  of  ducks,  In  found  than  variablity  the  control.  vagotomized  procedure  the  experiments  unilaterally  baroreceptor  out  open-loop  studies.  stimulation  large  been  and  which the  these into  contrast lose  ability  changes  account,  in the  to a to the  18  interpretation different  of  results  conclusions  from the  about  the  two  role  groups  of  will  lead  baroreceptors  to  in  diving. It about  is  clear  the  role  differences analyzing  of  in  methods  rather  per  se.  The  time  appears  to  be  than  the  functional  factor,  as  both  well  as  the  the  function  cardiovascular  development standard  of  most  chosen I that  the  aim,  means  this  arterial  of  of  for  thesis,  to  baroreceptors  system,  in  A  role  order  by  to  controlling The and  electrical appear  problem,  this  is  procedure,  pathway  investigate a  ducks  effects  submersion.  this  also  activation  in  baroreflex  in  dived  progressive  afferent  play  blood  barodenervates  the  forced  work  of  animals.  baroreflex  attacking the  the  barodenervated  baroreceptors  the  of  are  barodenervation  activating  approaches in  to  baroreceptor  profitable  these  the  of  responses  of  of  in  denervation.  denervated  cardiovascular  arterial  of  animals  chronic  analysis  the of  and  standardized  method  stimulation the  a  acute  limb  from  employing  chronically  effects  resulted  maintenance  the  acutely  views  baroreflex,  methodology  which  with  the  an  on  at  have  effector  studies  in  from  of  in  barodenervation  clarify  those  differences  study  diving  required,  a  or  differently  detailed  during  of  a  other  the  one  in  conflicting  diving  activating  post-denervation  responding more  of  in  of  and,  barodenervation,  summary t h a t  baroreceptors  responses  baroreflex pressure  from t h i s  I  to  be  have  study.  the in  hypothesis control  of  the  19  cardiovascular to  attempt  have  to  been  system define  designed  deafferentation response  in  and  this  to  by  analyze  intact  effects  intermittent  role.  bilateral  vagally  cardiovascular  during forced  of  submergence  The e x p e r i m e n t s  the  acute  aortic  one  ducks,  in of  section  and t o  baroreflex of  effects  nerve  animals,  stimulation  in  Section  aortic  on t h e  dive  the  by  nerve  I  baroceptor  examine  activation  and  continuous  during  diving. In  Section  II,  I  set  out  to  adjustments  o c c u r r i n g during the  the  barodenervated  chronic  resting  factors  to  ensure  implicated  experimental alone,  procedure  and t h e r e f o r e  eliminate  possible  anaesthesia perform  on  the  circulatory  system  barodenervation to  the  after in  to  the  were  effects  full  examined  as  changes  establish  that to  of  the It  was  only  the  designed  to  surgery  was  try  from the  animals  to  surgical  for  of  the  load  a possible  to  or  developed  pressure  in  the  to  barodenervation  adaptations  increased  acute  transition.  recovery  preparing the  cardiovascular  to  to  were  A procedure  The s t r u c t u r a l  from the  responses  related  experiments  results.  cardiovascular  experiments  those  complicating  involved  experimentation.  factor  the  order  circulatory  were  barodenervation  manipulations  to  the  in  during this  during these in  the  transition  state,  circulatory conditions  important  analyze  subsequent  contributing  chronic  barodenervates. The  experiments  in  Section  III  were  done  to  investigate  20  the  changes  the  time  in  the  course  of  barodenervation. a  continuous  the  seen  ducks.  In  in  presented  for  after This  weeks  after  made  between  in  distinct  I  aortic  were  and  in  different  a trivial  problem i n  given  changes  the  between  which  electrodes  implantation.  in  to  investigate  possible  the  chemoreflex  and t h e  in  the  during  and  type  the  was  after  stimulus  different to  of  in  be  times compared.  long-term  occur  in the  section,  baroreflex of  the  A protocol  mechanisms  operation  diving  ducks.  at  this  obtain  determine  examine  and n e r v e  Also  of  to  barodenervated  to  can  was  order to  animals,  this  chronic  study  setting  obtained  over  stimulation  before, for  to  types  nerve  extended  index  results  attempting  to  circulatory control  baroreceptor  function  contribution  of  blood  changes,  diving  of  the first an  few  attempt  interaction  w h i c h may  baroreflex  underly  during  dives.  In in  this  stimulation  enable  alterations  forced  the  Section  denervation, not  IV,  aim of  two  to  acute  and c h r o n i c a l l y  a biological  relationship  the  acutely  nerve  to  experiment,  was  in  the  from  c h r o n i c a l l y barodenervated  using  is  these  behind  of  responses  parameters  transition  The p r i m a r y  Section  experiments  diving  the  r e c o r d of  mechanisms  response  cardiovascular responses  pressure  analyze during from  diving,  role  of  submersion,  two  baroreceptor during  the  related  input  to  and t h e  the I  baroreceptors  have  focused  perspectives: the role  maintenance of  these  on  the of receptors  i n the i n i t i a t i o n and maintenance of the adjustments t o d i v i n g .  cardiovascul  22  SECTION  Cardiovascular  I  Responses  Stimulation Acute  to  During  Aortic  Diving  Nerve  in  Barodenervates  INTRODUCTION  The  efferent  limbs  of  the  peripheral  resistance,  than  those  from baroreceptors  from  central  1982).  afferent  pathways  all  the of  animal. the  reflex  investigator separating  test  during a in  nerve  The (1983)  to  effects  experiments aortic  which  sectioned,  dive.  in  done in  the  in  which  by  of  the  which then  in  the be  effects,  of  in  missing  invoked  at  provides  baroreceptors  Milsom  any  input  an  factor time  a method  from those  of  other  in  section  by  electrically  stimulating  ducks  with  complete  the  left  the  for  accomplished  Series  is  by  is  as  when  intact  This  presented  and  these  difficult  concert  only  input  baroreceptor is  and  other  including  (Jones,  during diving  operate  output  inputs  influences  baroreceptor-deafferented  experiments  were  its  of  this  can  the  effects  pathways in  influenced  during diving,  of  system  A preparation  baroreflex,  inputs  from the  cardiac  chemoreceptors  Separation  cardiovascular the  both  and p e r i p h e r a l  Gabbott,  on  are  baroreflex,  the one  animals. 1  in  Jones  aortic  barodenervation  et  al.  nerve  was  effected  by  23  interruption indicated  of  that  the  contralateral  baroreceptors  cardiac  response  in  animals  may h a v e  been  vagotomy one  to  vagus  body  the  complete  nerve  chemoreceptors  control  of  Hindlimb  the  experiments,  by  indicator  the  diving. limb  of  during  behaviour  c o u l d be  this  good  pressure  index  of  true  use  modulating in  from  measured  unilateral  perfusion  the  carotid  impaired.  these  technique,  peripheral resistance that  case,  blood  flow  through the  in  constant-flow  cutting  parasympathetic  been  in  as  in  system  an  during  in  the  web  hind  or  (Djojosugito  changes  the  these  Specifically,  connections  in  experiments  of  efferent  the  changes  in  results the  were a  role  input  shunted  1969),  perfusion  was  of  arterio-venous  if  These  d i v i n g may h a v e  non-nutritive and  by  and t h e  a possibility  diving  the  reduced  constant-flow  There is  during  have  resistance  a  but  a  denervation.  by h a l f ,  heart  vascular  dive,  play  complicated the  would  do  vagus.  other et  al.,  hindlimb would  not  peripheral resistance  be  a  during  diving. The the  experiments  in  this  cardiovascular responses  barodenervated nerves Total  at  once,  output  sectioning  leaving  peripheral  cardiac probes  by  the  resistance  measurements  section to  were  diving  both  in  left  are  made w i t h  monitoring pulmonary a r t e r i a l  animals  and  c a r o t i d body changes  designed  right  to  acutely aortic  innervation estimated  intact.  from  electromagnetic flow.  assess  flow  24  METHODS  Experiments ducks  (Anas  colony  experimental for  at  light-dark  C,  the  least  carried  photoperiod,  for out  24-48  intramuscular  removed, skin  in  a  10  the  vessels which syrinx in  and  are was  females  was  the  Before  and  the  opened  illustrated retracted  in  to  smaller  and  on  made  air the  were  held  with  20-22  a  12  degrees  Animals  up t o  mg/kg  of  1.  to  the  air  to  view  not  need  sac  the  aortic be  the  great  thorax,  birds,  to  were  exposed.  anterior  the  sodium  through  was  reveal  In male  and  Montreal,  longitudinally membrane  were  table,  50  clavicular  midline  did  implantation  operating  of  sac  side  syrinx  of  electrode  an  the  Figure one  kg  any  lighting  Laboratories,  structures in  British  + 0.1  animals  experiments.  Abbott  was  out,  2.8  of  laboratory.  covering  associated  the  mean).  injections  cm i n c i s i o n  midline  The membrane  was  Pekin  breeding  University  a temperature  upwards  (Nembutal;  The f e a t h e r s  the  white  from a  artificial  hr before  side  female  animals  barodenervation  were  Quebec).  of  carried  at  as  ventral  pentobarbital  the  1 wk u n d e r  restrained given  of  and  obtained  these  were  same t e m p e r a t u r e  Surgery  8 male  campus  of  error  on  var.)  the  procedures  hr  was  on  Body w e i g h t  + 1 standard  indoors  done  platyrhynchos  established  Columbia. (mean  were  the  large  nerves;  moved.  25  F i g u r e 1. V e n t r a l view of the l a r g e a r t e r i e s i n the a n t e r i o r t h o r a x of a f e m a l e w h i t e P e k i n duck. The i n n e r v a t i o n o f t h o r a c i c s t r u c t u r e s i n t h i s r e g i o n i s shown s c h e m a t i c a l l y .  right vagus nerve thyroid gland nodose ganglion  common carotid artery  left aortic nerve subclavian artery brachiocephalic arch  1st cardiac nerve 2nd cardiac nerve  heart  27  The  aortic  nerve  on  of  fascia  which  forms  artery,  the  sheet  common c a r o t i d dorsal  body  in  course  its  trunk, sheet  possible,  nerve and  electrodes. wire  (0.2  diameter, formed  nerve  fascia.  the  as  far  These  embedded  them,  to  structures.  with  a polyvinyl  rings to  before  the  the  ligature,  through  sufficient lumen.  minimized  chloride  to  one  lumen, the  Mannheim,  tissue West  an  and t h e  of  cement  Germany),  aortic and  was  the  tied as  stimulating  two  solid  1 mm  silver  inside  An o p e n i n g  was  epoxy  electrode  leads  leakage were  wire  soldered  to  formed  from  insulated  to  the  silver  sectioned  distal  tie  was  passed  through  central  cut  end  of  nerve  was  The k n o t end  in  from  the  the  ligature  slipping  fixed  to  (Histoacryl  blue;  Bohringer,  taken  not  being  the  out  then  care  artery  the  nerve  body  the  ganglion  and t h e  was  the  artery  resin.  copper  of  the  small  silk  current  The n e r v e  end  the  and  the  the  enclosed  stranded jacket  free  of  rings  stimulus  electrodes.  prevent  epoxy  both  to  miniature  The e l e c t r o d e  flexible  The e l e c t r o d e  with  of  a  nodose  consisted  in  by  surgical  the of  of  approximately  encapsulation.  electrode  drawn  wall  of  to  provide  surrounding  pair  of  free  root  in  a r c h and  ganglion  5-0  a pair  centre  which  twisted  of  1 mm a p a r t  through the  the  accompanied  nodose  distal  rings  arrangement  a  is  electrodes  mm t h i c k )  prominent  between  dissected  through  is  brachiocephalic  left  was  side  a web  A ligature  led  encapsulating  left  The n e r v e  from the  and the of  around  wall.  the  to  of  dorsal  let  was  was the body  cement  28 flow  onto t h e nerve  muscles adjacent strain-relief of  itself.  The w i r e  to the electrode s i t e  loop  i n s i d e the chest,  t h e neck o u t s i d e t h e i n c i s i o n .  was  given  a brief  effectiveness heart  electrical  and, a f t e r  leaving a  were s u t u r e d  At this  t o the skin  point, t h e nerve  s t i m u l a t i o n t o check t h e  o f t h e e l e c t r o d e s ; an i m m e d i a t e r e d u c t i o n i n  rate occurred  i n a successful preparation.  Some d i f f i c u l t y without  l e a d s were a n c h o r e d t o  extensive  i n identifying the right  aortic  nerve  d i s s e c t i o n was e n c o u n t e r e d due t o t h e  presence o f s e v e r a l s m a l l nerves l e a d i n g towards t h e h e a r t from t h e r i g h t animals  side  ( F i g u r e 1 ) , and a p r e l i m i n a r y s t u d y  was made t o i d e n t i f y  electrophysiologically.  the right  Electrical  n e r v e and f e w - f i b r e p r e p a r a t i o n s branch i n t h i s discharge with  carried  similar  by Jones  (1973).  from t h e r e a d i l y  Once f u n c t i o n a l l y  t o the pressure  these  animals,  the  right  extensive  Activity  i n this  identifiable  left  branch had  s i d e and s e c t i o n e d  aortic  the baroreceptor  nerve.  n e r v e on t h e  t o the root of the  H a v i n g e s t a b l i s h e d t h e anatomy i n  t h e c o r r e c t nerve could then  dissection.  p u l s e , and  described f o r aortic  r i g h t was t r a c e d f r o m t h e n o d o s e g a n g l i o n i n each p r e p a r a t i o n .  whole-  t h e c a r d i a c c y c l e as d i d a c t i v i t y  identified,  aorta  from  showed t h a t o n l y one v a g a l  c h a r a c t e r i s t i c s t o those  same r e l a t i o n s h i p w i t h  recorded  recordings  nerve  e f f e r e n t information with a  pattern corresponding  baroreceptors the  area  baroreceptor  in4  be i d e n t i f i e d on  i n the barodenervates  without  29  The  right  aortic  separate  from,  the  ganglion  to  separates over  the  towards  from the  the  retracting dissected cut  vagus,  a point  anterior  between  lateral  aspect root  from  the  to  and of  in  the  the  the  1).  aorta  aorta. and  pulmonary The n e r v e  medially,  a  but  short  it  medially  was  right  Here  artery  and t h e  and the  as,  nodose  ventrally  surrounding tissues,  descending  sheath  from the  right  aorta  same  descending  courses  (Figure  descending  free  runs  posteriorly  vagus  aortic the  nerve  and  exposed length  nerve  by  was  was  pulmonary  artery. Electromagnetic Laboratories; both  pulmonary  artery  in  tubing  with  put  selected  to  the  the  arteries  the the  for  a  skin  other fit  In  in  of  these  the was  chest. closed  a  area.  reduction  wall  The c l a v i c u l a r over  the  flow  of  leads and  air  repaired  sac air  plastic  probe  sac.  10-20  sutured  outside was  was  were  about  were  led  pulmonary  of  The p r o b e s  Probe  body  the  around  one  a piece  as  artery.  placed  around  2 animals,  provided  ventral  and  diameter  pulmonary  the  (Biotronex  M a r y l a n d ) were  internal  which  probes  6 animals  cross-sectional  muscles in  same  flow  Springs,  animals.  vessel  incision and  2  around  % in  Silver  blood  the  repaired  30  Experimental On t h e catheters  Procedure. day  were  2 % without  90  P E 50  New J e r s e y ) .  Inc.,  cannula  Hato Rey,  transducer a  was  twice  for  the the  zero  end  with  an  flow  in  each  was  above  artery  Statham  recorded P23Db  or  adjustable recorded  with  one  pulmonary flow  both  calibrated  experiment, overdose each  and below the  and Jones  with  of  the  the  vessel (1975)  Blood  was  the  flow BL  in  610  obtained  two  as  probes  artery  segment have  or  in  were  was  saline with  as  animals baseline  situ  at  In  exposed at  the  established  The  killed  pentobarbital.  and  the  during diving.  animals  sodium  probe  calibrated  The e l e c t r i c a l  pulmonary the  in  diastole  after  and  The  pulmonary a r t e r i e s ,  artery  in  the  Laboratories  a Biotronex  probe.  established  Parsippany,  (Bio-Tec  heart  output  one  transducer.  height.  and c a r d i a c in  (Statham  the  in  (Clay-Adams PE  through  pressure  of  Ltd.,  Co.,  B i o - T e c BT70  level  (Xylocaine,  and v e i n  polyethylene  was  flows  run through  Langille  of  venous  anaesthesia  Pharmaceuticals  the  procedure,  and  Becton-Dickinson  the of  was  local  California)  implanted was  arterial  ulnar  made  Rico)  was  intravenous  cannulated  probe.  at  column  system  calibration  rates  Puerto  sum o f  of  a  flowmeter,  one  flowmeter the  with  set  flow  only  were  the  venous;  arteries  pulsed-logic either  Astra  in  Pasadena,  saline  pulmonary  under  Blood pressure  Instruments,  with  implanted,  The c a n n u l a s  arterial  experiment,  Ontario),  arterial,  with  the  epinephrine;  Mississauga, wing.  of  known  the and flow  attached that  this  31  procedure either  blood  ducks.  rate  was  results  is  used  checked  effectiveness with  0.2-0.5  obtained  a pressor  ml b o l u s  of  the  test.  mmHg,  functioning  the  cardiac  Ontario)  of  saline  was to  bipolar wire  a n i m a l was  blood  ratemeter  were  the  fluid  in  electrodes  on  Diego,  pressure,  d r i v e n by  written  out  rectilinear an  on  heart  the  IL13 b l o o d  taken gas  Lexington,  keep  of  the  the  animals.  FM t a p e  for  machine  later  be  2  in  a  ug/kg.  rise  bereft  at  and  mixtures  of  was  derived  of  of  Warwick,  41°  done  C, of  with  the the  Rhode  were  Analysis  cannula  was  also  done  thermostat  pH, oxygen  precision  of  1 ml  with  Laboratories,  normal body  known c o m p o s i t i o n ,  Island)  (Hewlett-Packard,  analysis.  the  a  recorder  A l l variables  recorder  with  from  and pulmonary  chart  (Instrumentation  Calibration  electrodes  Inc.,  arterial  Massachusetts)  dioxide gas  of  pressure  ECG s i g n a l ,  a heat-writing  from the  electrodes  rate  coordinates.  8 channel  California)  samples  to  dose  was Canada  intravenously  ensuing to  procedure  (Parke-Davis  a total  considered  on  recorded  injected  make  writing  Inc.;  when  electrocardiogram  barodenervation  Techni-Rite Electronics  an  calibration  from the with  (TR888,  blood  the  same p r o b e  baroreceptors.  Arterial  San  the  Epinephrine  b r a d y c a r d i a accompanied  flows  for  conventionally  Scarborough,  20-50  for  subcutaneously.  The  no  same  saline  recorded  placed  If  the  or  Heart  (ECG),  Inc.,  gives  temperature  and  buffer  before  adjusted  each  carbon solutions blood  32  sample  was  inserted.  On t h e animals  were  operating the  dive  then and  day  table. with  there  water  in  dive  the  longer was  than  used  postdive, In the  all  after  stimulus  ms,  via  artefacts  pressure  at  a  before  stimulus-induced the  dive.  in  the  up  made air.  cover  a  the  head.  Few o f  could tolerate  dive  of  1 min  30  aortic  nerve  level  Instruments; isolation  a p p e a r i n g on parameters pulse  which  submergence. changes  Two s t i m u l u s  in  was  end  acute  dives to  2 min  for  2 min  resumed. was  Quincy,  the  funnel  spout,  the  sec  Recording continued  (Grass  of  was  At the  unplugging the  square  from  before  large  experiments  stimulus  min  submersion  d r i v e n by monopolar  a  an  and p o u r i n g 1 0 ° C  clamp.  length  the  The head  mouth of  spout  on 1-2  Involuntary  the  which the  Stimulus  and a m p l i t u d e  experiment  from  side  were  d r a i n e d by  b r e a t h i n g had  stimulator  traces.  a  in  to  experiments.  were  Massachusetts)  flow  so  experiments  S4  was  cannulation,  breathing  funnel  funnel  these  ventral  clamp.  the  released  in  electrodes  Grass  the  2 min,  for  downwards  funnel  was  barodenervates  rest,  plugging  the  head  at  after  recordings  a padded  quickly into  the  and  Predive  beak  by  experiment,  restrained  animals  positioned held  the  lightly  accomplished  of  of  either  ranged  voltage  gave  unit  large  This  was  was  the  ECG o r  in  each  were  used  in  blood 1-3  blood emphasize  cardiovascular variables  patterns  a  prevent  Hz,  in to  from  1-20  set  falls done  pulses  to  from  stimulated,  each  during  animal,  33  with  some v a r i a t i o n  nerve  was  stimulated  submergence;  or  20  trains  sec  dive, were  pulse and at  train,  Several 45  min to  sec of  in the  running  a  pressure  total  in  each  were  pressure be  calculation;  experiments,  since  than  mean  10  % of  Data  from  2 min  over  start  were  2 min  of  each  in  the  experiments.  separated  obtained  by  before  at  least  and at  At the  end  barodenervation and the  flow  90  was  probes  above. FM t a p e  (Digital  system  were  Equipment  flows was  time to  drop across equivalent  output  the  to  has  a r t e r i a l pressure  barodenervates  as at  arterial  was  not  shown in  of  the a  quotient  in  measured  ducks  dived without  it  the  in is  during  of  time.  pressure  that  blood  output,  given  beds  into  After  cardiac  vascular  the  pressure (1973)  obtain  fed  Corp.)  periods.  calculated  and c a r d i a c  Jones  of  stimulus  immediately.  preselected  venous  after  consisting  p r o g r a m w h i c h p r o d u c e d mean v a l u e s  pulmonary blood  to  to  aortic  Cardiovascular variables  examination,  computer  a r t e r i a l pressure  assumed  1 and  animal,  on t h e  peripheral resistance  was  before  sacrificed,  outlined  recorded  and flow  total  at  analyzed  post-mortem  data  the  samples  animals  custom  The  this  done  the  intermittent,  predive,  after  and were  as  from  intermittent-stimulation  PDP L a b 8e  summing t h e  mean  the  calibrated  Digital  sec  Blood  during  Analog a  were  was  parameters:  2 min p o s t d i v e .  the  dive,  day,  confirmed were  in  1 hr.  the  continuously  given  10-15  dives  stimulation  stimulation  1 and  measured  pulse  in  body  for these less  diving.  stimulation  were  34  compared given each a  with  times  using  group,  data  two-factor  Computing tests  and  either  a one-way were  with  analysis  as  the  with  least  1967). means  type  ANOVA  compared at  significant  Cochran,  presented  from  Centre program,  were  compared  data  (P  of  stimulated  (SPSS,  ANOVAR). <. 0 . 0 5 ) ,  significant  dive  measures  times  over  pairs  of  means  difference  1 standard error  of  in  this  the  time for  the  using (UBC these  were  test  (Snedecor  study  mean.  at  Within  Where F v a l u e s  A l l numerical data +  ONE-WAY).  different  repeated  dive  are  35  RESULTS  1)  Continuous Cardiac  output  the  denervated  min  30  of  sec  the  heart than  of  25  but  % of  As  a  significantly pressure  a  to  fall  By t h e  significantly  different  When c o n t i n u o u s before  Stimulation  the  significantly,  end  so  stimulus-induced  this  remained  significantly  dive,  stimulated The  time  and  heart  in  course rate  blood  despite  which  of  either in  continued  above to  the the  in  the  same  in  the  in  cardiac in  the  the  dive  in  the  start  was dive  of  pressure  the  was  by  nerve  not  the  the  or  stroke was  dive,  value  stimulated  in  volume due  to  blood and  for  response dive  was  61 %.  pressure  and p r o p o r t i o n a l d e c r e a s e were  in  stimulation,  pressure as  decrease  times  rate  predive  decreased  1  24 %  less  aortic  blood  Early  in  level.  fell  heart  a  1 min  blood  the  by  by  early  with  that  fell  the  predive  pressure  decrease  contrast  dives,  dive,  the  vasodilation.  increased  the  the  from  affect  pressure  of  of  9.2  until  coincident  to  volume  than  so  diving  dropped to  due  by  and n o t  1,  flow  pressure  stimulation  dive,  d i d not  stroke  course  blood  predive,  bradycardia.  begun  largely  time  result,  begin  was  TPR i n c r e a s e d  during  Table  blood  predive;  faster  above  in  total  This  predive.  with  response.  did  value. 30  progressively  represented  submergence,  to  % of  decreased  animals  predive rate  dive,  Stimulation  the  rest  during  non-  progressed. cardiac  dives  as  output in  dives  36  TABLE  1  E f f e c t s o f c o n t i n u o u s a o r t i c n e r v e s t i m u l a t i o n on cardiovascular v a r i a b l e s during d i v i n g i n acute barodenervates. A r t e r i a l p r e s s u r e (MAP), c a r d i a c o u t p u t (CO), h e a r t r a t e (HR), s t r o k e volume (SV) and t o t a l peripheral resistance ( T P R ) a r e e x p r e s s e d a s mean + 1 S . E . M. f o r 8 o b s e r v a t i o n s i n 8 d u c k s . T h e (+) s i g n s indicate s i g n i f i c a n t ( P <. 0 . 0 5 ) d i f f e r e n c e s at each d i v e time between u n s t i m u l a t e d d i v e s (DEN) and d i v e s i n w h i c h t h e a o r t i c n e r v e was c o n t i n u o u s l y s t i m u l a t e d ( S T I M ) . A s t e r i s k s (*) indicate s i g n i f i c a n t c h a n g e s i n DEN o r S T I M d i v e s f r o m t h e respective predive value.  1: 0 0  0: 3 0  HAP MH|  CO  •I/sin  HR  beats/rain  6V  ml  TPR P. R.  0.  PEN  BTIM  DEN  STIM  DEN  137 ±8  54 •4 •  213 • 13 *  107 • 10 • •  142 ±11  864 264  517 ±70  280 •50 *  303 ±55 *  141 ±24  294 • 16  282 • 16  130 • 18 *  165 • 22 •  2.26 •0.22  1.97 •0.27  2.15 ± 0 . 38  1.83 ±0.33  0.22 •0.026  0.12 ±0.017 "•  RECOVERY  DIVE  PREDIVE  0.78 •0.09 ~»  0.36 •0.052 * •  1: 3 0 STIM  DEN  STIM  DEN  164  134  ±11  •11  147 ±13  102 • 13 * •  802 ±81  1155 •98 *  1018 +98  1091 +84 •  363 ±16  381 + Z9  413 • 13 *  388 • 21  2.21 •0.28  2.11 •0.21  2.80 •0.24  2.62 •0.25  0.26 •0.029  0.19 +0.023  0.15 +0.021  0.11 +0.012  STIH  DEN  82  133  ±9 * •  •U  77 ±5 * •  126 ±25 *  157 ±40 •  130 ±22 *  802 ±101  99 • 15 •  74 • 10 *  91 •1* •  82 ±18 *  1.43 ±0.24 *  1.70 ±0.34  1.73 •0.44  1.58 •0.21  1.47 •0.26 *  1.10 •0.31 *  2.05 •0.49 ~»  0.81 •0.35  1: 0 0  BTIM  DEN  •  0: 3 0  0: 10  •f  ±  1: 3 0  2: 0 0  STIM  DEN  STIM  DEN  STIM  154  94  •11  ±9 * •  211 ±17 *  139 • 14 * •  169 ±15  89 • 10 * •  914 • 87  1000 • 84 •  818 ±101  873 +97  785 +66  384 • 15 *  336 • 12  374 + 16 *  297 • 16 •  371  258 • 12 +  2.84 •0.22  2.72 •0.26  2.67 •0.22  2.75 •0.34  2.35 •0.26  0.16 „ „ 2  0.11 ±  „  0  H  0.20 ±  „  0.14 <.„ „ 1  9  •1« *  3.06 •0.26 *  0.24 ±  Q  M  4  ±  0  0.16 0  3  4  38  TABLE  2  A r t e r i a l b l o o d gas t e n s i o n s a n d pH d u r i n g d i v i n g i n acute barodenervates. Oxygen t e n s i o n (Pa02), c a r b o n d i o x i d e tension (PaC02) a n d p H (pHa) a r e p r e s e n t e d a s m e a n ± I S . E . M. f o r 8 o b s e r v a t i o n s i n 8 a n i m a l s . D i v e b l o o d samples were t a k e n 90 s e c a f t e r s u b m e r g e n c e . A s t e r i s k s (*) represent s i g n i f i c a n t d i f f e r e n c e s between r e s p e c t i v e d i v e and p r e d i v e values, for unstimulated dives (DEN) a n d d i v e s i n w h i c h t h e a o r t i c n e r v e was s t i m u l a t e d e i t h e r c o n t i n u o u s l y (CONT S T I M ) or i n t e r m i t t e n t l y (INT STIM).  PREDIVE  DIVE  DEN  INT STIM  CONT STIM  DEN  INT STIM  CONT STIM  81.4 + 1.3  85.2 +5.2  83.9 + 5.0  33.4 + 1.8 *  34.6 ±2.5 *  32.4 ±3.1 *  PaC02 mmHg  25.6 +0.5  25.1 +1.1  26.0 +1.2  38. 5 ±2.3 *  35.7 ±1.2 *  33.5 ±3.0 *  pHa  7.57 ±0.01  7.56 ±0.02  7.58 ±0.04  7.45 ±0.02  7.45 ±0.01  Pa 02 mmHg  *  *  7.46 ±0.02  *  39  without  stimulation,  prevented  from  but  rising  total  as  peripheral resistance  much as  in  animals  dived  was  during  stimulation. During  the  stimulation, predive  remained heart  heart  value,  resistance  dropped to  rate,  blood  peripheral  However,  level  sec  in  dioxide (Table  remained highest  of  from  oxygen  during  heart  the  tension  tension  rose  significantly  also  decreased  stimulation  levels  of  of  blood  rate  and  the gases  while  throughout  recorded  the 1 min  not  output  levels after  at  did  cardiac  up t o  this from  or 1  time. the  period.  less  arterial  nerve  at  90  carbon  diving  significantly  or pH.  and  a r t e r i a l pH  during  aortic  the  postdive  significantly  significantly  predive,  high  recovery  recovery  at  pHa  the  rate,  reduced  were  of  predive  unstimulated  only  was  at  elevated  heart  the  as  above  peripheral  pressure  than  2).  dive  result  dive  Continuous the  as  throughout  blood  postdive  level  levels  barodenervates  the  sec  a  without  significantly  stimulation  pressure  dives  same  and a f f e c t e d  blood  Arterial acute  the  resistance  unstimulated  in  alter  postdive,  10  pressure  Continuous  significantly  by  the  with  after  remained  Primarily  period,  postdive.  rate  although  there.  recovery  min  2 min p e r i o d s  in  the  h a d no  dive.  effect  on  40  2)  Intermittent Table  34  %)  the  decrease  due  almost  dive,  to  of  min  of  dive  by  was in  continuous  (Table  49  s t i l l  the  produced  cardiac  no  2).  dive,  (by  the  Predive  to  the a  29  pressure to  37  This of  stroke  % fall  were  %)  nerve  less  in  heart  at  to  27  not dive  only  was  19  experiments, differences  was  2 min i n t o due to  to  in the  the  stimulation. heart Heart  in rate  prestimulation stimulation  maximal.  intermittent in  output  predive  on t h e  % during  bradycardia  not  reduced,  volume.  when t h e  of  intermittent  % of  partly  stroke  half  rate.  of  1 min and was  resulted  cardiac  effects  (by  before  than  volume  in  % and t h e n  but the  the  output  occurred  progressively  decrement  and by  significant  to  remained e f f e c t i v e  in  stimulation  22  peripheral resistance  rate  when  cardiac  aortic  decrease  stimulation  % early high,  both  c a r d i o v a s c u l a r changes  so  stimulation  via  of  proportionate  falling  response  nerve  dropped rate  dive,  bouts  the  in  a r t e r i a l pressure  value.  respectively.  Aortic the  mean  on b l o o d  pressure  response  these  entirely  the  stimulation with  stimulation  stimulation,  During  loss  in  prestimulation by  reductions  peripheral resistance  and t o g e t h e r ,  affected was  that  intermittent  diving, a  shows  and t o t a l  during  in  3  Stimulation  dive  blood  As  at  in  2  the  stimulation gases  o r pH  41  TABLE  3  E f f e c t s o f i n t e r m i t t e n t s t i m u l a t i o n o f t h e a o r t i c n e r v e on cardiovascular v a r i a b l e s during d i v i n g i n acute barodenervates. V a r i a b l e s a r e t h e same a s i n T a b l e 1 a n d v a l u e s a r e e x p r e s s e d a s mean + 1 S . E . M . , f o r t h e n u m b e r o f observations i n brackets under each v a l u e , i n 8 animals. The (+) s i g n i n d i c a t e s a s i g n i f i c a n t d i f f e r e n c e b e t w e e n t h e p r e s t i m u l a t i o n v a l u e ( P R E ) a n d t h e v a l u e d u r i n g a 20 sec s t i m u l a t i o n p e r i o d s t a r t i n g at the i n d i c a t e d time i n the dive (STIM). A s t e r i s k s (*) indicate significant differences in PRE o r STIM v a l u e s f r o m t h e i r r e s p e c t i v e p r e d i v e v a l u e s .  PREDIVE  DIVE  RECOVERY  1:00  2::00  1::00  2::00  DEN  STIM  DEN  STIM  DEN  STIM  DEN  STIM  DEN  STIM  MAP mmHg  180 ±10 (12)  82 ±6 (12) +  219 + 16 (12) *  136 ±9 (12) * +  172 ±14 (12)  125 ±10 (12) * +  186 ±18 (10)  137 ±20 (10) *  209 ±17 (10)  115 + 16 (10) +  CO ml/min  850 ±84 (10)  564 +78 (10) +  278 +63 (10) *  146 +25 (10) *  145 + 17 (10) *  114 + 19 (10) *  1142 ±82 (10) *  928 +90 (10) *  948 +92 (10)  734 +64 (10)  HR beats/min  296 ±18 (11)  214 +8 (11) +  106 + 19 (11) *  52 +9 (11) * +  71 +8 (U) *  54 +7 (11) *  420 +20 (9) *  316 +19 (9) * +  388 ±24 (9) *  264 ±11 (9) * +  SV ml  2.58 ±0.24 (16)  2.30 +0.30 (16)  2.71 ±0.46 (15)  2.38 +0.3( (15)  2.00 +0.16 (10)  2.23 +0.32 (10)  2.83 ±0.14 (9)  3.03 +0.16 (9)  2.80 +0.35 (15)  3.04 +0.34 (15)  TPR P. R. U.  0.27 ±0.053 (10)  0.18 ±0.023 (10)  1.32 ±0.40 (10)  1.39 +0.31 (10)  1.41 +0.19 (10)  1.60 ±0.32 (10)  0.17 ±0.016 (10)  0.15 ±0.017 (10)  0.16 0.25 +0.034 ±0.021 (10) (10)  43  Intermittent the recovery blood  s t i m u l a t i o n of t h e a o r t i c nerve  1 min i n t o  p e r i o d produced the same p r o p o r t i o n a l changes i n  pressure,  h e a r t r a t e and c a r d i a c output as d i d end-dive  s t i m u l a t i o n , w h i l e t o t a l p e r i p h e r a l r e s i s t a n c e responded a t t h i s time w i t h n e a r l y t h e same p r o p o r t i o n a l change as b e f o r e the d i v e .  Of a l l t h e c a r d i o v a s c u l a r v a r i a b l e s , p e r i p h e r a l  r e s i s t a n c e had most n e a r l y returned min  postdive,  recover.  t h e other v a r i a b l e s t a k i n g s e v e r a l minutes t o  By 2 min p o s t d i v e ,  the h e a r t  s t i m u l a t i o n had a l s o recovered the p r o p o r t i o n a l blood restored.  t o t h e p r e d i v e v a l u e by 1  pressure  r a t e response t o  f u l l y and so, by t h i s time, response t o s t i m u l a t i o n was  44  DISCUSSION  Acute the  baroreceptor  aortic  nerves  bradycardia  cardiac  however, response  baroreceptors ablation dive  of  heart  intact  that  were  the rate  animals  (1974),  on  the  the  reserpine,  in a  the  When t h e s e  to  (Butler basis  is  an  in  blood  The a u t h o r s  Blix.  the  These  1974,  drop  blood  concluded  to  to  and an that  show 2),  portion  expected  if  reflex  did  as  in  A n d e r s e n and  for  treated agent,  diving with  order  to  accompanying  dived,  a  diving.  slight  pressure in  early  occurred,  from these the  heart  and  the  dive  produced  immediate  fall  in  heart  d i v i n g b r a d y c a r d i a must  activation in  Blix  concluded  ducks in  the  prevent  degree  evidence,  of  although  peripheral vasoconstriction,  baroreflex rise  be  same  norepinephrine  pressure  of  Figure  were  of  secondary  authors  animals in  larger  responsible  depleting  diving  animals.  1971).  authors  of  bradycardia,  vasoconstriction  large  a consequence  that  the  sectioning  degree  the  would  pharmacological  catecholamine  a  to  primarily  ducks.  began  for  and J o n e s ,  of  injection  resistance  as  the  intravenous  was  diving,  reserpinized  be  eliminate  from d e c r e a s i n g  and  therefore  intact  rate  bradycardia  rate.  in  the  baroreceptor-heart  neurogenic  increase  that  d i d not  performed by  reduced  responsible  baroreflex  bradycardia  prevent  bilaterally,  compared w i t h  Denervation, the  denervation,  the  as  dive.  experiments rate  dropped  and  peripheral In  the  only  (Andersen somewhat  data  and as  45  blood then  pressure this  fell  drop i n  in  the  pressure  tachycardia  mediated  experiments  demonstrate  dive, for  but  their  baroreceptors  fixed  level  of  cardiovascular tonic  outflow  by  in  and  blood  significantly.  resistance total  in  rate  the  limiting times  the  with  the  by  in  is  active  for  in  the  a primary  role  nerve  provides  which  the  the  since fall  in  heart  in  in  resting  appear  of  to  output forced  animals,  the  contribute  d i d not  the  groups  baroreflex  and a f t e r  rate  nerve  cardiac  blood pressure  operation  from  the  is,  neurones  receptor  of  during  d i d not  That  baroreceptor  seen  stimulation  the  assessed.  other  a  change  during  peripheral  The p r o p o r t i o n a l change predive  continuous  to  was  the  during  baroreceptor-hind limb resistance  reflex  rise  to  6.6  non-stimulated  nerve  end-dive  in  stimulation  resistance  increase  of  baroreflex.  affected  authors'  against  changes  reflex  The l a r g e  true,  dive  and p a r a s y m p a t h e t i c  responses  control,  arm o f  submersion,  aortic  modulations  the  occurred through  most  one  from  and t h e s e  peripheral resistance  variable  9.2  inputs  continuous  pressure  stimulation  of  stimulation  apparent  During  conclusive  is  response.  sympathetic  diving,  baroreceptor-heart to  of  peripheral resistance  dives.  baroreflex  d i v i n g c o u l d be  from  be  not  The  effects  modulated by  then  the  contention  produced a  activation  would  would  have  baroreflex  constant  in  is  stimulation  by  involved  their  baroreflex.  that  this  produced be  if  should  the  evidence  Continuous  dive;  times, dives.  compared w i t h Despite  the  a  46  reduction pressure in  in  during  stimulated  non-stimulated  dive the  as  predive.  dive  could  this  must  other  be  a  receptor These  effects the  vasoconstriction  dives,  not  blood  prevent  reflection groups  on  point  of of  relation  between  various  blood  such  pressure,  rather  controlling  blood  James,  and E i s n e r  the  Daly  relationship  pressure  is  suggestions relationship  is  been also  cardiac  relationship  the in  cardiac diving  reset  pressure-vasomotor  per  role  the  of  have  that  making  the  pressure in  itself  diving:  emphasized  of  and in  Angell  that,  in  a n d mean  and  the  the  seals,  arterial  previous  (Angell that  the  James  et  operates  James  during al.  which  are  and  Daly,  baroreceptordiving,  (1978)  more  C o n c e n t r a t i o n on p r e s s u r e - h e a r t relationships,  from  resistance,  depressed  baroreflex  and  vasomotor-pressure  mammals  is  throughout  baroreceptors  interval  the  at  inputs  have  suggested  suggested  ducks  end-  For instance,  bradycardia,  in  of  vascular  se.  same  system.  components  made b y A n g e l l  limb of  seals.  in  has  of  blood  function  cardiac  made  (1980)  claims  on t h e  or  while  rising,  investigations  the  (1978)  towards  Millard  to  rate  than  between  1972).  contrary  necessity  effector  pressure  reset have  up t h e  heart  from  blood  predive  stimulation  influences  baroreceptor  as  the  cardiovascular  baroreflex  studies  above  was  pressure  activation  previous  baroreflex,  pressure  the  the  stimulation,  remained  blood of  point  baroreflex  central  dives  by  Baroreceptor nerve  findings  of  caused  likely  that  efficiently rate to  and be  47  reset  in  the  activated 1963a,b; 1972), and  dive  by  trigeminal  Butler  apnoea  central  and J o n e s ,  from  1968;  inputs  result of  the  of  and P u r v e s ,  baroreceptors  the  and  (Andersen, Daly,  pulmonary 1976),  1970;  picture  in  area  James  (Jones,  a misleading  processes  facial  inactivation  (Jones  in  the  Angell  r e s p i r a t o r y neurones  will  importance  input  and e n s u i n g  chemoreceptor 1982),  by b a r o r e c e p t o r - i n d e p e n d e n t  in  dive  afferents  and  Jones  et  a l . .  which  the  response  may  be  nerve  animals  over-emphasized. Intermittent at  rest  produced  continuous of  the  larger  stimulation,  baroreflex  response.  In  stimulation  dive  be  only  have  been Of  the  operates blood  experiments,  two  of  in  baroreflex  intermittent  rate after  the  the  to  did  trains  reduced was  as  the  the  absence  dive  modified  in  reflex while  conclusion  control  arms  of  ineffective.  the  to  than  pressure  attenuated),  rendered lead  pressure,  in  the  baroreflex  (although  heart  occur  the  was  in  and p e r i p h e r a l  baroreceptor-cardiac  a r m was  via  established  the  the  of  pressure  experiments  (which  pressure  cardiac  ability  blood  effective  these  adjustments  blood  short  results  regulating  in the  aortic  dive,  resistance  in  the  to  peripheral  baroreflex  with  of  contributing equally  affect  that  to  of  falls  The o p e r a t i o n  so  continued  the  to  progressed. the  stimulation  the  The that  cardiac  the  output  cardiovascular of  baroreceptors)  dive.  activation stimulation  paradigms is  used  in  p r o b a b l y more  these likely  48 to  produce  during give  useful  diving.  the  would  simulates  the  baroreflex  could  be  provide  input  of  the  brief  before which  picture two  the  degree  diving,  baroreflex  function.  pressure  changes  during  before of  diving,  a  of  agents  nerves  preparation.  the  the  were  used  variables  These  setting  but  selected of  blood with  controlled without  and  part  technique times  experiment pressure  the  the  nerve  The  type  in  in  in  and  advantage  level  of  input  affecting  directly. show t h a t ,  c a r o t i d body a  at  alter  input, a  of  the  pathways  experiments  produces  to  resulted  thus The  reflected  protocols.  simulates  provides  baroreflex  the  two  baroreflex  baroreceptor  present to  in  diving  stimulation  innervation  w h i c h may h a v e  s t a n d a r d i z e d method  parameters  central  to  than  and  output  cardiovascular  aortic  circumstances  cardiac  change  The  of  these  during  these  rise  a much g r e a t e r  animal  to  which  of  pressor  nerve  baroreceptors  Under  to  in  proportional contributions  and d u r i n g  that  observed  nerve  also  activation  to  aortic  is  lack  thus  the  dive.  intact  peripheral resistance  the  pressure  from  engaged  an  the  the  and c o n t i n u i n g p r e s s u r e  would be in  blood  of  function  protocols  stimulation  to  length  between  stimulation  of  large  baroreflex  stimulation  in  an  an u n r e a l i s t i c  different total  a  expected  difference  from  decreases  represent  throughout the  Continuous  large  experiments  i n f o r m a t i o n about  region  completely  results  in  ducks  intact,  with  the  sectioning  the  barodenervated  confirm the  work of  Jones  (1973),  who  stated  that  all  of  arterial  baroreceptors  nerves.  Abdel-Magied  have in  claimed,  chickens  common  that  there  carotid  authors, their  on  It  afferents  nerves  in  The  do  days  the  is  presented was  from  the no  cardiac but  if  It  anaesthesia  experiments  this  observed  in  which  denervation  is  was  the  of  the  begun,  of  (Jones  the  most  done  nerve  a l . ,  rest  section,  to  in  back  up  (1973) these  ducks,  these  animals section,  that  performed  were  the  made  effects  worn o f f  which would have  by  the  These  present in  that  of  and B u r g e r  in  nerve  resting  prominent at  (1984)  baroreflex.  were  ablation 1983; these  in  the  u n i l a t e r a l l y vagotomized  of  by  the  confounded  different animals  of  Series  of  and t h e  1-2  cardiovascular  experiments  et  aortic  walls  evidence  case  completely  completed  hypertension  aortic  are  the  possible  had not  were  the  the  u n i l a t e r a l l y barodenervated  experiments),  rate  is  series  vagus  bilateral  in  and o b s e r v a t i o n s  addition,  contralateral  of  zone  receptors this  anaesthesia,  in  systemic  and A b d e l - M a g i e d  r e p o r t e d by E s t a v i l l o  surgery.  in  carried  functional  aortic  In  from  carotid bodies.  bilateral  by  those  heart  a baroreceptor near  fibres  u l t r a s t r u c t u r a l evidence,  were  results.  lack  of  experiments  variables  the  basis  (1982)  present  or  the  al.  are  in  after  time  ducks  participate  general  surgery  afferent  not  barodenervated under  et  the  chickens,  receptors  in  arteries  however,  claim.  the  very  in  the 1  differences  animals  from  being  with  high  resting  barodenervates.  These  50 and  other  differences  procedures  used,  anaesthesia, of  animals  before  was  possible  after  these  state  were  observations  to  compare  had been  alone  were  al.  were  The  for  arterial  and  in  the  pressure  heart  rate  reflex  on p e r i p h e r a l  next  the  to  on  and  in  done  of  and  in  In  so  it  obtained in  the  unilaterally although  since  animals  one  aortic  unilateral  vagotomy  1 experiments from  dives.  where  or  the  animals  differences  of  Jones  intact  These  problems  a procedure  is  barodenervation. here  diving  diving,  but  its  reduced  due  to  and complete  show t h a t s t i l l  denervation.  resistance.  surgery  begun,  same  shams,  series  section,  presented  responses  is  true  rest  artefact-free  during  blood  at  made  section,  The e f f e c t s in  of  barodenervation.  were  the  were  vagal  represent  both  baroreceptor  functional  in  cardiovascular  experiments  cardiovascular  before  examined  found  addressed  presented  not  of  denervation  cardiovascular variables those  sectioned.  also  (1983),  animals  with  animals do  nerve  are  studies  procedures  the  effects  effects  "Sham" r e c o r d i n g s  barodenervated  et  combined  from  true  denervation  state.  this  the  either  the  barodenervation  intact  in  from  masking  neither  not  or  may s t e m  occur  the 1-2  The b a r o r e f l e x effectiveness  an  loss  attenuated of  in  days  after  is altering  baroreceptor-  baroreceptor  influence  51  SECTION  Cardiovascular Acute  to  II  Changes  in  the  Transition  Chronic  Barodenervation  From  INTRODUCTION  Ducks unilateral  which have aortic  contralateral series  1).  This  from  nerve  was  before  in  the  were  of  al.  vagotomy,  in  animals  were  one  itself  absolute  the  lack  may a l s o  were  affect  and p r o p o r t i o n a l h e a r t  of  control  section,  for  no made  made  before  contralateral these  sham  1  do  assessed.  rate  data  cardiovascular  Series  resting  may  denervation  heart  responses  aortic  not  cardiovascular  never both  difference  measurements the  1983,  acutely  measurements  "sham" b u t the  a l . .  the  the  In the  with  because  nerve  on  et  of  previous  (1983),  labelled  shams  aortic  a  n o r were  et  of  diving.  of  the  and t h i s  barodenervation  barodenervation.  genuine  the  addition,  performed,  constitute  vagotomy  I,  of  by  with  (Jones  methodology  Jones  sectioned,  cutting  in  experiments  bilateral  unilateral nerve  acute  the  experiments  however,  variations  of  denervations  true,  Section  the  In  not  acutely,  combination  hypertensive  in  There i s ,  system.  are  in  animals  procedure. effects  barodenervated  section  vagotomy,  barodenervated result  been  effects  Unilateral rate  and  during  52  It  is  conceivable  barodenervation compromised general  by  acute  incomplete  cardiovascular time  such  a  Franklin  ducks,  the  of  function during  a cardiac  same  stimulus  depression To this  of  this  address  section  nerves  snares  were  In  after this  way,  (Vatner  by t h e  1971).  used  effects  on  for  factor  in  a  has  been  results awake, 1975;  In b i l a t e r a l l y aortic  implantation procedure,  while  nerve  anaesthesia,  produced  a n i m a l s were  d e m o n s t r a t i n g an  given  acute  anaesthetic.  a preparation  snares  placed  surgery under general complete  observations  were  animal  as  acted  the  agents  in  the  check  by the  of  of  and Braunwald,  b a r o r e c e p t o r s were  use  of  and  to  problems,  withdrawn a f t e r  each  responses  later,  response  loss  and t h i s  1-2  days  an e f f e c t  and p o s s i b l y  t h a n when t h e  during  control  the  been  trauma  r e l a t i n g the  under general  i n which the  aortic  reflex  the  have  surgical  response  these  instantaneously,  and  the  acute  could  deleterious  s t i m u l a t i n g the  s t i l l  I  the  anaesthetic  anaesthesia,  and Braunwald,  a n i m a l s were  less  General  invoked during  to  of  surgery,  unrelated to  behaving animals  barodenervated  the  after  complication in  experiments  electrode  Section  mammals h a v e  general  serious  spontaneously Vatner,  in  reflexes  after  considered from  days  themselves.  experiments  short  1-2  in  results  r e c o v e r y from  w h i c h would be  baroreceptors  the  experiments  anaesthesia  experiment  that  is  presented  denervated around  its  in  both  anaesthesia.  r e c o v e r y from made  in  the  surgery,  intact  own c o n t r o l  The  for  state. the  53  effects  of  The  barodenervation per  forced  ducks  (Section  those  in  and  arterial  some  responses  monitor  of  must  heart  in  the  of  rate,  chronic  (Jones, the  weeks  after  at  least  the  and b l o o d  flow  once  of  of  those  I,  Section  pulmonary a r t e r i e s .  weeks  in  the  total  measurements obtained  several  of  from  including partial  the  present  of  new  probes  occlusion  the  was  pressure  flow  introduced of  ones  acute  arterial  electromagnetic  These  these  peripheral resistance  central  of  acute  development In  arterial  estimation make  required.  studies.  of  to  existing  the  following  order  and t h e  of  the  was  animals in  earlier  In  already  techniques  my a i m  measurement for  but  the  denervated  in  of  ducks, in  achieved,  s i m i l a r to  the  loss  in  Therefore,  reported  Lillo  cardiovascular  differences  in  from  1973;  c a r d i o v a s c u l a r adjustments  were  output  markedly  documented  values  ducks  recordings  from  problems,  few  groups.  to  a period  adaptation  experiments  the  rose  include  over  instrumentation  cardiac  two  of  these  peripheral resistance.  measurements  assessed  into  barodenervated  denervation  for  animals  been  barodenervated  differ  b a r o d e n e r v a t i o n had been  Documentation  pressure,  the  pressure  chronically  study,  1983)  first  not  insight  acutely  course  the  has  of  cardiovascular variables  blood  changes  a l . ,  The t i m e  baroreceptors  provide  until  et  occurring in  artefact-free to  Jones  1982b).  adaptations  diving  I;  responses  c h r o n i c a l l y denervated  Jones,  might  diving  se.  and  probes  on  several  arteries  (about  54 10-20  %)  ratio,  to  the  get  the  occasional  blood  flow  nerve  stimulation,  signal  particularly nerves  in  problem these  was  of  nerves  decided  flow  by  rest  during  proposed  resistance ducks  but in  a in  (Butler Heart  is  the  as  intacts  peripheral (Jones, Jones,  resistance level  in  cardiac  index  the  in  in  due  to  of  dives  the in  1971;  to  higher same  than  requirement  the  of  this  of  intact  end-dive  1973),  in  that  However,  in  chronic  in  animals  (Jones,  the  to  bed,  documented  total  at  been peripheral  barodenervated  ducks intact  hind  at  rest  animals  denervates  as  limb  barodenervates  intact  ducks  dive,  rises  1973).  and p e r i p h e r a l a d a p t a t i o n s  I  vascular  chronic  resting  in  reasons  1973).  resting  level  whereas  doubles  rest.  in  the  have  and  that  using  well  behaviour  latter  after  limb,  been  Jones,  aortic  to  here  that  the  The  changes  both  aortic  probes,  For these  has  of  root.  hind  chronic barodenervates  intact  the  some t i m e  the  artery,  compared w i t h at  levels  c h r o n i c a l l y barodenervated  resistance  1971)  aortic  and f l o w  and J o n e s ,  (Jones,  1973)  flow  ischiatic  forced  rate  to  the  The b e h a v i o u r  diving,  microvolt-range  some  instruments.  blood  the  pulmonary a r t e r y ,  normally for the  signal-to-noise  p r o x i m i t y of  to  probes.  good  significantly drops  right  good  of  from  p a r t i c u l a r concern  supplied and  and t h e  implant  a  susceptibility  pathway  measure  ultrasonic  for  interference  function  to  to  to  on t h e  their  operation  required f i t  to  (Butler  peripheral only  Therefore, loss  of  and  half while  the both  baroreceptors  55 occur only  in the  the  ability  chronically There  to  are  several  for  possibility  is  the  at  vasculature,  which  a  given  of  This  of  this  intact  A  second  structural increase produce  the  wall  in  change  pressure  the  evident  in  a  in  the  than  the  hind  that,  arterial loading  and t h u s  days  induction  of  hypertension  significantly chronically  to  the  changes,  increased  barodenervated  histological  comparison  hypertensive  animals.  of This  if  hind  limb  intact  hind  limb  animal  comparing  for  the  tract  to  due  to  a  vascular  animals,  maintained walls  in  ought  mammals are  to  tissue  hypothesis  is  could  vascular  occurring within  they  vascular  One  neuroeffector  outflow  peripheral  ducks,  in  electrical  altered  changes  be  change  hypertensive  the  the  Any s t r u c t u r a l  to  tree  of  could  animals.  in  to  1982).  in  vasoconstrictor  by  vasomotor  analogous  the  altered  different  limb  responses  the  is  hypertrophy,  the  investigated  of  the  dive  resistance.  in  resistance, of  in  and b a r o d e n e r v a t e d  in  is  which  sites  resistance  possibility  changes  in  a  be  is  a portion  the  and the  peripheral  resistance  hypothesis  in  periphery  adaptation,  the is  activity  stimulation in  of  should  the  state,  mechanisms  barodenervate  limb vascular  bed  possible  there  the  the  level  fibres. hind  in  resting  ducks.  long-term  that  relationship  its  vasoconstrict  during diving,  resistance  in  barodenervated  responsible response  circulation  to  few  (Folkow,  contribute  resistance be  a  seen  identifiable  from normoinvestigated  and by  in by  56  o b t a i n i n g h i n d limb a r t e r i a l w a l l c r o s s - s e c t i o n a l areas over a range of v e s s e l diameters i n both groups of animals. A t h i r d p o s s i b i l i t y i s t h a t the d i f f e r e n c e s i n v a s c u l a r r e s i s t a n c e at r e s t and d u r i n g d i v i n g a f t e r b a r o d e n e r v a t i o n are the r e s u l t of a change i n the output p r o f i l e s of vasomotor d i s c h a r g e from the b u l b a r neurones i n v o l v e d i n v a s c u l a r c o n t r o l , as the medullary r e g u l a t o r y pathways adapt t o long-term l a c k of b a r o r e c e p t o r i n p u t .  However, b e f o r e  t h i s h y p o t h e s i s can be examined, the e f f e c t s of c h r o n i c b a r o d e n e r v a t i o n on the v a s c u l a t u r e must be a s c e r t a i n e d . The r i s e i n h e a r t r a t e i n a c u t e l y barodenervated may  ducks  r e s u l t from an i n c r e a s e i n c a r d i a c sympathetic tone, a  withdrawal of v a g a l tone, or both.  The r e l a t i v e r o l e s of  sympathetic and parasympathetic c o n t r o l of the h e a r t a f t e r acute b a r o d e n e r v a t i o n were i n v e s t i g a t e d by comparing r e s t i n g h e a r t r a t e s i n i n t a c t and denervated ducks b e f o r e and b e t a - a d r e n e r g i c r e c e p t o r blockade.  after  57  METHODS  1)  Bilateral  Barodenervation  a)Preparation. Eight  adult  white  experiments.  The age  1  mass  yr  and body  0.2  kg).  the  syrinx  smaller of  the  Only  clavicular in  the  were  held  weight  of  air  sac  at  stopped  and water  ad  those For  placed  that  holding  so  its  d i d not  restrained.  back  taped  to  eat  ( P E 10)  the  the  joint  was  Pharmaceuticals,  for  18  (mean  this  wks  mass  study  3.1  +  because  primary bronchi not  to  obstruct  is  much  the  view  the  A l l animals  were  kept  indoors  in  Section  before  before  was  the  tibial  of  lower  into  surgery  because  they  in  unit.  was  all  this  and  animals,  study. an  animal  a  with  below  the  aid  was  ( S o m n o t o l , MTC mg m l  the  polyethylene  The c a n n u l a  65  was  lightly  located and  vein  Sodium p e n t o b a r b i t a l Ontario;  in  surgery  leg,  the  were lost  table  vein  and  animals  used  day  Animals  intact  monitored  not  I.  surgery,  Some  operating  Mississauga,  from  when  were  placement  kg  these  area  period  the  ranged  does  libitum.  inserted  catheter foot.  of  in  thoracic  days  on  The p o s t e r i o r  metatarsal-tibial  intravenous  on  upper  used  3.7  the  and  weight  anaesthetization  on  cannula  body  to  described  3-4  eating,  to  opened.  least  during the  2.4  selected  the  facilities  for  food  from  males  in  were  animals  trachea  the  is  ducks  these  were  the  vessels  holding  allowed  and  females  that  great  of  ranged  joining  than  Pekin  - 1  )  was  of  then  an  58 delivered  undiluted,  followed  with  surgical  procedure.  anaesthesia the  further  in  The t o t a l  mg k g - i  body  the  feathers  clavicular in  the  puncturing either  nerves fine  the  puncture  the  two  steel  positions  of  grooved or  The  the  membrane  then  on  together loops  loss  35  of  the in  around the prevented  nerves.  their  inside  the  were  thoracic  on  drawing The  disturbed Waxed  ends  pairs,  cavity,  aortic using  from  surgical  with  sliding  The f r e e  respective  placed  vessels  nerves  the  punctured  repair.  blood  the  45  before  facilitate  not  and  covering  were  sutures  were  15-30  anaesthesia,  Just  surrounding fascia.  which  of  skin  sac  later  of  hours.  plane  I.  accompanying but  response  between  air  to  for  of  was  area  silk  surgical  within  1-2  was  the  cornea)  of  and  site,  passed  this  the  silk of  aid from  thread  formed and  into  led  incision.  air  previously  the  tugging  4-0  needles,  mg;  the  Section  edges  from  director  relief  outside  in  were  twisted  strain  membrane  separated  in  two  40  produced  surgical  skin  described  of  were  catching  and t h e  sac,  snares  were  as  a  from the  air  silk a  sac,  stainless  their  removed  animal course  reached  of  by  touching  the  the  side  together  each  over  dose  (evaluated  dose  for  bolus  required throughout  initial  to  were  midline  as  membrane  animal  air  initial  doses  birds  weight  When t h e  an  The  most  nictitating  min.  in  sac  placed  edges  membrane sutures  together,  was to then  carefully draw t h e  r e p a i r e d by  centres  stitching  with  of 4-0  using  the silk  the  cut on  an  59  atraumatic  needle.  the  membrane  was  closed  through  of  the  skin  cavity  free the  of  with  site  ends  of to  the one  the  membrane  the  of  the  veterinary  Laboratories,  Montreal, near  healed  few  alone  during Within  a  blood  a  1-2  flow  probe left,  made  the  skin  iliotibilalis  tissue.  by  wound  days,  and  days  the  reached  antiobiotic 250  the  natural  and become  a  the  securely  animals  (Ampicillin,  to  a  Ayerst  injected  surgery.  animals  a  which  closure,  some  after  underside  skin  sutured  was  to  producing  skin  mg)  site  used  the  process  In  skin  placed  the  prevent  and  incision.  the  was  overlying  knotted  Quebec;  line  healing  The  left  The  the  wound  wound  site  preening.  usually in  to  watching  stitch  against  Following  were  a  eventually  and t h e  infection.  wide-spectrum  within  animal  during the  snares  suture  done  by  achieved.  and  of  membrane  intramuscularly  sac,  sac  of  side  was  air  T h i s was  fluid  for  air  confirmed  the  incision.  the  seal,  breath,  repaired  movements  f i l l  skin  the  each  surface  between  possible  with  centre  outer  breathing  could  over  the  draw t h e  move  An a i r t i g h t  of  was  the  implanted  under to  lateralis  Parks  local  expose  tunnelling  the  between  Doppler  principle  (Parks  Oregon)  were  in  this  to  implant  a r o u n d one  anaesthesia. posterior  muscle.  ultrasonic  used  operation  The  this  blood Medical study,  flow  artery,  An i n c i s i o n  margin  of  probes  required  was  underlying  working Inc.,  was  the  artery  and t h e  Electronics and  snares,  ischiatic  ischiatic  muscle  the  on  the  Beaverton,  extensive  60 modification The  correct  artery local by  before probe  size  the  exposed  after  anaesthetic  completely  After  the  halves into  the  the  is  days.  rapid  the  body  leads  twisting  of  the  probe  returned  margin  was  reattached  under  the  skin  joint  and the  suturing sutured over the  the  the  this  to  thigh  incision  connector Polyvinyl  stable  were by  was  the  vessel.  ends  of  the  from a of  incision.  small the  was  stitches  not  probe  has in  the a  into  the  and the to  angle  The  overlying  and  its  was  at  to  the  hip  covered  incision  anchored  The  pushed  near  then  of  posterior  leads  was  few  prevent  leads.  placed  shown  within  back  incision  leads  two  injected  probe  The c o n n e c t o r  itself  loose  probe  wall.  transmission  adjusted  emerging  was  traces  artery  in  diameter  cavities  former p o s i t i o n  length  by  the  bathed  and t h e  if  flow  pushed  the  vessel  vessel  which,  of  on  its  the  saline  flow  then  probe  over  connector  in  crystal  on t h e  its  emerge  entire  the  in  body  free  to  and the  into  fit  had been  acoustic  type  Appendix).  maximize  together,  as  (see  loose  around the  this  from the  was  on  with  a  muscle  well  occupied  muscle  connector  as  and probe  emerging  to  a i r bubbles  results  originally  be  segment  smooth  tied  growth  and  to  minutes  placed  healing  The v e s s e l  position  few  displace  tissue  implanted  chosen  the  Experience  local  lumen  probe  hinder  processes.  a  be  arterial  had been  lumen t o  dislodged,  that  for  could  was  relaxing  probe  of  they  the  each  was  by then  skin corner  of  housing. chloride  tubing  (PVC; B o l a b ,  Lake  Havasu  City,  61 Arizona) was  was  treated  (TD-MAC; heparin  filled to  was I.  to  the  a  1:1  sec,  flushed of  tubing  chronic  with  then  patent  wing,  under  local  vessels  were  PVC t u b i n g  so  that  vena  the  cava,  the  of  in  chronic  side  cannula  ends  use.  of  After  closed,  of  the  kept wing  and  was  weeks  the  Side the  because  it  normal wing  with of  short small  was  the  covered  with  a  cm  of the  be tape  second  these lengths  8-10  trunk or  cm the  for cannulation  as  to possible  and venous tips.  gauze  500  the  of  desirable  and c o u l d  cannulae,  in  used  circulation  pieces  every  12  occlusive  from the  tubing  inserted  were  Both a r t e r i a l  very  and  were  usual  for  would  branches  brachiocephalic  more  mm b a c k  which  and v e i n  side  branches  was  containing  flushed  artery  diameter  tubing  air-dried  when  small  bind  blood  and t h e  saline  surrounding tissue  the  1-2  withdrawn  avian  ulnar  within  placement  cleaned  of  to  and t o l u e n e  provided cannulae  animals.  were  was  of  solution  The t u b i n g  vessels,  cut  the  ml  to  A length  TD-MAC  three  than  much o f  holes  underside  20  from  rather  as  order  mixture  respectively.  preserve  had  of  ml.  lay  major wing  these  prevent  appropriate  tips  cannulation of  in  anaesthesia,  freed  of  walls  up t o  exposure  solution  Pennsylvania)  with  After  tubing  Warrington,  the  day.  This  Inc.,  procedure  for  cannulae.  a heparin-containing  preparations.  heparin per This  with  mixture  slowly  overnight. remain  intravascular  internally  in  90  U.  for  Polysciences  clotting  60  used  The  cannulae exposed  secured when  incision  pad taped  to  not  the in  was in  place.  62  These  cannulae  repeated made b y  remained  open  wing movements, the  birds  in  observation  days,  the  concentrated  and t r o u b l e - f r e e  such  the  as  course  cannulae  solution  of  stretching of  normal  were  heparine  and  spite  of  flapping,  behaviour.  filled  (1000  in  I.  with U.  Between  a  ml  -  )  1  in  avian  saline.  b)Experimental  On t h e snare  Procedure.  day  of  the  implantation,  supine  position  pressure  were  cardboard movement  baroreflex  was  tested  25-50  ug  of  normal,  were sec, the  then and  animals  barodenervation.  was  used  d i s t u r b i n g the  r a i s i n g the  of  0.1-0.2  response by  pressor were  after in  flow  to  to  forcibly tests  of  The with  saline  (Neosynephrine  this  Ontario),  pressure  responses  acceptable  and  rise.  submerging the  and d i v e  considered  a  and  pressure  ml b o l u s e s  and  prevent  animal  blood  a  and  minimised  Laboratories, Aurora,  dived  if  and b l o o d  noise  was  phenylephrine  cardiac  the  table  days  c a r d i o v a s c u l a r measurements.  by  injections  table,  Laboratory  room f r o m  monitoring  30  restrained  around the  Winthrop  min  lightly  operating  hydrochloride,  Animals  a n i m a l was  steady-state  intravenous carrying  5-7  recorded.  the  influencing  usually  the  on the  shield in  experiment,  for  head were  for  2  63  Aortic freeing  nerve  the  the  threads  the  body.  ends;  of  gently  the  snares  until  both  procedure  denervation,  then  day.  no  were  Pressor  the  because  danger  of  of  the  blood  vessels  snare  withdrawal 24  hrs  were  c)Recording,  Phasic signal  were  tape  as  were  also  first  if  Data  blood  up t o  described written  data 16  pressure, on  on  electrodes.  Mean p r e s s u r e  the  of the  were  was  small the chest.  again  tested  responses begun.  to  Animals  postdenervation.  flow  chart,  was  in  cardiac  collection  the  acute  to  a result  animals  after  until  in  damage  growth  no  of  denervation  Procedures.  and an  as  well  from b i p o l a r obtained phasic  event  recorder  Mean p r e s s u r e  ECG waveform  filtering  after  8-channel  the  the  electrically  hrs  were  hrs  w e r e made  performed  the  phasic  an  1-2  not  as  free  instantaneous  up t o  any  by  withdrawing  entirely  and C a l i b r a t i o n  previously. out  for  bilaterally  and  this  tissue  days  Collection  displayed  to  occurred  there  pressure, for  were  exacerbating  experiments,  by  24  postdenervation,  blood  monitored  were  d i s t u r b i n g new  and,  skin  measurements  w h i c h may h a v e  a baroreflex  increased  from the snares  tests  within  for  accomplished  recorded  further  barodenervates  At  was  Cardiovascular responses  denervation  following  destruction  in  and  stored  a n d mean as,  in  marker on  flow  some  subcutaneous most  pressure  experiments  signal  with  a  64  low-pass  filter  prevailing mean  heart  pressure  obtained areas  using  from  were  rate  "area under the  computed  from  filtering  the  the  filtered  heart  d u c k was  trace  was  c a l i b r a t e d by  to in  known  levels  closed  This  manometer.  gauge  transducer-tubing  in  was  over  the  flow  was  the  different  same heart  at  the  as  than  40  the  a  Hz,  level  table,  and  pressure  fluid-filled a  same  at  of a as  0-350  dial  a mercury gave  linear  mmHg.  determined 1974).  chart  The  damped n a t u r a l  McDonald,  the  syringe  sphygmomanometer against  the  by  resonant an  impulse  The damping  estimated.  barodenervation  implanted  on t h e  setting  combination had  greater  not  the  for  from  clamped  range  "Hansen p o p - t e s t " ,  (the  in  by  of  r e c o r d i n g system  test  probes  phasic  representative  calibrated  of  were  several  which  as  with  frequency  In  areas  position  with  circuit  The p r e s s u r e  displacements  factor  in  that  accepted  was  the  connected  pen  transducer  when  transducer  gauge.  4 % at  m e a n was  of  This  with  simultaneously  calculating  within  method  traces  the  1 sec).  animals,  curve"  chart  for  pressure. pressure  pressure  than  several  obtained  and by  agreed  mean The  pressures  trace  so  for  fast  suitable  greater  the  electrical  true  (usually  compared,  Mean  rates,  constant  was  pressure.  pressure  a time  on t h e first  experiments,  ischiatic  two  comparison with  animals, that  artery to  pneumatic  downstream  establish  obtained  towards  occluders of  a true the  the zero  end  of  flow  65  diastole  at  occluders that be  easily  daily  with and  the  end  hip  the  calculated  were  ischiatic  blood  d)Experimental  As  was Data  observed have  the  in on  in  experimental  sessions  compressing  the  artery  of  pressure the at  before  applied  baseline the  start the  the  in  of  of  recording  probe  at  the  during  were site  in  could  a thumbnail,  trace  a  found  artery  against  the  session.  was or  known f l o w  arterial  to  anaesthetized  situ  limb vascular  mean  was  flow  vivo,  probe Hind  by  animals  flow  calibrated  Protocol  above, After  and D a t a  control  exposed, in  vitro,  rates  as  resistance  pressure  was  and  each  each  day been day  Analysis.  data  denervation,  barodenervates  therefore  observations  It  ischiatic  quotient  described  observed  experiments.  and  flow.  barodenervation. were  agreement,  the  Appendix.  the  good  in  through the  the  as  later  experiments,  running blood in  showed  flow  pentobarbital,  probes  described  of  procedures of  in  with  setting  sodium the  used  cessation  the  setup  the  not  These  produced by  near  confirm  by  were  a brief  femur  At  end-dive.  for  the  were  collected  cardiovascular  up t o  16  entire to  group.  The a n i m a l s  denervation,  within  one  but  variables no  experimental  grouped  environment  make  days,  equal  or  and t h e r e a f t e r  animal period.  numbers  became  two  before  of  used  to  observation  cardiovascular  66  variables of  being  settled placed  observations pressor made  at  Mean  on  were  tests  for  to  the  were  least  an h o u r  analyzed  using  these  individual  blocks  and w i t h days. Tukey's  were  replicated  In  the  case  multiple  significant considered  of  circumstances  be  more  (Zar,  no  heart  from  within  recording of  4-6  15-20  min  session,  hours  and  observations  rate  the  and h i n d  recording  if  were  in  a blocked  treated  as  a  with  repeated on t h e  comparison between  robust  than  single  same  test  used  the  of  block  (Zar,  and  over  time,  experimental  (P  was  were  design  measures  F-values  pairs  limb  sessions  variance  was  1984).  rest  further  significant  means  each  course  measurements  differences to  of  analyzed  at  afterwards.  values  analysis  In  the  pressure,  resistance  Each  over  performed,  arterial  values  table.  made  vascular  1984).  baseline  <. 0 . 0 5 ) ,  means.  LSD t e s t  to  detect  This under  test these  is  67 2)  Effects  of  Responses to  Five kg)  Beta-Receptor  w h i t e P e k i n ducks  were i m p l a n t e d w i t h  measured  aortic  After recovery  and t h e  baroreflex  induced with phenylephrine a n i m a l was  given  propranolol  the  was  injections. dose of  beta-blockade  eliminated  after  was  accomplished pressor  barodenervation, propranolol  the  was  each  Quebec).  Barodenervation c o n f i r m e d by  after  r a t e s were r e c o r d e d b e f o r e success of  which  This tachycardia  two  days  mg  Ontario),  tests.  c h e c k e d by m o n i t o r i n g t h e  rises  (Isuprel  s n a r e s and was  and t h e  was  Montreal,  by p u l l i n g t h e  heart  rate  t e s t e d w i t h 0.2  ducks.  0.2  beta-antagonist  propranolol treatment.  treatment,  isoproterenol.  heart  One h o u r l a t e r ,  isoproterenol  One t o  +  described  t e s t e d by p r e s s u r e  a tachycardia in untreated  repeated  s n a r e s as  Winthrop L a b o r a t o r i e s , Aurora,  was  was  nerve  Ayerst Laboratories,  beta-agonist  hydrochloride; causes  of  (mean body mass 3 . 0  from s u r g e r y ,  a 1 mg b o l u s  (Inderal;  The e f f e c t i v e n e s s doses of  Cardiac  D i v i n g and B a r o d e n e r v a t i o n  female  previously.  B l o c k a d e on t h e  the  and  after  beta-blockade  c a r d i a c responses to  injected  68  3)  Hind  Limb  Three  ducks  sympathetic limb and  were  outflow  circulation. venous  injection  mg k g  for  table  musculature  The was  iliotibialis  in  were  muscles  the  mass  of  these  the  lumbar and  sacral floor  this  Extensive exposed  were  ridge  side  down  in  the  which ala  plexuses  ganglion  chain  was  with  bone was  required  particularly in  from to  (see  for  when  and  their the  hip. exposed  separated  synsacrum.  and t h e  gained  rongeurs  general  preacetabularis,  lateral  nerve  by  lumbo-  removing  the  spongy  the  ala  the  F i g u r e 2).  hemostasis bone  of  of  access  to  removing the  ventrolateral  the  floor  inter-ganglion aspect  of  the  of  nerves fused  lying  the  the  preacetabularis, along  synsacral  the  vertebrae  a  Acess  synsacrum. After  on  35-45  induce  ventro-laterally  the  were  cranialis  anterior  muscle,  exposed  surface  electrocautery  probes  surrounding  separated  muscles  caudalis  and  ischiatic  hollow  tissues,  hip  iliotibialis  i l i a l  origin,  sympathetic of  the  and t h e  Reflecting  to  ventral  drug  to  the  hollow  positioned  and  flow  hind  arterial  intravenously  of  lozenge-shaped  with  recording artery  the  given  removed,  synsacral  of  (Somnotol,  side  its  implanted  pressure  overlying  iliotrochantericus  control  pentobarbital  the  from  were  locate  sodium  was  lateralis  to  in  ischiatic  on  the  involved  animals  and  skin  experiments  blood  and  weight)  anaesthesia.  origins  These  The a n i m a l s  body  - 1  used  respectively,  operating  Stimulation  pathways  cannulae  implanted. the  Sympathetic  was  69  Figure 2. Schematic diagram of t h e sympathetic ganglion c h a i n on t h e l e f t s i d e i n t h e p e l v i c r e g i o n o f t h e d u c k . The s i t e o f s y m p a t h e t i c n e r v e s t i m u l a t i o n w h i c h p r o d u c e d maximum h i n d l i m b b l o o d f l o w r e d u c t i o n i s shown b y t h e s c h e m a t i c s t i m u l a t i n g e l e c t r o d e s , and t h e s i t e o f n e r v e s e c t i o n i s shown b y t h e d r a w i n g o f t h e s c i s s o r s .  71  obtained nerve  by  from  ventrally  surrounding fascia  stimulation around  the  ganglia,  of  these  nerve  the  nerve  ganglion,  used  draw t h e  to  the  more  electrodes aortic  procedure last 21  two  and  caudal  At  while  limb  consistent  lumbosacral spinal the  each  the  flow and  site  The  denervated  denervation,  28,  greatest  2  and  to  had been  and  animals  was  and p r o c e d u r e s  stimulated for  between  in  the  were  ganglia the  from  (Figure second in  denervation  at  which  set  of  2  days and  was  2).  barodenervated 14  The  first  plexus  done  tried  monitored.  to  a  at  the  segments  vasoconstriction  arises  4 bilaterally were  were  established,  for  This  patterns  ischiatic  experiments  described  lumbosacral  rostral  limb  was  attached  segment  3,  hind  the  vertebral  sympathetic  the  of  thread  section.  sixth  of  and  tied  stimulating  connective  pressure  was  s t i l l  those  stimulus  just  For  silk  of  succeeding  degree  ganglia.  ligature  between  the  each  a pair  between  to  the  of  a pair  the  each  and b l o o d  stimulation  baroreceptor-intact  on  5-0  nerve,  previous  various  connective  nerve  this  sympathetic  site,  contributing  ischiatic Once  segment  segments  nerve  at  the  than,  (located  repeated to  the  of  freeing  ligature  the  smaller  first  ganglia  of  through  performed  then  at  but  the  of  and  adjacent  rostral  end  end  ganglion, to,  more  free  cut  kidney  ligature  between  in  direction  obtained  longer  thoracic  hind  the  cut  the  between a  stimulation  was  22),  to  and t h e  similar  ganglion.  most  was  caudal  nerve  nerves,  close  rostral to  displacing  ducks.  postinstrumenting  72  the  animals  previous the  in  both  sections.  experimental  generated  by  a  Grass  pair  units to  of  (Grass  the  groups  procedure.  two  Grass PSIU  differential  S48  Quincy,  within  separated  by  pulse  stimulus at  a  intensity  fixed  increasing until  no  the  for  are  discussed  was  found, of  in  selected  possible  were  then  erected frequency  each  of  successive in hind of  applied  each  animal.  for  both  groups, the  limb vascular  in  tandem  were  pair  ms,  set  and  a  by  the  stimulating  Hz  while  bouts  of  stimulation occurred  parameters  and  maximum to  the two  curves  sympathetic  p r o p o r t i o n a l change during  waveform  Usually  response  by p l o t t i n g  (the  intensity  cover  order.  Stimulus  resistance  on  were  20-30  random  to  applied  waveforms  pulse  frequencies  in  pulses  Beaverton,  0.5  Once t h e  in  throughout  allowed  limb flow  stimulus  in  isolation  and v o l t a g e  r u n was  range  stimulation  against  which  biphasic  given  Appendix).  Hz w e r e  were  hind  on  choice  the  connector  the  decreases  this  0.2-30  calculated  in  stimulus  d u r a t i o n was  any  current  runs  stimulus  for  frequency  further  rationale  range  ms,  connected  ( T e k t r o n i x 5113,  The p u l s e s  wave  Massachusetts)  current  Oregon).  described  anaesthetized  stimulators  stimulus  oscilloscope  0.5  were  as  B i p h a s i c square  through a  the  same  constant-current  Instruments,  of  the  The a n i m a l s  electrodes  monitoring  were  in  stimulation.  73  4)  Hind  Limb A r t e r y  Four wks  of  adult  age  Structural  female  were  used  white  in  cross-sectional  areas  barodenervated  animals.  innervation  were  days  being  before  were  3.1  and  Pekin  in  the  hind  to  while  of  with  two  approximately  intact  of  barodenervates  arterial  intact  were  Body w e i g h t s  the  of  compare  limbs  Two a n i m a l s  killed. kg;  ducks  experiments  sacrificed,  2.9  Analysis 25  wall  and baroreceptor  barodenervated the  intact  weighed  2.7  14  animals and  3.2  kg. All  animals  pentobarbital As  soon  in  the  as  thorax  and the  with  the  was  sacrificed  mg i n j e c t e d after  the  exposed.  lower  body,  The a o r t i c  warm a v i a n  saline  vasodilation,  two  from the  vessels  drained  from the  punctured  the  saline, blood  perfused from the  % formalin buffered 1974),  also  over  of  tissues. with  containing  cavity).  clavicular  at  its  area air  junction  metal  aorta,  cannula  facing  posterior  vena  cava  connected  to  reservoir  % sodium the  lower  right min,  was  buffer  was  also of  for  and b l o o d  Perfusate suction.  enough  Perfusion  % sodium  nitrite  body.  was  a  animal,  a t r i u m by  phosphate  0.25  sodium  circulatory  A large-bore  above  the  5-6  central  severed  0.25  meters  flushed  of  was  of  peritoneal  descending  and t h e  containing  held  was  the  cannula  overdose  the  the  trunks.  into  an  puncturing the  aorta  brachiocephalic and t i e d  by  by  into  death  exposed  descending  inserted  towards  (150  possible  sac,  was  were  2  was  was litres  to  clear  most  of  then  begun  with  10  to  nitrite,  pH 7 . 2 from  (Culling, a  74  reservoir  at  perfusion  continued  was  the  clamped,  open,  same h e i g h t  the  and t h e  for  line  overnight  leakage  occurred but  reservoir pressure  after  to  animals  were  and  limbs  until  free long)  10  then  was  the  was so  reservoir in  proceeded. fluid  was  assumed  over of  this  the  removed  at  the  hip,  stored  in  buffered  vena  was  the  left  left  the  vascular  period.  vessels  at  the  the  formalin  at  This  was  a  hind  skinned,  body  venous  in  that  cava  lower  Some  time  fixation  Formalin  posterior  s t i l l  it  After  tank.  maintained  fixation  fixation  limbs  feet room  of  the  removed, temperature  sectioning. As  much o f  the  of  the  musculature,  of  leg  arterial  representative were  cut  the  of  freezing  stage  segment  as  blade  a  nearly as  um t h i c k n e s s . under  saline  fixative  maintained  diameters  the  head  there  diameter.  the  min,  the  hours,  ensure  physiological  the  while  had been  important  to  pressure  tissues  10  as  either  tree and  arterial  from the  perpendicular to and  These  sections  a compound m i c r o s c o p e  Switzerland)  or  Model  M5),  depending  on  diameter.  Inner  and o u t e r  diameters  with  an  ocular  the  the  a  (Wild  dissecting  of  micrometer  was  were as  placed axis of  on  of  the  travel  cut  at  wet  mounts  40-60  Model M i l , microscope  cross-sections (Wild  1 mm  various  long  examined  dissected  (approx.  direction  cross-sections were  of  A segment with  was  pieces  segments  microtome  possible,  possible  short  tree.  Heerbrugg,  measured  as  15XSK),  (Wild  were which  was  of  75 calibrated both  at  each  microscopes  2000 um s c a l e ) . resolved  with  sections  which  measured. axis  vessel  which  of  the  outer  sectional  which  enclosed  by  of  (see  diameter.  lumen  in  and  Lomb,  which  could  Only  at  an  angle  to  elliptical,  or  those  from  cut  into  diameter  in  was  at  the  taken  contrast Figure  subtracting  from the  were  total  the  edges  across  the  in the  7). Wall  area  was  inner  than  the  a  cross-  diameter  distinguishable  higher  by  inner  section,  arrows  so,  a non-circular The  be  those  nearly  easily  calculated  the  10 um.  used  or  the  having  (Bausch  dimension  discarded.  media, as  slide  shape,  compressed  adventitia was  in  The o u t e r  mounts  area  about  had been  lumen  the  magnifications  linear  appeared  were  the  of  was  circular  fixed,  wet  outside  smallest  had been  borders  different  a micrometer  setup  were  across  surrounding  the  this  epithelium.  unstained  area  The  and t h u s  when  measured  the  with  Sections  vessel  section  of  cross-  circular  derived  from  76  RESULTS  1)  Bilateral No  Barodenervation  sham d e n e r v a t i o n s  presented  here,  returned  to  5-7  days  after  The  responses  blood  the  of  phenylephrine  bolus  3.  1  mmHg  - 1  mmHg u g  .  mmHg  (1.03  a  - 1  larger  aortic  system  Table 4  for  in  over  the was  in  to  on  the  of  in  any  59.5  was  caused  was  dose  min  of  to  days  baroreflex  successful  in  ug  in in  heart  beats  min  abolished  mmHg;  with  1.21  no  number  repeated  of  pressor  denervation  response  and the  50  phenylephrine  innervation.  period,  in  pressure  - 1  was  (60.6  after  in  of  by  -1.16  test  by  snares.  illustrated  The l a r g e r  due  nerve  elevations  beats  this  all  animals  phenylephrine)  barodenervates, rate.  had  a mean b l o o d  increase  baroreceptor  observation  to  same  different  considered  experiments  injection  and  sensitivity  the  heart  r e t u r n of of  mmHg u g - i fall  denervates  animals  the  produced  mean p r e s s u r e  change  the  unoperated  intravenous  response  phenylephrine)  same  technique  in  implant  in  rate  destruction:  regeneration occur  the  summarized  The c a r d i a c  observations  check  by  p r o v o k i n g a mean  significant  the  to  phenylephrine  51.5  nerve  produced  those  cardiovascular  Baroreflex-heart  aortic  in  are  as  operation  the  in  cardiovascular variables  levels  induced  of  of  controls, rate.  the  performed  The p e r i p h e r a l v a s o c o n s t r i c t i o n  doses  increase  same the  pressure  Figure  since  were  due This  to  to did  denervation  eliminating  tests  not  -  by  77  TABLE  4  E f f e c t s o f i n t r a v e n o u s p h e n y l e p h r i n e o n b l o o d p r e s s u r e (MAP) and h e a r t r a t e (HR) b e f o r e a n d a f t e r b a r o d e n e r v a t i o n . Values a r e m e a n s + 1 S . E . M . , f o r 31 o b s e r v a t i o n s b e f o r e ( I N T ) a n d 87 o b s e r v a t i o n s a f t e r d e n e r v a t i o n ( D E N ) i n 8 d u c k s . The (~) s y m b o l i n d i c a t e s a s i g n i f i c a n t d i f f e r e n c e b e t w e e n I N T a n d DEN values ( t - t e s t w i t h u n e q u a l n ; P <. 0 . 0 5 ) a n d t h e (**) s y m b o l means t h a t t h e v a l u e d u r i n g t h e p r e s s o r t e s t i s significantly d i f f e r e n t ( t - t e s t , e q u a l n) from pretest.  PRETEST  PHENYLEHPRINE  MAP mmHg  HR beats/min  MAP mmHg  HR beats/min  INTACT  161.9 +4.7  152.8 ±4.5  213.4 + 5.9  93.3 +4.8  DEN  195.2 +7.1  264.9 + 10. 5  255.8 +8.1 ~ #  260.4 +9.2 ~ *  78  F i g u r e 3. A r t e r i a l b l o o d p r e s s u r e (ABP) t r a c e s f r o m t h e animal before (INT) and a f t e r b i l a t e r a l b a r o d e n e r v a t i o n (DEN). At the arrows, bolus i n j e c t i o n s o f 50 u g p h e n y l e p h r i n e were g i v e n intravenously.  same  79  80  baroreceptor Chart are  shown  days the  recordings in  after  until from  Figure  has  the  being  700-800  a  mm o f  decline,  The t i p  evident well  brodenervation The nerve  are  along a  hind  Stroke  but  then  and  is  has  been  site  and  time  as  cardiac 3b,  be  in  first  the  cardiac from  the  rapid as  the  in  the  latency response within  picked  up  receptors  pulse  in  the  in  the  denervated  pressure  pressure  after  both  heart  rate  increase  in  by  the  after  chart  limb blood  aortic or  before  nerve  blood  1-2  and  snares  at  in  occurred  the  min,  flow  presure  flow of  in  by  barodenervation  widening  aortic  recordings  pulse,  stroke  about  bilateral  obtained  pressure of  of  and h i n d  after  moderated  3a)  fully  the  have  slower  minute  seen  after  c a n n u l a was  response  frequency  withdrawal  first  (Figure  cardiac  should  2  seen.  illustrated  changes  test  reached,  tests  and a t  expressed  cardiovascular effects  with  a  not  and a  reduction  pressor  well  arterial  the  a r t e r i a l presure  limb bed,  flow  a  ratemeter  within  a  until  of  Figure  are  No o b v i o u s  animal,  of  control  to  same  also  8 min f o l l o w i n g  occurred  the  can  Phasic  4.  shown,  once.  this  as  immediate  triggering for  in  destruction  Figure  the  the  change  baroreceptor at  during  animal before  begin  peak  ms.  The l a c k  as  In  rise,  pressure  pressure same  not  of  changes  is  to  pressure  the  themselves. animal  the  does  started  beginning  pressure  blood  3 for  response  after  few  of  barodenervation.  cardiac  pressure  input.  flow  but  the  in  trace. mean  81  F i g u r e 4. Immediate e f f e c t s of b i l a t e r a l b a r o d e n e r v a t i o n on cardiovascular variables. Traces from top to bottom: a r t e r i a l blood pressue (ABP), instantaneous heart rate d e r i v e d by a c a r d i a c r a t e m e t e r t r i g g e r e d from the pressure signal (HR), and h i n d l i m b b l o o d f l o w ( H L F ) . At the arrow marked DEN, s n a r e s around b o t h a o r t i c n e r v e s were withdrawn.  83 flow up  increased  and b l o o d  minutes,  rate  the  after This  but  flow  two  developed.  within litre  the  of  These  trends  animals  in few  Figure  4.  the  to  for  10-15  rise,  plateaus  above  and  sec,  at  was  In  about  seen  rest  and  of  to  the  the  study  to  than  all  two,  a  developed circulatory as  drink  taking  continued  in  these  and p a t t e r n  began  15-20  maintained.  was  then  barodenervation, hour,  and heart  change  course  few  until  respectively  A l l animals  of  first  throughout  next  output  continued  denervation.  same t i m e  minutes  the  b r a d y c a r d i a and h y p o t e n s i o n  lasting the  the  after  cardiac  continued  reached  cardiovascular  transitory  within  fluids  rate  and h y p e r t e n s i o n  pattern  the  Over  heart  resistance  section,  followed  a  rise.  nerve  denervation,  presented  to  drove  levels  of  changes  began  rate  predenervation  marked but upon  heart  fell,  and p e r i p h e r a l  below min  rising  pressure  mean  hypertension  as  those copiously  in  0.5-1  drink  more  before  denervation. Loud the in  noises,  lighting  in  the  cardiovascular  either  direction  operating  table  pressure,  then  result  a  in  pressure  talking,  laboratory  variables, or  when  produce  repeated  decrease.  barodenervation,  all  but  magnitude.  would  and h i n d  touching  animal,  produced  these  first a few  an  were  not  The v a r i a b i l i t y  illustrated  of  resistance by  the  altering  in  later, heart  changes  consistent  tapping  increase  minutes  or  transient  F o r example,  limb vascular as  the  blood would  rate,  increased  approximate  the  blood after  doubling  in  84  in  the  standard errors  at  rest  (Table  Figure and  hind  5 represents  plateau acute  in  the  increased  pressure  at  resistance  With  the  heart  intact  and  rate  this  end  of  contributed  the  resistance in  gradually  16  day  increase  of  were  prolonged  blood that  40  pressure  r e p o r t e d by  denervation. barodenervates  hrs  this Jones  this  is  after  level  to  a  levels, was  however, to  double  time  rise  Figure  p e r i o d the continued  rise  of  75  a  due  rate,  16  days had  (1973)  since  intermediate 11-16  % above hind the  days the  limb  intact  vascular  control  increased  mmHg,  value  nerve the  ducks  30-50  in  when  refers  to  used  By  resulted  same  because  level  days  animals  an  Observations  section  to  the  peripheral  representing  level.  reached  "chronic", study,  after  in  stage.  tachycardia  predenervation  5  and  to  was  heart  this  40  in  denervation,  and by  s t i l l  days  maintained hypertension.  the  time  shown  in  fell  16  rate  pressure  with  at  pressure  beyond  4  unchanged  the  the  blood  % increase  increased  The term in  Figure  declined,  % over  by  70  rate  combined w i t h  in  and up t o  The p r e s s u r e  acute  to  before  progressively  observation  a maximum b l o o d  not  a  rate  level.  and  heart  24  days.  was  heart  As h e a r t  % at  to  postdenervation,  resistance  a r t e r i a l pressure,  The r i s e  rise  11-16  peripheral  the  variables  resistance  20  to  barodenervates  time,  cardiovascular  recording in by  continued level  between  mean  barodenervation.  illustrated have  these  4).  limb vascular  following  to  of  as  post-  describe in  which  85  F i g u r e 5. Cardiovascular adaptations to b i l a t e r a l barodenervation. A r t e r i a l b l o o d p r e s s u r e ( M A P ) , h e a r t r a t e (HR) a n d h i n d l i m b vascular resistance ( H L V R ) a r e g i v e n a s m e a n + 1 S . D . f o r 15 observations in 8 animals. A s t e r i s k s (*) indicate s i g n i f i c a n t d i f f e r e n c e s from the p r e d e n e r v a t i o n l e v e l (Pre) i n each day group. The range of days p o s t d e n e r v a t i o n i n c l u d e d i n each group i s given under the b a r s .  86  250r E E  Q_ <  200h 150h 100 h 500400  T  pre  1  2-3  4-5  6-7  8-10  11-16  A-5  6-7  8-10  11-16  8-10  11-16  r  c ?  300  X  a -° 200 cr 100  x  0  L  pre  1  2-3  10r 3  V. CL  8X  6 -  >  X  4h 2 0  ft pre  1  2-3  4-5  6-7  87  blood  pressure  (1973), within  and a  pressure  was  "acute"  few  days  had not  denervated  the  of yet  animals.  same  refers  as to  in the  the  barodenervates  condition  of  of  barodenervates  complete  denervation,  in  risen  the  chronically  to  level  in  Jones  which  blood  88 2)  E f f e c t s o f B e t a - R e c e p t o r B l o c k a d e on t h e C a r d i a c R e s p o n s e  to Barodenervation. Mean h e a r t r a t e i n u n t r e a t e d b a r o r e c e p t o r - i n t a c t was  180  ±  15.9  (S.  E. M.)  b e a t s min-1 , and t h i s d i d n o t  change a f t e r b e t a - b l o c k a d e barodenervation produced o f 32  %,  t o 267  + 20.4  ducks  (172  + 8.2  beats m i n  - 1  ).  Acute  a significant increase i n heart  beats m i n  - 1  , but a d m i n i s t r a t i o n  p r o p r a n o l o l i n these animals caused h e a r t r a t e t o f a l l level  (198  + 12.6  beats m i n i ) not s i g n i f i c a n t l y _  from t h a t b e f o r e d e n e r v a t i o n .  rate  of to a  different  89  3)  Hind  Limb  Sympathetic  The  site  of  access  Stimulation  to  a  sympathetic  vasoconstrictor  vasculature  was  the  joining  lumbosacral  at  location  this  obtained of  the  at  any  start  plateau  level  site  used  Hz)  lower  the  at  locations  segments  frequencies  resulted  interganglionic  segments  decreased  by  (control)  animals,  0.3  barodenervated proportional 9 % in  in  to  control  while  2.  2.9  P.  R.  IL  in  1.4  to  2.84  26  % in  animals.  of  caudal and  the  here.  to  in  this  two  connective  At this  connective hind  of  intensities  location, (50-100  intensities  low uA, and  vasoconstriction.  3,  This  a  experiments,  higher  and  and by  or  sec  of  stimulation  2  animals.  change  of  1-2  vasoconstriction  rostral  1 and  Stimulation  reaching  vasoconstriction,  produced v a s o d i l a t i o n  lumbosacral  and  stimulus  from s t i m u l a t i o n  limb  connective  within  frequencies  produced pure  hind  vasoconstriction  train,  of  the  the  duck.  developing  all  of  chain  the  preliminary location  and h i g h  frequencies  3 in  intense  pulse  sec  intense  resulted  When t h e  only  response  at  lumbosacral  intensities >10  less in  vasodilation between  the  always  stimulation  produced  animals  and  most  5-6  innervating  Various combinations  frequencies  Maximal  2  portion  ganglion  the  stimulus  within  stimulation. and  segments  gave  a  fibres  paravertebral  site,  of  substantial  cut  limb vascular  between resistance  baroreceptor-intact  decrease the  was  P.  R.  U.  in  represents  denervates,  Stimulation  of  an  average  compared this  with  connective  90  in  two  intact  stimulus from  to  intensities  0.2-30  Figure  6.  flow  animals  groups.  the  highest  hind  but  groups. limb  In b o t h  response  intravenous  injections  at  blockade  lasted  %.  doses  of  for  which time  at  nearly  of  limb  30  -  1  both in  the  the between  and b a r o d e n e r v a t e s ,  were  Canada  and t o  abolished  Ltd.,  resistance  this was  50  the ug  following  antagonist  body weight.  min i n  occurred during  alpha-blockade.  in  in  alpha-adrenergic  mg k g  of  resistance  higher  stimulation,  Ciba-Geigy  least  frequencies  a proportional basis, animals  the  was  at  curves  7-fold  differences  phenylephrine  1.7-2.0  hind  No v a s o d i l a t i o n  after  of  (Regitine,  Alberta)  no  sympathetic  boluses  phentolamine  on  control  to  uA a n d  frequency,  resistance  were  curves,  intravenous  during  stimulation increased  there  frequency-response  hind  limb  100-600  animals,  frequency-response  The p r e - s t i m u l a t i o n  barodenervates  the  r a n g i n g from  Hz p r o d u c e d t h e At the  in  and 4 b a r o d e n e r v a t e d  Calgary, Alpha-  preparation, reduced by  sympathetic  10-15  stimulation  91  F i g u r e 6. E f f e c t s of sympathetic g a n g l i o n c h a i n s t i m u l a t i o n on h i n d l i m b v a s c u l a r r e s i s t a n c e (HLVR) i n i n t a c t and barodenervated ducks. R e s i s t a n c e changes at each s t i m u l a t i o n frequency are expressed as:  stim  HLVR X  prestim  100  HLVR  E r r o r b a r s r e p r e s e n t 1 S. E . M . 6 observations in animals and 6 o b s e r v a t i o n s in 4 barodenervates are  2 intact presented.  700r E  I  intact baroclenervate 14-18 clays  600|  -*-> in  ^5001  400  cr  300  1 1  T  200  1  1 1  100" 0  5  10 sympathetic stim  15 freq.  Hz  20  25  30 to to  93  4)  Hind  Limb A r t e r y  The  two  arterial S. +  E. 12  and  pressures  while  206  15  mmHg  There  appeared  to  be  trees  dissected general  both  locations  of  7),  of  the  with  a  media  sections sharply  medial  lamellae  observed  have  been  In  none  of  a  the  of  these  good  in  from  ischiatic  groups,  the  intima,  media  a highly  particularly  when  was  among  in  organized sections  wall  the  of  did  was  the the  of  similar  the high  collapse,  enough  and  was  vivo  thus  likely state.  subendothelium  largest  arterial  high  from  lamellar  structure  was  under  sections  magnification.  diameters  viewed  tunica  of  all  were  (Figure  the  that  in  was  diameter.  sections  their  under  The  the  between  substantial in  in  nor  195  groups).  group.  cross-section of  were  +  arterial  um i n  indicating  vessel  (mean  segmentation  sections,  examined  sections  each  during fixation  a  even  the  No c r e n e l l a t i o n  the  vessels  both  cross-section  separation  animals,  level  in  400-500  appearance  artery  in  of  in  differences  representation  sections  the  of  significant  apparent  Within  in  animal  circular in  any  + 8 mmHg  and v e s s e l  than  had  barodenervates  limbs  adventitia.  pressure  appearance  the  were  in  vary  prevented  to  each  minor  smaller  from d i f f e r e n t  intravascular  the  with  two  animals  156  differences  4 hind  delineated  tunica  was  have  + 7 and  the  for  gross  from the  groups,  intima  to  in  (n=5  no  branches  and the  diameters  162  (control)  branching structure  common t o  Most  of  pressures  +  same  Analysis  baroreceptor-intact  blood  M.),  Structural  both evident,  polarized  94  F i g u r e 7. Photographs of s e c t i o n s of t h e i s c h i a t i c a r t e r i e s f r o m a n o r m o t e n s i v e ( a , INT) and a h y p e r t e n s i v e (b, DEN) duck. S e c t i o n s were c u t a t 60 um t h i c k n e s s , and t h e s c a l e b a r s r e p r e s e n t 500 um i n e a c h p h o t o g r a p h . The a r r o w s r e p r e s e n t t h e m e a s u r i n g p o i n t s between which i n s i d e d i a m e t e r ( I . D.) and o u t s i d e d i a m e t e r ( 0 . D.) were t a k e n .  96  light, it  but  without  could not  composed muscle  of  be  in  from  Scatter sectional measured  in  and  8b  um,  and the  or  arteries  plots  this  diameters values,  both  these in  but  branching  of  are  of  data  is  groups;  occurs  natural  in  the of  very  detailed  comparison,  diameter  enlarged (Figure  scales, 9).  limited  a  the  low  two  data  and examined  parts  of  of  the  co-relationships,  in  85  to  2200  indicates  a  larger to  striking  points  of  cross-  proportion A  result  study.  (intact)  groups  arteries.  plots at  8a  and a r e a :  walls  between  diameters  from  two  no  at  not  the  larger  of  missing  vessels  as  tree. showed  larger  in  and a h i g h  For purposes  ranged  the  this  wall  Figure  segmentation  s i m i l a r except  into  is  vascular  the  in  clumping of  this  in  versus  diameter  smaller the  distinguished  arterial  the  had h e a v i e r  did  the  in  between  than  both  plots  smooth  Consequently,  animals  of  presented  were  combination of  diameter range  techniques,  lamellae  fibres.  Diameters  the  groups  appeared  linear  entire  study  Superposition  these  internal  relationship  of  a  and h y p e r t e n s i v e  the  shapes  in  staining  these  or  collagenous  of  for  diameters,  feature  by  alone,  (barodenervated).  non-linear  specific  l a m e l l a r makeup c o u l d be intact  area  of  determined whether  and e l a s t i c  sections  use  smooth muscle  differences  their  the  for  each  they  diameters. plot  range,  were  were  and r e g r e s s i o n  area  For a  more  partitioned  replotted  significant  comparison,  curves  that  on  differences and d i a m e t e r  assumed  to  lines  were  have drawn  on  97  F i g u r e 8. R e l a t i o n s h i p between i n s i d e d i a m e t e r ( I . D . ) and wall cross-sectional area for hind limb arteries in intact a n d b a r o d e n e r v a t e d (14 d a y ) d u c k s . a) D a t a f r o m i n t a c t a n i m a l s (164 c r o s s - s e c t i o n s f r o m 4 h i n d l i m b s i n 2 a n i m a l s ) ; b) d e n e r v a t e s (163 s e c t i o n s , 4 h i n d l i m b s i n 2 a n i m a l s ) .  98  2.0 a) Intact csi  1.5 + ++ + +  +  ++  1.0  +  CC <  0.5  0  500  1000  1500  2000  2500  1500 2000 microns  2500  2.0 b) Den CNJ  1.5  •  1.0 CC  <  05 . * ***** **" 0  +  500  1000 I.D.  99  F i g u r e 9. I n s i d e d i a m e t e r s and w a l l c r o s s - s e c t i o n a l areas f o r two d i a m e t e r r a n g e s o f h i n d l i m b a r t e r i e s i n i n t a c t s (a) and barodenervates (b). Data i n t h i s f i g u r e have been a b s t r a c t e d from F i g u r e 8 f o r r e g r e s s i o n a n a l y s i s . Regression lines were f i t t e d by the l e a s t - s q u a r e s method.  b) DEN  101  through  the  computer  program  regression and  points  there  fits are  (S, are  area  ranges.  The s l o p e  for  and  arteries  different  from  barodenervates, range  of  the  same  no  significant  the  of  from that  smaller  the  simple  diameter  intact  arteries  1984).  these  line  the  animals  was  the  between  animals  the  range.  data  than  animals.  area-diameter  that,  in  limited  walls  from  for  significantly  indicates  thicker intact  data  slope  admittedly  in  diameter  of  over  diameter  (F-test),  correlations  This  this  The  sets  steeper.  difference  diameter  least-squares  data  over  animals,  significantly  in  all  linear  regression  being  have  for  barodenervated for  a  and Chambers,  significant  internal  barodenervated  graph using  Becker  internal  barodenervates  diameter  each  significant  between  larger  on  intact  do  There  those was  and  relationship  over  102  DISCUSSION  Blood hind  limb vascular  snares of  pressure,  were  normal  1968;  values  Millard, which  et  1980;  had been  1971;  Lillo  5,  for  a l . .  hind  5-7  (Figure  reported  and J o n e s ,  rate,  resistance  implanted  Djojosugito  Butler  heart  Jones,  Pre)  after were  1973;  as  aortic  (Butler  in  The l a c k  circulatory differences  animals that  group  from  control  other  after-effects  the  snares,  the  snares.  the  It  in  lag  in  these of  time  heart  in  measurement was  within  the  writing  of  the  a few of  therefore study  that  any once  baroreceptor 700-800  ms  pressure  (Figure  3a)  pressure,  mm o f  the  this  animals,  of  ducks  is  the  pressure  Lillo  experiments taken  had f u l l y  or  the  b a r o d e n e r v a t i o n was  phenylephrine-induced the  present  anaesthetic  follows  consequence The  of  before  the  studies  animals  any  occurring  in  1980;  ducks  chronic  1982a,  control  1973;  and f o r  (Jones,  the  Jones,  1969;  experiments of  range  and  barodenervation 1982b).  nerve  and J o h a n s e n ,  1982b)  controls  and  the  and Oda,  Bech  1982a,  flow  within  ducks  Kobinger  and J o n e s ,  sham-operated  days  intact  1969;  limb blood  and  and  Jones, between  intact  as  evidence  recovered  operation  to  performed by  cardiovascular  from  implant removing  changes  barodenervated,  were  solely  loss. from rise was  the to  not  because  the an  the  baroreceptor signal  beginning first  arterial  on t h e  the  slowing  artefact  site,  of  of cannula  and d e l a y  chart  of  recorder  tip  in was  103  negligible.  This  estimated  P i c k e r i n g and Davies  by  latency  smaller  pressure  present  experiments  means  cardiac  interval  pressure  of  no  use  in  rises,  was  to  ducks  as  baroreflex-cardiac regulated of  on  which  a beat-by-beat  heart  rate  was  -1.16  beats  boscas. return  occurred snare  as  the  of  receptor of  The  by  with nerve  a  of  day  the  response  is  The most the  .  This  this  heart  in  arterial  their  (Figure  et  a l . .  their  aortic  not  indicator the  pressure, same  in  Anas that  no  shows  study  that  the  prevented  and t h a t  no  stead.  4) w e r e  (1985)  in  less  experiments,  to  snare  extreme  rabbits,  in  than  carotid  the  other  had p r e v i o u s l y  those  which  occurred in  c r u s h i n g one  nerves  the  pressure-related  and h y p o t e n s i o n by  of  is  elevations  c a r d i o v a s c u l a r adjustments  ducks  of  The f a c t  period  the  relating  the  (1980)  duck.  in  basis  useful  was  much  obviously  arterial  pressure  in  line  magnitude in  observation used  time  sensitivity  rise - 1  the  pressure  domestic to  of  for  a beat-by-beat  the  was  value  humans,  arterial baroreceptors,  barodenervated  and b o t h  of  mmHg  - 1  assumed  In  on  the  in  slope  since  response  bradycardia  snare.  the  given  group  Ludbrook  transient rabbits  in  long  basis.  denervation  of  a  r e p o r t e d by M i l l a r d  16  immediate  withdrawal noted  the  a  min  species  the  reinnervation  control  for  double  (1973)  rise  function  cardiac  over  method  other  that  another of  that  response,  in  sensitivity  and such  a measure  baroreflex-cardiac  change  about  5 of  sinus  nerve  carotid  been  6  sinus  sectioned  104  during  the  pressure  surgery  and h e a r t  denervation, both  to  significantly the  moderated,  rate  Ludbrook  variables  however,  et  al.  continued  decline at  barodenervation  to  heart  (Figure  always  no  hypertension  hypertension  consequent in  Ito,  and  also  (Alexander Korner,  for  1981).  been and  more  reported de  fetal  (Yardley  et  reported  that,  extensive  al.,  rabbits,  5)  general  than  was  arterial  in  Cuir,  rabbits  1970;  to  1984)  and  through the  1983).  Cowley,  dogs  monitored  and m e t i c u l o u s l y  produce  maintained  longer,  although  termed  1958).  Chronic  after  2-4  1 yr  wk  denervation in  8 days  lability  of  and (Ito  barodenervates  post-denervation 1979;  sino-aortically  last  Liard over  over  has  post-  (Scher  third  of  gestation  and Guyton 24  hour  (1973)  periods,  performed barodenervation  hypertension  the  workers  barodenervation  up t o  in  of  arterial  B l o m b e r r y and K o r n e r ,  sheep  in  that  monitored  a year  post-  rabbits.  earlier  1976),  days  not  same p a t t e r n  and N e i l ,  dogs  al.,  4)  agreement  what  total  (Figure 16  in  plateau ducks,  the  in  a In  until  seen  to  post-  level.  Maintained hypertension  Head and B a d o e r ,  denervated  decline  followed  conscious  (McRitchie et  has  a net  in  (Heymans  to  denervation  Scher,  reported  pressure  produces  "neurogenic"  and  min  increase  rate  present  demonstrated  in  initial  10-15  pre-denervation rise  an  at  the  increase  1979),  (1985) week  After  peaked  above  while  been  which  next  denervation,  is  snare.  the  immediate  and  rise  the  over  but  There  implant  the  blood  course  pressure  of was  did  a year  not or  doubled  105  in  these  al  (1981)  days the  animals.  and B u c h h o l z  reported  Cowley term  lack  was  (1979)  (Alexander  by  and  study  of  blood  pressure  Jones  an  1970)  in  table  the  ducks,  in  which  of  normal  that  long-  the pressure.  levels  of  chronic  also  30  while  "apparent"  a period  at  sino-aortic  artefact  in  both  denervation heart  rate  Similar  reported  up t o  recording  and  to,  end  of  and  the  recording protocol  kept  and  in  over  These in,  important  barodenervation.  In  with  in  and  chronic ducks  by  in  a  restrained  minimum  course  animals  the  cages  blood  the  pressure  at  of  16  days  appeared  to  be  recording environment  recording sessions and  in  lightly  hours  increases  5).  the  been  4-6  session  relaxed  control  ducks  daily,  continued  well  following  an  that  for  (Figure  have  that  nearly  after  handled  post-denervation  to  in  monitoring blood  to  barodenervated  showed  the  contended  et  (1982b).  successive  appear  for  and t a c h y c a r d i a were  operating  adapted  (1981)  remained markedly elevated.  environment,  disturbance, each  (1973)  was  Norman  monitored  barodenervation,  maintain  "resets"  by  rats  hypertension  workers  to  reported  in  and S c h e r  denervates  rate  was  (1986)  incomplete  similar  my s t u d y ,  constant  to  other  and Jones In  Ito  deCuir,  barodenervation  Lillo  al.  chronic  in  heart  hypertension  result  and c o - w o r k e r s  used  rabbits,  of  due  hypertension  protocol  on  et  post-denervation.  denervates  In  T h e same  laboratory factors  in  fact,  both  before  denervation,  environment the  do  hypertension  control  by  and  not  106  barodenervated of  the  animals  recording sessions,  cardiovascular pressures  variables.  and h e a r t  barodenervates but  within  levels  and  were  15-20  to  not  an  a  On a  given  put  asleep  on t h e  ducks, result  when  had  of  the  loss  lability,  has  been  a  in  for  the  of  observation,  rest  dogs  lower  the  hypertension  baroreceptors,  a maintained  of  to  of  chronic the  blood  the  monitoring procedure.  feature  reported  in  stabilized  therefore, of  portions  r e c o r d i n g day,  table  variables  for  changes  elevated  accompanied by  pressure also  slight  first  genuine  was  with  were  In  artefact  hypertension  fall  maintained throughout  session. be  often  rates  min these  w h i c h were  recording seems  would  This  increase  in  chronic barodenervates (Cowley,  Liard  and  which  Guyton,  1973). Heart by  vagal  rate  activity  effectors  were  rate  occurred.  rate  was  outflow;  in  After  because  with acute  when  no  cardiac vagal  Blood time  peripheral  in  because  level  pressure after  increase  heart  in  these  does  not  denervation  resistance  representative  of  the  in  rate  drive  change  resistance  in  5),  the  hind  changes  cardiac  in  heart heart  after  the  beta-blockade.  heart so  set  cardiac  occurred  after as  is  however,  returned to  decrease  occuring  rest  sympathetic  animals  (Figure  at  sympathetic  barodenervation,  an  change  ducks  p r o p r a n o l o l , no  d r i v e n up b y  predenervation  be  alone,  blocked  barodenervation,  with  baroreceptor-intact  the  rate  declines  increases  limb are  throughout  in  likely the  to  107  vascular time. the  beds  One o f  genesis  resetting", thickness thicker  at  the  the  mechanisms  a  decrease  lumen  a  constant  to  hypertrophy  should  vascular the  and thus  bed  change  degree  of  in  resistance  a  large  years.  inflow  birds of  The u s u a l  isolated  matched  in  structural  amount  in  of  in the  the  then  greater higher  reported,  work  done  in  pressure, From  these  that  on t h e  variables,  to  bed, in  flow in  a  power  only  a  animals  of  Figure  beds  although  age-  rats,  pressure, and  in  small  limb 5.  in there  has  mammals  changes  in  of  tonic  in  constant-flow  pre-  than  hind  in  of  after  of  estimating  outflow  lumen  level  doubling  area  and h y p e r t e n s i v e  venous  of  vasculature  this  hind-quarter vascular  wall  fourth  change  been  depends  that  the  with  has  hypertrophy  flow  in  the  structural  blood  vessels  of  becomes  same t o n i c  in  Since  analysis  mammals  the  of  wall  degree  the  in  wall  wall  resistance  no  (1982)  arterial  proportion to  produce  for  of  muscles  with  "structural  a vessel  barodenervated  method  Folkow  (arterial  alteration.  would  normotensive  measured.  a  hypertrophy,  seen  hypertensive of  result  change  drive,  hypertensive  smooth  is  cumulative  a consequence  1962)  produce  radius  wall  sympathetic  No  will  as  pressure  the  structural  If  be  by  ratio  (w/r).  Furuyama, to  the  radius,  increased  drive  the  in  radius  to  discussed  or  sympathetic  before  and a p p e a r  mammalian h y p e r t e n s i o n  hypertension,  reduction  body,  of  to  adaptation in  of  in w/r  been recent  in  perfusion  and  weight-  which  and b l o o d  arterial flow  postcapillary  are  108  resistances resistance then the  to  two  Folkow  is  the  groups  easily  Folkow  (Furuyama, Short,  1966;  Several arterial results  his  of  of  sectional  In  the  simple  Friberg,  in  Figure  a  is  the  Nakashima  with  have  been  varying  (1962)  because  on  the  wall  thickness,  for  wall  Furuyama, without  on  the  tension  some  the  amount at  fixation  pressurizing  the  a  the was the  1967;  of  The  for  wall the  material fixed  of  on  arteries  measured  control  of  level,  morphometry  to  dimensions  the  1971).  regard  not  not  been  small  success.  did  is  and G l a g o v ,  for  the  depend  the  the  have  of  he  resistance  of  degrees  with  1985).  of  Most  and Mar,  used  the  arteriolar  Wolinsky  in  1976;  change  mammals to  beds  morphological  suggested.  aorta  is  in  limb  majority  the  hypertensive  from  the  the  at  Friedman,  will  immersion,  if  1970;  sets by  have  hind  resistance  occurring  in  Sectional  study  but  Wolinsky,  fixation  which  ducks,  others  dubious  area,  show t h a t  functional  techniques  are  5  particularly  Furuyama  study.  vessel,  and  ranging  sections  thickness effects  Folkow,  Nordlander  bed  the  1974;  studies  and  of  al..  and  1962;  behaviour  et  1978;  arteriolar  vascular  (Lundgren  adaptation  vessels  in  the  changes  such  (1982)  of  structural  hypertensive  of  morphological  resistance  of  to  1977,  in  contribution  attributed  accomplished,  structural  larger  is  presented  elevated  and t h e  Any d i f f e r e n c e s  et_al.,  data  total  vessels  confirmation  as  calculated  estimated.  resistance  The  are  in  cross-  pressure  time  used  of  carried  in  the  fixation. out  vasculature,  by and  109  the  result  lumen  border,  stated the  was  that  time  as  both  of  variables  a  crenellated  and d e f i n i t e l y  pointed  by  the  (whether  for  pathological  vessels,  reached  from  such  vessels  to  present  study  was  physiological flushing  fluid  wall  and  and t h e  to  arterial  wall  relaxed),  between errors  so  a vasodilator  is  to  ensure  o c c u r r i n g as  barodenervated  measure  for  ducks,  comparison  cross-sectional  with  area,  the  is  circular  cross-section.  were  subjected  to  wall  should  in  area  to  a higher be  comparison  between  though  might  from to  develop  the  the  two  higher  the  and  used  the  in  the  reasonable both  that  the  the  greater  control  expect  groups blood  of  for  than This  result  vessels  most  was  of  an  internal  animals  pressure  in  to  be  the  area,  be  unlike as  after of  wall  long  as  time,  for  then  of  different  in  denervates,  it  a  the  vessel  my  animals.  diameters  if  being  equivalent  basis  and h y p e r t e n s i v e  the  would  Theoretically, wall  the  reasonable  diameter  a period  that  of  controls  vessel  a thicker  pressure  a normotensive.animal.  one  and  causes  a in  because  of  in  the  a  the  independent  vessel  at  at  conclusions  method  perfusion,  is  given  the  fixation  thickness, vessel  normal  in  the  vessels  has  relaxed.  in  variable  or  fixative  thickening  hypertension  contracted  distort,  with  (1986)  the  Immersion  by  Lee  of  induce  fixation  pressure,  were m a x i m a l l y If  can  (1966).  state  comparison  studies.  collapse  Short  physiological  fixation  selected  out  non-physiological  Even  arteries vivo, must  due be  110  appreciated  that  population. animals  This  animals  therefore  no  selected  variable  for  compare  vessel  The  area  to  the  rise  theory  presented  opposite  to  basis  physiological  of  should  that  occur  level.  to  of  in  with  diameter  structural evidence in  the  wall any  intact,  size  range  % contribution to (Folkow arterial the  et  areas  a l . ,  wall  arterial  degree in in  resting so  as  thickening,  resting  the  intact I  independent area  of  ducks.  diameter  is  greater  animals,  in  the  the  to  in  larger  may c o n t r i b u t e  resistance. this  to  According  finding  is  the  on  the  a r t e r i a l hypertrophy  towards  the  present  arteriolar  study  smaller  so  been  same  same  groups  vessels  hind  the  in  the  (1982),  the  in  in  the  mammalian h y p e r t e n s i v e s  may h a v e  examined  to  in  normotensive  1966),  tree  Folkow  the  had o c c u r r e d .  and t h e r e f o r e  reliablility,  adaptations  in  two  measurements:  used  at  those  limb vascular by  of  cross-sectional  control  9),  greater  The t e c h n i q u e  estimations  in  predicted  a  the  internal  than  hind  wall  part  barodenervated  areas  as  diameter  in  (Figure in  wall  from  structure  against  given  ducks  limb vessels chronic  same  internal  a  vessels  wall  morphology for  initially  diameters)  in  plotting  barodenervated  the  (and  change  were  that  had the  pressures if  vessels  means  would have  internal  hind  the  than  a whole missed.  ducks  that  present  There  is  um  vessels  make  a  20-30  resistance animals  c o n t r i b u t i o n of resistance  of  conduit  limb vascular  allow  80-100  range  study  barodenervated  d i d not  this  c o u l d be  with segment  even  of  Ill greater. The chain limb 2 of  site  of  stimulation  of  the  sympathetic  p r o d u c i n g maximal v a s o c o n s t r i c t i o n was  and  between  3.  There  vertebral  ganglia is  some  associated  appears  to  similar  mammalian e x p e r i m e n t s ,  within  from the  sympathetic Kjellmer Jarhult  (1976)  ganglia  at  one  first  trunk  (1965), in  studying  side  of  ganglion  the  vasoconstriction frequency  was at  (Pick,  by  in  The by  5.  In  produced by  of  Folkow  dog,  (1952),  and  was  between  maximum h i n d  stimulating 2  in  number  Lundvall  the  ducks  site  limb vasomotion  4 and  1970;  used  segment  cats and  in  that  vertebra.  lumbar segment  curve  in  continued  increasing  level  at  resistance  at  the to  frequency,  prestimulus  level,  hind  of  segments  on  either  (Sonnenschein  and  1978).  ducks,  however,  counting  hind  correspondence  effective  segments  (1971)  duck  the  a n d mammals  used  al.  lumbar segments  the  two  cervical  Folkow et  vasoconstriction  In  or  the  lumbosacral  about  found most  stimulation  limb  Weissman,  site  birds  1979),  caudally  the  in  Baumel,  be  but  with  disagreement  segmentation  in  ganglion  a  relating hind  rise to  30  limb to in  a  degree  sympathetic  smooth,  Hz  (Figure at  6).  9.5-10  frequency  of  graded  1952).  Increasing  the  produced  a  decline  resistance  in  In  times  fashion  of  the  stimulation  7 times  cat  the  frequency in  hind  with the limb,  prestimulus  approximately  (Folkow,  small  of  a maximum r e s i s t a n c e  plateaus  stimulation  the  10  Hz  further,  to  30  the  The h i n d  cat.  Hz,  112  limb  vascular  sympathetic degree the  of  hind  a  chain  (1904). site  is  since  the  hind  by more  lack  of  thickness  and  produce compared  a  is  greater  relationship  the  distributed  contrary to view  likely  than  is  not  10  in  the  can  the  case  between  two  control  in  weeks  of  neuroeffector  denervates.  intact  group.  and h i n d  function  stimulation to  at  produce intact curve  experiments, limb  vascular  dives. and  chronically  control  given  the  of  hind  increase  after  the  increase to  in  resting  sympathetic  resistance  sympathetic  fibres  my  sympathetic  at  increase  in  forced  surprising,  amount  of  which the  during  significantly  set  of  to  the  sufficient  hind  If  fibres  opinion  correct, be  in  The f a c t activity  could  at  wall resistance  drive  should  these  animals,  that in  the  in  the  the  limb resistance  b a r o d e n e r v a t i o n may m e a n t h a t ,  vascular  the  of  same  frequency-response  is  5).  the  in  increase  fold  difference  between  vasoconstrictor  generate  level  vasoconstrictor  distorted  animal  contributes  with  a  (Figure  a  a higher  limb vasoconstriction  resistance  barodenervates,  to  the  c h a i n would  vasoconstriction  resting  or  birds,  animals  barodenervation  the  a  cats,  Langley's  This  barodenervated  after  If  conscious  resistance  in  in  capable,  result.  The  in  more w i d e l y  on t h e  of  would  limb  than  may r e q u i r e  vasoconstriction,  degree  animal  ducks  l i m b may b e  single  the  in  activity  sympathetic Langley  bed  is  unchanged  resistance  actually  be  sites,  reduced  in  113  The  act  lumbosacral electrodes  of  segments caused  barodenervated animals. the  sectioning  It  than  in  is  of  the  The  in  total  in  this  increase  the  in  ducks  rest  baroreflex. sympathetic blockade  over  changes  after  is  is  greater  lack  the  anaesthetized  suggests a  in  baroreceptor-intact  of  that  in  animals,  generated  by  barodenervates  neurogenic  baroreceptor  neurone  pool  chronically elevated  at  limb vascular  rest  may b e  resistance.  is  at  least  peripheral  in  the  vascular  outflow  tree of  to  experiments do  periphery is  works  the  in not  appear to  systemic  of  the  mainly through the  control  results  in of  changes  presented and have  a  role  hypertension  deafferentation.  baroreceptor control  This  representative  vasoconstriction  and maintenance  expressed  resistance  From t h e  neurogenic  baroreceptor  baroreceptors the  in  in  vasomotor  the  stimulating  limb resistance  tone  from  hind  both  development  Tonic  the  in  ducks  section,  in  for  peripheral  structural  even  finding  between  limb resistance  change  hind  trunk  barodenervates.  barodenervated in  no  that,  central  apply the  hind  but  arising  responsible  resistance  in  resting  This  sympathetic  3 to  vasoconstrictor  vasoconstriction  partly  fall  apparent  intacts.  inhibition  2 and  animals,  p r o p o r t i o n of  sympathetic  at  a  the  by  heart,  acutely exert  evident  circulation in cardiac  limb of  i n h i b i t i o n of as  ducks  i n d i c a t e d by  the  the the  beta-  barodenervated animals. the  from  same the  degree lack  of  That  of  control  an  immediate  114  change i n p e r i p h e r a l r e s i s t a n c e upon b a r o d e n e r v a t i o n  (Figure  5 ) , but the b a r o r e c e p t o r s must have an i n d i r e c t i n f l u e n c e on r e s t i n g r e s i s t a n c e , f o r the long-term l o s s of these  receptors  d i d produce i n c r e a s e d  limb.  sympathetic d r i v e t o the h i n d  115  SECTION  Cardiovascular in  the  to  III  Responses  to  T r a n s i t i o n From  Chronic  Diving  Acute  Barodenervation  INTRODUCTION  The  conclusions  controlling  the  studies  and J o n e s ,  depending dived. short  on  the  The to  heart,  time  intervals  post-denervation  due  1982a;  A systematic time  reduced  an  relative  was  to  diving  are  intact  and d e n e r v a t e d  receptor  baroreceptor  during diving, ducks  Jones  et  (Section al.,  II;  1983  denervation of  Jones,  series  the  the  dive  to  bradycardia in in  sympathetic  loss of  to  of the  the by  ducks  acute or  sympathetic  control  of  and  differ, were  16  controversy.  control  input. and  may of  be  the  The  parasympathetic rate  heart  after  at  days  denervates  heart  comparing dive before  this  vagal  baroreceptor  various  responses to  in  1973;  I)  animals  undertaken  resolve  input  drawn from  barodenervation  investigated  blockade.  of  from acute  the  pathways  role  investigation  contributions  cardiomotor  in  after  dive  alteration  related  the  circulation  barodenervation Lillo  about  during  rates  in  beta-adrenergic  116  METHODS  1)  Diving The  Responses  animals  barodenervation that  the  min  30  rate  in  sec.  were  postdive, end  the  the  If  these  hours  the  apart.  intact  so  a  in  Diving  blood  30  gases  made  at  20-30  in  to  be  a n i m a l was  dive,  to  an  least  min  one  gas  (Lillo  double  the  min  have  head  3 min  ml)  were  the  dive  gas  times and  in a  shown  one  half that,  in  all  variables and J o n e s ,  this  II.  following  blood  one  2  heart  until  required for  and b l o o d  than  to  for  Section  (0.6  several  studies is  and  after  15  days  lasted  2 min i n t o  I L 13  dived  min d i v e s  more  experiments  in  of  were  flow  samples  sec  repeated-dive  present  and  and c o n t i n u e d  blood  a n i m a l was  of  I,  outlined the  same  Dives  1 min r e c o r d taken  1 min  2-4  on t h e  limb blood  methods  ventilatory  each  hind  position,  least  in  Section  min before  at  were  a priori  in  Arterial  same  designed which  dive  time  the  as  the  1-2  following  recovery  adequate  way  pressure,  of  at  cardiovascular, normal  taken.  Other  ducks,  to  were  and  dives  circulatory effects  measurements  dive.  before  of  dived  further  analysis  machine. day,  a  study were  begun  with  Barodenervates  II  Blood  the  the  Section  same  in  of  withdrawn for  the  was  placed  the  in  Bilateral  in  m o n i t o r e d by  Recording was  used  resting  performed  in  to  return  1982a),  p e r i o d was  deemed  experiments. presented analyzed treated  in  this  using as  one  chapter  were  a b l o c k e d ANOVA block.  On a n y  model day  before dive  or  after  values  successive dive"  on  changes  of  the  that in  were  day  the In  were  was  the  For the  with  obtained variable  case  with  purposes  considered  time,  of  predive,  the  and  to  as  means  at  Tukey's multiple of  this  control  were  determine  for  as  significant dive  different means the  dives  post-  "within-  within-dive  analysis,  values  and  analyzed for  if  the  significant of  dive  an F - v a l u e  occurred  a  comparisons  done  the  cardiovascular variable  given  pair-wise  dive  test.  each  treatments  progressed. value,  barodenervation,  F-  times  in  comparison predive  on  any  values  given  day. Longitudinal  analysis  denervation  was  ANOVA m o d e l  employed  cardiovascular denervation  time.  multiple  If  acute  mean  +  to  mean  the  during  + 1  of  standard  significance  for  set  to  a priori  dive  error  0.05.  was  of  time,  after  to  diving  in  the  an  data  mean.  statistical  tests  have  The in  of  the  the  pre-  and  post-  and  analyzed  day  at  any  given a  cardiovascular the  been  estimate have  after  significant, A l l  give  Other  was  by  done.  barodenervation  data.  all  F-value  for  days  differences  test and  all  time  version  Values  for  deviation  the  II.  each  with  expanded  on  within-days  chronic  an  recorded  comparison  1 standard  variablility  using  significant  before,  from  variations  Section  grouped  for  means  variables  in  variables  were  "within-days" dive  performed  of  been level this  transition presented of  as  the  presented of section  was  as  118  2) to  Effects Diving  Heart were sec  of  Before  rates  duration,  which  on  the  Cardiac  Acute Barodenervation.  in  and a c u t e l y  intact forced  before  and  These  dives  resting  Blockade  and A f t e r  recorded during  propranolol. for  Beta-Receptor  dives  after were  observations  of  barodenervated  1 min  30  beta-receptor made are  Response  during reported  sec  to  ducks 2 min  blockade  the in  with  experiments Section  II.  30  119  RESULTS  1)  D i v i n g Responses The  effects  cardiovascular Section 11a,  II,  lib  values  for  Forced  10)  studies. limb  dives  in  each  similar  dives  (Figure  the  heart  was  hind the  limb body  to  in  lib).  little  the  (Fighre since  11c)  blood  are  ducks (for  in  in  degree not  these of  have  fell  by  about  dives  degree  of  performed  days  dropping  by  less  response  to  submersion  and  by  the  end  of  1 min  b r a d y c a r d i a was  1-5  than  the  60  after % of  began  as  Figure  control  ducks  10.3  by  in  to  % and  in  hind  2 min  volume  30 of  baroreceptor-intact  been  matched  18  % (Figure  in  the  the  in  the  throughout 11a).  control  state  dive.  considerably  predive  improve  experimental  Figure  previous  85  stroke  barodenervation, the  in  times  the  see  vasoconstriction  were  The  in  recordings,  reduced  by  b r a d y c a r d i a and v a s o c o n s t r i c t i o n by  serve  in  barodenervation  intact  was  increased  pressure  % complete  described  and  typical  those  must  resting  represented  before  Both  90  been  Assuming that  the  on  group.  changed  dive,  have  se  panels,  controls  resistance  sec  in  of  per  values  day  responses  rate  ducks  Predive  submergence  vascular  in  These  the  Heart  animals  5.  by  were  Barodenervates  barodenervation  11c  diving  which  Bilateral  variables  Figure  and  produced  of  in  value.  after  period  the  reduced heart  in  rate  This  1 wk,  however,  proportional  120  F i g u r e 10. A r t e r i a l p r e s s u r e (ABP) and h i n d l i m b b l o o d f l o w ( H L F ) r e c o r d i n g s f r o m p o r t i o n s o f 2 m i n 30 s e c d i v e s i n t h e same d u c k b e f o r e ( a ) a n d a t d i f f e r e n t t i m e s a f t e r b i l a t e r a l a o r t i c nerve s e c t i o n (b, c ) . Times i n t h e d i v e , and t h e s u r f a c i n g time, are marked by arrows.  HLF ml-mirf  j  o  HLF ml-min -1  ABP mmHg M  U)  03 o o o o o o O O P  I I I I I  o  I I I I I I "I  1  HLF ml'min  ABP mmHg  _» ro OJ o o o o o o o o o  U  CP  0  I I I I I I I  1  &  CD  o o  I I I I  ABP mmHg _»  o  ro  O  I I I I I I I  o m  D m z  >  a o  a Q  fD  g <' 6 o  fD  < b fD  O  I  i 'I  r.  I  i  u O  o o o o  r-  I  122  F i g u r e 11. C a r d i o v a s c u l a r r e s p o n s e s d u r i n g d i v i n g and r e c o v e r y i n the t r a n s i t i o n from acute t o c h r o n i c barodenervation. a) A r t e r i a l b l o o d p r e s s u r e ( M A P ) , b ) h e a r t r a t e (HR) a n d c) h i n d l i m b v a s c u l a r r e s i s t a n c e (HLVR) b e f o r e ( P r e d e n , s h a d e d b a r s ) and a f t e r (unshaded b a r s ) b i l a t e r a l b a r o d e n e r v a t i o n . M e a n s + 1 S . D . f o r 15 o b s e r v a t i o n s i n 8 a n i m a l s . The range of each day group i s g i v e n under t h e b a r s . Asterisks (*) i n d i c a t e s i g n i f i c a n t d i f f e r e n c e s from p r e d i v e f o r t h a t day group. C l o s e d c i r c l e s (•) represent significant differences between t h a t day group and t h e p r e d e n e r v a t i o n v a l u e a t t h e same d i v e t i m e . N o t e t h e c h a n g e i n HLVR s c a l e a t t h e two dive times.  2:30 Dive  1:00 Dive  •*  • ix  N  1  2-3  4-5  6-7  8-10  11-16  Pre den  2:30 Rec  1  2-3  4-5  I  *  K  6-7  8-10  TM6  6-7  8-10  TH6  15:00 Rec  •m  1  2-3 4-5 Day  6-7  8-10  11-16  Pre den  2-3  4-5 Day  to CO  1:00 Dive  Predive  2:30 Dive  500 • T  i wo •  •1* • I*  1* J* 1  2-3  4-5  6-7  8-10  TM6  Pre den  1  2-3  4-5  6-7  8-10  6-7  8-10  11-16  15:00 Rec  2:30 Rec  •I  •I*  •  2-3 4-5 Day  6-7  8-10  TM6  Pre den  1  2-3  4-5 Day  to  tOO Dive  Predive  2:30 Dive 60  40 •  20  1  2-3  4-5  6-7  8-10  11-16  0 "  Pre den  1  2 30 Rec  1  2-3 4-5 Day  2-3  4-5  6-7  8-10 11-16  6-7  8-10  15:00 Rec  6-7  8-10  11-16  Pre den  1  2-3  4-5 Day  11-16  ro Ol  126  fall  in  heart  although  rate  absolute  in  was  level,  diving  was  predive  did  the  same  period blood at  control  did  pressure stage  Two t o magnitude  of  level.  with  time  by  in  related aortic  days  before  nerve  post-denervation  of  of  as  the being  the  the  by  to  time  same as  the  days  value,  during when dive  much p r o p o r t i o n a l l y  since  resistance the  it  after  resistance 11-16  only  dive.  to  due  the  as  rose  to  denervation  the  level  of  prevailing dive  heart  rate  section. barodenervation,  bradycardia  depth  but,  rose  denervation,  the  pressure  with  in  as  day  barodenervation,  throughout  following  blood  As t h e  dives  to  dives  (Figure  response  control  half  1-7  However,  However,  dives  dive  dive  only  in  1 min i n  resistance  the  controls,  significantly  resistance  until,  in  course  the by  11c).  double  level  was  the  predive  time  following  reduced  dives.  in  three  mean  the  denervates  days  was  after  result,  control  delayed,  predive  increased  it  in  p r o p o r t i o n a l change  absolute  as  each  of  resistance  in  was  (Figure  gradually  resistance it  all  dives  the  that  that  controls  bradycardia  limb vascular  on  increase  denervation,  the  decreased,  chronic  hind  control  of  chronics in  End-dive  gradual  rate  in  % complete  course  s i m i l a r to  heart  bradycardia  in  as  than  denervates  did  %)  chronic barodenervates  The t i m e  end-dive  (81  was  lib).  absolute  same  rate  in  60  the  heart  higher  end-dive  was  was rose  the  and t h e  at  the  a minimum and  significantly  dive degree  bradycardia of  as  above  a the  improved  vasoconstriction  127  remained days  constant,  post-denervation,  developed, predive  end-dive  level  Blood returned  (Figure  2 min  at  stages  than  1 min  heart  denervates  before  in  stages blood  resting  intact  that  controls.  and  controls  11c),  while  lib).  t a c h y c a r d i a was but  by  2 min  levels.  oxygen  pHa w a s  45  % from  levels  and c a r b o n  control are  more  the  recovered barodenervates  maintained 30  sec  for  in  r a p i d l y than  tensions,  presented  5.  blood  in  Table  were  gases.  variables  similar The  after  barodenervates  more  postdive,  animals  these in  of  and b a r o d e n e r v a t e d  dive  lower  in  dioxide  a n d pH v a l u e s  were  1 min  Blood pressure  barodenervation.  in  16  fully  rate  However,  of  as  By  resistance  heart  predive  gas  fall.  by  within  to  difference  dive  in  predive  blood  animals,  decreased  limb vascular  diving,  in  to  group.  (Figure  during diving,  significant was  to  pH l e v e l s  and  groups,  sec  returned  Arterial arterial  11a  began  b r a d y c a r d i a was  pressure  levels  a post-dive  fell  most  day  pressure  the  and h i n d  following  rates  at  30  when  that  predive  within all  in  blood  blood  pressure  to  surfacing  rate  dive  heart  and  In  both  to  those  only  denervation  than  in  128  TABLE  5  E f f e c t s o f b i l a t e r a l b a r o d e n e r v a t i o n on b l o o d g a s e s and pH during diving. D a t a a r e r e p r e s e n t e d as means ± 1 S. E . M. f o r t h e number o f o b s e r v a t i o n s in brackets, i n 6 animals. D i v e b l o o d s a m p l e s w e r e t a k e n a t 90 t o 120 s e c after submergence. A s t e r i s k s (*) indicate dive values s i g n i f i c a n t l y d i f f e r e n t from predive i n i n t a c t or b a r o d e n e r v a t e d a n i m a l s ; t h e c l o s e d c i r c l e (•) means t h a t pH i n b a r o d e n e r v a t e d d u c k s was s i g n i f i c a n t l y d i f f e r e n t from that in intact animals.  PRE-DENERVATION Pa 02  PaC02  pHa  PREDIVE  83.4 +1.6 (9)  26.5 +2.6 (9)  7.561 ±0.015 (9)  DIVE  44.1 ±2.0 (6)  34.6 ± 4 . 3 (6)  7.409 ±0.032 (6)  POST-DENERVATION  PREDIVE  81.9 ±2.1 (12)  22.0 ± 1 . 3 (13)  7.557 ±0.013 (13)  DIVE  44.6 ±1.9 (12) *  36.2 ± 2 . 3 (12) *  7.283 ±0.017 (12) * •  129  2) to  Effects  of  Beta-Receptor  B a r o d e n e r v a t i o n and The  resting  effects and d i v e  barodenervation (here  labelled  blockade diving  of  in  beta-adrenergic rates  in  presented  Predive)  d i d not  are  animals.  blocked  barodenervates  but  the  predive  was  significantly  heart  was rate  lower.  receptor  ducks  in  before  Table  repeated  significantly  intact  on t h e  Cardiac  Response  Diving  heart are  Blockade  6.  from  affect  heart  also  same  in  the  these  Section rate  rate as  animals  on  and a f t e r  Resting  heart  End-dive  blockade  values II.  Beta-  during  in  before after  acute  betablockade, blockade  130  TABLE  6  E f f e c t s o f b e t a - a d r e n e r g i c b l o c k a d e on p r e d i v e and d i v e h e a r t r a t e i n i n t a c t ( I N T ) a n d a c u t e l y b a r o d e n e r v a t e d (DEN) d u c k s . H e a r t r a t e s a r e g i v e n a s mean + 1 S. E . M . f o r t h e n u m b e r o f observations in brackets, in 5 animals. Asterisks (*) i n d i c a t e s i g n i f i c a n t d i f f e r e n c e s between p r e d i v e and d i v e v a l u e s i n e a c h g r o u p ; c l o s e d c i r c l e s ( • ) mean s i g n i f i c a n t d i f f e r e n c e s from the r e s p e c t i v e p r e d e n e r v a t i o n v a l u e before o r d u r i n g d i v i n g , a n d t h e c l o s e d t r i a n g l e (*) indicates a s i g n i f i c a n t d i f f e r e n c e between t h e u n t r e a t e d and b e t a - b l o c k e d heart rates. A l l c o m p a r i s o n s w e r e made u s i n g a t - t e s t .  INT  DEN  PREDIVE  DIVE  PREDIVE  DIVE  UNTREATED  180. 3 ±15.9 (5)  37.3 ±11.6 (5)  266.7 ±20.4 (7)  102.0 ±10.4 (7)  BETA-RECEPTOR BLOCKADE  172.0 ±8.2 (5)  38.7 ±11.2 (5)  198.0 ±12.6 (6)  99.5 + 10.6  *  4  131  DISCUSSION  The  cardiovascular  barodenervation  were  in  (Butler  intact  ducks  sham-operated (Jones, to  1973).  diving  result  ducks  It  Thus,  clear  ends  graded  of  a  detailed  transition show t h a t diving  any  by  to  provides responses  changes  brainstem  in to  of  of  the  circulatory to  the  pathways,  role  of  responses  acutely  and  obtained  1973)  and  in  studies adjustments  were  this  study  solely  that  the  the  change  do  but  are  rather  for  the  time  during  chronically  the  (Figure  alone  11) in be  from denervation  to  which  in  system  Section  the  adaptation,  the  the  baroreceptors  examined  the  at  must  pathways of  not  adaptations.  cardiovascular  and t h i s control  of  over  the  conditions  experiments  elapsed  account  ,  barodenervation  interruption  baroreceptor  ablation  responses  baroreceptors, of  Jones  cardiovascular  the  the  responses  circulatory  states,  diving  of  bilateral  baroreceptors.  chronic  superimposed,  in  nerve  from b a r o d e n e r v a t i o n  background  due  in  the  The a d a p t a t i o n  are  the  the  of  before  dive  1971;  results  continuum  considering  the  the  barodenervated  assessment  loss  in  aortic of  dives  barodenervation  circulatory  from acute  observation.  any  to  changes  derived  qualified  itself  changes  and c h r o n i c a l l y discrete  to  chronic  from the  represent  The  in  to  and J o n e s ,  deafferentation  is  acutely  identical  subsequent  of  responses  II,  diving as  within  well  as  the  afferent  differences  barodenervated  in  dive  animals.  132  The  effects  of  peripheral  arms  peripheral  resistance  in  both  the  acutely  acute  animal  loss  to  The give  comparing  Furilla  of  of  responded  intense  of  the  into  rates  present  in  with  (1987)  heart  set  by v a g a l  The  estimated of  heart  level  is  based rate  on  in  beta-receptor increase drive,  in  in  with  rate  activity  heart  experiments drive,  this  animals,  ability  stimulation, of  these  intact  but  of  the  experiments  control.  rates  way  11).  and  the  By  and u n t r e a t e d  heart  same  animals  obtained  by  and an  estimation  efferent  of  pathways  and b a r o d e n e r v a t e d  to  animals  diving.  Resting  levels  made  nerve  the  during diving  during sympathetic  contributions be  on  the  the  during  in  blockade  control  and  different:  impaired the  beta-blocked  cardiac  can  were  submersion  beta-receptor cardiac  study  and Jones  rate  cardiac  bradycardia (Figure  parasympathetic  heart  to  barodenervation  heart  approximate  on t h e  response  baroreceptors  insight  consequences  diving  loss  and c h r o n i c a l l y b a r o d e n e r v a t e d  results  the  the  generate  some  from  of  baroreceptor  animals  alone,  of  vagal  rate  in  the  about  25  % of  the  data  of  as  blockade, drive  so  drive  to  intact the  the  barodenervation  out  in  produce  animals  in  Section the  and Jones  animals  was  95  contribution.  % of As  II.  these vagal  (1987).  Dive  unchanged  bradycardia resulted % to  is  resting  maximum a v a i l a b l e  Furilla  f r o m 25  sympathetic  before  pointed  baroreceptor-intact  vagal no  in  maximum in  from  by an  vagal  intact  133  animals,  the  cardiac  contribution rate  after  rate  fell  62  % of  to  of  to  a  level  maximum.  the  The heart  heart  lack in  resulted  (1987)  in  dive  both  cardiac have  sympathetic in  in  in  in  drive  the  dives  dives  do n o t  in  heart of  only  approximately diving.  setting  dive  observations  diving  support  a  dive  and F u r i l l a  and F o l k o w e t  end-dive  the  of  in  in  output  during  component  confirms  but  of  deficit  innervation plays  effects  studies  of  of  al.  role  of  and  Jones  and d a b b l i n g  the  contention  (1967) in  baroreceptor  the  that  by the  forced  the  a  smoke  resistance  animals,  and W h i t e ,  returned with  on  the  response  in  ducks  but ducks  1974). time,  is  the  in  (White  and  cardiac  ducks,  rate  an  in  is  however,  and c h r o n i c a l l y  and  by  McRitchie,  response,  diving,  The  initiated  heart  unaffected  during In  rabbits.  inhalation,  decrease  peripheral resistance in  diving  loss  on b a r o d e n e r v a t e d  to  include  barodenervated  (McRitchie  change  a vagal  removal  forced  (1963)  responses  The r i s e  (no  no  ducks.  input,  barodenervated  response  vagal  and p e r i p h e r a l arms  trigeminal  acutely  acute  an  findings  differential  cardiovascular  1973).  in  and f o r c e d  and Uvnas  a parallel  increase  that  (1971)  free  dive  means  sympathetic  The p r e s e n t  response The  a  the  made  barodenervates),  my e x p e r i m e n t s  and Jones  cardiac  in  available  of  Butler  Hollenberg  in  component  corresponding to  This  total  rate  ducks.  rate  beta-blockade  baroreceptors 1/3  sympathetic  as  in  reduced the  cardiac  barodenervated  134  animals would  were  able  suggest  that,  cardiovascular ducks  is  after  loss  of  to  chronic Dive  the  course  level  in  and  as  Blood  heart  blood of  effector by  for to  animals the  full  neural in  the  of  the  in  then  rabbits  that  transition  from  acute  ducks. barodenervated  behaviour, the  half  This  barodenervated  response  rising  limited  peripheral  the  ducks  followed  from the  predive  bradycardia could  predive  resistance  value  pressure  in  pressure-regulated  systems  is  a  and t h e  function  in  limbs  neurally  are  perfusion  which  maintained  activity  of  of  discussion this  adjusted  control  arterial  adequate  the  not  response,  chronic  loops  within the  the of  means  the  organs  animal  that  to  the  brain  body  of the  these fashion from  an  et  required  Sagawa  in  which  system,  (Arndt  control  changes  against  information  limits in  levels  coordinated  the  level  (see  barostatic  a  using  signal  pressure  in  unregulated  relative  a pressure-regulated  baroreceptors mean  of  and  hydraulic resistance  In  dive,  integration  acutely  smoke  in  bradycardia.  bradycardia returned.  is  forced  in in  as  dive  baroreceptors,  maintained  nearly  Pressure  detailed  the  pumping.  integrated  current  of  change  rate  negative-feedback  arterial  dives  pressure  heart  output  is  in  arterial a  a normal  central  barodenervation  circulatory cardiac  the  that  undergoes  falling  animals  if  to  the  acute  compensate  develop  responses  similar  integration  to  al. . for  during  (1983) theory).  peripheral  1977).  the  for In  a a  resistance  135  are  approximately  the  opposite  adequately the  perfused  control not  so  while  system  by  changes  that  the  blood  is  to  defended  the  cardiac  resistance  in  hemodynamic  consequence  of  the the  dive,  The f a c t  still  dives  acute  continue lay  to  to  occur  rest  the  Blix  and Folkow  role  in  large  of  adjustments in  the  the  dive in  to  of  the  pressure,  receptors dive  there  pressure levels these  in  in  is  simply  of  these  should  (1974), have  the  within  a  and  a  and primary  However  the  and below  demonstrate  balancing  pressure  pressure  animals,  above  animals,  no  adjustments  ducks.  both  is  peripheral  baroreceptors  responses  no  when  A n d e r s e n and B l i x  dive  blood  and  that  is  the  the  circulatory reasonable  animals.  James  bradycardia  by that  maintain  rest  and b l o o d  denervated  barodenervated  these  intact  Angell dive  in  level,  importance  limits  (1984),  in  are  the  barodenervation,  chronically  argument  generating  swings  predive  in  after  there  Thus,  changing  variables.  in  of  because  output  cardiovascular occur  most  animals  disturbances.  occur  output,  and b r a i n  mechanism,  baroreceptor-independent changes  to  system  regulator  against  cardiac  reduced.  pressure-regulation  signal  in  heart  flow  baroreceptor-deafferented  functioning  is  direction,  circulatory In  balanced  et in  study  of  Jones  protocol,  in  the  al. the  (1978)  have  suggested  that  chronically barodenervated  (1973),  and by  chronically  virtue  denervated  of  a  the  full  ducks  in  similar  animals  in  the  136  present  study,  drive.  Their  denervated would  occur  are  than  in  the  chemoreceptor  input.  with  intact from  does  diving  in  after  little  but  up t o  rose  (Figure  rises  to  the  that  aid  gases  of  denervates,  the  loss  of  and  the  greater of  dive  blood  not  done  in  the  presented  in  Table  blood  gases  diving.  baroreflex  conservation  It in  of  an  gas  between  is  apparent, intact  oxygen  to  days  after  barodenervation,  the  same  level  as  11).  Jones  only  half  the  changes  in  has  end-dive  the  in  shown,  during  This  occurs  of  the  animals  during that  This  suggests  peripheral  is  16  and  30-50  examined  section. baroreceptors  contribute  during  d i v i n g by  forced  to  the  control  operating  in  resistance  between  possibility  peripheral  however,  level.  integration  submersion  intact  peripheral  predenervation  barodenervation.  after  to  (1973)  days  pressure  to  analysis  during the  the  response  The  the  by  in  blood  16  barodenervates,  further  next  for  in  because  in  due  differences  resistance  the  animals  measurements  animals  to  chronically  changes  response  chemoreceptor  ducks.  resistance  day  when  greater  intact  enhanced  b a r o d e n e r v a t i o n was  significant  ducks  30-50  that,  compensated  experiments,  animal  that  time  no  these  diving  of  A systematic  and d e n e r v a t e d  In  in  be  experiments,  showed  was  cardiac  would  5  result  dived,  those  baroreceptors  present  the  peripheral vasoconstriction  deficit  levels  be  suggestion  ducks  incomplete any  could  of  through  blood the  in  137 c a r d i a c limb of the b a r o r e f l e x i n ducks.  However, d i v e blood  p r e s s u r e i s only maintained w i t h i n f a i r l y broad l i m i t s i n t h e i n t a c t animal, and so p r e s s u r e maintenance by t h e b a r o r e f l e x appears  t o be secondary  t o the development of t h e oxygen-  c o n s e r v i n g c a r d i o v a s c u l a r adjustments, by b a r o d e n e r v a t i o n .  which are unimpaired  The i n t e g r a t i o n of t h e d i v i n g  responses  changes w i t h i n the f i r s t two weeks a f t e r barodenervation, as c a r d i a c c o n t r o l r e c o v e r s from the e f f e c t s of b a r o r e c e p t o r loss.  138  SECTION  Cardiovascular Stimulation from  Responses  During  Acute  IV  to  Diving  Chronic  to  Aortic  in  the  Nerve  Transition  Barodenervation  INTRODUCTION  Chronic presented can  in  provide  barodenervation  experiments  Section  limited  about  cardiovascular baroreflex on  the  by  is  employed  the  aortic role  of in  nerve  this  barodenervated  state.  and  in  alterations  nerve  is In  to  diving  barodenervation, by  the  the  the in  responses  with  way  Section  that  in  input  they  in  provides  the  The changes  in  information  Activation  extend in  type  baroreflex  technique  animals  reported in  to  the  the  baroreceptors  section  ducks  the  stimulation  stimulation  barodenervated  variables  of  in  during diving.  of  the  are  function  control  dynamic  modification  III  of  of  the  information  diving,  used  in  study  and  a  Section  of  acutely  chronically resting  cardiovascular  time  III,  after  may b e  from the  accompanied  baroreceptor  processed. trial  chronically,  attempts it  was  configuration  used  (1983)  the  and  in  to  found by  stimulate that  Jones  the  the  experiments  in  aortic  enclosed  and West the  I  electrode  (1978), first  nerve  Jones  et  al.  section  of  this  139  thesis  d i d not  work  implantation. aortic  and  for  A technique  carotid  rabbits  has  various  electrode  been  sinus  systems.  Electrodes phrenic  respiratory (Picaza  et  treatment  pump a l . .  of  Chronically  deVilliers al, of  1970; these  nerve,  The  et  the  implantation  The  blood  the  for  and Hahn, of  carotid  were  healthy  study  present nerve  the  be  supply  to  which  nerve  configuration  used  nerve  that  used  et  in  the  animal  al..  al..  1977; (Bourde 1979).  enclosed which  normal After  had  had  to  et A l l  the  were  be  not  acute  by  the  afferent  traffic  deafferentation, be  nerve  to  would in  for  1974).  hindered  surrounding the  the  in  supplies.  blocked.  deafferentation  other  control  stimulation  nerves  not  baroreceptors  tissues  been  blood  the  pain  sinus  Barone  on  for  failing  al.,  vagal  type  done  a  in  and  several  (Kaneyuki et  1975;  the  electrodes (1980),  in  for  have  the  chronically  augment  et  of  described  nerves  (Borst  were  and  electrode  on  al.  been  1977),  experiments  of  of  to  al..  and  were  implanted  implanted  electrodes  with  stimulated  destruction  local  and  studies  intact,  reinnervation  et  1964)  electrodes  of  been  after  stimulation  have  diaphragm pacing  al.,  above  with  days  Karemaker et  pectoris  Slaughter  requirement in  1975)  few  peripheral  have  implanted  and the  otherwise  of  (Glenn  for  by  a  chronic  stimulation  angina  preparations  for  configurations  stimulation  for  than  nerves  reported  long-term  humans  more  prevented, during  minimized be  yet  so  that  compromised.  stimulation  140  experiments  in  barodenervated  severing  the  could  pulled  be  deprived  the  electrode risk the  of  nerve  so  through  nerve  body,  fibre  that  of  involved  damage,  n o r m a l movement  of  These  "patch"  type  surface  situ,  and  with  crushing  electrode time The  of  contralateral  complete  for  which  the  barodenervation  are  the  bilaterally  presented  in  the  last  1976;  mammals,  et  al..  wide  This  where  the  it  and by  the  use  of  over  the  nerve  the  and  the  determine  the at  the  control  animals  prior  to  control  baroreceptor-intact to  at  electrodes.  intact,  with  a  ligation  supply  denervated  from  the  sacrificed  implanting  compared  resulted  a nerve  was  the  attendent  during  by  blood  left  procedure  entered  nerve  solved  the  was  section,  is  many  al.,  1974;  range  of  arterial et  1976;  1980;  Marshall, inputs  by  studies  Heistad  al..  and O b e r g ,  1981;  recent  influenced  Wennergren et  Wennergren et  on  stump  the  animals effects  of  barodenervation.  baroreflex (Bristow  of  unilaterally  of  In  body.  One n e r v e  nerve  responses  partial  left  sake  aortic  these  central  implanted  trauma,  required  handling with  were  electrode,  unimpaired. for  the  supply  excessive  problems  procedure  surgery  responses  electrode  blood  a minimum o f  site  of  I)  surrounding structures  cycle.  in  (Section  length  and t r a c t i o n  cardiac  of  a  the  its  ducks  have  1974;  Pisarri  from other  et  input  al..  groups,  et  al..  1981;  Kidd  1979;  and K e n d r i c k ,  receptor  the  Attinger  and K o r n e r ,  Chruscielewski  1981;  that  chemoreceptor  a l . .  Iriki  shown  1984).  such  as  A  141  cardiac al.,  and  1981;  receptors face  Holmberg et (Kalia  and upper  nerve rate  low-pressure  (for  et  summary,  see  baroreflex  (Davidson  receptor  et  a l . . of  diving of  are  in  control  by  (Millard, Jones  the  and  a l . .  in  in  the  the  during  d i v i n g may a t t e n u a t e  interactions situations  in  investigated  the alter  1970).  is  affect the  al..  1978),  affected  among  baroreflex  during  of  or  and  barodenervated  the  stress  during  the  may b e  in  in  several  blood  diving  heart  the  exercise  1982),  attenuation  chemoreceptors  Increased the  baroreflex (Korner,  using  are  to  at  least  pressure  intact ducks  of  ducks (Section  primary  forced  chemoreceptor  baroreflex  same m a n n e r a s  mammals here,  a l . ,  c i r c u l a t o r y responses  and P u r v e s ,  in  et  acutely  (Jones  centrally,  pressure  trigeminal  with  Gandevia et  the  1983).  d a b b l i n g ducks  importance  the  1983)  et  joint  of  circulatory control  on the  baroreceptors  1980) et  for  and  the  influences  Interactions in  by  interact  produced by  (Jones  inputs  responsible  and  1976;  involved  ducks  these  and Thames,  blood  1972).  muscle  innervated  Respiration also  control  a l . ,  groups  influence  In  et  somatic  (Kidd  and e x t e r o r e c e p t o r s  directly,  cardiovascular states  (Cunningham  I,  well.  baroreceptor  partly  1981),  Abboud  pressure  as  forced  1983),  respiratory tract  and b l o o d  altered  a l . .  a l . ,  baroreflex  and  pulmonary mechanoreceptors  by  submersion drive  over-riding  it  chemoreceptor-baroreceptor  behaviour 1979).  stimulation  in This  of  the  non-diving possibility aortic  nerve  was to  142 invoke the  baroreflex,  i n ducks under v a r y i n g  c h e m o r e c e p t o r l o a d i n g and diving situations.  unloading  conditions  i n b o t h d i v i n g and  of non-  143  METHODS  1)  Aortic  Nerve  There a  viable  and  also  were  technical  electrode  having both  of  approaches miniature  this  aortic  nerve  distal  failed  and t h e s e  cardiovascular have  a  of and  the  of  the  In  this  loss  of  one  observations  the  after  nerve  not  made one  in  before  served  as  the  pre-  all  intact  the  on b o t h  the  aortic  a n d shown present  nerve,  site,  from  be  experiments.  snare  was  the  both  effects  resting  barodenervation,  controls  for  then  aortic  surgery, in  to  w h i c h was  and a  assessed  left  attempts  Since  II)  complete  nerves,  the  contralateral  recovery  c o u l d be  for  on t h e  but  aortic  intact  aortic  having  including implanting a  unit  (Section  with  different  pursued.  electrode  otherwise  way,  tried,  p l a c i n g snares  i m p l a n t e d on  diving conditions  these  were  c o m p r o m i s e was  to  Several  electrodes,  established  distal  around  nerve.  effects  were  interrupted placed  trials  been  negligible,  the  the  intact  electrocautery  to  associated of  nerves  p r o b l e m were  heated-wire  Electrodes  these  on one  c o n t r o l measurements. to  Diving  difficulties  stimulating  denervation  nerves  Stimulation During  this  set  and of  experiments. 12  female  experiments (S.E.M.) observed,  white  during  kg. the  Pekin  diving.  Before animals  ducks  used  Mean b o d y mass  and a f t e r were  were  held  surgery, in the  in was  stimulation 3.2  a n d when same  +  not  holding  0.2 being  144  facilities Section  and u n d e r  the  same  stimulating  patterned  after  electrodes  those  designed  surface  electrical  activity  Hoffer,  University  of  These  electrodes  steel  wires  3-4  reinforced these skin  electrodes  with  in  more  the  central  but  aortic nerve fat,  as  described  in  from  was  with  both  of  over  the  spinal  personal 40  the  which  for  earlier  were  and  attached  on t h e  sac  to  to  made  to  needles anchor  side  of  Section  the  any 6-0  the  left  free  the  overlying Vicryl  swaged  the  is  the  in  to  remove of  a  general  after  sutures  to  began  expose  under  was  to  electrodes  Implantation  procedure  curved  medial  of  implantation  except  used  patch,  cm l o n g  No a t t e m p t  8 mm a t r a u m a t i c  sewn  leads  thorax,  cm l o n g  Co.,  The  air  snare  1985).  silk.  and t e s t i n g  the  were  silicone-rubber  Appendix.  in  located.  suture  15  of  (A.  stainless  ends  clavicular  region  stranded  Cooner Wire  mm t h i c k  of  communication,  Ga.  were  cord  (AS631;  about  from the  nerve  mammalian  left  Two 3 0 - 5 0  each  the  fine-mesh  the  study  recordings  with  in  this  long-term  bare  surrounding tissue,  present.  ends  0.5  for  for  Teflon  the  described  differed  (Ethicon)  patch  of  circulatory  nerve  if  detail  developed  two  Construction  opening  anaesthesia, II,  were  connector.  given  by  internally  of  with  California), mm s q u a r e  in  Calgary,  consisted  insulated  Chatsworth, a  as  I.  The  into  conditions  onto  electrode  fascial  sheet  145  (see  Figure  12).  The f a s c i a  was  pierced  from  the  medial  F i g u r e 12. M e d i a l view of t h e l e f t a o r t i c n e r v e and surrounding t i s s u e i n a duck. The method o f a t t a c h i n g s t i m u l a t i n g electrodes to the f a s c i a over the nerve i s as w e l l as t h e s i t e o f n e r v e l i g a t i o n and c r u s h i n g .  to  the shown,  147  the to  lateral one  the  side  side  of,  fascia.  emerged away  on  its  the  A  suture  nerve  emerging which the  from from  the  the the  suture  along  the  needles,  course  of  then  manoeuvered  medial  side  of  entry  two then  medial  the  site.  about  the  until  sheet,  The whole  the  about  the  placed  in  a matching position  side  patch  of  a total the  c o u l d be  of  sheet  slid  of  to  its  four  tip  then  length. across  threads  fascia,  its  in  was  to  leaving  of  mm  2 mm  suture  centre  1-2  nerve  holes,  first,  electrode  down  position  over  nerve. Each  of  hole  in  each  thread  one  the of  free  suture  slight four  and  to  secure  it,  patch  In  some  of  that  then the  of  was  the  then  the  matching in  in  its  fascia,  carefully final  dorsal  required resetting  the to  prevent  and h e l d  with  slid  down  the  position  over  the  back  of  relief  body w a l l angle  A l l  Matching  chest,  of  the  a  exposed  the  loop  after by  with  fascia.  12.  the  a  the  two  at  the  patch,  the  knotted  A strain  through  with  Figure  animals  the  clamped together  in  inside  pushed  electrode  as  short.  the  thread  p a t c h was  nerve,  leads  anchored to  corners  centred  the  and c u t  electrode  stitch.  were  against  were  needles  a p a r t i c u l a r hole  lie  across  ends  four  while  flat  suture  suture  position  tension  oriented  were  the  ends  threads  nerve  four  through  corresponding  the  was  the  was  original  through the  the  of  and midway  threaded second  one  The n e e d l e  again  from  with  was  single  traction  free  patch  which  lead  wires  to  taken  the  in  leads  loose  wires  on t h e  to  the  nerve.  148  When t h u s and  implanted,  flexible  nerve  during  cardiac  point runs  close  ligatures exposed  was  mm d i s t a l to of  the 5-0  nerve  stopped  slowed  usually  great blood  at  this  heart  These  as  up t o  three  were  on t h e  was  fascia  during  to  a  light or  the  the  and  estimated  were  tied  jaws  above  of  2-3  Section animals, with  flow  cardiac  nerve  were  the  and h e a r t  before  an  the  and  acute was  p r o d u c i n g an  rise  tested  immediate  great  implantation  around the  rate  rate  ligation,  electrodes  electrode  of  tied,  Then h e a r t  of  Two  the  sharp p a i r  indicating the  a  macerated  beats,  collapse  placed  a  at  side.  around  was  of  that  of  the  the  the  left  ligatures  stimulation  was  along  with  on t h e  of  a partial  where  arch  distended,  success  in  site,  min afterwards.  level  2 mm o f  surrounding tissue  the  The e f f i c a c y  these  measure  the as  about  segment  equivalent  snare  fitted  this  soon  visibly  rate  of  of  electrode  with  electrical  a  secured,  free  then  1-2  to  described  be  vessels  pull  assembly  nearby v e s s e l s  were  the  As  the  When t h e  verified,  to  the  times  pressure.  vessels.  In  for  vessels  point,  in  nerve  did not  2mm a p a r t ,  segment,  increased  in  was  for  to  silk,  forceps.  been  electrode  brachiocephalic  jeweller's  drop  of  dissected  several  the  it  electrodes  thoroughly  was  that  movement  the  nerve 6-10  heart  entire  cycle.  After aortic  enough  the  right  had  aortic  II. total hind  probes output.  peripheral  limb vascular on t h e In the  central  resistance resistance. systemic  experiments  in  149 Section  I,  pulmonary a r t e r y  cardiac  output,  experiments nerve  One  this  because  function,  dissected  but  free  of  since  ultrasonic  probe  from  the  left  brachiocephalic  already a  course  ligated  of  the  same  the  aortic  fit  on  equalize  was  necessary  because  barodenervation.  leads  were  moved  freely  anchored  After any  site  brought skin to  out  to  of  incision  the  skin,  the  the  as  their  hour cages  the  the  next  two  the  nerve,  in  Probe  size  the  connectors  observed  of  surgery,  blood  of for  flow  to  the  cuff  of  position This  the  implants  was  evident  snare  were  snare  and  was  table  anchored and during  transferred  were  at  the  electrodes  recovery  probes  for  cycle.  repaired  were  the  chosen  nor  cardiac  the  the  vessels  the  operating  then of  bodies  the  on  trunks.  these  and t h e  away  left  two  bleeding  on t h e  remainder  days,  the  was  probe.  aorta  was  and thus  sac  end  the  corresponding  during the  air  be  threat  on t h e  probe  leads  to  aortic  and a p l a s t i c  in  residual  with  present  and a n o t h e r no  a  the  place  posed  tissue,  all  in  descending  probe  the  The f r e e  following for  no  obtain  have  to  enlargement  nearby  chest,  were  the  Neither  chest,  closed.  the  it  placed  the  that  the  would  vessels,  vessels  A n i m a l s were  first  During  to  ensuring  within  probes. the  with  on  resistances  of  after  suitable  nerve  nerve.  as  to  interference  aortic  the  diameter  on  to  measured  not  of  right  right  t r u n k was  right  risk  placed  brachiocephalic the  was  t r u n k where  left  internal  was  pulmonary a r t e r y  was  the  non-constrictive  site  the  from the  flow  back  period. implanted  on  150  •the  ischiatic  described  arteries,  previously.  unilateral  Aortic  Bourassa This  the  index  (1981),  for  the  present  different the  it  be  was  calibration, at  the  on t h e  set  at  as of  set  current pressure  ms,  the  (the  stimulation)  previous  using  a  tract  to  described the  the by  of  stimulation  so  that  the on  a  each a  In  same p r e p a r a t i o n be  compared  over  an  current  stimulus  or  Hz)  of  delay  a maximal index  each  of  to  and  the  of  Instead,  day,  the  pulse  was  known t o  curve  (i.  e.  the  paired  0.5  ms,  and  in  blood  F r e q u e n c y was  be  produced  of  effectiveness  in  which  which  decrease  in  of  standard  voltage. each  in  a period  absolute  r u n on  (20-30  interpulse  obtained.  each  daily  duration  until  in  a preparation  stimulus-response  the  parameters.  electrodes  use  and  biological  could  basis  for  limb.  Swett  stimulating  to  level  the  results  time.  hind  stimulus  relative  in  biphasic described  intensity  biological was  the  a  across  the  these  previously  days  as  wk.  setting  stimulus  to  of  increased  done  in  of  practical  response), 0.5  was  cannulated  use  between  such  was  1  different  and  not  plateau  maximal  on  in  about  outflow  in  were  period as  system  the  changing  beginning  frequency  used  the  animals  could  weeks,  was  experiments,  relationship  nerve  the  involves  and  same  "biocalibration",  setting  preparation,  with  sympathetic  of  principle  the  stimulation  generated  principle  was  animals  recovery  experiments,  nerve  stimulating The  The  denervates  barodenervation  waveform  and the  pulses  the  of  reduced  until  blood  151  pressure  fell  by  an  duration  of  20  sec  ususally  between  The in  obtain were  the  were  by  over  tested  that  of  obtained, nerve from  in  intact and  if  heart  complete  the  operation  and  cardiovascular  the  the  stimulation dive.  The  identical  and  at  2 min  20  animals  then  corresponding  to  the  end  Arterial  blood  samples  assumed  of  sec were  was the  end  the  and  15  taken  point.  dive. min  a  similar  aortic  have  recovered  was  to then  repeated,  during  of  for  the  that  2 min  applied of  If  were  to  was  levels  were  or  electrodes  animal  and  was  two  withdrawn  a total  the  dived  tests  to  stimulus  for  function  response  of  animals  response  pressor in  To  the  this  cardiac  trains  dive,  10  force-dive  The  at  control  dived  were  hours.  before  the  stimulus  to  experiments.  snare  the  variables  2 min  a  The head  the  1 min,  the  ducks  baroreflex  the  single  as  the used  trains  were  in  at  was  animals  dropped  sec  repeated  10  sec  and  position,  was  frequency  that  three  pulse  rate  recorded  animal  and  train  diving  were  of  during  barodenervation. in  for  barodenervation,  table,  dive,  and the  clamped  to  and t h e  animals  stimulation, the  before  short  the  pre-stim  diving  barodenervation  course  with  This  for  similar  tests,  the  deep b r a d y c a r d i a to  was  % of  Hz.  operating  pressor  times also  the  train.  20  responses  on  45-50  protocol  earlier  control  placed  three  and  experiments in  checked  10  pulse  experimental  these  animals  a  estimated  30  sec,  at  1 min  last  pulse  Stimulation  was  postdive.  before,  at  2 min  in  152  the  dive,  control an  and a t  replaced  routine  of  At  gas  15  with  multiple 20  the  blood  samples  c a r r i e d out  as  described  anaesthetized  period  the  high  in  neck.  using  the  the  response  to  neural  no  structures.  electrodes  to  the  microdissection The the  analyzed Section occurred  effects using III.  either  in  stimulation  a  themselves  significant  during diving  analysis was  of  not  sectioned  and  was  last  then  dive,  of  done.  (P or  that  current  cardiac the efferent to  relation  confirmed  nearby of  the  by  examination. during  variables,  ANOVA m o d e l <. 0 . 0 5 ) as  a  also  assumed  the  proportional order  to  to  diving, were  described  absolute  result  was  In  no  during  stimulated,  and n o t  and t h e  on t h e s e the  Appendix.  exposed  stimulus  mortem  calibration  and  afferent  were  saline.  haematocrit.  and t h e  cardiovascular variables  p r o p o r t i o n a l change  Statistical  nerve  avian  were  dive-recovery  indicating  Barodenervation  a variation If  of  ml)  in  calibration,  nerve  the  vagal  leakage  aortic  of  in  occurred,  during post  changes  was  aortic  as  stimulating  T h e r e was  probe  analysis  of  probe II  both  (0.6  affect  Section  nerve  When t h e  stimulation were  for  vagus  same p a r a m e t e r s  electrodes fibres.  left  volumes  flow  in  gas  volumes  during a  experiment, in  dive  blood  significantly  each  this  for  equivalent  min d i d not  the  The sample  of  were  min a f t e r  animals  end  Animals  the  and  machine.  immediately  Withdrawing  and  2  and b a r o d e n e r v a t e d  IL13 b l o o d  was  1,  of be  in  change  stimulation, significant.  differences  analyze  differences  153  between  means  recommend  the  comprising  the that  the  normally  to  the  When t h i s  distribution  untransformed this  proportions,  transformation  a mean  proportion. data,  of  distributed  of  was  done  (1984)  each  arcsine  of  data data  but  and the  other  of  root the  normality  more  there  still  was  the  for  authors  proportions  square  a part  fulfilled required  of the  for  approached  proportions  transformed  Zar  ANOVA.  that  present closely some  assumptions  the  of  of  than  doubt  154  2)  Chemoreflex-Baroreflex  a)  Aortic  Nerve  Interactions  Stimulation  During  Dives  After  Exposure  to  Oxygen. Four  of  electrodes in  the  the  were  diving sheet.  through  the  of  and  Oxygen  funnel  to  gas  spout to  oxygen  breathing,  then  dive  removing  and  previously and  the  results  b)  Blood Pressure  Stimulation  in  were  by  a  delivered rate  obtain  for  gas  was  flow  normoxic  Response  to  2  in  implanted clamping with  to  animal  1.  the  min i .  response  a  were  similar  Graded  and E f f e c t s  5  min  the  spout. analysis  used  fashion.  Aortic of  into  the  gas  aortic  after  poured  and b l o o d  head  a  The  _  closing  dives  the  funnel  quickly and  protocols  analyzed  Normoxia,  of  a predive  water  the  stimulation  described  with  % oxygen  was  at  stimulated  after  100  ducks  surrounding the  was  funnel The  exposed  funnel  plastic  nerve  barodenervated  Nerve  Hypoxic  Hypercapnea. Three  of  stimulating a in  the  barodenervated  electrodes  frequency-response animals  parameters pulse  at  rest,  were  trains  at  set  were  curve  used for  breathing as  in  fitted  air  with  experiments  baroreceptor  described  different  ducks  nerve  (normoxia). previously,  frequencies  in  the  to  establish activation  Stimulus then range  20 of  sec 0.2-30  155  Hz w e r e were was  given  in  random o r d e r .  repeated  on  the  only  given  response  animals  =79  mmHg;  was  stimulated  were  blood  for  gas  before  6  on  used  the  was  in  were  the  ligated  (40  to  except  animal  stimulus  gas  proportional  mixture  gases  nerve  responses  samples  animals  hypoxic  (PO2  pressure  Arterial  normoxic  hypercapnic  -  established,  Blood pressure  in  and  for  just  hypercapnea.  were  given  animals.  the  During  body  of  mass  their - 1  left for  3.0  arterial  by  )  the  of  the  backs,  side  in  + 0.3(S.E.M.) to  kg)  test  chemoreceptor  et  al.  (1982)  carotid  clavicular area  carotid  of  loading surgery for  with  air the  the  body.  anaesthetized  the  common  Perfusion.  The p r e p a r a t o r y  Jones  and the  Body  experiments  baroreflex.  described  on  Carotid  perfusion  levels  mg k g  the  one  2 min and the  frequency. in  runs  had been  for  Hz.  and p e r f u s i o n  placed  on  15  these  while  5 complete  stimulation  body  that  day,  responses  taken  carotid  isolation  arteries  at  against  (mean  to  were  sec  ducks  of  animals,  a hypoxic-hypercapnic  Stimulation  operation  pentobarbital All  to  different  similar  Animals  these  were  nor  Nerve  of  vascular  of  converting  nerve  female  effects  20  by  hypoxic  Aortic  were  for  analysis  independently  c)  given  plotting  aortic  Neither  observation  (total  Once  two  PCO2 = 48 mmHg) t o b r e a t h e  normalized  changes  run  curves).  the  were  one  next  In  sac  sodium opened.  carotid  artery,  body  on w h i c h  a  156  balloon Figure  occluder 13).  downstream towards  of  the  the  by  missed  inflating  and  were  cut  to  chemoreceptors incision carotid right in  were  operating  to  Texas) (Figure by  the  the  table  in  and  14).  a heating  lightly  infusion  which  constant-temperature  was  water  as  in  of  neck,  a  anaesthetic,  and  sac  under  and  skin  the  leads,  the  chest.  local  The  anaesthetic  and t h i s  an  had  described  the  upright  cannulas  (Harvard  an  arrangement  (Narco  syringe was  incision position  on  led  50  were  The  to  also  at a  body  to  a  Apparatus, of  Biosystems,  kept  connected bath.  were  pump  via  transducer  to  also  artery  electrode  out  was  restrained.  artery  flushing  the  facing  and t h i s  nerve  local  cannulated  T h e pump s y r i n g e coil  tube  (see  Stimulating  low  in  tip  carotid  The a i r  exposed  Massachusetts),  saline  occluder,  aortic  passing  body  Cannulation  baroreceptors  turned  carotid  a Harvard  a pressure a  and  heart.  soaked  occluder  was  cannula  located  side.  after  the  procedure.  was  both  carotid  cannulated  from the  left  was  right  repaired  venous  and  nerve  denervate  and  the  vagus  The a n i m a l  Natick,  which  on  occlusively  the  South  branches  the  then  carotid  were  closed.  syringe  the  of  with  and t h e  and v e i n ,  was  ml  body,  artery  wing,  The  the  on  cannula  ulnar  the  placed  of  was  ligation  The r i g h t  section  then  side  during the  previously. short  carotid  any  upstream  artery  chemoreceptors  showed w h e t h e r  electrodes  placed  The c a r o t i d  facilitated  been  was  stopcocks  Houston,  attached temperature  recirculating  arterial  cannula  was  157  F i g u r e 13. Schematic v e n t r a l view of the r e g i o n of the left common c a r o t i d a r t e r y i n a d u c k . The r e l a t i o n s h i p of the c r o t i d a r t e r y c a n n u l a , p n e u m a t i c o c c l u d e r and a r t e r y ligation s i t e s t o the c a r o t i d body are i l l u s t r a t e d , a l o n g w i t h the l e f t a o r t i c n e r v e and s t i m u l a t i n g electrodes.  158  159  F i g u r e 14. Arrangement of the experimental apparatus for p r e s s u r e r e c o r d i n g and b l o o d p e r f u s i o n of the v a s c u l a r l y i s o l a t e d l e f t c a r o t i d body i n a duck.  pneumatic occluder syringe  o  161  connected arterial hours  to  a  second  pressure.  before  the  pressure  T h e a n i m a l was  experiment  infiltrated  the  and e x p e r i m e n t ,  heparinized  (100  I.  U.  with  ml  -  1  )  recording  to  recover  A l l wound  local and  for  allowed  began.  periodically recovery  transducer  anaesthetic  cannualae  avian  sites  saline  3-4  were  throughout  were to  for  flushed  prevent  with  blood  clotting. Stimulus  parameters  adjusted  according to  section,  while  carotid  body  the  with  (autoperfusion; pressure control venous in  blood  blood  occluder  carotid  body.  loss  pulsatile  and  the  small  through with  venous  infusion the  the  the  innervated  of  occluder  these  then  blood was  blood  into  in  The  the  inflated was  About  infusion  to  verified  gradual  decrease  in  set  carotid  to  region  The a o r t i c  the  syringe  as  mean  of  pump was  the  nerve  was  and  change  isolate  the  immediate  region  cannula, as  the  drained  carotid  begun,  the  the  pressure  same mean  during the  (no  the  the  was of  carotid  carotid  Perfusion  produce  heart  ml  pump  by  from the  from the  left  10  vascularly  recorded  outflow.  previous  blood  procedure),  pressure  in  were  during autoperfusion  from t h i s  trapped  the  from the  deflated).  experiments.  isolation  blood  venous  autoperfusion.  arterial  stimulation  was  This  rate  isolated  perfused  resulted  subsequent  volume  animal  withdrawn  carotid  of  out  to  pressure  activation  set  for  was  nerve  criteria  normoxic  response  aortic  the  carotid  response  for  body  and  pressure  the in  previous  stimulated  again  after  162  1-3  minutes  pressure  the  in  each  body  carotid  carotid  perfusion  responses  performed carotid  of  was  animal  evaluate  itself  on  the  from the  carotid  body  analysis  of  the  blood  with blood  with  effects  of  response.  pump s y r i n g e  gases  arterial in  an  blood  blood  the  runs  intervals,  stimulation  arterial  pressure  both  min  and t h e  similar  arterial  nerve  with  blood,  Several 15-20  Aortic  perfusion  to  withdrawn  at  perfused  served  venous  recorded.  artery.  body  with  then  given  from the  Samples  blood  of  from  during syringe  were  blood, gas  the  process  during perfusion  I L 13  were  obtained  perfusion  and venous  blood  the  for  machine.  163  RESULTS  1)  Aortic  a)  Blood  Nerve  Pressure,  Resistance The ducks  was  hind  midway  limb  rate was with  just  aortic  nerve  there  heart  significantly a  transient  no  aortic  Vascular  the  and h i n d  heart  in  in  the  heart  higher  Section  but  II  of  1  and had  both  barodenervates as  the  animals  remaining heart  pressure.  were  not  barodenervation 3 and  in  on t h e  blood  resistance  days  to  baroreceptor-heart  effects  resting  17b  which  mmHg-i)  -  rate  5 days  17a,  unilateral  min *  complete on  completely  (Figure  Section  limb  rate  and  all  baroreflex  rise  by  in  barodenervated  pressure,  were  beats  intact.  further  in  blood  11),  tests  (-1.0  affected  rise  intact  nerve  animals  (Figure  nerves  rate  of  resistance  eliminated  was  Limb  unilaterally  that  control  effective  Diving  and H i n d  Resting  one  intact  of  during pressor  as  both  Resting  the  nerves  reflex  aortic but  in  between  of  Rate  state  vascular  During  Stimulation.  animals.  removal  than  aortic  to  circulatory  wk a f t e r 17c)  Heart  Responses  barodenervated and  Stimulation  4  except  for  post-  denervation. During  control  dives,  predive  value  at  dropped  by  % (Figure  83  1 min,  heart  rate  fell  and by  2 min  30  17b).  Over the  sec  by of  first  78  % of  the  diving  had  minute  of  these  164  F i g u r e 15. A r t e r i a l p r e s s u r e (ABP) and h i n d l i m b b l o o d f l o w ( H L F ) r e c o r d i n g s f r o m p o r t i o n s o f 2 m i n 30 s e c d i v e s without (a) and w i t h (b) p e r i o d s o f a o r t i c n e r v e s t i m u l a t i o n . Dives were r e c o r d e d 1 day a f t e r b a r o d e n e r v a t i o n . Times i n the dive and t h e t i m e of s u r f a c i n g a r e i n d i c a t e d by t h e a r r o w s . The b a r s u n d e r t h e t r a c e s a t (b) i n d i c a t e t h e d u r a t i o n of the stimulation periods.  a) Dive without stim. DEN. 1  day  t 10  *  sec  b) Dive with stim. 300  r  0  t  Predive stim  1:00 Dive  stim  2:00 Dive  2:10  stim  up  166  F i g u r e 16. A r t e r i a l p r e s s u r e s and h i n d l i m b b l o o d f l o w s r e c o r d e d d u r i n g d i v e s w i t h o u t and w i t h a o r t i c nerve s t i m u l a t i o n i n t h e s a m e a n i m a l a s i n F i g u r e 1 5 , a t 21 d a y s after barodenervation. L a b e l s a n d e v e n t s a r e t h e same a s i n Figure 15.  a) Dive without stim. 300 cn 2 0 0 h r  DEN.  ' ^ ^ ^ ^ M ^ ^ ^ ^  < t  21 day  E 100 80r  'c  0  10 sec  b) Dive with stim. 300  E 200 E 100  Q- i m <  T  c  0 80 0  L  L  Predive stim  168  F i g u r e 17. C a r d i o v a s c u l a r r e s p o n s e s t o d i v i n g and t o aortic nerve s t i m u l a t i o n . a) A r t e r i a l b l o o d p r e s s u r e (MAP), b) h e a r t r a t e (HR) a n d c ) h i n d l i m b v a s c u l a r r e s i s t a n c e (HLVR) a r e p r e s e n t e d a s mean + 1 S . D . f o r 14 o b s e r v a t i o n s i n 12 u n i l a t e r a l l y barodenervated animals before (Preden, shaded b a r s ) and a f t e r complete b a r o d e n e r v a t i o n . The r a n g e i n c l u d e d i n each d e n e r v a t e day group i s i n d i c a t e d under the b a r s . For each day g r o u p , v a l u e s a r e p r e s e n t e d j u s t p r i o r to s t i m u l a t i o n (unshaded b a r s ) and d u r i n g s t i m u l a t i o n (solid bars). A s t e r i s k s (*) indicate prestimulation values s i g n i f i c a n t l y d i f f e r e n t from p r e d i v e f o r t h a t day group. Closed c i r c l e s (•) indicate values in denervates s i g n i f i c a n t l y d i f f e r e n t from the p r e d e n e r v a t i o n v a l u e at that dive time. T h e (+) symbols r e p r e s e n t s i g n i f i c a n t e f f e c t s of s t i m u l a t i o n i n each day group a t each d i v e t i m e .  Predive 300r  1:00 Dive r  2^10 Dive r  CD  to  Predive  100 Dive  210 Dive  70 60 50 AO 30 20 10 0 Pre den  1  2  3  4  5-6  7-8  9-10 11-14 15-23  5-6  7-8  9-10 11-14 15-23  1:00 Rec 70 60 50 40 30 20 10 0«Pre den  1  2  3  4 Day  Pre den  1  2  3  4  5-6 Day  7-8  9-10 11-14 15-23  Pre den  1  2  3  4  5-6 Day  7-8  9-10 11-14 15-23  172  dives  hind  and by  limb vascular  end-dive  17c).This vascular  degree beds, even  large  fall  in  blood  pressure  and  to  17b  in  had  the  times Figure  clearly  dives  the more min  and  first than 10  4  in  in  the  face  of  the  control  within over  of  the dive,  predive  1 min of  the  all  not  cardiovascular  barodenervation, of  next  depending  after  to  value  variables  surfacing,  15  min  that  (Figure  deepened  in 5-6 in  of  seen  in  the  animal  two  b r a d y c a r d i a c a n be  section, dives  rate  chronic,  (Figure  dive  (Figure  heart days  state  15a;  at  in  dive  at  17b),  and  absolute  rate  1 min  was  baroreceptors and  For was and  2  the  from p r e d i v e  without  seen  15a).  heart both  at  the  Figure  control  both  denervation  (acute,  nerve in  same  resulted  limb  after  can be  from the  submergence  After  diving  The p a t t e r n  denervated  after  time  diving  recordings  decrease  17b).  on t h e  performed.  acutely  days  forced  b r a d y c a r d i a and h i n d  responses  double  bradycardia  was  % from the  all  times  (Figure  occur  pressure  end  24  significantly  The r e d u c t i o n  proportional (Figure  by  levels  barodenervation  the  sec  By t h e  5.5  value  d i d not  dive,  recovery,  predive  were  flow  16a). in  blood  the  decreased  degrees  after  in  rate.  complete  cardiovascular pressure  predive  by  17c).  vasoconstriction, which  the  since  1 min  change  variable  times  increased  vasoconstriction  During  and  After  at  their  did not  17a,  of  heart  17a).  returned  6.5  however,  maintained  (Figure  was  resistance  reduced the  proportionate  dive  173  terms:  heart  rate  Figure  17b),  as  rate,  as  in  was  well  control  bradycardia period  dropped to  in  to  days  following  nerve  this  time  rises  of  the  4.2  same  was  times  times  same  (Figure  percentage course  control  of  of  the  controls,  the  in  17c).  in  to  diving  up t o  However,  significantly,  predive  predive  dives.  as  (Figure  the  observation  response  that  16a,  the  resistance  reduced  o r more  level  throughout  in  section  response  to  5.5  that  the  same  The t i m e  limb vascular was  only  the  dives.  barodenervates  rising  by  barodenervates  similar  The h i n d  as  the  value,  control  in  14 after  resistance  compared  and a c u t e l y  with  denervated  animals. Dive the  blood  in  proportional reduction  without  baroreceptors  progressive toward  trend  increasing  submersion pressure  was  was  level  as  in  Blood arterial  blood  barodenervated animals  animals  towards  with  with  reduced  dive  in  i n which  one  16a,  while  by  length  17a).  the  than  heart  rate  of  followed  cardiac  in  2 5 - 5 0 %, time  This  barodenervates,  higher  the  the  hypotension  acute  from  samples ducks  15a,  of  fell  the  trend  response  to  blood  chronic  fell  to  the  same  dives.  values  both  depending  bradycardia:  control gas  barodenervates  (Figures  significantly  barodenervates,  in  pressure  predive,  taken  are  nerve  intact  and  postdive  unilaterally  presented  aortic  nerves  from  dive  in  Table  intact (Table  was 5).  and  completely  7.  Resting  Pa 02  the  same  in  When  as  unilateral  174  TABLE  7  A r t e r i a l b l o o d g a s e s a n d pH d u r i n g d i v i n g a n d r e c o v e r y i n u n i l a t e r a l (a) and b i l a t e r a l (b) b a r o d e n e r v a t e s . Means + 1 S . E . M . (mmHg) a r e g i v e n f o r t h e n u m b e r o f o b s e r v a t i o n s in brackets, in 6 animals. A l l d i v e b l o o d samples were t a k e n at 2 min. A s t e r i s k s (*) i n d i c a t e d i v e and r e c o v e r y v a l u e s s i g n i f i c a n t l y d i f f e r e n t from the p r e d i v e v a l u e w i t h i n each dive group.  a)  PRE-DENERVATION  Pa02  PaC02  PREDIVE  85.3 ±1-6 (6)  26.9 ±2.2 (6)  7.488 ±0.040 (6)  2:00  53.4 ±3.1 (6) *  38.3 ±2.7 (6) *  7.383 ±0.041 (6) *  1:00 REC  99.7 ±3.2 (6)  21.5 ±2.1 (6)  7.451 ±0.034 (6)  2:10 REC  105.2 ±3.3 (6)  21.9 ±1.9 (6)  7.490 ±0.039 (6)  15:00  86.6 ±3.5 (6)  24.5 ±2.2 (6)  7.522 ±0.033 (6)  DIVE  REC  pHa  b)  POST-DENERVATION  Pa02  PaC02  pHa  PREDIVE  86.5 ±0.8 (U)  22.7 ±1.0 (11)  7.469 ±0.010 (U)  2:00  59.0 ±1.5 (9) *  36.2 ±1.4 (10) *  7.333 ±0.014 (9) *  1:00 REC  102.9 ±2.4 (8)  17.9 ±0.6 (8)  7.436 ±0.020 (8)  2:00 REC  97.8 ±1.9 (8) *  20.1 ±0.5 (8)  7.437 ±0.012 (8)  15:00 REC  92.8 ±3.3 (6)  21.1 ±1.3 (6)  7.430 ±0.015 (6)  DIVE  177  denervates in  however,  baroreceptor-intact  animals.  animals,  at  and  rest  did  variables,  and  changes  blood  in  above  this end  that  section of  both  the  in  Figure  in  Figure  reductions  almost  entirely  stimulation. observed nerve  due  of  to  A uniform  but  (same the  35-42  at  to  part  1  quickly  the 46  cardiac % drop  of at  the  in  performed  this  time  dark  9-10 in  of  pressure  therefore, aortic  14  to  post-  pressure  32  Figure  responded  blood  up t o a  post-  bars,  days  rest,  only  induced  times  however,  blood  and  chronically  nerve  (solid  at  before  (acutely  all  effects in  nerve  aortic  2 and  stimulation  beyond  ducks.  breathing  animal,  % at  diving  only  during stimulations  section,  in  of  15b  The r e d u c t i o n  by  same  denervated  aortic  resistance,  17c).  produced  of  before  stimulation  (Figure  17a)  16b  Stimulation  animals  gas  barodenervates.  illustrated  and  Total  continued  resumption  are  limb vascular  (Figure  dive.  barodenervates  as  unilateral  had the  barodenervates  much  intact  blood  dived,  the  17b).  denervation  resting  of  in  nerve  the  unilaterally  After  denervation  predive  in  stimulation  rate  Hind  in  as  in  Pa02, PaCO2 a n d pHa r e c o v e r e d  barodenervated). heart  resting  when  bilateral 5).  as  the  did  of  a n d pHa  to  barodenervated)  mean  as  fall  PaC02  changes  animals,  and t o t a l  Responses diving  alter  the  dive,  unilateral  during  not  group  (Table  same  same  gases  in  the  the  these  Pa02 i n t h i s  Dive  were  showed  barodenervation  be  Pa02 d i d n o t  dived,  denervates  were  days  was  nerve was after  % pressure  drop  178  occurred  despite  an unchanged  effect  of  stimulation  on  heart  rate. When t h e in  aortic  barodenervated  nerve  was  animals,  a  response  (40-60  % reduction)  produced  by  the  same  reduction)  (also  see  heart  during  rate  greater was  stimulus Figures  stimulation  on t h e  effective  p r o p o r t i o n a l l y when  as  days  1-4  which  resistance  stimulation the  in  early  was  in  dropped  cardiac by  only  representing  a  not  the  baroreflex-induced  enhanced  dive  than  dive  time  heart in  was  significant  in  not no  more  was  high,  Hind  affected  stimulation,  reduction  was  low.  d i d not  stimulation  was  rate  c i r c u l a t o r y changes.  % during  be  chronic  rate  so  rate  The d e c r e a s e  significantly  to  dive  (35-42 %  16b).  dive  and  the  could  stimulation  heart  dive,  response 32  than  predive  this  the  in  proportional heart  and  rate:  post-denervation,  barodenervates, vascular  prestimulus  at  early  obtained  given 15b  dependent  at  stimulated  Despite  at  from  by  contribute  blood  to  the  pressure  1 min the  limb  in  the  dive,  predive  response. Aortic  nerve  stimulation  rate  inconsistently,  some  days  effective was  less  after on than  the  in  the  dive  producing significant  denervation. heart,  that  late  the  When e n d - d i v e  effects  predive  (Figure  16b,  effects  on h i n d  limb vascular  in  Stimulation resistance  the  dive  h a d no at  heart  only  stimulation  proportional reduction  occurring earlier 17b).  affected  any  in  or  on was  rate  at  significant time  after  179  barodenervation. response had  no  As  and t h e  lack  significant  after  a  rate,  hind  blood  animals  diving,  of  after  emergence.  remained return  below  to  the  post-dive levels.  reduction  in  response,  end-dive  pressure  blood  cardiac  stimulation  pressure  in  throughout stimulation predive  levels  surface, rates  of  were at  in  ducks  all  surfacing. heart  recovery  d i d not  period,  return  and d u r i n g the  change  returned  rate  15 hind  during stimulation  within  1  however,  following in  which  predive  barodenervation,  to  nerve  but  control  2 min  respective  predive  levels  stimulation  and b l o o d  until dive,  levels  than  after  Aortic  in  barodenervates  their  times  and,  barodenervates,  more  acute  above  quickly  predive in  for  in  resistance  altering  the  even  resistance  recovered  returning to  By c o n t r a s t ,  1 min  not  limb vascular  predive  heart  effective  did  on  Blood pressure  limb vascular  within  at  the  a peripheral  effect  consequently,  hind  of  of  denervation. Heart  min  result  pressure  the  full  min  after  limb  was  response the  dive.  vascular  d u r i n g the  to As  resistance  recovery  period.  b) to  Cardiac  Output  Total  Peripheral Resistance  Responses  Stimulation. Measurements  blood the  and  pressure,  unilateral  of  heart  cardiac rate  output  were  obtained  and h i n d  limb  blood  barodenervates  with  electrodes  along  flow,  in  implanted  with 3 on  of  180  F i g u r e 18. C a r d i a c and p e r i p h e r a l r e s i s t a n c e r e s p o n s e s t o a o r t i c nerve s t i m u l a t i o n i n b a r o d e n e r v a t e d ducks b e f o r e and during diving. a) C a r d i a c o u t p u t (CO) a n d s t r o k e v o l u m e ( S V ) ; and b) t o t a l p e r i p h e r a l r e s i s t a n c e (TPR) and h i n d l i m b vascular resistance (HLVR) a r e p r e s e n t e d a s mean + 1 S. D . for 6 observations in 3 animals. The range of each day group i n denervates i s i n d i c a t e d under the b a r s . Notation, bar s h a d i n g and symbols i n d i c a t i n g s i g n i f i c a n t d i f f e r e n c e s are t h e same a s i n F i g u r e 1 7 .  Predive  5  cc  Q_  m rtnnnriri Pre den  1  2  3  4  5-8  9-16  Predive 60 3  40  cc :>  20  ri ^ ^ ri r , r. 1  0  L  i  Pre den  1  Day  5-8  9-16  183  the  aortic  and  hind  during and  nerve.  limb vascular  diving,  the  18a,  Prior decreased was  then  animals  (Figure  Stroke  to  84  % in  2 min  and the  complete  by  resistance  while  limb  18b).  16  Hind  followed  rising  within  1 min i n  days  sec  nerve  resistance  before  was  and  destroyed  post-denervation  limb  in  % of  dive  (Figure  dive  by  4.9  time  diving  times  animals  end-dive  was Total  end-dive,  rose  by  5.8  times  resistance  during value  volume  18a).  at  peripheral  course  output stroke  the  these  their  while to  and t o t a l  same  cardiac  response  increased  the  10  30  cardiac  resistance  responses to  for  barodenervation,  a  peripheral  (Figure  estimated  remaining aortic  dived  complete  unchanged,  hind  were  peripheral  18b).  by  virtually  total  resistance  the  were  volume,  the by  dive,  1 min  of  diving. Complete the  absolute  variables  after  to  diving  25-35  the  same  rate time  output  in  in  of  the  Figure  resting  18,  nor hind  significantly  and n e i t h e r  limb vascular  affected  cardiac  the  only  18a).  During  decreased whole  by t h e  group  course.  The e f f e c t s  the  (Figure  dive  of  18a)  of  output,  diving same  in  resistance  rose  the  nerve  aortic  reducing 3  followed  and w i t h on the  this  animals  p r o p o r t i o n as  stimulation  also  total  these  denervates,  of  affect  cardiovascular  Stimulation  output in  any  d i d not  denervation.  % (Figure  cardiac  heart  of  resistance  time  prior by  level  presented  peripheral with  barodenervation  did the  cardiac same  184  pattern 1 min  in  output at  as  on  the  as  cardiac volume and  was  was  also The  change the  the  all  in  first  data  any  time  of  in  presented  in  Figure  following  magnitude  or  the  over  day  vascular during  time  period.  resistance  diving  in  nerve  peripheral  in  output heart  removal  Neither  of  change  total to  animals.  Stroke  show t h a t in  the  d i d not  hind  cardiac  limb  the  level,  than alter  volume  was  the less  in  before either  the  vasoconstriction  peripheral nor hind  aortic  were  dive.  while  dive  but  stroke  predive  in  at  in  Dive  rate.  stimulation 18b  on  during diving  barodenervation  course  3  delivered  barodenervation,  from the  resistance  responded  these  of  denervation.  cardiac  decreases  baroreceptor  16  after  by  days  Stimuli  p r o d u c e d no  significantly  denervation,  a  stages  influenced  total 4  most  stimulation  reductions  not  18b).  same p r o p o r t i o n a l e f f e c t  for  altered  result  (Figure  had the  same at  not  the  rate  predive,  output  thus  solely  dive  at  end-dive  heart  nerve  limb  stimulation  185  2)  Chemoreflex-Baroreflex  a)  Aortic  Nerve  Interactions  Stimulation  During  Dives  After  Exposure  to  Oxygen. Ducks  with  100  % oxygen  1-2  wk.  to  levels  (Figure in  blood  normoxia  above  the  dives  hyperoxic  exposure  normoxic  was  animals  hyperoxic  before  decrease  in  pressure  resistance decrease  in  resistance  and  the  the  provoked  a  (Figure heart by  higher  nerve  % fall  pressure,  rate  Hyperoxic by  1 min  factor  of  in 3.3,  as in  in  in  well  during  predive in  significantly  rate  no  hind  in  normoxic  heart  animals the  s t i l l  hyperoxic  with in  showed  during dives  pH f e l l  level  Analysis  sec  dives.  animals and  a  54 %  contribution limb  dive,  and b l o o d  to  vascular  showed while  a  not  hyperoxic  dives  90  than  did  rate,  in  17).  was  recorded  from changes  19).  a  same  42  but  for  respective  hyperoxic  Arterial  aortic  arterial  response  rose  7).  that  pressure  PaC02 a t  value.  above  to  of  mean  in  sec  significantly  dives,  diving  90  but  Heart  Figure  significantly  (Table  Stimulation  the  at  (cf.  given  oxygen  level  from t h e i r  diving  normoxic  hyperoxic  blood  normoxic  and b l o o d  were  barodenervated  raised  the  unchanged  before  taken  resting  been  exposure  4 times  were  Pa02 h a d d e c r e a s e d  that  in  to  having  resistance  19)  samples  after  electrodes  PaC02 o r pHa ( T a b l e 8 ) .  affect  limb vascular  animals  stimulating  hyperoxic  significantly  significantly  of  breathe  5 min of  tension  hind  implanted  43 % hind  pressure  limb was  186  TABLE  8  A r t e r i a l b l o o d g a s e s a n d pH b e f o r e a n d d u r i n g o x y g e n d i v e s i n barodenervated ducks. Means + 1 S. E . M . f o r 6 o b s e r v a t i o n s in 4 animals. P r e d i v e b l o o d samples were t a k e n a f t e r 5 min o f b r e a t h i n g 100 % o x y g e n , a n d d i v e s a m p l e s w e r e t a k e n 2 m i n a f t e r submergence. A l l dive values are s i g n i f i c a n t l y d i f f e r e n t from p r e d i v e .  Pa02 mmHg  PaC02 mmHg  pHa  PREDIVE  359. 6 +7.1  24.7 +2.4  7.447 +0.038  DIVE  264.0 +29.1  48. 2 +5.3  7.218 +0.044  187  F i g u r e 19. Cardiovascular responses to a o r t i c nerve s t i m u l a t i o n d u r i n g oxygen d i v e s . A r t e r i a l blood pressure ( M A P ) , h e a r t r a t e (HR) a n d h i n d l i m b v a s c u l a r resistance (HLVR) means + 1 S. E . M . a r e g i v e n f o r 7 o b s e r v a t i o n s i n 4 barodenervated ducks. A s t e r i s k s (*) o n d i v e v a l u e s indicate s i g n i f i c a n t c h a n g e s f r o m p r e d i v e a n d (+) s y m b o l s m e a n t h a t , a t a g i v e n t i m e , t h e s t i m u l a t i o n v a l u e s ( s o l i d b a r s ) were s i g n i f i c a n t l y d i f f e r e n t from the p r e s t i m u l a t i o n values (unshaded b a r s ) .  189  maintained. change drop in  in  in  Nerve  hind  heart  blood  stimulation  limb  vascular  rate,  pressure  leading  as  stimulation.  By t h e  by  66  a total  vascular  of  values.  the  % with  no  effect  of  the  the  during  dive,  end-dive  hind  heart  pressure predive  however,  rate  a  on b l o o d  61 % decline  in  had  hind  was  fallen limb  not  or  1 min  reduced  limb vascular  stimulation  induced  no  predive  increase  from e i t h e r  on  but  produced  same p r o p o r t i o n a l  further  stimulation,  effect  time  resistance to  of  and  this  obtained  no  different  End-dive  with  net  end  resistance,  significantly  half,  that  at  dive  heart  rate  resistance,  pressure  was  a  by  and 42 %  decrease.  b)  Blood Pressure  Normoxia The response 20.  Hypoxic  to  aortic  a  nerve  stimulus  smoothly  curve  the  prestimulation produce  Stimulation  frequency  graded  blood value.  significantly  for  activation  a maximum d e p r e s s i o n  frequency,  Nerve  Frequency  in  Hypercapnea  stimulus-response  Increasing  produced until  and  and A o r t i c  the is  at  pressure  a maximal  obtained fell  to  38  Further increases greater  pressure  presented  proportional was  blood  fall at  in  intensity  in  20  Hz.  % of  the  in  hypotension.  Figure  pressure At  frequency  this  do  not  190  F i g u a r e 20. Normalized a r t e r i a l blood pressure responses to a o r t i c nerve s t i m u l a t i o n i n normoxia and h y p o x i c h y p e r c a p n e a . P r e s s u r e a t e a c h s t i m u l a t i o n f r e q u e n c y i s e x p r e s s e d as p e r cent change r e l a t i v e t o the p r e s s u r e j u s t b e f o r e stimulation:  MAP MAP % p r e s t i m  =  1  change  -  X  100  p r e s t i m MAP  Closed c i r c l e s (•) r e p r e s e n t mean v a l u e s d u r i n g 5 c o m p l e t e s t i m u l a t i o n r u n s i n 3 n o r m o x i c a n i m a l s , and t h e closed t r i a n g l e ( » ) i s mean p r e s s u r e c h a n g e d u r i n g 3 s t i m u l a t i o n s in a n i m a l s a t 15 H z , a f t e r b r e a t h i n g a h y p o x i c , h y p e r c a p n i c g a s mixture. E r r o r b a r s r e p r e s e n t + 1 S. E . M . , e x p r e s s e d as a percentage of the p r e s t i m u l a t i o n value.  u u i . i s a j d °/o  dVlAl  192  Table breathing to  erect  inspired  shows b l o o d  and h y p o x i c the  of  hypercapnea,  in  blood  the  symbol  baroreflex  Pa02 was  92.1  rate  was  15  carotid  7.347  nerve  reduced  for  with  + 0.009  min *. -  set  are  + 0.015),  blood  the  pressure  same by  to  7).  as  much,  stimulus  Body  shown  The  Perfusion.  stimulation  of  the  in  Figure  21.  19.2  + 2.9  mmHg  carotid  parameters pressure  carotid  body  stimulation 33  %.  was  aortic  down b y  was  of  body  for  47  perfused  mmHg, PvC02 4 8 . 5  only  on  spontaneous  bring blood  + 3.2  (Table  same  mmHg, PaCC-2 was  Stimulation  (PvC-2 4 5 . 5  close  half  chemoreceptor  When t h e  inspired  hypoxic  Carotid  pH u n i t s .  to  the  an  levels  only  the  of  used  20).  animals  (S.E.M.)  were  blood  pHv  body  by  during autoperfusion  activation  mmHg,  Reduction  during  decreased  air-  animals  during dives  stimulated  conscious  breaths  venous  animals  During  % during autoperfusion. with  three  combined  Stimulation  + 2.1  ventilation  nerve  half,  Figure  in  7.536  + 1.5  the  curve.  Hz i n  of  a n d pHa was  18.7  in  d u r i n g normoxia  at  effects  same  pressure  as  A o r t i c Nerve The  the  nerve  proportionally,  c)  hypercapnea  a n d pHa d u r i n g  %, p r o d u c e d Pa02 a n d PaCO2  6.4  aortic  (triangle  values  approximately  recorded  When t h e  gas  frequency-response by  02  CO2 l e v e l those  9  +  the  That the  2.9 aortic carotid  193  TABLE  9  A r t e r i a l b l o o d g a s e s a n d pH i n b a r o d e n e r v a t e s during a i r breathing, and d u r i n g b r e a t h i n g a h y p o x i c , h y p e r c a p n i c gas mixture. Means + 1 S. E . M . a r e p r e s e n t e d f o r t h e number o f observations in brackets, i n 3 animals.  P02 mmHg  PC02 mmHg  pHa  AIR  87.9 +1.6 (10)  25.5 +1.8 (10)  7.532 +0.023 (10)  HYPOXIC HYPERCAPNEA  62.3 +1.9 (3)  43.8 +4.3 (3)  7.349 +0.021 (3)  194  F i g u r e 21. E f f e c t s of c a r o t i d body p e r f u s i o n w i t h venous b l o o d on t h e a r t e r i a l p r e s s u r e r e s p o n s e t o a o r t i c nerve stimulation. N o r m a l i z e d b l o o d p r e s s u r e c h a n g e s (MAP % p r e s t i m ) d u r i n g s t i m u l a t i o n were c a l c u l a t e d as f o r t h e data i n F i g u r e 20. M e a n s + 1 S . E . M . a r e g i v e n f o r 15 o b s e r v a t i o n s w h e n t h e a n i m a l was p e r f u s i n g i t s own c a r o t i d body w i t h b l o o d from the h e a r t (auto p e r f ) , 15 observations d u r i n g p e r f u s i o n of the v a s c u l a r l y i s o l a t e d c a r o t i d body w i t h v e n o u s b l o o d f r o m a n e x t r a c o r p o r e a l pump ( v e n p e r f ) a n d 6 observations d u r i n g i s o l a t e d c a r o t i d body p e r f u s i o n w i t h a r t e r i a l blood (art perf) i n 6 animals. The a s t e r i s k (*) i n d i c a t e s a s i g n i f i c a n t d i f f e r e n c e b e t w e e n "ven p e r f " a n d "auto p e r f " .  auto perf 100  ven perf  art perf  196  body  chemoreceptors  were  perfusion  was  frequency  to  25.5  + 1.1  perfused  with  arterial  was  ventilation aortic  nerve  pressure  as  indicated  in  rate  was  the  stimulation did  by  fact an  increase  breaths blood  same  stimulated  as  min  -  1  venous  ventilation  When t h e  from the  carotid  syringe,  during autoperfusion  produced the  stimulation  .  in  during  during  same  decrease  autoperfusion.  in  and  body  197  DISCUSSION  The  sacrifice  implantation variables Figure  occuring  were  when  the  higher  baroreceptor  nerve  put  a  train  one  It  week  substantial  animals  barodenervated.  nerve  was  sectioned  represented This in  was  this  take  a more  also  in  dive  barodenervated  animals  blood  rose  pressure  17)  is  least  to  that  loss  at  when  the  a had  when  intact  other  aortic  these  whereas same  the  in  in  animals  adaptation.  of  decreased  the  in  other  develop  responses  17,  during diving  of  than  cardiovascular  circulatory  pressure  Figure  much s m a l l e r  denervates, of  were  denervation  the  (cf.  changes  animals  removing the  of  diving  ducks  circulatory  a week t o  stage  blood  intact  were  Therefore,  the  in  in  clear  unilateral  in  cardiovascular  bilateral  prior  advanced  evident  section:  at  electrode  barodenervated  portion  which  of  and t h e  simultaneous ducks.  for  those  (Figure  adjustments are  than  values),  barodenervated  baroreceptor-intact  nerve  levels  unilaterally  o c c u r r i n g at  in  aortic  resting  predenervate  completely those  one  produced  which  11,  of  animals  the  Figure  stage  acutely 11  of  barodenervation. By  14-23  resistance it day  days  response  resembled  the  barodenervation,  to  d i v i n g was  response  barodenervated  end-dive  of  decreased  ducks. with  obtained  reduced by  The d e g r e e  time  after  the  peripheral to  Jones of  the  point  (1973)  in  where 30-50  vasoconstriction  denervation  in  the  at  animals  198  of  Figure  17  and,  half  the  is  similar result  a  amount  by  obtained bears  by  out  circulatory animals  of  seen  Jones  the  14-23 before (at  (1973)  adaptations  (at at to  Section  resistance  complete  3 weeks  suggestion  that  days,  the  weeks end  loss  of  not  risen  barodenervation.  post-denervation)  5-8  were  had o n l y  to  This that  post-denervation),  of  Section  the  III  that  baroreceptors  complete  by  16  days  rest  in  the  by  and the  in  the  post-  denervation . Stimulation barodenervated different  in  In  the  latter  as  stimulation in  section, uniform  resistance fall  in  experiments baroreflex In  parameters dive,  limb.  both were  the  responses  to  study  in  at  in  by  set the  the  alone,  nerve  whereas  and p e r i p h e r a l  54%,  in to  the give  present a  stimulation  the  the  by  I.  experiments.  pressure in  Section  substantial  stimulation  engage  blood  set  I  of  decreased  and  a  intermittent  experiments were  acutely  produced  produce  Section  d i d not  cardiac  to  predive,  aortic  the  during  pressure  parameters  drop  Thus  that  blood were  while  than  rate  present  barodenervated ducks  experiments,  less  at  acutely  experiments  heart  the  nerve  from  activation  present  of  stimulation  was  Baroreflex  aortic  pattern  46% p r e s s u r e  intensity  the  the  the  the  the  animals  response  stimulation  changes  of  at  rest  in  peripheral response  earlier limbs  of  was  due  to  stimulation the  engaged.  present  experiments,  s t i m u l a t i o n were  proportional cardiovascular  consistent  over  time  after  a  199  barodenervation  even  constant,  which  implies  inputs  to  the  little  change  this  time,  change  pressure of  a  stimulus  that  even  b r a i n s t e m were in  not  in  though  the  only  responses  changing  rest  but  the the  the  days  between  not  baroreceptor there  baroreflex  the  was  the  was  active,  dive  obtain  different  relationship  of in  required to on  though  tonically  functioning at  intensity  not  intensity  as  arc  well.  same  during The  blood  probably the  aortic  was  nerve  product  and  the  electrodes. The  proportional fall  early  in  the  rate:  in  acute  predive to  62  dive  heart  beats  22  rate  rate  min 1  beats  The  min"i  in  ducks,  that  in  order  ,  a  1 min i n  %)  that  dive.  rate  before  the  heart  fall  1 min of  which rate  depress  heart  reduce  rate  given  by b a r o r e f l e x dive,  the was  vagal  from the  rate  102  same  low  in  the  reduces  from  from  41  to  and  22  to  beats  41  heart means  beats  min  may h a v e dive  two  min~  required - 1  in  p r o p o r t i o n a l decrease the  to  17b).  (1987),  would be  for  102  predive  outflow  and Jones  62  reduces  (Figure  drive  stimulation  baroreflex  rate  heart  chronic  diving  from  which  decline  Furilla  by  in  in  described to  rate  a  stimulation  prestimulus  frequency  between v a g a l  Therefore,  heart  when  to  on t h e  dive;  a heart  during  relationship  a proportionally greater  than  the  frequency  after  rate  stimulus  % produces  % produces  (46  non-linear  35  heart  dependent  stimulus  34  rate  1  a  by at  -  by  not  denervates  barodenervates heart  was  in  the in  conditions  been  more  (chronic)  than  effective when  it  200  was  high  (acute).  The  results  experiments Sections heart  I  in  this  and  rate  from  II  substantial  aortic  nerve  response  contribute animals,  if  The after  the  changes  in  changes  in  these  to  whole  altered  stroke  volume  period  in  barodenervates reports  of  the  were  a  experiments presented  in  end-dive  stimulation  Total  in  heart  et  compared w i t h  dives  up t o  4  rate  hind  days  a l . ,  was  in  to  dive.  heart  with  heart  rate  rate  of the  changes  denervation in  and confirms  acute earlier  intact  1979).  whole  diving  were  group.  in  resistance  post-denervation.  ducks  Cardiac  and d u r i n g the  under  significant  results  in  and  fitted  responses  different  limb  intact  the  animals  volume  before  peripheral resistance  barodenervates animals,  of  Jones  in  diving before  to  the I,  stroke  responses  those  of  The l a c k  Section  output  to  may  of  due  the  baroreceptors  pressure  supports  discussed  and  d i v i n g throughout  1972;  similar  and  via  16b),  during  Blood  and H o l e t o n ,  also  15b  similar pattern  (Jones  to  as  o c c u r r e d when  beginning  subgroup  in  primarily  bradycardia  volumes.  during  unchanged  the  suggestions  dive,  the  the  stimulation  operates  Figure  therefore  stroke  the  rate  output  group.  change  these  at  nerve  the  that  of  followed  circumstances  not  (see  suggests  rises  in  heart  cardiac  probes  the  Early in  in  out  baroreflex  initiation  barodenervation flow  bear  stimulated  pressure  central  and  drops  pattern  to  the  diving.  above,  this  baroreceptor  Section  that  during  was  the  in  the  Hind  same limb  201  resistance as  before  response  rose  in  was  degree  and  This  in  the  beds  of  flow  Jones  the  to  response,  These  changes  in  the  which  bed  easily  more  In  mammals,  (i.e.  attenuates)  1983)  to  the  nature  same  in  of  body  in  the  flow  during  non-uniform  force-dived  animals.  ducks,  before  since the  From  5-16  resistance  predenervation was  the  same  denervation. animals  at  least,  during diving in  the  total hind  central  interacts  baroreflexes  strong  blood  ducks  resistance  changes  than  Butler  regional  the  as  by  vascular  recorded  resistance  chemoreflex  that  who  the  The  to  the  intact  of  with  animals  in  barodenervated  unfortunate  sinoaortic  extent  as  stage  limb.  peripheral  period  accessible  the  in  of  resistance  this  resistance that  denervates  after  hind  these  limb vascular  index is  in  the  limb vascular  resistance, is  the  at  intact  (1979),  total  show t h a t ,  an  in  in  responded  the  than  the  denervation  as  beds  artery  during diving  hind  hind  reliable  al.  dives  dives  as  more  factor  peripheral  in  that  throughout  d i v i n g was  results  in  work  differential  while  throughout  total  vascular  with  et  same  reduced  carotid  post-denervation,  response  the  reported  the  vasoconstriction  not  who  redistribution  days  the  that,  increased  by  and by  indicating  all  concur  limb  supplied  diving,  not  (1971),  hind  means  by  vasoconstriction  results  Jones  but  significantly  barodenervation,  present  dive  denervation,  denervation.  same  the  are  peripheral limb  vascular  circulation.  occlusively (Abboud and  chemoreceptor  drive  with Thames,  can  202  reverse  pre-existing  There  is  ducks  (Jones  this  certainly et  situation  diving  strong  a l . . by  ducks  with  reduced these  experiments,  attenuation stimulated  to  in  increase  in  in  would  rabbits  breathing  reached  this  elegant  analysis  of  cardiovascular  nerve  discharge  enhanced the  peripheral in  vascular  in  mixtures  to  pressure  but  to  The r e s u l t s  be  an  analogue  hypoxia,  of  which  (Figure  (Iriki  resistance  the  after  the  gain  of in  the  This  ducks:  was  not  marked  experiments  of  in  the  pressure 1979).  they  These  some v a s c u l a r  baroreflex  the  had  The done  an  resetting  of  authors  also  baroreflex-sympathetic  implying that  the  were  situation  baroreflex-independent during hypoxia.  by  gain  and K o r n e r ,  only  20).  baroreflex  the the  to  breathe,  these  and b a r o r e f l e x - b l o o d  conclusion  of  in  of  non-  breathing  and p e r i p h e r a l animals,  in  similar  confirmed  rabbits. bed  levels  was  relationship  limb  to  hypercapnea  during hypoxia,  chemoreflex limb  that  simulate  chemoreceptors  variables  however,  to  chemoreceptors  on b l o o d  normoxic  reduced  authors  attempt  force-dived  the  period  were  in  That  during arterial  relationships  drive  circulation.  spontaneously  gas  rate  rate.  appear  baroreflex-heart  found,  effect  occurred.  hypoxic  on t h e  gases  presenting  in  an  arterial  blood  heart  those  s t i l l  the  made  high-C02  baroreflex  similar  ducks  by  low-oxygen,  the  I  Setting  during diving,  were  1982).  conditions.  effects  chemoreceptor  loading  those  In  baroreflex  the is  was  cardiac  but  not  o v e r - r i d d e n by  the  stimulating  beds  case  the  for  aortic  the  the hind  nerve  at  203  an  intensity  presssure limb  at  rest  produced  reduce  the  made  by  giving  animals  This  was  was  above  the  PaC02 b u i l t u p t o in  al.  animals (1982)  level  dives  dived  have  are  the  reduction  19)  compared  (Figure Under  17)  these  stimulation  in  conditions,  blood  indicate  less  chemoreceptor  In nerve when  pressure central  a normoxic,  the  in  to  the  nerve  as  was  but  dives  hyperoxic  of  the  dives  (Table  (Table  7).  8)  Jones  p r o p o r t i o n of  the  adjustments  hypercapnea, dives  in  the  and  that  in so  (Figure  same  chemoreceptor  nearly  stimulation  inhibition  in  animals,  dives  fact  before  normoxic  hyperoxic  reduced  breathe  Pa02  air  to  during  animals drive.  end-dive as  effective  before  the  baroreflex than  in  in  dive  may  by  dives  in  animals.  stimulation  venous  aortic  input  than  hind  end-dive  and p e r i p h e r a l  normoxic  then,  drive to  oxygen  greater  responses  ascribed  the  a  in  since  successful,  in  blood  diving.  % 02  breathing  that  in  100  in  changes  chemoreceptor  hypoxia  those  may b e  reducing  normoxic  dive  during  non-diving  cardiac to  or  level  after  shown  due  with  of  in  a higher  chemoreceptor-induced forced  rest  partially  changes  significant  to  remained  et  no  An  attempt  at  substantial  either  dive.  than  produced  resistance  diving the  which  on  non-diving blood  chemoreceptors  blood.  procedure,  This  since  was  carotid  in not  animal,  pressure one an  body  are  the  of  substantially  carotid  body  artefact  of  perfusion  effects  are the  with  aortic reduced  perfused  with  perfusion  arterial  blood  204 had  no  such  effect  on  the b a r o r e f l e x .  w h i c h c h e m o r e c e p t o r d r i v e was b r e a t h i n g animals, this  may  have been a f a c t o r  baroreceptor the  ventilation  animals  nerve  elevated in frequency  during diving,  chemoreceptor d r i v e i n hyperoxic  nerve  pressure  and  stimulation, while  heart  these  dives after breathing a i r .  responses  i s independent of  previous heart  responses diving those  to aortic  in chronically  that  the  responses resistance  of h i n d  c a n n o t be body.  used  aortic in  the  conclusions i n  i n the  dive.  stimulation before  barodenervated animals,  and  The during  d u c k s were s i m i l a r  to  which i n d i c a t e s t h a t  the  relatively  t o t h r e e weeks a f t e r b a r o r e c e p t o r  loss.  The  l i m b v a s c u l a r r e s i s t a n c e and p e r i p h e r a l  during diving  barodenervation,  to  an  act primarily v i a  pathways of t h e b a r o r e f l e x remained  u n c h a n g e d f o r up  the  blood pressure  i n a c u t e l y denervated  central  a c c o m p a n i e d by  ventilation.  s e c t i o n support  nerve  reduced  chemoreceptor  s e c t i o n s t h a t the baroreceptors  rate to control  However,  were a t t e n u a t e d  This suggests  stimulation  in this  pressure. and  and  e f f e c t i v e n e s s of  r a t e response  of t h e b a r o r e f l e x d u r i n g  results  also increased,  d i v e s was  attenuation  The  spontaneously  i n reducing the  s t i m u l a t i o n on b l o o d  were a p n e i c  enhanced b l o o d  In t h e e x p e r i m e n t s i n  and  as an  differ,  over index  this  up  time,  t o 5 days hind  after  limb r e s i s t a n c e  of r e s i s t a n c e changes  throughout  205  GENERAL  1)  Baroreceptor In  to  the  intact  function  adjusting This  in  (West  et  regulating  a l . ,  regulation  on  partly  heart  due  than  1981)  which  integration  mechanisms  information  which  instead the  the  two  in  heart  fact  would  the  sets  set in  for  of  than  is  given  that  higher  body  size  pressure  central  baroreceptor  in  mammals.  baroreceptor  and t h e lower  in  pressure  the  et  al.  (1969)  sensitivity quantified  of  the  the  first  nerves,  sensitivity ducks  rise  of  (less  in  pulse  during drug-induced pressure between  slope  this  of  reflex.  operate  that  linear This  plotting  beat  r a p i d l y enough  lengthen  as  the  and t h e  relationship  analysis  pressure  workers  baroreflex-cardiac  be  interval  by  were  could  to  have  ducks  than  mammals). Smyth  the  mammals.  have  those  arterial  than  beat  of  appears  in  equivalent  may a l s o  mammals,  reflex a  birds  processing  different  system  as  make b e a t - b y  birds  rest.  rather  basis,  that  of  at  control  pressure,  mammals  for  one  rate  the  but  baroreceptor-cardiac  change in  of  are  only  circulation  barostatic  mean  to  rates  have  the  a beat-by-beat  impractical,  Ducks  of  duck the  pressure  may b e  resting  control  DISCUSSION  systolic rises next  gives  presupposes  that  the  is  s t i l l  cardiac  to  relationship  pressure  against  the  successive the that  propose  of  pulse  beat.  The  sensitivity the  each  of  reflex  can  will  begin  interval  ramping upwards,  and  in  fact  206  this  feature  of  the  mammalian b a r o r e f l e x  and D a v i e s  (1973)  about  400  ms  baroreceptor-cardiac reflex  their  study,  interbeat at  heart  the  the  latency  interval  from  of  estimate  the  the  first  below  75  beats  min  ducks,  which  commonly h a v e  - 1  ,  by  conduction in  lengthening  beginning  rates  a  used  Pickering  for  to  was  of  the  time  of  man.  of  In  the  pressure  ramp,  was  taken  as  the  reflex  heart  rates  of  150  beats  latency. In min-i  or  cardiac better the  greater reflex  suited  pulse  is to  of  short-term  4,  of  Figure  pressures operates  in  an  (assuming,  operating  the  time  the  pressures  at  same  measurements over  a wide  the  evidence  for  changes  this  in  adjustments  with  lower  are  rates  as  animal  course, point" being  range  adjusting  removes  are  is  to  the to  for  in  plotted  in  output  heart  of  which  of  the  range,  rates  and  baroreceptor-cardiac  the  In  pressure  system  pressure  taken).  lack  pressure  correct  that  the  buffer  the  c i r c u l a t o r y system  correlate  "set  to  is  barodenervates  a wide  of  reflex  brainstem  over  intact  this  than  that,  higher  disturbances  so  baroreceptor-  c a r d i o v a s c u l a r system  closed  expected  with  to  p a r t l y by  would  humans,  the  heartbeat.  input  a  for  regulation  next  the  In  regulated  pressures  in  pressure  3).  would be  reflex  of  induced  pump,  lower  the  The p r i m a r y  is  higher  latency  that  baroreceptor  pressure it  of  capability  correction  the  mean p r e s s u r e  pressure.  (Table  rest,  double  pressure  Loss  blood  at  during  Figure  against  is  22,  their  the blood  207  F i g u r e 22. E f f e c t o f b a r o d e n e r v a t i o n on t h e r e l a t i o n s h i p b e t w e e n mean a r t e r i a l b l o o d p r e s s u r e (MAP) a n d h e a r t r a t e (HR) a t r e s t . In ( a ) , s p o n t a n e o u s l y o c u r r i n g HR a r e p r e s e n t e d f o r 81 MAP m e a s u r e m e n t s i n 8 i n t a c t a n i m a l s . In ( b ) , s p o n t a n e o u s HR o b s e r v a t i o n s c o r r e s p o n d i n g w i t h 189 MAP o b s e r v a t i o n s a r e p r e s e n t e d f o r t h e same a n i m a l s a f t e r barodenervation. R e g r e s s i o n l i n e s were f i t t e d by the least squares method.  208  500 F b) Den .£  M  400  K  E  "a (/) ai  JQ  cr  M  M M M « *  « M M M  300  H  It «  S  200  « i I S  m  *  M  « M  M  u  *  M M uM M *  M M M  i ;  M M  M  M « M *  *  «M M| •« 2 " "M  M  « M  *  I S  M  100 OL  100  150  200 MAP  250 mmHg  300  209  corresponding  heart  rates  line  data,  p r o d u c e d by  for  shows and  this  that  heart  an  inverse  rate,  significant  as  line,  rate  relationship,  test)  value for  fit  the  rate  zero,  there  and h e a r t  The  at  pressor Table  slope  in  that  of  at  by the  in  rest  mmHg-  1  is  ducks  (1980)  slope  of  ,  but  (F-  is  r-squared  about  rate, for  40  % responsible  with the  of  pressure-  rest.  the  This  baroreceptor  (Figure  22b).  no  longer  heart The  different  a  slope from  controlled  baroreflex.  22  intact  The  significant  significantly is  s t i l l  of  c o r r e l a t i o n between  spontaneous  pressure-heart  about  half  that  (calculated  presented  the  pharmacologically min-i  not  the  Figure  Millard the  is  but  pressure-heart  was  section  barodenervates  line  low  mmHg-*.  - 1  The  responsible after  a  pressure  correlation  heart  significant  rate  in  tests  4).  during beats  no  least  relationship  show  is  regression  variable,  being  the  min  pressure  particular  method,  The s l o p e  of  (t-test).  blood  regression  between  with  line  significant  disintegrates  and p r e s s u r e  the  regression  any  exists  beats  The  least-squares  0.386.  the  factors  relationship  of  -0.50  a  ducks.  although  was  that  determining  the  sensitivity  variables  indicates  nerves:  the  was  two  independent  of  of  and t h e r e  between  predicted,  and t h u s  of  intact  relationship  r-squared value  this  goodness  for  data  baroreflex-heart  induced pressure he  found that  derived  from in  when  rate  the  from  data  in  Anas boscas  to  rate  changes the  response was  -1.17  pressure-  210  cardiac  relationship  pressures, 3.3  times  reverse  the that  was  rate  in  boscas  in  cardiac  sensitivity  induced  pressure  point  changes  both  of  pressure  a misleading the  present  levels  output  heart  rate  is  cats  the  higher  sensitivities to  sinus,  a  vascular than  given  with  new  and,  the  rest  in of  to  a r m may  different  required  to  alter  That  is,  nerve  of  these  in  one  lower  al  pressure  changes pressure.  effector  limbs  species,  species, (1971)  nerve  baroreceptor  with in  discharge  thresholds  one  a  ducks,  blood  nerve  in  for  than  varying with  sympathetic  the  the  be  within  had  in  to  sympathetic  cardiac  change  appear  level of  linked  function.  Ninomiya et  beds  other  contribution  controversial,  that  the  aortic  engagement  found  and k i d n e y  carotid  greater  technique,  spleen  response  the  barodenervation.  anaesthetized  input  tightly  baroreflex  resistance.  of  to  relative  experimental of  a  resistance  baroreflex  state  make  with  there  22.  illustrates  the  baroreflex  baroreceptor  stimulation  the  arm of  experiments  of  changes  I n mammals,  of  and p e r i p h e r a l  of  peripheral  the  picture  Figure  pharmacologically  studies  relationship  amount  in  in  in  was  the  The d i f f e r e n c e  and  the  given  the  spontaneous  range  whereas  much more  platyrhynchos.  occurring  pressure  shown  be  one  cardiac  with  to  of  threshold  by  appear  manipulation  In  in  experiments  A. to  spontaneously  a much n a r r o w e r  that  obtain give  the  in  at  pharmacologically,  and p r e s s u r e than  plotted  over  obtained  true  Heart A.  slope  was  to  and activity,  isolated sites  211  denervated. fixed  In  carotid  activity  to  sinus  the  results  would  plays  greater  a  pressure  Schmidt  cardiac were  heart  role  does et  obtained  al  in  blood  and  systemic  input.  Allison reported  resistance evoked  by  The animals,  means  above  pressure  nerves was  In  were  the  of  one,  placed  the  the  to  done these  of  be the  blood  these  sinus to  results  aortic the  aortic found  participated  that equally  baroreceptor  sinus  denervated  from t o t a l  peripheral  baroreflex  responses  in  aortic  results in  awake in  to  the  animals  which  to  had  by  been  sinus.  alter  and t h u s  is  all  sinus,  innervated  adjusted  arch.  anaesthetised  carotid  sinus  carotid  carotid  rabbits a  of  they  isolated  around the  could  wall  to  function  conscious  but  pressure  across  in  These  resistance  but  the  carotid  to  beds.  preferentially  denervated  in  a  sympathetic  the  experiments,  output  baroreflex  certain.  with  contribution  application  of  that  resistance  (1969),  experiments  a capsule  pressure  al  cardiac  and t h e  intra-capsule  the  at  cats.  control,  dogs  that,  adjustments  resistance  responses  greater  changing  baroreceptor cut,  a  than  understanding no  et  in  found  When t h e y  pressure  less  peripheral  sinus  pressure  and p e r i p h e r a l  the  dogs,  also  reported  peripheral  output  repeated  was  that  anaesthetized  baroreceptors  in  the  peripheral  intact.  output  to  carotid  (1971)  for  authors  there  indicate in  baroreceptors  cardiac  than  cardiac  employed  output  these  pressure,  seem t o  than  baroreflex  addition,  The  transmural  stimulate  the  212  baroreceptors al,  1981).  from  Most of  such  opening  the  baroreceptor  peripheral and  without  West  recurrent  baroreceptors in  arterial  in  In  heart  that  rate  that  control  of  blood  pressure  not  exist.  contributions in  both  differences.  of  stimulation.  nerve  the  adjustments, responses, without pressure  to  (Faris  changes  stimulation  arch,  Vliet of  the  from  produced  resistance  in  Van  fibres  et  resulting  however,  carries  to  of  needing  to to  in  above used,  in  are  equal  reduce  correct  the  would  baroreflex  the  due  well  control.  as  animals,  to  depends for  diversity genuine  in  in on  that  the the  resistance  that  heart  than  pressure  involve  pressure  showed  resistance  periphery.  also  to  experiments,  rapid  groups  relative  are as  the  vertebrate  to  implies  small  for  baroreflex  ducks  much more  engage  the  threshold  response  disturbances  resistance  the  peripheral  The h i g h e r  cardiac  serve  in  conscious  stimulation  which  of  pattern  various  The p r e s e n t  engagement  of  the  cited  breathing,  aortic  for  in  limbs  studies  to  than  toads,  common e f f e c t o r  and p r e p a r a t i o n s  spontaneously degree  a  The d i f f e r e n c e s  of  the  methods  species  change  due  bilateral  which  system  pressure. clear  of  was  and a o r t i c  is  control  pressure  pulmocutaneous  It  does  awake  nerve,  the  vascular  stimulation  reported  laryngeal  decreases  arterial  resistance.  (1986)  the  the  response intensity changes  rate  peripheral disturbances  Presumably the  larger  peripheral  If  this  probably  is  does  peripheral  not  was  change  a n d when  effects  not  apparent  become  in  at  two  Little pathways Langley  weeks  of  could  produced by  be  the  chickens  after been  that over  in  birds  exclusively associated.  in  the  temperature  trunk  to  of  ducks  alter  each  spinal  Bamford  brain  than  by  blood  a n d mammals,  the  seemed  to  an  there  outflow  was  to  hind  no  since  skin  the  specific  be did  hind  limb  the  outflow  nerve  in  to  heat  although  no  the  to  were  body  trunks  that run  in  post-  almost  to  was  influence  sympathetic  retes of  the  much  ganglion  able  cervical  details  the  p e r i p h e r y was  stating  exchange  and  the  which that  (1983) the  of  that  appeared  with  stimulating  birds.  sympathetic  mammals,  ganglion  in  portions  He c o n c l u d e d  in  efferent  vasoconstriction  various  and E c c l e s  flow  of  limb  which  innervation  stimulating  more  hind  animals,  there  the  view:  deafferentation  on t h e  vascular  and p i g e o n s .  of  elevated  from  barodenervation.  done  sympathetic  this  innervation  However,  of  Evidence  supports  show  vasoconstrictor  feathers  fibres  not  some t i m e ,  of  ganglionic  II  baroreceptors  level  baroreceptor-intact  distribution limited  the  animal.  Section do  from  resting  sympathetic  determined  movement  intact  baroreceptor  sympathetic  (1904)  input the  occurred.  work has  of  to  ducks  for  sympathetic  ducks  in  in  of  elevated  an  the  resistance  peripheral  ducks,  in  studies  interrupted  in  tonic  contribute  barodenervated  resistance, limb  then  resistance  barodenervation acutely  true,  the  in  the  heads  stimulation  214  sites  are  given.  experiments skeletal duck,  designed  muscle  stated  was  in  to  the  forced  details  vasculature  in  study,  electrical determine  of  birds..."  (p.  belied  sympathetic  mammals  by  of  of  hind  submersion  chain  for  limb in  the  direct,  329-330). the  This  experiments  Langley  been  well  (1893)  used  the  stimulation the  segment.  these  fibres  the  nerve  also  to  spinal  that  ganglion.  the  length  observations  of  a  with  of  the  in  on  skin  the  arising general  scheme  and  Green,  1955;  Donald and F e r g u s o n ,  (Kjellmer,  1965;  Lundvall  1951)  innervation  and  have  in  a  shown  from m u l t i p l e  Studies  has  investigations.  1978)  in  comparative there  vertebral  was  to  outflow by  post-  the  not  only  up w e l l  dog  1976; in  to  but  and p o s t e r i o r  held  study is  to  chain  associated,  1970),  and J a r h u l t ,  that  the  anterior  subsequent  Weissman,  segment  contributed  ganglion  both  an  response  ganglion  the  vasoconstriction  that  ganglion  to  In  sympathetic  chain  concluded  given which  nerves This  he  documented.  paravertebral  of  outflow  pilo-motor  distribution  procedures,  ganglionic spinal  of  segmental  From h i s  neuroeffector  have  by w o r k i n g t h r o u g h t h e  (Kuntz,  course  impossible,  sympathetic  was  the  responses  technically  the  view  the  in  II.  The  during  (1966),  examine  expose  pessimistic  Section  early  to  "It  stimulations  somewhat  to  al  and v a s c u l a t u r e  that:  unfortunately, graded  Folkow et  to  in  (Clonninger  in  cats  Sonnenschein cats  and  and  humans  sympathetic  segments  to  one  vascular  215  bed. the  Some  however,  lumbar sympathetic  rabbits and  authors,  do  total not  stimulation intact  in  (Humphreys and J o e l s ,  5 gave I  cord  have  believe  site  animals  control  used  were  hind  limb vascular  limb  sympathetic  of  this in  able  claimed  cats  (Folkow,  1982)  between  vasomotion to  be  true  generate  resistance  stimulation  than  stimulation  1952)  and  lumbar segments  the  hind  for  the  lumbosacral  in  ducks,  greater  were  experiments  limb.  since  increases  obtained in  of  in  in  my e x p e r i m e n t s to  that  in  the  Section  II.  in hind  4  216  2)  The R o l e  During  Baroreflex  baroreflex  ducks  control  at  system  standpoint pressure Butler  the  of  rest,  blood by  prevailing cardiac  blood  The of  Blood  whether  or  predive,  the  nerve  is  the  pressure  the  to  the  accomplished  by  balance  blood  than  in  animals  was  active  showed  removed, of and  in  with  the  a  at  the  cardiac  1 min i n  the  dive,  responded  operation  in  the  to  cardiac of  early  output. the  change  in  peripheral resistance  to  maintain  beds  the  baroreceptors  bradycardia  which  dive  during  against  adequate  remain open  (1974)  have  suggested  that  was  of  the  pressure in  dive. and White  did  during  In terms  of  vascular  in  but  stimulation  reflex  baroreflex  regulation  function the  of  degree  McRitchie  and  that  to  the  are  pressure  is  of  III;  h y d r a u l i c consequence  diving  perfusion  blood  (Section  baroreceptors  the  and p e r i p h e r a l r e s i s t a n c e ,  experiments  pressure  the  barostatic  End-dive  animals  "in-circuit",  changes  then,  in  optimum from  baroreceptor-peripheral resistance  Therefore,  barostasis,  of  than  peripheral resistance  contribute  diving.  for  Pressure  reflex.  baroreflex not  less  much more w i d e l y  aortic  regulating  intact  output  barostatic  the  in  When t h e  pressure  receptors  fluctuates  functional  not  of  regulation.  % in  1971).  the  limb  Control  performance is  pressure  level  these  the  diving  18-20  and J o n e s ,  without  effective but  during  drops  of  is  the  dive  in  Diving.  The intact  of  the  the  217  arterial to  the  baroreceptors  rise  in  that  innervates cessation  lung  peripheral  for  the  on  input  cardiac  was  baroreceptors  to  peripheral resistance  the  integrative  control  similar  of  minute  maintained.  (1973)  were  cannot  be  The  central  to  not  results  strengthened  acted  during  the  that  diving in  However,  in  the  of  the in  beyond  White and  about results  30  blood  ducks  is  in  the rate  at  that  least  sec,  in  the  reduced  cardiovascular of  as  so  suggesting  ducks  yet  end-dive  the  input,  during  diving,  The e x p e r i m e n t s  and  responses  rabbits  were  reflex-heart  diving,  circulation is  extended  neurons  through heart  the  studies  nervous  also  The  continued  bradycardia In  authors  apnea.  by b a r o r e c e p t o r the  not  which  bradycardia  of  compared t o  interaction  of  stimulation.  first  with  vasoconstriction.  not  control  the  to  baroreflex  baroreceptor  nerve,  but  to  These  initiates  along  facilitated  and  nasopharyngeal  rabbits.  The t r i g e m i n a l  study,  qualitatively  the  response  and vasomotor  both  contributed  due  bradycardia,  in  trigeminal  present  are  awake  vasoconstriction.  rose  the  receptors,  generating  relationship  pressure  in  afferent  influence  responsible  the  from  nasopharyngeal  trigeminal  rate  stimulation  input  of  to  peripheral resistance,  nasopharyngeal propose  contribute  the  after  the  adjustments McRitchie so  their  present  data study.  chemoreceptor-baroreceptor Section  attenuation  chemoreceptor  of  IV s u g g e s t the  drive  in  that  baroreflex ducks.  some  degree  results  from  Chemoreceptor  of  218  stimulation blood  in  and Jones,  baroreflex  same  that  only  a  experiments made  even  input  more  from  analyze inputs study  diving  has,  There  which  are of  control two  close  to  their  dives.  If  is  assumed  the  same  outflow  outflow the  degree would  of  of  other  pushed  are  needed  This  of  chemoreceptor  the  the  rate  that the  and  produce  clearer  mechanisms  less  during  is  fact  that  integration  the  relative  periphery, diving input,  effector  and  the  present  line  of  understanding  for  as  the  diving.  during  In  then  response  in drive  the  these  are  forced  vagal  before  of  diving.  changes in  of  to  and p e r i p h e r a l r e s i s t a n c e adjustment  baroreceptor  the  baroreceptor  in  for  during  ensure  The a t t e m p t  fruitful  effectiveness  limits  same  a  the  circulation during  possible  heart  to  to  to  situation  by  to  complex  during  groups.  lead  both  heart,  are  result  nervous  which p r o j e c t  a very  studies  could  animals,  the  diving  central  is  1983).  the  of  observed  a possibly  intact  sympathetic  being  1970;  over-ride  inputs  pathways  begun  baroreflex  it  sensory  receptor  of  may  and n o n - d i v i n g s i t u a t i o n s  however,  integrative  reduction  in are  interaction  input  graded  and P u r v e s ,  The s t u d y  and Thames,  difficult  g r a d u a l l y as  (Jones  controls  is  many d i f f e r e n t  investigation the  rigid  adjustments  the in  two  effect  (Abboud  circulatory  even  and  single  occur  and t h i s  common o u t p u t  however,  increase  centrally.  between  final  problem,  should  1971),  function  interactions the  dive  a n d CO2 c h a n g e s  oxygen  Butler  the  dive,  changes  because  of  to for in the  219  more  limited  difficult  scope  to  for  verify  directly:  sympathetic  outflow  whole-nerve  discharge  needed in  to  animals.  relationship resistance  between  in  that  it  is  in  sympathetic  obvious  is  low.  heart  rate-vagal  Jones  (1987) The  effect  in  of  of  afferent  long-lasting  hypoxia  was  the  develops.  found  to  be  chemoreceptor later  of  dependent  input, be  transmitter  is  implicated  be diving  and  (Figure  4),  and  proportional is  high in  for  change  would  drive  the  reported  is  that  not  when  the  non-linear  by  central  pathway input  in  to  Furilla  and  in  on  serotonin in  (Antonaccio,  nervous  diving  the et  some  period.  intact  carotid  the  central  1984),  indirect as  proposed  exposure  to  ponto-medullary This  tachypnea  body  neurotransmitter et  an  (1980a)  after  hypoxic  (Millhorn  is  brainstem  al  cats  a b u i l d u p of  and t h e  to  circulation  true  during  activity  change  Millhorn  during the  shown  the  same  tachypnea  result  neurotransmitter  the  would  ducks.  baroreflex  that  and  and  non-linear  resistance  relationship  possibility  hypoxia  the  a given  T h e same h o l d s  increased  before  be  (integrated  candidate)  established  that  the  much as  arterial the  good  would  vagal  organs  sympathetic  been  data  when  drive  the  a  limb  has  dabbling  second  inhibition  bed  as  be  This  of  different  activation  hind  drive  index  Nevertheless,  from t h i s  resistance  resistance  was  would  adjustment.  some  several  during baroreflex  conscious  alter  effector  al.  involved 1980b).  autonomic  and F r a n z  et  al  was This  control (1982)  of  220  have  suggested  depression tachypnea  of in  proportion Jones,  serotonin  ducks,  to  the  the  d u r a t i o n of  length  of  the  integrity  during  the  dive  to  Jones,  1982a)  of  full  blood  pressure  stimulation  after  diving  the  predive about  therefore  exists  increased  afferent  enough  inhibit  to  that  ducks.  by  1 min p o s t - d i v e  present  Certainly  at  brainstem with  and w i t h o u t  made  to  dive  for  after  a  indirect  9).  the  baroreflex the  blood  (Table  6),  so  M.  The  (Lillo  to  and  the  return  nerve  possibility  neural  dive  is  Shimizu,  ventilation  aortic  during  gases  the  1982a;  required for to  and  tachypnea  2 min d i v e  central  during  in  chemoreceptor  post-dive  response  (Figure  post-dive  (Lillo  post-dive  and J o n e s ,  of  this  may  effects linger  recovery  have  from  long  from  diving  returned to  normal  continued  direct  baroreflex  problem would  neurotransmitter  Neurotransmitter  be  this  carotid  could not  arterial  stimulation  duplicate  the  areas,  chemoreceptor  measurements  require  concentrations  cardiovascular control  chemoreceptor  a  central  be  time.  Investigation of  There is  the  which v a r i e s  same t i m e  i n h i b i t i o n of  this  measurement  the  input the  in  chemoreceptor  level  in  c a r o t i d body  The t i m e  return  is  of  involved  preceding  of  (Lillo  (1987)).  the  the  and a p o r t i o n  on  unpublished  may b e  circulatory reflexes.  1982a),  dependent input  that  would  alone, possible  during  within  the  submersion  stimulation.  also  and an  the  be  needed  attempt  effects  of  during  would have  diving  on  to  221  t r a n s m i t t e r s e c r e t i o n by the a p p l i c a t i o n of v a r i o u s known transmitter involved diving.  substances t o those r e g i o n s  of the brainstem  i n the c o n t r o l of the c a r d i o v a s c u l a r  system  during  222  3)  Role  the  Cardiovascular Adjustments I  of  the  have  presented  development input  Baroreceptors  of  the  evidence  diving  the  baroreceptors.  baroreflex  did  contribute  first  minute  peripheral  to  forced  input.  cardiovascular must  In  occur  at  the  Jones,  Receptors  and  water,  C02 t o  rise,  increases. and  in  in  the  of  chemoreceptor submersion.  drive  the  Up t o  about  the  the  to  first  changes  so  heart  rate  Pressure unloading reflex  reflex  changes the  in  the  help  to  in  drive  heart to  the  these  of  of  the animals,  area, begins  on to  fall  chemoreceptors in  heart  rate  as after  diving,  and c a r d i a c  if  the  output  the  baroreceptor-  intensify  the  bradycardia.  direction  (that  probably would not  rate  degree  (Bamford and  time of  in  the  oxygen  changes  the  rises,  opposite  baroreceptors)  increases  chemoreceptor  will  pressure  of  and o r a l  minute  that  rate  the  for  intensifying  between p e r i p h e r a l r e s i s t a n c e arterial  in  with  depend  independent  arterial  rise  not  heart  train  blood  the  shown  that  was  in  balance  that  in  diving  set  occur,  does  integration  facial  from  Maintaining  that  have  submersion  be  continues  I  dive  Baroreceptor-independent  peripheral resistance  ducks  and a l s o  apnea,  input  thesis  decrease  forced  to  initiate and  this  the  time  adjustments  contacting  in  overall  to  cardiovascular 1974).  Diving.  However,  in  the  responses  to  dives,  vasoconstriction  baroreceptor  apnea  of  G e n e r a t i n g and  responses  from  the  in  because  vagal  motor  of  the  is, produce  strong  neurones.  Input  from  on  223 the on  baroreceptors the  level  of  baroreceptors adjustments  later  in  to  the  diving in  is  rises.  The r e d u c t i o n  barodenervates  to  heart  increased  the  to  Dive  blood  to  remains  that  but  blood  there on  Heistad  in  et  these drive  in in  a  could  is  change  in  loss  of  have  produces  a  such  effect  for  should  this  is  be  most  no  the  would the  precisely evident.  the  contribution though  resting (Table  heart  6).  and  animals  be  of  even  the  reduced, the  input  perhaps  carotid  denervation. the  neurones,  that  a  of  the  change  input.  In  reduction  in  facilitation  explain  acutely the  If,  this  nervous not  body  possibility  effectiveness  baroreceptor  central  mechanism  control  altered,  shown  resistance  animals  after  the  diving bradycardia in  however,  vagally  animals  through  not  the  acute  makes  denervated  (1974)  This  the  resets  intact  changes  input  to  animals,  intact  patterns  sudden  al  input  animal, an  in  of  cardiovascular  vagal  c a r d i o i n h i b i t o r y motor  chemoreflex.  reduction  is  in  effect  The r o l e  bradycardia in  acutely  flow  little  peripheral  component  similar in  the  the  chemoreceptors  from the  baroreceptor the  are  of  deficit  than  chemoreceptor  resulting  a  from c i r c u l a t o r y  chemoreflex  dogs,  level  gases  altered  however,  to  the  have  variables.  as  sympathetic  arterial  resulting  rate, of  will  contribute  during diving  barodenervates,  due  to  sympathetic  a higher  the  due  cardiac  rate  from  heart  is  rate  dive  integration  fall  since  the  cardiovascular  mediated  heart,  in  the  of  abrupt  denervated  situation  in  which  224 With time a f t e r barodenervation, r e t u r n s , but t h i s dive blood  i s not  the  bradycardia  c o r r e l a t e d w i t h g r e a t e r changes i n  gases i n c h r o n i c barodenervates than i n a c u t e l y  denervated animals mechanism b e h i n d  ( s e e d i s c u s s i o n i n S e c t i o n I I I ) , and  this  recovery  explanation i s t h a t the to cardiomotor  remains u n c l e a r .  The  c a u s i n g the depth of the b r a d y c a r d i a  rise  i n r e s t i n g hind limb  r e s i s t a n c e i n the t r a n s i t i o n from acute barodenervation  a given  to  to  vascular chronic  i n v o l v e s b o t h n e u r o g e n i c and  Given these  structural  c h a n g e s , i t m i g h t be  amount o f s y m p a t h e t i c  expected  outflow to the hind limb  c h r o n i c barodenervates d u r i n g d i v i n g would produce a r i s e i n h i n d l i m b r e s i s t a n c e t h a n t h e same o u t f l o w animals.  to  loss.  gradual  adjustments.  input  after  i n c r e a s e as t h e c e n t r a l n e r v o u s p a t h w a y s a d a p t baroreceptor  possible  r e l a t i o n s h i p of chemoreceptor  o u t p u t changes w i t h t i m e  barodenervation,  One  the  Instead,  in  greater  in  as t h e c a r d i a c r e s p o n s e waxes w i t h  a f t e r barodenervation,  that  intact time  t h e p e r i p h e r a l r e s p o n s e wanes.  The  changes i n t h e p e r i p h e r a l v a s c u l a t u r e documented i n r e s t i n g animals  ( S e c t i o n I I ) do n o t  possibility  account f o r t h i s ,  i s l e f t t h a t the degree of  and  neurogenic  v a s o c o n s t r i c t i o n during d i v i n g decreases with time barodenervation.  If this  i n the opposite  after  i s t r u e , a change i n t h e  r e l a t i o n s h i p b e t w e e n c h e m o r e c e p t o r i n p u t and output,  the  vasomotor  d i r e c t i o n t o t h a t suggested f o r  the  225 chemoreceptor-cardiomotor Such a " c e n t r a l afferent control  system,  may  reorganization"  after  centrally. the loss  o f an  pathway h a s n o t b e e n r e p o r t e d f o r t h e c a r d i o v a s c u l a r system,  but t h i s  mechanism h a s b e e n p r o p o s e d  explain the return  of v e n t i l a t o r y  mediated  receptors, after  by a o r t i c  denervation  i n mammals  a l . , 1983).  However,  systemic c i r c u l a t i o n  of t h e a o r t i c  nerve  carotid  pressure-related  to  t o hypoxia, chemoreceptor  1980; Majumdar e t  control  of the  i n ducks d i d n o t r e t u r n over t h e c o u r s e i n S e c t i o n IV. Y e t ,  i n c h r o n i c a l l y barodenervated  a s t r o n g pressure response,  degenerated  responses  ( S m i t h and M i l l s ,  of t h e d e n e r v a t i o n experiments  showed  occur  centrally.  so t h i s  stimulation ducks  pathway had n o t  226  4)  Consequences  Conclusions The is  an  of  these  of  Different  About the  method  used  important  Denervation  Effects to  of  deafferent  consideration  experiments.  Acute  Some  procedures  cardiovascular  effects  loss  baroreceptors,  and t h e s e  of  the  account. results  To i l l u s t r a t e from v a r i o u s  barodenervated from  is  experiments  experiments The  of  aortic  preparatory during  during  3)  followed  1 week  by  vagus  nerve  total  barodenervates  denervation. 23, by  if an  not  4)  Cardiovascular  1 week  of  or  after  (P  results  due  taken  to  the  into  of  the  ducks  were  based  on  from the  acutely  data  Series  variables  after  the  1)  drawn  1  simultaneous  recovery aortic  section  contralateral aortic  section  within  of  nerves during  aortic  nerve  the  from  section  contralateral  A l l observations 24-48  differences the  of  nerve  surgery.  made  <  were:  section  aortic  from w i t h i n  t-test  23,  unilateral  cooling  were  be  which  and  bilateral  significant  derived  in  not  comparison  employed  section,  section  hours  The  unbalanced  2)  a  the  (1983).  protocols  and  then  24-48  al  baroreceptors  produce  are  must  Figure  thesis  unilateral  later;  surgery,  et  nerve  surgery;  surgery;  surgery, nerve  Jones  in  will  which  point,  experiments  this  denervation  bilateral  this  presented in  arterial  interpreting  artefactual  on  Barodenervation  the  when  Methods  cited  hours  of  indicated study,  in  in  were  Figure  obtained  0.05). measured  at  rest  and  during  227  F i g u r e 23. C o m p a r i s o n of the e f f e c t s of v a r i o u s methods of b a r o d e n e r v a t i o n on r e s t i n g and d i v i n g c a r d i o v a s c u l a r variables. A r t e r i a l b l o o d p r e s s u r e ( M A P ) , h e a r t r a t e (HR) and h i n d l i m b v a s c u l a r r e s i s t a n c e (HLVR) means + 1 S. E . M . are p r e s e n t e d from d i f f e r e n t s t u d i e s . A: Section III, F i g u r e 11 ( P r e d e n , s n a r e s o n i n t a c t a o r t i c n e r v e s after r e c o v e r y from s u r g e r y ) ; B: S e c t i o n I I I , F i g u r e 11 ( d e n , both a o r t i c nerves s e c t i o n e d by p u l l i n g s n a r e s ) ; C: Section I, T a b l e 1 (DEN, b o t h a o r t i c n e r v e s c u t d u r i n g s u r g e r y ; resistance is total peripheral resistance; d i v i d e HLVR s c a l e by 10); D: S e c t i o n I V , F i g u r e 17 ( P r e d e n , o n e a o r t i c n e r v e c u t d u r i n g s u r g e r y , s n a r e on i n t a c t a o r t i c n e r v e ) ; E : S e c t i o n I I I , F i g u r e 17 ( s n a r e o n a o r t i c n e r v e p u l l e d t o complete denervation); F: Jones e t a l (1983) S e r i e s 1 ( l e f t a o r t i c nerve cut d u r i n g s u r g e r y ) ; G: Jones et a l (1983) S e r i e s 1 ( r i g h t vagus cut to complete b a r o d e n e r v a t i o n ) . P r e d i v e v a l u e s are i n d i c a t e d by unshaded b a r s , d i v e v a l u e s by solid bars. A s t e r i s k s (*) indicate significant differences f r o m t h e p r e d i v e v a l u e s i n A , w h i l e p l u s s i g n s (+) m e a n t h a t t h e d i v e v a l u e w i t h i n any group i s s i g n i f i c a n t l y different from t h a t g r o u p ' s p r e d i v e v a l u e .  to to  CO  229  diving  in  the  from  Figure  with  the  by  pressure  11,  other  submersion offset  both  large  by  III)  fall  nerve  rate by  animals  denervated  experiments measurements  in  control  are  total  data  mass  for  same  stroke  was  only  animals.  in  0.22  P.  R.  U.,  in  the  blood  to  When (Group C ) , the  rest  in  the  to  a  decrease  used  in  intact  or  of  0.34  P.  drop  C animals  in  no  comparison,  peripheral that  so  ducks  was  in  these  barodenervated  than  resistance  For  1982a)  total  resting  in  denervation,  at  Group  a  sham o p e r a t i o n s  group.  % less  to  significantly  due  this  in  Blood  hypertension  for  as  withdrawal  though  not  of  was  prior  animals 65  The p e r i p h e r a l  barodenervation  lack  and J o n e s ,  volume  owing  even  was  either  animals  latter  surgery.  The p r o t o c o l  include  (Lillo  the  completely  after  increase.  ensued  volume  resistance  body  but  rate  and t h e  available  similar  ducks,  Stroke  intact  not  and e n d - d i v e  during surgery  resistance.  peripheral  the  heart  during surgery  d i d not  comparison  forced  was  B animals  barodenervation  performed  denervation,  peripheral  rate  resistance  hypertension  altered  total  cardiac  for  During  1 wk a f t e r  after  doubled.  here.  snares  was  heart  measurements  reference  Group  barodenervation  acute  in  the  became  mediated  no  are  (control  20 %.  sympathetically  however,  Group A  presented  about  increased  in  peripheral  animals  aortic  pressure  Section  increased fell  ducks  groups  the  Group A of  intact  R.  Group C resistance  intact  after  may h a v e  U.  been  the  230  result the  of  incomplete  surgical  pressure the  trauma of  rise  Comparison  rate in  but  pressure  former  the  of  the  to  in  that  no  fall  was  predive);  greater must  resistance  in  in  case  neither  change  in  can  taken  be  C total Group  as  did  an  responses  limb  barodenervation compounding eliminated.  lack an  not  in  change  heart  than  C was dive  the  in  of  or  a  artefact  of  of  animals  B  change  that  revealed  an  in  only  that  denervated  the Group C  30  in  in  B  Group of  total  9.3 6  but  % of  since  the animals peripheral  valid: times  effects after  pressure during  B,  Group while  times.  and a n a e s t h e s i a acute  the  peripheral  appears  the  in  44 % o f  If  by  fall  pressure,  change.  by  of  heart  but  to  C (to  (to  than  increased  surgery of  Group  rose  in  dive  blood  behaviour  only  groups  similar  owing  Group  proposal  shows  were  in  resistance  this  a  the  dive  pressure  the  two  denervation.  greater  blood  resistance  of  in  also  diving,  alone  rate  that  mean t h a t  in  the  B,  significant  comparison  in  Group  was  The absence  barodenervation  anaesthesia  differences  occured  index  effects  In  of  intacts  peripheral resistance  above  c o u l d be  B and C shows  limb vascular  during  B hind The  Group  hind  resistance  diving  significant  this  the  and t h e  variability after  p r o p o r t i o n a l drop  predive)  operation,  pressure.  in  pressure  showed  either  denervation  in  blood  group t h i s  increase also  in  from  protocol.  denervates not  the  following  experimental  bilateral  recovery  of the  were rise  after  surgery  is  231  misleading, animals  since  a  significant  deafferented  after  cumulative  effects  peripheral  resistance,  denervation groups. and  Differences  animals, both  pressure  was  remaining  in has  by  and t o t a l  baroreflex, aortic  input  pressure  Section  in  IV,  already  is the  that  begun  to  of  submersion  primarily  of  are  on  post-  experimental of  between  not  the  cardiac B and C  comparable  baroreceptors resulted  and h i n d  limb  above  was  the by  s t i l l  normal  to  in  in  fully  and  level.  It  is  in  system  partial  in  blood  the bilateral  maintain clear,  in  Even  functional,  required to  the  increases  baroreceptors  range.  (Group D  resistance,  intact  cardiovascular  adapt  The  intensities  removed)  evidently  the  both  in  procedures.  mediated  nerve,  occurred  be  degree  in  responses  these  nerve  same  relative head  significantly  baroreceptor blood  diving  aortic  rate  the  the to  seem t o  present  deafferentation  one  heart  though  the  denervated  Partial  in  the  rise  from surgery.  operation  since  responses  show t h a t  animals  the  recovery  t a c h y c a r d i a was  vasomotor  also  of  pressure  as  resting outlined  this  state  baroreceptor  deficit. When t h e s e pressure during animals  fell  proportional in  hind  more,  diving. was  unilateral  the  barodenervates  proportionally,  The a b s o l u t e  dive  same  in  drop  in  limb vascular  as  that  heart  rate,  resistance  than  heart  in rate  intacts, but in  were  the Group  as  dived,  intact in was  blood  animals  Group D the  proportional D animals  change (9.1  232  times)  was  less  peripheral the  dive,  than  that  resistance a  similar  in  increase  by  Lillo  results  is  that  possess  the  same  facility  maintaining  dive  blood  there the  was  dive,  animals  section no  blood  and Jones  responses  After  further  however,  responses  were  decrease  blood  dive  cardiovascular cannot is  be  state  in  states.  Comparison of  those  Group  resulting and  not  from  of  B  kind. to  for  the  studying  Group  one  baroreceptor nerve  do  not  although  the  cardiac  similar. nerve  (Group  E)  In  acute  more  tachycardia.  in  to  reduction in  a  Group E than  in  D.  in  and t o t a l l y  show  animals  that  the  Group  baroreflex  animals,  of  Group E  but  with  differences are  nature E can  of of  magnitude these  then  activation  nerve. animals  The  barodenervated  protocols the  greater  animals  intact  denervates  in  in  resulting  that  the  and p e r i p h e r a l  relative  established  represents  and  an  total  of  for  to  denervation  the  aortic  the  animals  while  intact  effects  F also  these  p a r t i a l l y barodenervated  Having use  intact  peripheral resistance,  pressure  two  in  in  of  bradycardia,  however,  the  differences,  stimulating  ,  times  in  analogous  the  4.9  baroreceptor-intact  with  in  considered  midway b e t w e e n  of  due  Total  The i m p o r t a n c e  proportional cardiac  than  by  remaining aortic  change  reduced,  times).  reported  qualitatively  the  vasoconstriction in  one  pressure,  rose  the  that  (1982a).  as  (10.3  D increased  to  with  are  of  pressure  intacts  Group  animals  peripheral  in  unilaterally  by  be  used  233  barodenervated but of  observations recovery,  week in  to  However,  in  increase  resistance  the  of  group  in  increase The cooling  in  or  this  of  in  suggested  unilateral that  dive  blood  in  in  the  the  since  resistance. would  the  F were  in in  groups, F, the  resting  d i d not  enhance  the  F  despite  with  as  that  accounting a  of  those  in  in D.  for  greater group.  barodenervated nerve  heart  rate  the  affect  may  maintained  vagus  for  an  responses  latter  completely  U n i l a t e r a l vagotomy  probably  was  vascular  this  was  proportion  two  of  after  contrast  pressure  responsible  vagotomy  just  The d i v i n g  same  as  peripheral  Group  contralateral  was  total  in  blood  1  same  group  despite  hypertension  pressure  highest  limb  then  resistance  Group  If,  also  days  had  the  other  C,  nerve.  1-2  which  Group  the  between  only  1),  hypertension.  F animals  for  Series  F was  the  resistance,  denervates  end-dive  in  and h i n d  intacts.  Group  resting  tachycardia  conditions  in  limb vascular  cutting  hypertension, vascular  rate  than  after  to  heart  peripheral  resulted  contrast  F and D,  baroreceptor  animals  pressure  developed  difference  maintained  group  1983;  Group D animals  blood  a b r a d y c a r d i a of  The m a j o r  and  of  D,  despite  This  one  al.  which  been  lack  the  et  D,  depressed  has  this  (A), i n  higher  hind  the  Group  the  both  (Jones  in  to  Resting  animals  was  as  loss  this  contrast  were  in  surgery,  made  denervates,  resistance  explain  were  recover.  unilateral  F  in  unoperated  in  during surgery  by  (Group G ) . of  any  group,  acute hind  under  limb these  barodenervation-induced  234  increase portion the  in of  vagal  central  mediated lack  of  sympathetic  interplay  not  low  The effects  as  of  in  the  comparing  the  interpretation experiments account.  of  must  the  the  animals in  (Jones  Section  without  after  baroreceptor  the  these from  in  of  dive  et  heart  animals  studies, acute  methodology  is  that  was  1983). the  allows returned to  responses and  barodenervation It  rate  studying  animals  denervation,  the  a l . .  for  Control  loss.  The  bradycardia  complications  surgery. before  II  disrupting  effects.  loss  of  were  the represented  apparent,  on  the  barodenervation of  a  vagally  baroreceptor-intact  baroreceptors  results  by  other  diving  level  of  as  cardiovascular  absolute  animals  take  the  the  in  by w i t h d r a w i n g  well  to,  following  results  as  addition  the  of  heart  in  adaptations  effects  the  from  affected  developed  of  these  cardiovascular only  with  barodenervation  condition  obtained  inputs  unoperated  technique  to  restraint,  vagotomy  in  deafferentation normal  and  since  unilateral  as  also  of,  baroreceptors,  of  groups  vagus  independently  after  cardiac  receptor one  drive  denervation  into  a  235  SUMMARY  1)  Arterial  the  cardiovascular responses  heart  rate  baroreceptors  to  help  vasoconstriction minute  2)  after  in  balance  as  these  to  cardiac  of  the  intact  response  to  pharmacologically This  ducks  was  response  chronically  3)  In  ducks  barodenervated  1 week  after  implantation  weeks return  to  rose  develop  This  acute  was  in  in  to  an rise  by b i l a t e r a l  of  snares  increase was  pre-denervation unaffected  the  first  in  acutely  cardiac  but  diameter  ratio  increases),  ducks.  nerve  section  nerves,  sympathetic the  next  three  did  Hind  limb  vascular  after  arteries  of  (wall  wall thickness  and p a r t l y because  vasoconstriction.  The i n i t i a l  barodenervation elevated  not  barodenervation  p a r t l y because leg  day)  rate  level.  muscular  (1  heart  immediately  time,  over  in  blood  around these in  rate  mmHg-i,  - 1  aortic  moderated  small  after  min  changes  eliminated  barodenervation,  neurogenic  beats  induced  in  rate  against  baroreceptor-deafferented  gradually with  increased heart  due  the  hypertrophy lumen  wk)  rose  following  resistance but  (3  -1.16  was  and  activity.  to  modulating  arterial baroreceptor-heart  in  rate  d i v i n g by  output  adjustments  response  heart  forced  contribute  submersion.  The s e n s i t i v i t y  pressure.  d a b b l i n g ducks  arterial  of rise blood  in  to  236 pressure week  4)  and t h i s  observation  During  increase the  diving  total  in  degree  of  to  remained  near  component  However,  d i v i n g was  in  the the  barodenervates, bradycardia drive  to  one-third  of  In  peripheral  intact  was  pressure  baroreceptors, function  of  the  proportional  the  three  blood  dive  but  no  diving  reduction  in  the  due  deficit  outflow  the  blood  a  animals,  cardiac  acute of  deficit  required to  a  a  in  loss  produce  a n d was  the  sympathetic  in  represented  ducks,  pressure  degree  to  by  blood  barodenervated  T h e r e was  was  balanced  dive  to  that  animals,  than  so  not  vagal of  about  the  result  of  the  input.  so  to  was  rate  so  the  response  intact  resistance  modifications blood  in  recovered in  ducks,  unchanged  level.  This  vagal  seen  was  c h r o n i c a l l y barodenervated  as  over  acutely  denervation  baroreceptor  response same  and t h e  the  heart  reduced,  cardiac  heart.  of  bradycardia loss  in  predive  after  the  intact  in  vasoconstriction  response  maintained  peripheral resistance  proportional decrease fell.  was  period.  forced  in  pressure  5)  hypertension  was  the  intact  of  the  reduced.  pressure  degree  degree  while  produce in  animals  a  of  rate  bradycardia  The n e t  animals. during  heart  was  p r o p o r t i o n a l change  greater  cardiac  the  fall  effect in  of  the in  these  end-dive  Without  d i v i n g was  slowing,  so  primarily  dive  a  237  hypotension returned  became  with  bradycardia  6)  time  stimulation  of  aortic  baroreflex  baroreceptor  discharge.  threshold.cardiac to  Correction reflex  in  adjustments, only  during larger  aortic  nerve  baroreflex  7)  d i d not  pressure  changes hind  limb  effects dive  in  diving,  and  a  30  2 min  breathe  the  sec  before  dive. diving,  to  rest  time  produced  by  by  the  lqwwas  barostatic  cardiac participating  limbs  of  total to  pressure  effects  of  the  denervation.  entirely  were  to  in  during diving  the  clear.  ducks,  The r e l a t i v e  responded  with  not  intensity  after  nerve  arterial  is  resistance.  efferent  effects  In  at  vasculature  neither  resistance  diving  electrical  change  a higher  which were  since  stimulation  a  changes.  with  compared  for  disturbances  aortic  on  Why t h e  peripheral  the  response  barodenervated  accomplished  on  change  stimulation reduced,  in  pressure  rate,  vascular  but  peripheral  responses  heart  of  were  of  in  simulating  was  stimulation  Stimulation  blood  by  pressure  the  cardiac  barodenervates  Stimulation  ducks  with  the  developed  nerve  changes  small  intact  were  depression,  invoke of  chronic  electrodes the  as  barodenervation.  in  the  required  profound  after  recovered  Implantable  activate  more  the  produced result  peripheral  of  nor  stimulation. at  pressure  1 min  in  response  eliminated  by  animals  given  100  % oxygen  reduce  input  from c a r o t i d  The  the  the before end  to body  of  238 - a  chemoreceptors  during  the  response  to  aortic  nerve  the  as  before  the  same  inkhibit and  the  progressive  8)  animals  one  anaesthesia,  during the  week  of  observations  after  from  are  was  was  partly responsible the  baroreflex  preparatory surgery  the  effects  animals  of  made m u s t  be  taken  and c h r o n i c a l l y d e n e r v a t e d  experiments  represented  two  ends  of  progressive  circulatory adaptation.  after into ducks a  diving.  depend  by nerve  on  section,  general alone.  section  arising  barodenervation account, in  the  continuum  since present  of  the  in  nerve  under  complications  The t i m e  the  barodenervation  denervated  compromised by  for  to  ducks,  changes  aortic  nearly  shown in  during  Cardiovascular  instantaneous  procedures. are  end-dive  barodenervation experiments  represent  surgery  at  pressure  The c h e m o r e f l e x  denervation.  obtained  surgical  acutely  of  of  arterial  non-diving situations  been  b a r o d e n e r v a t e d by  performed  Results  in  attenuation  The r e s u l t s  methodology  have  the  stimulation  dive.  baroreflex  may t h e r e f o r e  dive,  from that  238  BIBLIOGRAPHY  Abboud,  F . 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W. a n d M c R i t c h i e , R . J . 1973. Nasopharyngeal reflexes: i n t e g r a t i v e a n a l y s i s of evoked r e s p i r a t o r y and c a r d i o v a s c u l a r effects. A u s t r a l . J E x p . B i o l . Med. S c i . 51: 17-31. , M c R i t c h i e , R. J . and F r a n k l i n , D. L . 1974. Autonomic c a r d i o v a s c u l a r e f f e c t s of n a s a l i n h a l a t i o n of c i g a r e t t e smoke in the r a b b i t . A u s t r a l . J . E x p . B i o l . Med. S c i . 52: 111-126.  Wolinsky, H. 1970. hypertension. and G l a g o v , s t r u c t u r e and  Response of C i r c . Res.  the 26:  rat aortic 507-522.  S. 1967. A lamellar f u n c t i o n i n mammals.  media  to  u n i t of a o r t i c C i r c . R e s . 20:  medial 99-111.  Y a r d l e y , R. W . , Bowes, G . , W i l k i n s o n , M . , C a n n a t a , J . P . , M a l o n e y , J . E . , R i t c h i e , B. C . and W a l k e r , A . M. 1983. Increased a r t e r i a l pressure v a r i a b l i l i t y after a r t e r i a l baroreceptor d e n e r v a t i o n i n f e t a l lambs. C i r c . R e s . 52: 580-588. Zar,  J.  H. 1984. Biostatistical Analysis. H a l l , Englewood C l i f f s , New J e r s e y .  (2nd  ed.)  Prentice-  251  APPENDIX  1)  STIMULATING  ELECTRODE CONSTRUCTION  AND S T I M U L U S  PARAMETERS  a)  Electrode  The were  electrodes  made  steel  of  wire  threaded silk  construction.  40  gauge  (AS 631;  through  mesh The  patch  molded  About  ml  be  used)  vessel  until  was was  removed  by  to  732 the  made  was  these  pieces  mold.  The m i x t u r e the  placed  was  larger  stranded  stimulation  stainless California)  rubber reinforced  with  sheet  rubber  thinned  R T V 732  with  flowed  The i n c l u s i o n  a  flat  of  then  a  on  silicone  bathtub  xylene  when  of  bubbles  air  process,  of  0.5  the  hollow  square  another  sheet  the  edges  732  and x y l e n e  swatch  of  of  and t h e was  this  3 cm o n of  bottom  also  mixing in  the were  dessicator.  Teflon.  The  material  was  a  Teflon  then  can  and t h e s e  mm t h i c k  piece  caulk.  (toluene  a vacuum p u m p - e v a c u a t e d  5 cm s q u a r e inner  of  slowly  during this  in  defined  mold,  nerve  Chatsworth,  silicone  from a  mixture  an  frame  into  of  from sheets  of  make  aortic  Co.,  f r o m Dow C o r n i n g  degassing  section  removed  cut  inevitable  m o l d was  centre  Cooner Wire  tipped.  mixture  The  of  chronic  A l a and A l b ) .  was  w h i c h was  for  Teflon-insulated  a patch  (Figure  2-3  used  side. and  surface poured  This together of  the  slowly  252  Figure A l . Electrodes f o r stimulating l e f t a o r t i c nerve in ducks. a) Nerve side, showing bare strands of s t a i n l e s s steel wire. b) Insulated side, showing p o s i t i o n of S i l a s t i c t u b i n g and t h e manner o f s e c u r i n g t h e f r e e ends of t h e w i r e s by wrapping. The s i l i c o n e r u b b e r i n s u l a t i o n has been l e f t off a t b) f o r c l a r i t y .  253  254  fine-mesh remove  silk  air  mixture. into  top  two  sheets  of  then  The  Teflon  the  of  thick  and  blade  into  of  3 cm o n 3-4  anchoring  hypodermic in  the  Towards  the  punched  using  on  a  also side.  Corning) the  tubing oven the  to  A 1.5  tubing  centre  60  then  side.  of  near  off  the  cut  it  poured subsided  placed  over  sandwiched squeezed  for the  24  assembly  hours  frame  to  to  cure.  reveal  reinforcing, with  between  excess  The e n t i r e  0.5  a new  razor  of  each  patch  w e r e made  with  a  and w i t h  another  of  the  the  with  a  mm  This  a  dab  with  (Figure  tubing  Ala),  about  2 mm (Dow  A adhesive  end  of  and p u t  the  was  These  Silastic  Type  formed  sharpened  above.  one  gauge  4 holes  Ala),  of  20  for  borer.  of  mm d i a m e t e r  patch,  edge  cork  as  (Figure  0.8  rim  group  prepared  pattern  attached  over  the  a conventional  needle,  projecting  corners  holes  patch  mm l e n g t h  1 hour.  mesh  4  blunt as  of  for  off  was  the  These  square  was  the  to  patches.  gauge a  then  C oven  silk  of  gently  mold.  peeled  xylene  T e f l o n was  was  the  This  in  procedure  degree  side  electrode 15  a  one  set  of  of  out  same m a n n e r  formed  of  air  cut  23  prodded  This  sutures.  a  surface  glass.  punched  centre  the  sheet  rubber with  needle,  soaked  whole  were  a  was  and t h e  mm s q u a r e  were  on  was  A third  into  silicone  side  swatch  plate  sheets  Holes  holes  laid  mold  placed  sheet  act  and  and t r a p p e d  was  to  a  bubbles,  mixture.  the  the  cm o n  When t h i s  the  mixture  2.5  in  the in  support  the for  leads.  cm l e n g t h s  of  wire  were  cut  and  about  1 cm o f  Teflon  255  insulation difficult in  a  and  to  a  hole  drilled  edge  could  hole.  blade be  hole, was  but  not  was  then  spun  made  a  was  acid-core  square.  set  first  tinned  in  to  the  a  place,  any  the  correctly of  the the  the  in  from the  with  commercially  tip  of  the  The p r o c e s s  of  tinning  for  tinned the  the  the  an  depth so  of  the  into the  that  it  insulation The  so  wire  that  the  and  the  depth  of  stripped  fraying. steel  solder  p o r t i o n was was  strands  containing  soldering  wires  the  that  strands.  stainless tin  of  by  insulation,  no  wire  inserted  layer  was  a  blade,  occlude  adjusted  insulation  4 % silver-bearing  axis  set  If  exposed  razor  arm so  block.  wire,  the  and thumb,  the  this  which  then  wire  spot,  with  and the  outer  finger  cut  the  was  weak  block  the  was  was  slot,  hole  between  sharply  hole  is which  solve  partially  the  of  to  swinging  to  through the nick  any  into  to  This  wires,  single-edged  The w i r e  into  at  a plastic  angle  to  blade  break  other, a  slot  enter  way  (sold  the  for  the  swung  end  the  wire.  invented  of  right  arm.  2 mm o f  with  flux  then  a  circumferential  from the  The  steel),  in  withdrawn  blade  cleanly  enough  was  attached  the  to  the  at  the  blade  all  far  was  on  to  slot,  into  of  allowed  almost  were  stop the  cut  the  swung  wires  each  n i c k i n g the  eventually  side  being  of  or  consisted  block  The d e p t h  adjustable  blade  these  A fine  the  end  damaging  will  f r o m one  into  the  blade  for  snugly.  cut  f r o m one  The s t r i p p e r  hole,  wire  implant  stripper  fitted  the  removed  do w i t h o u t  chronic  problem.  was  was  an  stainless cut  done  off simply  to  256  bind and  the it  was  strands later The  strands  important  for  tinned on  nearest  other  end  pulled  was  the  Alb.  was  This  manner  teased surface  until  through  which  around the ended,  the  the  side  of  of  the  patch  c u r i n g the  wires  on out  was  as  slightly  side to  close shown  anchored from  1 hour  the  increase  in  other  patch the  in  the  insulated  for  of  the  The  away  then  the  was  short,  adhesive  nerve  of  wire  furthest  via  jacket  bare  and  fine  then  Teflon  patch  the  patch  wire  of  with  e n d was  the of  of  electrodes.  the  holes  one  portion  off  the  through  the  of  section  After  fanned  end  was  piece  patch  the  bare  and c u t  one  centre  of  the  tissue). the  the  bared  end  The f r e e  the  through  whole  the  through  of  down  section  through  side  back  assembly,  in  with the  were  active  area.  The tinned  and  other  of  biological  threaded  and t h e  threaded  in  exposed  apart  hole  tinned  inserted  brought  completed  The t u b i n g  the  was  the  insulation  A adhesive.  oven,  to  threaded.  inserted,  tubing.  to  toxic  stage  from flowing  highly wire  times  solder this  patch  hole  several  similar  Type  the  prevent  next  2 mm b e c a u s e  e n d was  centre  during the  and t h e n  holes  first  where  Figure  a  the  through the  wrapped  lead  is  patch,  This  approached  to  of  centre  nearby  to  than  (tin  the  forceps.  wire  more  removed  tubing  together  other  and  ends  of  the  soldered  to  miniature  inserted  into  the  terminal  connector  body  of  leads  were  terminals  a modified  housing,  stripped  for  5 mm,  which  were  Molex Model  2695  originally  meant  for  crimp  circuit  257  board with  connections. suture  anchored the  the  the  together, whole  so  h o u s i n g was  that  skin,  h o u s i n g were  twisted of  to  holes  This  and the  sealed since  assembly.  the  modified to  form  connector housing could entry  points  w i t h RTV 732. twisting  of  the  The l e a d s  reduced the  flanges be  leads were  into  not  flexibility  258  b)  Stimulus  waveform  Monopolar in  acute  results  a  electrodes charge the  stimulation  experiments in  the  transfer and  results can  Bourassa,  1981).  consists pair  of  a  to  by  If  short  a  of  pulse  by  at  a  short  will  be  potentially pulses  are  charge  to  lead  pulse  reversed  the  pulse  currents  used,  to  which  occurs  offset  of  any  and  from  there  long-term waveform  1961),  also  of  when  chronic  within  first  cancelling  net  a  charge  from the  damage  that  any  two  transfer  of is  greater  monopolar  stimulation  implanted  pulse  reactions  When t h e  means  which  the  equivalent  electrolytic  than  decline  no  and  waveform  followed  pulse,  is  Swett  monopolar  is  nerve.  to  the  much o f  interface  on t h e  chronically  1977;  This  damage  and n e g a t i v e  prevents  second  employed  slow  of  electrochemical  the  effects  be  the  with  by  this  can  and t i s s u e .  Lilly,  polarity  waveform  the  and t o x i c  c a r r y i n g an  balanced,  nerve  Use  one  this  stimulating  positive  resulting  adequate  from  failure  after  nerve-electrode  exactly  to  a bipolar  delay,  of  polarity,  harmful  prevented.  of  nerves  a pulse  the  transfer  electrolytic  waveform,  second  opposite  occurring  in  is  experiments  charge  charge-balanced  stimulation.  but  net  The use  peripheral  time  chronic  nerves  (Brummer and M c H a r d y ,  "Lilly"  separated  damage  in  peripheral  eventually  electrodes  so-called  of  selection.  surrounding electrolyte  implanted  (the  but  substantial  to  nerve,  and p a r a m e t e r  pulses  are  effectiveness  stimulation  259  electrodes. The within this (a)  area  the  size  above,  by u s i n g  stranded  f a n n i n g out of  current  the was  0.0075  Weinman  (1965)  physiological  factor  of  ms)  0.5  stated  here the  ms was  chosen  for  that  the  surfaces  multiply  the  are  for  wires  500  w h i c h means  and  flat  on  of  this  2  a r e a were smooth  area  set  a  damage  for  single  increased  by  The and  stimulation.  Swett  67-  by  133  mA) a n d p u l s e  study  the  was  (1977)  c o u l d be  (0.5-2.0  present by  mA,  normal  without  33  Part  the  listed  for  in  each  0.5-2.0  b i p h a s i c waveforms.  have  surface that  wire  mA/cm2  transfer  nerve  in  c u r r e n t and a r e a )  A pulse  on t h e  basis  uC/cm2 width width of  and B o u r a s s a  (1981).  based  assumption  on t h e  surfaces.  m i c r o s c o p i c a l l y rough,  actual  of  upper l i m i t  that  the  recommendations  electrode  developed  The a r e a  pulses  of  current  aortic  calculations  lay  d e l i v e r e d between  during  above  steel  they  maximized  described  microcoulombs(uC)/cm  used  The  1976),  at  as  was  Brummer a n d M c H a r d y  o r more f o r  pulse  as  value  charge  40  but  developed  theoretical  the  for  done  pulse  nerve  electrodes  patch.  reasonable  limit  two  each  of  the  the  stainless  and f o r  stimulation.  pulses,  electrodes during  a  s t i m u l a t i o n of  monopolar  of  as  operating  during  below  was  rubber  cm2,  to  the  strands  (quotient  well  of  This  the  silicone  density  mA/cm2,  (0.5  requirements IV).  electrode  a  exposed  (Section  surface  safe  electrode  study  slightly  267  of  several  In  and t h i s times  c u r r e n t and c h a r g e  reality,  could  (Dymond,  density  260  could  have In  been  tests  even  lower  than  the  patch  electrodes,  of  electrode-saline magnification  interface  when t h e  was  I had  calculated. no  observed  electrodes  were  electrolysis  in  vitro  driven  a  b i p h a s i c waveform at  5 mA, 0 . 5  ms d u r a t i o n  a  0.5  the  pairs,  ms d e l a y  rate.  This  between  c u r r e n t and r e p e t i t i o n  the  levels  the  b i p h a s i c w a v e f o r m was  actually  formation  of  indicated  that  minutes  of  waveform  very  when  particular results  (1976)  trailing electrode  that,  rises  edge  of  voltage  and  this  will  stimulation.  voltage  pulse If  long  the  When t h i s  of  the of  effects simple  well  above If the  last  the  few  biphasic  of  been  tests  from  the  the  in  is  before on  an  too  the  His  finite electrolyte,  edge  charging of  particular  seen  any  of  leading  current is  to  exceeded.  electrodes  the  electrolysis  and c u r r e n t f o r  the  plateau  repetition  electrodes  in  use  to  easily  Hz  with  pulses,  %, h o w e v e r ,  the  due  for  min  both  were  constant-current pulses a pair  is  100  10  times  advantage.  reach a plateau  behaviour  at  and d e v i s e d  continuously  too  25  beginning  arrangement have  capacitance.  duration  was  gas  analyzed the  of  for  the  of  a distinct  limits  for  50  the  stimulation experiments.  u n b a l a n c e d by  bubbles  has  and  for  frequencey  and t h e r e f o r e  delivered to  the  during  stimulation,  electrode  voltage  pulse  tests,  the  show  duration the  fine  represented  electrical  detect  used  electrolysis  the  Bergveld in  pulse  at  at  high  the or  electrode  the  interthe in  use,  is  ended,  an o s c i l l o s c o p e  during  reached,  pulse  to  electrolytic  261  breakdown  will  electrodes.  begin,  It  producing local  follows  manipulated  so  between  electrodes  the  that  constant-current be  exceeded.  study,  in  that,  during  These  the  on  a  reaches limits  current  differential  pulse  the  at  steady  to  at  during  damage in  all  the  will  the  and p u l s e - w i d t h  oscilloscope  are  developed  state  neural  adhered  the  parameters  voltage  for  c r i t e r i a were  which voltage,  monitored  the  a pulse  never  pulse,  if  damage  not  present  were times  during  stimulation. When c u r r e n t  is  held  constant,  electrode  impedance  varies  electrode  impedance  which  stimulation the  nerve  will  intensity, not  (Dymond, not  which  vary within  one  constant-voltage It of  a  is  clear  set  must,  throughout  the  exceeded,  in  outlined  here  from  this  study,  of  experiment  have in  actual  the  to  an does  of  delivered  to  stimulus  nerve.  a  studies,  that  the  the  use  in  stimulus  continuously if  safe  nerve.  The  greater  which  justified  The  and r e a d j u s t e d the  is  will  give.  analysis  monitored  damage  assurance not  the  in  Therefore,  waveform  my e x p e r i m e n t s ,  and between  run,  aortic  permitted  bouts  as  b i o c a l i b r a t i o n technique,  simplistic  be  varies  changes  charge  impedance.  biphasic  however,  not  despite  stimulation  the  voltage  common d u r i n g  experimental of  order  repeatability  by  so,  the  vary with  mode  stimulation  parameters  are  1976),  constant-current,  chronic  same  is  and  the  degree  limits  are  methods  of  both  among a n i m a l s  than  would  in  otherwise  the have  been p o s s i b l e  263  2)  ULTRASONIC  a)  Flow probe  Parks supplied several bodies  ultrasonic  the  had  for  apposing  addition,  to  the  adapt  leads with  these  available  two  in  body  thick  halves  and  for  hind  limb,  and the  stock  styrofoam  possible  was  the to  lumens remove  lengths and Type  were  were sharp  of  36  gauge  insulated  A medical  the  adhesive,  modified  Molex  connectors,  weight  and  ends  leads  inherent  as were in  in  In  22  gauge  this  limited  space  off.  replaced  stranded  As  the  for  twisted probe  body,  with  copper  the  and  cm  wire,  tie  Silastic of  attached  3-0 to  stimulating  together.  design,  10  or  a new  were  much  internally  R T V 732  leads  described not  order  off  anchored  the  In  chamfered  with  tie  were  cut  filing  were  also  the  size,  surgical  were  bodies  and  body  of  lumen  a vessel.  leads by  leads  which  the  had  styrofoam  PVC i n s u l a t i o n .  probe  probe  The f r e e  light  the tie  The  silk.  very  stiff  form,  The  to  probes  Teflon-insulated at  and t h e  the  stock  braided  around  smoothed  surgical  electrodes,  flat  removed  enlarged, edges.  to  Oregon)  study.  implantation  disassembled as  their  relative  large  attached  probes  the  a  in  present  large,  and  (Beaverton,  which, the  were  corners the  wires  for  probes  sharp  Laboratory  probes  disadvantages of  AND C A L I B R A T I O N  modifications.  Electronics  and  copper  FLOW P R O B E M O D I F I C A T I O N  The  coupled  with  264 the t h i n f l e x i b l e leads and the p r a c t i c e of not anchoring any p a r t s of the probe t o the t i s s u e s except t o t i e the  two  h a l v e s of the probe body around the v e s s e l , promoted r a p i d healing.  The animals t h e r e f o r e r e g a i n e d f u l l use of the l e g  w i t h i n a day or two of the i m p l a n t a t i o n procedure.  No v e s s e l  o c c l u s i o n problems were encountered a f t e r proper placement the u l t r a s o n i c probes, which was e l e c t r o m a g n e t i c probes p r e v i o u s l y  not the case f o r the used.  of  265  b)  Calibration  Flow vivo.  from  probes  For  segment  Procedures.  in  were  vitro the  probe  leg  and  the  cannulae.  was  the  In  calibration  artery  cannulating the  animal  cut  vessel  was  at  obtained  from  and  downstream  pump.  run through  fixed  the  by  arterial  probe  as  entirely  after  at  segment  pump  known  and  probe  rates.  sectioning  and  with  tubing  obtained  outlined  in  vessel  perfusion  probe  the  or  wide-bore  exposing  of  a  animal  Heparinized blood  the  situ  removed  rotary  past  and  the  was  over  a  in  mortem,  from the  performed  of  vitro, post  tied  was  ends  perfusion  in  midpoint  ends  segment  upstream both  the  channeled  through  from  at  Whole b l o o d  heparinization  the  calibration  with  the  situ  calibrated  for  from  the  in  the  vitro  method. For with  sodium  probe  site  divided of the  vivo  vessel the  leg,  infusion  calibration  pentobarbital was  about  heparin  facing the  in  exposed, 10  cannulated  and b o t h  into  the  anaesthetized  the  end  the  experiment.  artery  901,  Blood the  to  were  be  probe,  and  into  the to  Apparatus,  withdrawn probe  at at  one  1000  I.  U.  ends  of  cannula  vascular a  The  and  The c u t  tubing,  connected  the  upstream  animal.  P E 190  Harvard  pump t h r o u g h  clamped  the  facing  could  of  from the  with  other  cannulae  (Model  Massachusetts). pressure  was  administered  heart,  pump  the  animal  mm d o w n s t r e a m  were were  at  the  bed  of  syringe-type  Millis, arterial known  rates,  266  after the  unclamping the  vascular  bed  pump t h u s  acted  driven  the  the  by  method  of  relationship undisturbed flow  work,  was  the  of  to  for  the  last  in  situ  resort,  ultrasonic  electromagnetic similar  into  was  each  which  to  the  the  probe.  first  in  method  flow  linear  run.  the  blood This  because wall  would  was  be  procedure  remained near-normal  sometimes  most  this  probe  animals,  used. used  early  characteristics  A l l of  the  a  if  range  of  did  experiments with  between 5-100  vivo  calibration  calibration  relationship  over  and  In v i t r o in  was  the  maintained  This  The  In  also  and t h e  calibration  to  c a l i b r a t i o n methods.  was  a n d was  pump  vessel  pressure  other  from the  pressures.  calibration,  probes.  results,  displacement  the  returned  after  arterial  tried  of  and  vivo  probe  do w i t h was  in  through  compare  pen  at  the  leg  sink,  choice  to  gave  a  and t h e  calibration not  as  the  heart  conditions  difficult  of  artery,  those  methods flow  and  ml/min.  


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