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The role of the abdominal muscles in breathing Leevers, Ann Margaret 1991

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THE ROLE OF THE ABDOMINAL MUSCLES IN BREATHING by ANN MARGARET LEEVERS B. S c . ( B i o l o g y ) Simon F r a s e r U n i v e r s i t y M. S c . ( K i n e s i o l o g y ) Simon F r a s e r U n i v e r s i t y  A THESIS  SUBMITTED IN PARTIAL FULFILMENT OF  THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  in THE FACULTY OF GRADUATE STUDIES EXPERIMENTAL MEDICINE  We a c c e p t t h i s t h e s i s as  conforming  to the r e q u i r e d s t a n d a r d  THE-UNIVERSITY OF BRITISH COLUMBIA 1991 CcS Ann Margaret L e e v e r s ,  1991  In presenting this thesis in partial fulfilment  of the requirements for an advanced  degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department  or  by his  or  her  representatives,  it  is  understood  that  copying or  publication of this thesis for financial gain shall not be allowed without my written permission.  Department of  fj^rirtri^6*{~^(  The University of British Columbia Vancouver, Canada Date  DE-6 (2/88)  ii  ABSTRACT Nine  tracheotomized  sonomicrometer  length  dogs  were  measurement  chronically  transducers  and  e l e c t r o d e s i n each o f the f o u r abdominal muscles: (TA),  i n t e r n a l oblique  (RA) .  To a s s e s s  transducers muscle  on  the  (10), effects  abdominal  in  the  of  resting  same dogs when awake,  awake  dogs were  The e x p e r i m e n t a l loading  also  (ETL) and C 0  and a f t e r  reversible  individual response  2  individual  these  be  recruited preferentially  and RA) i n importance muscle  response of  to  hypercapnia before  the  awake  and a f t e r  these s t u d i e s demonstrate sonomicrometer  changes i n awake dogs.  length  then  exhibit  were to  i n t e r n a l muscle l a y e r  the  external  stimuli.  reflexes  in  shortening  exposed  in the  of  tonic  (TA and 10)  would  muscle  control to  that  amounts  To a s s e s s the  before  determine  hypothesized  differing  the  threshold  rebreathing  2  expiratory  We  protocols.  expiratory  layer  the of  ETL and  r e v e r s i b l e vagal blockade.  Phasic  changes,  dogs and  experimental  changes,  and p h a s i c ,  dogs were  for  implantation of  days  The o b j e c t i v e s  the f e a s i b i l i t y  transducers  and  and ETL and C 0  would  of  abdominis  anesthetized  different  stimuli.  vagally-mediated  activation,  to  compared to  each  and r e c t u s  periods  tonic  and p h a s i c a c t i v i t y and t h a t the  abdominis  Over the d u r a t i o n o f the s t u d y  vagal blockade.  abdominal muscles  EMG  periods  rebreathing,  different  wire  transversus  on s u c c e s s i v e  were p o s t u r a l  abdominal muscle to  length  with  over  exposed  protocols  (E0)  fine  and c h r o n i c  were made i n the  r a n g i n g from two to e i g h t weeks. the  oblique  anesthesia  muscle  l e n g t h measurements  repeated  external  instrumented  (E0  relative abdominal  progressive  The r e s u l t s  of  of using c h r o n i c a l l y implanted  measurement  of  abdominal muscle  expiratory shortening of  the  length  T A , 10 and  EO was i n c r e a s e d by changes i n p o s t u r e from the  lateral decubitis  sitting  by  and  shortening conditions. under a l l  standing  of  the  positions,  TA a n d / o r  the  by  ETL and  10 was  also  three  conditions  d u r i n g ETL and C 0  2  and t h i s  preferential  rebreathing after  hypercapnia.  present  There was p r e f e r e n t i a l r e c r u i t m e n t o f  to  the  under  vagal blockade.  Tonic  all  internal  recruitment  the  three muscles  persisted  We c o n c l u d e  that  abdominal muscle a c t i v i t y i s mediated by v a g a l and c h e m i c a l r e f l e x e s and that  segmental  reflexes  m o d u l a t i n g the l e v e l  from  muscle  proprioceptors  o f i n d i v i d u a l abdominal muscle  play  activity.  a  role  in  iv  TABLE OF CONTENTS Abstract  ii  T a b l e o f Contents .  ....iv  L i s t of Figures  vi  L i s t of Tables  x  L i s t of Abbreviations  xi  Acknowledgement I.  xii  Introduction 1 Literature Review.. 1 Introduction 1 F u n c t i o n a l Anatomy o f the Abdominal Muscles 2 Methods o f Study 6 P o s t u r a l E f f e c t s on and R e g i o n a l D i f f e r e n c e s i n Abdominal Muscle A c t i v i t y 8 Abdominal Muscle A c t i v a t i o n by E x p i r a t o r y T h r e s h o l d L o a d i n g . . 1 0 Abdominal Muscle A c t i v a t i o n by Hypercapnia 11 D i f f e r e n t i a l A c t i v a t i o n o f the Abdominal Muscles 11 Summary 12 Objectives 13 Significance 14 References 15  II.  C h r o n i c I m p l a n t a t i o n and Length Measurements Introduction Methods Surgical Preparation Tracheostomy . . . I m p l a n t a t i o n o f t r a n s d u c e r s and EMG w i r e s Measurements Protocol Analysis Results ' Discussion References  III.  E f f e c t s of Posture Introduction Methods Measurements Protocol Analysis Results Discussion . . . References  on Abdominal Muscle Length ,  ..20 20 21 22 22 24 27 32 33 34 39 45 47 47 49 49 52 53 54 60 69  V  IV. Abdominal Muscle A c t i v a t i o n by E x p i r a t o r y T h r e s h o l d L o a d i n g Introduction Methods Measurements Protocol Analysis Results Discussion References • V.  VI.  Abdominal Muscle A c t i v i t y D u r i n g Hypercapnia Introduction Methods Instrumentation Measurements Protocol Analysis Results Discussion References E f f e c t s o f V a g a l Blockade on Abdominal Muscle A c t i v a t i o n Introduction Methods Measurements E x p i r a t o r y T h r e s h o l d Loading C0 R e b r e a t h i n g Protocol ETL C0 Rebreathing V a g a l Blockade Analysis ETL C0 Rebreathing V a g a l blockade Results E f f e c t s o f V a g a l Blockade on C o n t r o l Parameters ETL C0 Rebreathing Discussion E f f e c t s o f V a g a l Blockade on C o n t r o l Parameters E f f e c t s o f V a g a l Blockade d u r i n g ETL E f f e c t s o f V a g a l Blockade d u r i n g C 0 R e b r e a t h i n g References  99 99 100 100 101 103 • • 103 104 117 126  2  2  2  2  2  VII.  Summary and C o n c l u s i o n s Summary o f Major F i n d i n g s Conclusions References  .72 .72 73 73 75 76 76 91 97  ,  129 129 130 131 133 133 134 135 135 135 136 136 137 138 138 138 139 151 161 161 162 167 170 174 174 176 180  vi  LIST OF FIGURES Figure 1 Schematic diagram o f the c a n i n e abdominal muscles  4  Figure 2 Photograph showing a permanent tracheostomy i n a mongrel dog two weeks p o s t - s u r g e r y  23  Figure 3 Photograph showing the placement o f a p a i r o f sonomicrometer t r a n s d u c e r s and f i n e w i r e EMG e l e c t r o d e s i n the e x t e r n a l o b l i q u e muscle  25  Figure 4 Schematic diagram o f the canine abdomen showing p o s i t i o n s o r i e n t a t i o n s o f the f o u r abdominal muscles  and f i b e r 28  Figure 5 A r e p r e s e n t a t i v e r e c o r d i n g from an awake dog (lying i n left lateral d e c u b i t u s ) showing t r a n s v e r s u s abdominis (TA) l e n g t h changes and TA EMG a c t i v i t y 30 Figure 6 Example o f the e x p e r i m e n t a l setup w i t h the dog l y i n g i n the l a t e r a l decubitus p o s i t i o n  left 33  Figure 7 Two x - s e c t i o n s o f i n t e r n a l o b l i q u e muscle s t a i n e d w i t h Masson's t r i c h o m e . The muscle b i o p s y had been f i x e d i n f o r m a l i n w i t h the sonomicrometer t r a n s d u c e r i n p l a c e 38 Figure 8 A r e p r e s e n t a t i v e r e c o r d i n g from an awake dog l y i n g i n l e f t l a t e r a l d e c u b i t u s p o s i t i o n (top panel) and s t a n d i n g on a l l f o u r s (bottom p a n e l ) showing t r a n s v e r s u s abdominis (TA) l e n g t h changes and TA EMG a c t i v i t y , 50 Figure 9 Bar graph showing a c t i v e s h o r t e n i n g o f the TA, 10 and EO i n the l e f t l a t e r a l d e c u b i t u s (LLD), s i t t i n g (SIT) and s t a n d i n g (STAND) postures 55 F i g u r e 10 Box p l o t s o f the change i n r e s t i n g l e n g t h (LRL) w i t h s h i f t i n p o s t u r e from l e f t l a t e r a l d e c u b i t u s (LLD) to s i t t i n g ( S I T ) .  ..57  F i g u r e 11 Box p l o t s o f the change i n r e s t i n g l e n g t h (LRL) w i t h s h i f t i n p o s t u r e from l e f t l a t e r a l d e c u b i t u s (LLD) to s t a n d i n g (STAND). 58  vii  F i g u r e 12 A r e p r e s e n t a t i v e t r a c i n g from an awake dog ( l e f t l a t e r a l d e c u b i t u s p o s i t i o n ) showing t i d a l volume (VT) , airway p r e s s u r e ( P a o ) , i n t e r n a l o b l i q u e (10) l e n g t h changes and EMG a c t i v i t y 78 F i g u r e 13 L e n g t h changes (%LRL) o f t h r e e abdominal muscles (TA, 10 and E0) a t c o n t r o l (Pao=0) and f o u r l e v e l s o f PEEP (Pao=6, 10, 14 and 18 cmH 0) d u r i n g e x p i r a t o r y t h r e s h o l d l o a d i n g . ; . . . . .80 2  F i g u r e 14 T o t a l t i d a l l e n g t h e x c u r s i o n s o f t h r e e abdominal muscles (TA, 10 and E0) e x p r e s s e d as a percentage o f the i n i t i a l b a s e l i n e r e s t i n g l e n g t h (%LRL) p l o t t e d a g a i n s t i n c r e a s i n g airway p r e s s u r e (Pao) during expiratory threshold loading 83 F i g u r e 15 A c t i v e , p h a s i c e x p i r a t o r y s h o r t e n i n g o f t h r e e abdominal muscles (TA, 10 and E0) e x p r e s s e d as a percentage o f the i n i t i a l b a s e l i n e r e s t i n g l e n g t h (%LRL) p l o t t e d a g a i n s t i n c r e a s i n g a i r w a y p r e s s u r e (Pao) d u r i n g e x p i r a t o r y t h r e s h o l d l o a d i n g 84 F i g u r e 16 The change i n l u n g volume (<5Vol) produced by ETL p l o t t e d airway p r e s s u r e (Pao)  against 88  F i g u r e 17 I n s p i r a t o r y a i r flow d u r a t i o n (Ti) (top) and e x p i r a t o r y d u r a t i o n (T ) (bottom) p l o t t e d a g a i n s t airway p r e s s u r e (Pao) d u r i n g ETL E  F i g u r e 18 E x p i r a t o r y d u r a t i o n ( T E ) p l o t t e d a g a i n s t the change i n volume d u r i n g ETL  89  (6vol) 90  F i g u r e 19 A r e p r e s e n t a t i v e r e c o r d i n g from an awake dog ( l e f t l a t e r a l d e c u b i t i s p o s i t i o n ) showing t r a n s v e r s u s abdominis (TA) l e n g t h changes, TA EMG a c t i v i t y and t i d a l volume (V ) d u r i n g C 0 r e b r e a t h i n g . . . . 1 0 6 T  2  F i g u r e 20 V p l o t t e d as a f u n c t i o n o f e x p i r e d minute v e n t i l a t i o n ( V E ) C0 r e b r e a t h i n g T  2  F i g u r e 21 V p l o t t e d against T T  E  and T i d u r i n g C 0 r e b r e a t h i n g 2  during 109  110  F i g u r e 22 Length changes o f the t r a n s v e r s u s abdominis ( T A ) , i n t e r n a l o b l i q u e (10) and e x t e r n a l o b l i q u e (E0) d u r i n g a i r - b r e a t h i n g c o n t r o l and a t t h r e e l e v e l s o f e n d - t i d a l C0 113 2  F i g u r e 23 T o t a l t i d a l l e n g t h changes o f the TA, 10 and EO (%LRL) p l o t t e d a g a i n s t i n c r e a s i n g minute v e n t i l a t i o n d u r i n g C 0 r e b r e a t h i n g . 115 2  F i g u r e 24 A c t i v e s h o r t e n i n g o f the TA, 10 and EO (%LRL) p l o t t e d a g a i n s t i n c r e a s i n g minute v e n t i l a t i o n d u r i n g C O 2 r e b r e a t h i n g  116  F i g u r e 25 Photograph showing placement o f a s i l a s t i c c u f f around the c e r v i c a l vagus nerve i n one o f the dogs  132  right  F i g u r e 26 Abdominal muscle a c t i v e p h a s i c s h o r t e n i n g v e r s u s (Pao) d u r i n g ETL  airway p r e s s u r e  F i g u r e 27 Abdominal muscle a c t i v e p h a s i c s h o r t e n i n g v e r s u s volume d u r i n g ETL  the change  140  in 141  F i g u r e 28 R e p r e s e n t a t i v e r e c o r d i n g from an awake dog ( l e f t l a t e r a l d e c u b i t u s p o s i t i o n ) showing t i d a l volume ( V ) , airway p r e s s u r e ( P a o ) , i n t e r n a l o b l i q u e (10) l e n g t h changes and 10 EMG a c t i v i t y d u r i n g expiratory threshold loading 142 T  F i g u r e 29 T i d a l volume v e r s u s airway p r e s s u r e a f t e r vagal blockade Figure TXOT  30 v e r s u s airway p r e s s u r e blockade  (Pao)  F i g u r e 31 Tj and T v e r s u s airway p r e s s u r e vagal blockade E  (Pao) d u r i n g ETL b e f o r e and 146  d u r i n g ETL b e f o r e and a f t e r  vagal 147  (Pao) d u r i n g ETL b e f o r e and . a f t e r  F i g u r e 32 Change i n l u n g volume (<Svol) v e r s u s airway p r e s s u r e b e f o r e and a f t e r v a g a l b l o c k a d e  148  (Pao)  d u r i n g ETL 149  F i g u r e 33 R e p r e s e n t a t i v e r e c o r d i n g from an awake dog ( l e f t l a t e r a l d e c u b i t u s p o s i t i o n ) showing V , TA p h a s i c s h o r t e n i n g (%LRL) and TA EMG d u r i n g moderate h y p e r c a p n i a b e f o r e ( l e f t p a n e l ) and a f t e r ( r i g h t panel) v a g a l blockade 152 T  F i g u r e 34 Abdominal muscle a c t i v e p h a s i c s h o r t e n i n g p l o t t e d a g a i n s t e n d - t i d a l PC0 d u r i n g r e b r e a t h i n g , b e f o r e and a f t e r v a g a l b l o c k a d e . . . . 1 5 4 2  ix  F i g u r e 35 Abdominal muscle a c t i v e s h o r t e n i n g p l o t t e d a g a i n s t minute v e n t i l a t i o n d u r i n g r e b r e a t h i n g , b e f o r e and a f t e r v a g a l blockade F i g u r e 36 T i d a l volume ( V T ) p l o t t e d a g a i n s t minute v e n t i l a t i o n d u r i n g C 0 r e b r e a t h i n g , b e f o r e and a f t e r v a g a l b l o c k a d e  155  2  F i g u r e 37 T o t a l a i r flow d u r a t i o n ( T O T ) p l o t t e d a g a i n s t minute v e n t i l a t i o n d u r i n g C 0 r e b r e a t h i n g , b e f o r e and a f t e r v a g a l b l o c k a d e  157  T  2  158  X  LIST OF TABLES Table I R e s t i n g b a s e l i n e l e n g t h s (RL) o f the abdominal muscles in a n e s t h e t i z e d compared to awake dogs and a c t i v e s h o r t e n i n g i n awake dogs ( l e f t l a t e r a l decubitus p o s i t i o n ) Table II T i d a l volume and t i m i n g parameters Table III V e n t i l a t i o n and t i m i n g parameters  i n three postures  59  d u r i n g ETL  86  T a b l e IV A r t e r i a l b l o o d gas v a l u e s d u r i n g ETL Table V A r t e r i a l b l o o d gas  (%LRL) 37  87  and pH v a l u e s d u r i n g C 0 r e b r e a t h i n g 2  105  T a b l e V I I V e n t i l a t o r y Parameters f o r r e s t i n g a i r b r e a t h i n g c o n t r o l and three l e v e l s of e n d - t i d a l C0 Ill 2  Table VII V e n t i l a t i o n and t i m i n g parameters blockade  d u r i n g ETL b e f o r e  and a f t e r  vagal 145  Table VIII A r t e r i a l b l o o d gases d u r i n g ETL b e f o r e  and a f t e r v a g a l b l o c k a d e . . 1 5 0  T a b l e IX V e n t i l a t o r y Parameters f o r r e s t i n g a i r b r e a t h i n g c o n t r o l and t h r e e levels of e n d - t i d a l C 0 156 2  Table X A r t e r i a l B l o o d Gas and pH v a l u e s d u r i n g C 0 R e b r e a t h i n g b e f o r e a f t e r v a g a l blockade 2  and 160  xi  LIST OF ABBREVIATIONS 5Vol  change i n l u n g volume  EEL  end-expiratory  EELV  end-expiratory  EILV  electromyogram  EO  external  FRC  internal  LLD  left  LEE  length at  LEI  length  end-expiration  muscle l e n g t h change as a p e r c e n t  P C0 a  2  PETC0  2  2  PO2 RA SIT STAND  VT  decubitus  resting baseline  %LRL  TTOT  oblique  length at end-inspiration  LRL  Ti  lateral  active baseline  LABL  TE  oblique  functional residual capacity  10  TA  l u n g volume  e n d - i n s p i r a t o r y l u n g volume  EMG  PC0  length  length of  LRL  a r t e r i a l pressure  of carbon dioxide  e n d - t i d a l pressure  of carbon dioxide  p a r t i a l pressure  of carbon dioxide  p a r t i a l pressure rectus  o f oxygen abdominis  s i t t i n g p o s i t i o n o f the  dog  s t a n d i n g p o s i t i o n o f the  dog  transversus  abdominis  duration of expiration duration of  inspiration  t o t a l breath  duration  t i d a l volume  AKNOWLEDGEMENTS I support  would and  constructive the t e c h n i c a l  like  to  thank  encouragement criticisms staff  my  and  supervisor my  and s u p p o r t .  supervisory  the  Resource U n i t , e s p e c i a l l y  staff  of  the  Road  committee  for  for  his their  possible:  to  S a l l y Osborne and  UBC U n i v e r s i t y H o s p i t a l Animal  M i c h a e l and M i q u e l .  DEDICATION For my mother.  Jeremy  S p e c i a l thanks and a p p r e c i a t i o n  who made the experiments  Sharon Barwick and a l l  Dr.  1  I.  LITERATURE  INTRODUCTION  REVIEW  Introduction The be  f o u r muscles o f  the v e n t r a l abdominal w a l l  the major muscles o f e x p i r a t i o n (1,12,17).  been r e p o r t e d exercise active  to be p h a s i c a l l y a c t i v e d u r i n g  (1,35)  in  abdominis  the  and  their  posture  external  abdominis  o r i e n t a t i o n s and  (12,16,22).  oblique  (TA),  differ  surface area.  proportions  C0  2  expiratory threshold loading  upright  (RA),  transversus  The  of  fiber  (42,43,53),  (9,34,43)  tonically  four  and  muscles: (10)  oblique  (11).  The  presence  with  to  complex.  The  majority  of  the  abdominal muscles  the  i n d i v i d u a l muscles  on  humans  have  displacement, muscle  activity.  intramuscular to  depress  techniques,  do  hot  a  few  changes  (16,22,23)  allow  for  and/or  number  of  be  quite  assumed  Despite  studies  have  demonstrated upper and (54).  measured  the  of  investigators  animals but  (51).  hypercapnia  hence,  differentiated  differentiation  activity  and  in  that among  For the most p a r t , s t u d i e s done  i n anesthetized  i n the  could  generally  have not  electrodes  Alternatively, a  abdominal muscle a c t i v i t y  action  however, have  a u n i t and  surface  electrodes  muscle  as  muscle  (1,12,30,32,58).  used  which  abdominal  studies  act  fiber  o f such v a r i a t i o n s  s t r u c t u r e would suggest f u n c t i o n a l d i f f e r e n c e s and breathing,  and  origins, insertions,  i n anatomy and respect  rectus  There i s a l s o e v i d e n c e t h a t they v a r y  types  to  rebreathing  internal  in their  considered  abdominal muscles have  These  (EO),  are  abdominal individual have  anesthesia  l i m i t a t i o n s of regional  is  also  i s known the  above  differences  lower abdomen w i t h There  used  some  in  postural evidence  2  that  individual  deeper  muscle  (46,54). measure  layer  Recently, abdominal  expiratory  muscles  can a c t independently  (10 and TA) p l a y s t h e technique  muscle  threshold  T h i s technique which  abdominal  length  loading  allows  changes  i n anesthetized  by s u r f a c e  have d i f f e r e n t  degrees o f a c t i v i t y .  during  layer  confirm  that  individual  ETL (34) and h y p e r c a p n i a  passive  reflexes  s t r e t c h i n g o f t h e muscles  reflexly  stimulates  recruitment  (5,28,43).  muscle  may d i f f e r  activity  o r volume muscles  i t has been important  shown  one  (41) i n a n e s t h e t i z e d  f o r abdominal muscle r e c r u i t m e n t  in  dogs.  a r e thought  (7,23,48) and p r i m a r i l y due  (33,43,56). However, t h e r e i s a l s o  to chemoreceptors d u r i n g h y p e r c a p n i a segmental  during  abdominal  In particular,  to be p r i m a r i l y v a g a l l y mediated d u r i n g ETL  that  used t o  dogs  electrodes  (10 and TA) i s the more  The mechanisms r e s p o n s i b l e  evidence  has been  s e p a r a t e measurement o f i n d i v i d u a l muscle  The r e s u l t s  ventilation  i n ventilation  (34,43) and h y p e r c a p n i a  (ETL)  c a n n o t be d i f f e r e n t i a t e d  the i n t e r n a l  role  o f sonomicrometry  displacements.  that  a greater  and t h a t t h e  may be i n v o l v e d a c t i v a t e s muscle  activity.  The p a t t e r n s  depending on the r e l a t i v e  (31,49),  such  that  p r o p r i o c e p t o r s and o f abdominal  muscle  c o n t r i b u t i o n s o f these  mechanisms.  F u n c t i o n a l Anatomy o f t h e Abdominal Muscles The (RA),  f o u r muscles o f the v e n t r a l abdominal w a l l : r e c t u s  external  abdominis  oblique  (TA) d i f f e r  surface area. to the p u b i s  (E0), internal i n origin,  oblique  insertion,  (10) and t r a n s v e r s u s fiber  o r i e n t a t i o n and  The RA i s most m e d i a l and runs a x i a l l y ,  from t h e sternum  on e i t h e r s i d e o f the l i n e a a l b a . The E0 l i e s  superficially,  abdominis  extending  c a u d i o d o r s a l l y from t h e o u t e r  l a t e r a l l y and  surfaces  o f the  3  lower e i g h t lies  deep  ribs to  to  the  insert  E0  approximately r i g h t iliac  c r e s t . At  interdigitates  but  w i t h the  individual is  to  with  of  the  the  TA.  last  in  of  the  species.  g r e a t e r than the (37).  humans  functional The  The  six costal and  ventilatory  Based  lung  the  on  the  running  at  its origin  on  the  lower t h r e e r i b s , the The  deepest  cartilages  of  a r i s i n g from  where i t i s  and  position  the  continuous (4).  diaphragm  i n the  10 the  c a n i n e abdominal muscles i n d i c a t i n g  canine  abdominal muscles  shape o f the  In dogs, the  function  abdominal  appears  in  to  r i b cage i s q u i t e  the wall  be  rib  cage  very  different  r i b cage a n t e r o p o s t e r i o r  diameter  r e v e r s e i s the  shape  pull  down the  volume.  r i b cage.  and  the  10  separate stimulation  the  anatomy,  muscles o f  when  supine,  e f f e c t on and  TA  the no  o f b o t h the  were  the  may  case  produce  some  abdominal w a l l  and  to  an  compress  expiratory  abdominal  muscles  the  action were  they were found to have d i f f e r i n g a c t i o n s  anesthetized  dog,  the  lower r i b cage, the noticeable RA  has  electromyographical  thought  thus h a v i n g  individual  (17,37) the  they  lower r i b s ,  However,  In  of  from a n a t o m i c a l a n a l y s i s  their  have a d e f l a t i o n a r y effect  from  i n t e r d i g i t a t e s w i t h the  difference  stimulated separately on  E0,  fibers  10  v a r i a t i o n o f i n d i v i d u a l abdominal muscles.  abdomen and on  its  t r a n s v e r s e diameter, whereas the  been deduced p r i m a r i l y studies.  with  The  1.  anatomy  two  l i n e a alba.  I t runs c i r c u m f e r e n t i a l l y ,  s i m i l a r to humans. However, the  is  the  and  intercostals.  fiber orientation  shown i n F i g u r e  between the  crest  and  those o f  internal  i l l u s t r a t i o n of muscle  The  iliac  i t s p o i n t o f i n s e r t i o n i n t o the  transversus thoracis  A schematic  the  more m e d i a l  angles  abdominal muscles i s the inner surface  into  and  E0  effect  E0 (17).  RA an  was  found  to  inflationary In  i n humans r e s u l t e d  contrast, in  4  F i g u r e 1: Schematic diagram o f the canine abdominal muscles: t r a n s v e r s u s abdominis (•) , i n t e r n a l o b l i q u e ( O ) , e x t e r n a l o b l i q u e (A) and rectus abdominis ( A ) , showing the f i b e r o r i e n t a t i o n and p o s i t i o n i n the abdominal w a l l .  5  6  displacement  o f the r i b cage  and  reduction  a c t i o n s however were a c h i e v e d  differently:  anteroposterior  the  decrease  diameter  i n transverse  individual  muscles  of  e x p i r a t o r y and depends  stimulated  whereas  the  the d i f f e r e n t  separately,  on the r e c r u i t m e n t  (37)  volume  .  These  the RA produced a d e c r e a s e i n  r i b cage,  diameter. D e s p i t e  when  i n lung  the  EO  caused  actions net  a  o f the  effect  p a t t e r n and c o o r d i n a t e d  is  action  o f the abdominal m u s c l e s . The lumbar  abdominal  nerves  distributed  muscles  (4).  The  from T4-L3.  each abdominal muscle the  10  and  T9-L3  are s u p p l i e d by  motoneurons The  innervating  (38).  f o r the TA  motoneurons  primarily  i n the c a u d a l  intercostal  and  i n d i v i d u a l muscles  are  segmental d i s t r i b u t i o n  i s T4-L3 f o r the RA,  abdominal  the lower  T6-L3 f o r the EO,  Central  v i a projections  o f motoneurons  from  drive  T13-L3 f o r  i s conveyed  expiratory  for  neurons  to  the  located  p o r t i o n o f the v e n t r a l r e s p i r a t o r y group  (VRG)  (39).  Methods o f Study Most the  o f the i n f o r m a t i o n  regarding  abdominal muscles d u r i n g b r e a t h i n g  (usually  via  surface  electrodes).  the r e c r u i t m e n t i s derived  The  or a c t i v i t y  of  from e l e c t r o m y o g r a p h y  abdominal  muscles  have  been  s t u d i e d under a v a r i e t y o f c o n d i t i o n s u s i n g these t e c h n i q u e s .  However,  due t o the l i m i t a t i o n s imposed by s u r f a c e e l e c t r o d e s ,  activity  of  the  recent which  superficial studies have  Nevertheless, muscle  have  enabled there  muscles  (RA  utilized detection  and  EO)  can be  intramuscular of  and  neither  the  differentiated. wire  i n d i v i d u a l muscle  are l i m i t a t i o n s inherent  a c t i v a t i o n i s measured  fine  only  EMG  More  electrodes,  activity  (18,57).  to e l e c t r o m y o g r a p h y : muscle  resting  length  only nor  7  passive  activity  determined. from the of  ( i n s p i r a t o r y l e n g t h e n i n g and p a s s i v e  In  addition,  increase  abdominal  inspiratory  of  displacement  the  abdominal  lengthening  muscle a c t i v i t y c a n not be  muscle  i n background n o i s e .  muscle  contribution  tonic  is  as  Studies  provide  muscles  well  as  from a c t i v e  some  to  phasic  even more d i f f i c u l t  separated  activity  shortening)  can  only  utilizing  ventilation,  transit  time  transducers  of  a  a  In a d d i t i o n ,  wave  which  travelling  The t r a n s i t  time  allows  is  o f sound i n muscle  crystals  measured t r a n s i t  implanted  time.  Thus,  method f o r measuring muscle  in  muscle  can  be  length  changes.  i n conjunction with  s h o r t e n i n g can be The  first  use  of  1543  times  linear  muscles.  the  per  distance  obtained  is  no  G i v e n the known  that  (EMG),  from  it  the  i n vivo of  provides  activation passive  and  identified. sonomicrometry  to  measure  respiratory  dog diaphragm (40).  and found to  be  a useful  technique  in  muscle  Recently  has been used to measure abdominal muscle l e n g t h changes i n (5,34,41,43)  of  An i m p o r t a n t advantage  electromyography  l e n g t h changes was accomplished i n the  dogs  is  piezoelectric  o f q u a n t i f y i n g the mechanical consequences o f muscle  and when used active  there  sonomicrometry p r o v i d e s a d i r e c t ,  sonomicrometry i n the study o f r e s p i r a t o r y mechanics a means  two  the  tonic  techniques.  measured  (1580m/sec),  of  shortening  measurement  between  the  terms  However,  to a s s e s s and p a s s i v e  averaged to g i v e a continuous DC v o l t a g e .  conduction v e l o c i t y two  technique  sound  (crystals).  second and i s  between  is  about  in  shortening.  shortening.  inferred  measurements  information  means o f i d e n t i f y i n g i n d i v i d u a l muscle a c t i o n s w i t h these Sonomicrometry  be  can be  it  anesthetized  the  abdominal  8  P o s t u r a l E f f e c t s on and R e g i o n a l  D i f f e r e n c e s i n Abdominal Muscle  Activity Data  from  illustrated and are  EO.  the e f f e c t s  using  electromyographic  o f body p o s i t i o n on muscle  I t i s g e n e r a l l y accepted  inactive  Conflicting studies  studies  i n human results  i n man  displacement activity,  using  been  abdomen i n u p r i g h t ,  resting  o f t h e RA  with  have  i n t h e lower  (1,13,22,30,35).  supine  other  electromyography  (22,35)  measurements  especially  when found  either  activity  have  t h a t the abdominal muscles (RA and EO)  subjects  have  techniques  found  postures.  Several  (12,13,16,22)  and/or  tonic  abdominal  " g r a v i t y dependent"  quiet breathing.  muscle  portion  There i s a l s o evidence  of  the  o f phasic  abdominal c o n t r a c t i o n d u r i n g e x p i r a t i o n i n the u p r i g h t p o s i t i o n , i n some (13,35,52).  subjects position,  although  contrast,  other  suggested  that  subjects  S i m i l a r r e s u l t s have been r e p o r t e d with  a  lesser  degree  i n v e s t i g a t o r s observing t h e abdominal  at rest  (30,32).  muscles  of activity abdominal  were  to  abdominal  studies  displacement  internal  abdominal  activity  of  reasonable  The c o n t r o v e r s i a l r e s u l t s  phase  muscles muscles,  of quiet  (11,22).  techniques  intramuscular  those  EMG  electrodes  (TA and 10) ,  clearly  i n the s t a n d i n g breathing  (18,57).  In  displacements i n standing  may be  partially  Electromyography most  Indeed, were  compared  more  placed  demonstrated position  recent in  Therefore,  the  phasic  during  the  i t seems  t o conclude t h a t c o n t r a c t i o n o f the abdominal muscles  quiet breathing The  wall  a more s e n s i t i v e measure o f muscle r e c r u i t m e n t ,  i n which  expiratory  (13,16,35).  not active  e x p l a i n e d by the d i f f e r e n t methodologies u t i l i z e d . l i k e l y provides  f o r the seated  during  i n u p r i g h t man c o n t r i b u t e s to b r e a t h i n g .  abdominal  muscles  o f dogs  appear  t o be more  active  at rest  9  than  those  (5,23,28)  in and  dogs and  Phasic  muscle  s h o r t e n i n g has  length  activity  In  increases Phasic  i n those  EMG  the  small  were  activity  found  i n supine  number o f  made  in  the  the  studies  EMG  TA  anesthetized i n which  (sonomicrometry),  i n a s s o c i a t i o n with  dogs  the  are  tilted  previously  towards  inactive  has  phasic  when p r e s e n t ,  upright,  in  abdominal  supine  phasic  EMG  muscles  and  (20,23,28).  position  (19,53)  a l s o been shown i n awake s t a n d i n g  I n a d d i t i o n , t h e r e i s evidence  a c t i v i t y develops i n the u p r i g h t p o s t u r e s ,  and  to suggest t h a t t o n i c  p a r t i c u l a r l y i n the TA o f  the  (19,26).  dog  In upright muscles  is  expiratory  postures,  thought  to  length  (26)  phasic  help  muscles  to  tidal  volume  a n e s t h e t i z e d dogs t i l t e d The  assumption  (2,23).  The  increase  abdominal  receptors  muscle  and  tonic  maintain  and  r e l a x a t i o n at end-expiration  contribute (24,25).  has  been  (20,23)  and  evidence  awake  i n FRC  The  tidal  posture  to  when v a g a l  (19)  and  via  more  endtheir  abdominal  than  50%  in  in  FRC  (24).  to be  vagal  abdominal  diaphragm  volume  be  produces  i s considered  Indeed,  the  c o n t r i b u t i o n o f the  estimated  activation via a  dogs  to  of  defend  to the headup p o s i t i o n  of. u p r i g h t  (15,20,23).  activity  (23),  FRC  vagotomy, abdominal muscle a c t i v i t y was  also  been  (28)  EO  t h a t were a c t i v e i n the  s i t t i n g dogs (19).  for  has  (5,28,34,41,43).  anesthetized in  and  changes  been found  appears  activity  (34)  (19).  a n e s t h e t i z e d dogs When  EMG  o c c a s i o n a l l y 10  i n awake dogs  abdominal  supine  man.  an  increase  primarily responsible  reflex  from  lung  stretch  r e f l e x e s were e l i m i n a t e d  reduced i n u p r i g h t  anesthetized  (15).  However,  anesthetized  rabbits  suggests t h a t segmental r e f l e x e s from muscle p r o p r i o c e p t o r s  involved  in  abdominal  muscle  by  activation  in  upright  are  postures,  10  particularly abdominal outward,  tonic  contents  would  stretching  alluded previous  tend  i n man  (2)  muscles  i n tonic  abdominal  i n the d i s c u s s i o n  investigators found r e g i o n a l  activity  the abdominal  and thus,  of postural  differences  i n the upright  muscle  posture  i n abdominal  (35,50)  t o n i c muscle a c t i v i t y than the upper r e g i o n s  muscle during  I n man the lower r e g i o n o f t h e abdominal  (35,54).  This  forces  were  Several  and i n dogs  had g r e a t e r  regional  stimulating  effects.  (28,42).  hydrostatic  t o move  activity  hypercapnia  posture  wall  on t h e  (29).  differences  to e a r l i e r  Gravitational effects  t o cause  t h e abdominal  muscle p r o p r i o c e p t o r s Regional  (15,19,50).  activity  muscles  i n the u p r i g h t  i s thought to be due t o the p r e s e n c e o f l a r g e r evidence  of  d i f f e r e n c e s i n abdominal muscle a c t i v a t i o n i n dogs d u r i n g  CO2  rebreathing,  i n t h e lower  which  are  abdomen.  opposite  a c t i v i t y i n t h e upper r e g i o n )  to  There  postural  i s also  differences  (greater  (28,42).  Abdominal Muscle A c t i v a t i o n by E x p i r a t o r y T h r e s h o l d L o a d i n g Expiratory activity (34,43).  i n man  threshold  loading  (1,36,58)  and i n a n e s t h e t i z e d  Abdominal  muscle  demonstrated i n a n e s t h e t i z e d is  (ETL) s t i m u l a t e s  a c t i v e shortening dogs  (34,43).  cats  during  prevent  A c t i v a t i o n o f the  and dogs  ETL has a l s o  Expiratory  been  by t h e r e s p i r a t o r y  abdominal muscles d u r i n g ETL h e l p s t o  too g r e a t an i n c r e a s e i n FRC and hence, defends diaphragm  and t i d a l volume  (34,36,45).  (6,10)  muscle  Abdominal muscle a c t i v a t i o n  one o f t h e l o a d compensating mechanisms employed  system (14,36).  abdominal  length  (14,34,45). threshold  loading  I t i s the increase  produces  i n FRC which  an  increase  i s thought  in  FRC  t o be t h e  11  p r i m a r y mediator o f abdominal muscle a c t i v a t i o n v i a s t i m u l a t i o n o f v a g a l r e f l e x e s by l u n g reflexes  may a l s o  (7,49).  be i n v o l v e d  produced by ETL c o u l d s t r e t c h the muscle p r o p r i o c e p t o r s . paralyzed  dogs  (6,8,10,14,48).  s t r e t c h receptors  The i n c r e a s e  p a r t i c u l a r l y the TA and  segmental  i n lung  abdominal muscles and thus,  Indeed, p a s s i v e  resulted  However,  lung  i n lengthening  inflation  volume stimulate  i n anesthetized,  o f t h e abdominal  muscles,  (34).  10  Abdominal Muscle A c t i v a t i o n by Hypercapnia Abdominal  phasic  (5,43,56)  anesthetized hypercapnia.  and  Abdominal  demonstrated Activation  muscle  in  awake  muscle  anesthetized  o f t h e abdominal  a l l o w i n g b r e a t h i n g frequency activation  EMG  enables  tidal  activity (3,53)  phasic  i n humans dogs  shortening  (5,28,43)  dogs  is  to increase.  volume  and  stimulated has  during  muscles by C O 2 i n c r e a s e s  (55,57)  also  by been  hypercapnia.  expiratory  flow,  I n a d d i t i o n , abdominal muscle  to increase  by e n c r o a c h i n g  on b o t h  i n s p i r a t o r y and e x p i r a t o r y r e s e r v e volumes. Thus, the work o f b r e a t h i n g may  be r e d i s t r i b u t e d between the e x p i r a t o r y and i n s p i r a t o r y muscles when  v e n t i l a t i o n i s i n c r e a s e d by h y p e r c a p n i a . The  abdominal  muscle  response  to hypercapnia  appears  mediated p r i m a r i l y v i a p e r i p h e r a l and c e n t r a l c h e m o r e f l e x e s a f u n c t i o n o f an i n c r e a s e d d r i v e t o b r e a t h e . also  appears  t o be i n v o l v e d ,  since  (33)  However, a v a g a l  abdominal  muscle  t o be and i s  component  EMG a c t i v i t y i s  reduced i n vagotomized, a n e s t h e t i z e d dogs d u r i n g h y p e r c a p n i a  (28,42).  D i f f e r e n t i a l A c t i v a t i o n o f the Abdominal Muscles In a d d i t i o n t o r e g i o n a l v a r i a t i o n  i n recruitment  and a c t i v a t i o n  12  with  changes  in  posture,  differential  activation  abdominal muscles has been found d u r i n g e x p i r a t o r y hypercapnia flow  (28,42,43).  predominantly  loading. dogs,  It  R o b e r t s o n e t a l . . (46)  to  has a l s o  E T L produced  the  much  been  shown t h a t ,  greater  activation  the  loading  individual (34,43)  reported increased  TA and 10, d u r i n g  recently  of  expiratory i n supine  and  blood  resistance anesthetized  shortening  (43),  also exist  o f c o n t r a c t i o n o f the abdominal muscles  stimulation activity  by  CO2.  (28,43)  There  p a r t i c u l a r l y the 10 (34).  of  i n t e r n a l abdominal muscles i n the p a t t e r n  is  evidence  and s h o r t e n i n g  of  (41,43)  a p p e a r i n g t o be the most a c t i v a t e d .  In a d d i t i o n ,  found the TA to have the g r e a t e s t b l o o d flow  the  the  Differences  differences  among  and  of  with  b o t h EMG  muscles;  the TA  Robertson et a l . ,  (47)  d u r i n g CO2 r e b r e a t h i n g ,  in  a n e s t h e t i z e d dogs. With  a  abdominal  exceptions  muscle  anesthetized during  few  response  animals.  ETL and a f f e c t  response  to  CO2.  (3,19,53),  to  the  ETL and h y p e r c a p n i a  However,  anesthesia  the v e n t i l a t o r y These  majority  effects  r e c r u i t m e n t p a t t e r n o f the abdominal  of  used  vagal  and b r e a t h i n g  anesthesia  studies  have  may enhance  (44)  of  of  supine reflexes  pattern  (27)  affect  the  could  muscles.  Summary The  abdominal  expiratory a c t i v i t y and  Therefore,  muscles  and  stimulated expiratory  hyperpnea  f o r the r e c r u i t m e n t  stimulus.  abdominal  are  during both  hypercapnia-induced  responsible the  muscles  the  degree  pattern  contract  threshold  of  with  loading  (35,43,57).  are l i k e l y  the  to  The  to be d i f f e r e n t of  activation  recruitment  (9,34,58) mechanisms  depending on  of may  phasic  individual vary  under  13  different  conditions  and w i l l  local proprioceptive chemoreceptor  inputs  input  depend  on  (29,31,49),  the  relative  contribution  vagal afferents  (7,9,19,48)  of and  (5,33,43,56).  OBJECTIVES A c h r o n i c dog model was used the  abdominal muscles  of  the  i n the  muscles model  are has  although  there  primarily  dog have been s t u d i e d p r e v i o u s l y  p r e p a r a t i o n s and t h e i r l a r g e s i z e a l l o w s In a d d i t i o n ,  experiments  are  the t e c h n i q u e s  some d i f f e r e n c e s ,  used  extensively  and  there  the  is  in  acute  to be performed.  s i m i l a r i n anatomy and f u n c t i o n to humans been  because  a  dog's  abdominal  (21).  The canine  large  amount  of  i n f o r m a t i o n a v a i l a b l e on the r e s p i r a t o r y m u s c l e s . The functions variety  objectives of of  the  of  which  gravitational  effects.  examined  the  This  study  were  to  i n d i v i d u a l abdominal muscles  stimuli  with  this  information  In  aim may  produce  Therefore,  the  of  determining  also  further  major  i n the  hyperpnea,  addition,  between the abdominal muscles  assess  muscle the  awake  dog under a  recruitment  primary  and the o t h e r muscles of  ventilatory  increased  understanding  objectives  the  this  load  and  pattern  was  control  mechanisms.  of  interaction  the  of r e s p i r a t i o n .  study  were  to  test  the  f o l l o w i n g hypotheses: 1. That  the  activity  during quiet  muscles w i l l be g r e a t e r 2.  That  (standing position and  that  tonic on  and all  (lateral postural  of  all  of  the  abdominal  i n the awake s t a t e than i n the a n e s t h e t i z e d  phasic  fours  breathing  and  decubitus) effects  activity sitting)  will  be  position  due  to  the  will  be  more  greater  in  compared  hydrostatic pronounced  the to  pressure on  the  dog.  upright  the  lying  gradient internal  14  abdominal muscles  (TA and 10)  compared to  the  external  muscles  (RA and  E0) . 3.  That  greater  activity  of  the  internal  t h a n the e x t e r n a l  layer  l o a d i n g i n the awake dog, 4.  That  hypercapnia  muscles  in  the  i n d i v i d u a l muscles 5.  That  both  among the  will  than  greater  the  and  effect  anesthetized  on  the  one  be  threshold  dog  (34). abdominal  and  that  the  i n recruitment p a t t e r n .  segmental  reflexes  are  r e c r u i t m e n t and may e x p l a i n d i f f e r e n c e s  objectives  abdominal muscles  results  a  may e x h i b i t d i f f e r e n c e s inputs  10)  involved  in  in  recruitment  i n d i v i d u a l abdominal muscles.  The  loading,  (TA and  (E0 and RA) d u r i n g e x p i r a t o r y  produce  animal  vagal  abdominal muscle  layer  as was found i n the a n e s t h e t i z e d  will  awake  muscle  were  to  met  by  ventilation  C 0 - i n d u c e d hyperpnea those found f o r the  i n the  the  contribution  of  the  awake dog under c o n d i t i o n s  and p o s t u r a l  2  to  determining  anesthetized  changes  of  and comparing  dog and the  awake dog  the  post-  vagotomy.  Significance These  experiments  contractile  properties  expiration.  Since  awake  state,  performed stimuli the  to  on  expiratory  may  the  found  threshold  chronic obstructive  in  provide  the  results be  anesthetized  recruit  situations  of  the  they  will  insight  abdominal from t h i s  more  study  applicable  animals.  In  a number o f produces  lung disease  (52).  will  disease an  and  will  than  addition,  abdominal muscles  loading  muscles  into  the the  be  simulate  use to  conditions.  increase  in  vivo  control  derived  those the  in  in  the  from  studies  of  various  some For  degree  example,  FRC s i m i l a r  C o n t r i b u t i o n to the  of  to  understanding  15  o f the complex c o o r d i n a t i o n o f these muscles d u r i n g b r e a t h i n g and interaction  with  c o n d i t i o n s may  the  other  muscles  of  be v a l u a b l e i n some c l i n i c a l  respiration  under  their  various  situations.  REFERENCES 1. A g o s t o n i , E., and E.J.M. Campbell. The abdominal muscles. 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Dempsey.  19  D i f f e r e n t i a l responses o f e x p i r a t o r y muscles to c h e m i c a l s t i m u l i i n awake dogs. J . A p p l . P h y s i o l . 66(1): 384-391, 1989. 54.  S t r o h l , K.P., J . Mead, R.B. Banzett, S.H. L o r i n g and P.C. Kosch. R e g i o n a l d i f f e r e n c e s i n abdominal muscle a c t i v i t y d u r i n g v a r i o u s maneuvers i n humans. J . A p p l . P h y s i o l . 51: 1471-1476, 1981.  55. T a k a s a k i , Y., D. Orr, J . Popkin, A. X i e and T.D. B r a d l e y . E f f e c t o f h y p e r c a p n i a and h y p o x i a on r e s p i r a t o r y muscle a c t i v a t i o n i n humans. J . A p p l . P h v s i o l . 67(5): 1776-1784, 1989. 56. van Lunteren, E., M.A. Haxhiu, N.S. C h e r n i a c k and J.S. A r n o l d . R i b cage and abdominal e x p i r a t o r y muscle responses t o C O 2 and esophagel d i s t e n s i o n . J . A p p l . P h y s i o l . 64(2): 846-853, 1988. 57. Wakai, Y., M.M. Welsh, A.M. Leevers and J.D. Road. The e f f e c t o f continuous p o s i t i v e airway p r e s s u r e and h y p e r c a p n i a on e x p i r a t o r y muscle a c t i v i t y d u r i n g wakefulness and s l e e p . Am. Rev. R e s p i r . P i s . 141(4): A125, 1990.(Abstract) 58. Wolfson, D.A., K.P. S t r o h l , A.F. Dimarco and M.D. A l t o s e . E f f e c t s o f an i n c r e a s e i n e n d - e x p i r a t o r y lung volume on p a t t e r n o f thoracoabdominal movement. R e s p i r . P h y s i o l . 53: 273-283, 1983.  20  I I . CHRONIC IMPLANTATION AND LENGTH MEASUREMENTS  INTRODUCTION The  t e c h n i q u e o f sonomicrometry  v e n t r i c u l a r dimensions (18)  used  muscles,  t o measure  including  (1,4)  We p r e v i o u s l y muscles  (TA)  .  placed  i n various  i n anesthetized  other  respiratory  animals  (2,7,11,13).  i n anesthetized  abdominal  (8),  dogs  also  oblique  transducers  wall:  i n each  rectus  (10) and t r a n s v e r s u s  and were a b l e  have  However,  evidence  (14)  (6).  crystals  scarring  t o measure  active,  muscle  anesthesia  employing  abdominis  tidal  (15).  activity  reduces  muscle loading  sonomicrometry  and a n e s t h e s i a  affects  F o r example,  the r e s t i n g  a p o s i t i o n which may be l e s s n a t u r a l  or l a t e r a l  decubitus  p e r se may a f f e c t  or local  abdominal  animals  the  tone  o f the  I n a d d i t i o n , animals have g e n e r a l l y been s t u d i e d i n t h e  supine p o s i t i o n , t h e prone  that  studies  anesthetized  and r e s p i r a t o r y  suggests  diaphragm  the  study and most  p r e d o m i n a n t l y used  ventilation  to  that  of  abdominis (RA),  l e n g t h changes and a c t i v e s h o r t e n i n g d u r i n g e x p i r a t o r y t h r e s h o l d (ETL).  been  (20).  sonomicrometer  (EO), i n t e r n a l  muscle  S i n c e then, sonomicrometry has  changes  and sheep  o f the v e n t r a l  external oblique  t o measure  l e n g t h measurements (sonomicrometry) have  made i n awake dogs  four  length  the diaphragm,  R e c e n t l y , diaphragm  used  and was adapted t o measure diaphragm  l e n g t h changes by Newman e t a l . (10) been  was o r i g i n a l l y  muscle  expiratory  inhibition. tonic  position.  muscle  Finally,  shortening  compared  implantation o f  by such  f a c t o r s as  Consequently, i t was h y p o t h e s i z e d  activity  (reflected  by  s h o r t e n i n g would be d i f f e r e n t  to the a n e s t h e t i z e d a n i m a l .  f o r dogs  resting  that  l e n g t h ) and  i n the awake  compared  21  The  objectives  of  a n e s t h e s i a on abdominal comparing  individual  anesthetized further  dogs  methods  muscle  study  were  resting  abdominal  to  assess  length  i n the  same  f o r subsequent  similar,  of by  measured  in  dogs when  awake.  A  o f l o n g - t e r m use  of  l e n g t h measurements.  chapters are  effects  shortening  changes  t o determine the f e a s i b i l i t y  f o r abdominal muscle  the  l e n g t h and a c t i v e  muscle  those measured  o b j e c t i v e was  sonomicrometry the  to  this  the  S i n c e many o f description  methods f o r a l l the e x p e r i m e n t a l p r o c e d u r e s a r e d e t a i l e d  of  i n the p r e s e n t  c h a p t e r and o n l y the p r o t o c o l s w i l l be o u t l i n e d i n l a t e r c h a p t e r s . r e s u l t s from experiments on the e f f e c t s are  The  o f p o s t u r e , ETL and h y p e r c a p n i a  d i s c u s s e d i n Chapters I I I , IV and V.  METHODS Nine criteria similar  female  for selection size  b u i l d which Surgical  and  maintenance  dogs  were  shape  i s neither  and  Committee  Unit,  mongrel  a  between friendly,  (.ie. a b r e e d deep nor f l a t  experimental protocols  of  the  was  University  provided  by  18-30  of  even  such  as  were  selected.  temperament a  labrador  and  The  dogs  with  a  of  chest  i n the a n t e r o p o s t e r i o r d i a m e t e r ) . were  British  trained  kg  approved  by  Columbia.  the A n i m a l Daily  care  p e r s o n n e l i n the Animal  Care and  Resource  f o l l o w i n g the g u i d e l i n e s o f the Canadian Counsel on Animal Care. A permanent tracheostomy was  recovery period.  p r e p a r e d and  f o l l o w e d by  D u r i n g the r e c o v e r y p e r i o d , each dog was  a two  familiarized  w i t h the p e r s o n n e l and e x p e r i m e n t a l setups and t r a i n e d t o f o l l o w commands.  week  simple  A f t e r the s u t u r e s were removed from the tracheostomy, the dog  underwent t r i a l  s e s s i o n s w i t h a tracheostomy tube i n p l a c e .  22  Surgical  Preparation  All  the  conditions,  surgical  procedures  were  performed  under  i n the A n i m a l Resource U n i t o f the UBC acute c a r e  The dogs were p r e m e d i c a t e d 30 minutes p r i o r to s u r g e r y w i t h ( l . O m g / k g IM) and a t r o p i n e sodium p e n t o t h a l cuffed  #9  (20mg/kg  endotracheal  delivered  a  1.5%  appropriate maintained  and  areas at  shaved a  tab c o - t r i m o x a z o l e  halothane F10210  at  prepped.  pad.  Ringer's  and f o r f i v e  then  acepromazine  intubated  on an a n e s t h e t i c  O2,  hospital.  A n e s t h e s i a was p r o d u c e d w i t h  agent,  and  heating  lactated  i n the morning b e f o r e  and p l a c e d  supplemental  by  intravenously with  SQ).  The dogs were  inhalation  were  37°C  IV).  tube  combination  (halothane  (0.5mg/kg  sterile  which  and n i t r o u s  oxide  2  1/min.).  All  temperature  balance  solution.  a  machine  Body  Fluid  with  was  maintained  A n t i b i o t i c s were  to seven days a f t e r  was  given  surgery (either  1  (NOVO/DS) o r a l l y or 1 cc p e n i c i l l i n - s t r e p t o m y c i n mix  IM) .  Tracheostomy A midline, two  cm  inferior  2-4  cm v e r t i c a l  to  the  cricoid  skin  incision  cartilage.  o v e r l y i n g the t r a c h e a were c a r e f u l l y d i s s e c t e d removed from the  trachea.  the c i r c u m f e r e n c e o f the cartilaginous then  sutured  wound was and  the  rings (4.0  left  sutures  monofilament  were  permanent tracheostomy  to  nylon)  heal.  removed a f t e r is  flap to  fascia  and the c o n n e c t i v e  tissue  was  the  muscle  a p p r o x i m a t e l y one  shown i n F i g u r e  to 2.  14  third  three or four of  removed.  tracheal  The tracheostomy 10  approximately and  t r a c h e a , was made through resulting  made  The  A U-shaped i n c i s i o n ,  and the  uncovered  was  days.  The s k i n mucosa  was  the was  and  cleaned  An example  the  daily of  a  F i g u r e 2: Photograph showing a permanent tracheostomy i n a mongrel dog two weeks p o s t - s u r g e r y . The dog i s p i c t u r e d i n the s i t t i n g p o s i t i o n w i t h i t s head h e l d up.  24  Implantation  of  One  transducers  pair  of  and  2.5mm  EMG  wires  double-lensed,  piezoelectric  ( c r y s t a l s ) was s u r g i c a l l y implanted (10-15 mm abdominal  muscles.  stages. a  transducers  a p a r t ) i n each o f the f o u r  I m p l a n t a t i o n o f the c r y s t a l s was a c c o m p l i s h e d  i n two  The dog was p l a c e d i n the r i g h t l a t e r a l d e c u b i t u s p o s i t i o n and  horizontal  abdomen,  incision  was  below  the  just  laterally  from  made  i n the s k i n  umbilicus  the m i d l i n e .  First  and  on  the l e f t  then  side  extended  o f the  about  the r e c t u s abdominis,  10  cm  and then the  e x t e r n a l o b l i q u e muscles were exposed by b l u n t d i s s e c t i o n o f the f a s c i a . For  each  muscle,  parallel  muscle  fibers  were  separated  and  a  formed between the f i b e r s .  A c r y s t a l was p l a c e d i n the p o c k e t ,  in  the f i b r e s  the d i r e c t i o n  s t r i n g suture  i n which  (4.0 s i l k ) .  p l a c e d i n another p o c k e t The  crystals  r a n and anchored  were o r i e n t e d  p e r p e n d i c u l a r t o the muscle The placement  3 cm away from the c r y s t a l s . stainless  end o f each w i r e was  and  dental some  the w i r e  cement.  slack  steel  that  Bipolar,  f i n e wire fibers  2-  The  s t r i p p e d o f i n s u l a t i o n and then sewn d i r e c t l y  into  was  f o r muscle  under the f a s c i a .  so  Wire Co. #AS637).  anchored  A s m a l l loop was  muscle a r e a s was  fibers.  The EMG e l e c t r o d e s c o n s i s t e d o f F E P - t e f l o n wire  the muscle w i t h a s u r g i c a l needle. short  purse-  similarly  fibers  (EMG) e l e c t r o d e s were then sewn i n t o d i f f e r e n t  75-strand  a  of a pair of crystals  i n the e x t e r n a l o b l i q u e muscle i s shown i n F i g u r e 3.  coated,  with  away, between the same muscle  the l e n s e s were f a c i n g each o t h e r .  electromyogram  oriented  The second c r y s t a l o f the p a i r was 10-15 mm  pocket  movement  sutured closed  (Cooner  A knot was i n place  formed and  by  made, the f r e e covering  i n the c r y s t a l  the f a s c i a  (3.0 v i c r y l )  over  leaving  end c u t  the k n o t wires  the  two  with  to allow exposed  the l o o p o f w i r e s  Figure  3: Photograph showing the placement of a pair of sonomicrometer t r a n s d u c e r s and f i n e w i r e EMG e l e c t r o d e s i n the e x t e r n a l o b l i q u e muscle. The top o f the photograph i s towards the c r a n i a l end o f the dog.  26  A s m a l l m i d - s c a p u l a r s k i n i n c i s i o n was made and the w i r e s RA and EO were mid-scapular  incision.  sutured closed For the left in  lateral  the  tunnelled  (2.0  the  second  umbilicus  muscle. using  A pair the  overlying loop  of  the  exit over  procedure, A 6-10  internal  dorsally the  of  the  through  muscles  were  the  then  crystals  The e x t e r n a l  fibres,  layer  made 2-5  were  under the  cm above  oblique  sutured  were The  fascia.  placed  transversus  fibers  in  layer  vicryl)  A final  6-10  f a s c i a was b l u n t d i s s e c t e d  was  muscle and  leaving  direction  and c e p h a l a d .  The a r e a  At  this  TA and c r y s t a l s  fascia  point,  vicryl)  the wires  and 10  were  scapular  tunnelled  under the  underneath.  skin  to  exit  The w i r e s through  from the TA  the  d o r s a l mid-  were then s u t u r e d c l o s e d  (2.0  prolene).  the wounds were d u s t e d w i t h powdered c e f a z o l i n sodium (Ancef) bandaged  fitted  (3.0  incision.  Both s k i n i n c i s i o n s  and  the  and EMG w i r e s  The f a s c i a and muscle l a y e r s were c l o s e d  a loop o f  a  cm d i a g o n a l  p l a c e d as o u t l i n e d above. leaving  the  r u n n i n g i n the  located.  to expose the  were  oblique  the  (3.0  dorso-laterally  abdominis  2 cm  extending  internal  fascial  closed  the u m b i l i c u s ,  fibres;  m i d l i n e and  to expose the  earlier.  starting  o b l i q u e muscle  and EMG w i r e s  described  the  cm d i a g o n a l i n c i s i o n was made  between the RA and 10 muscles where o n l y the EO muscle and the 10 overlie  the  dog was p l a c e d i n  o b l i q u e muscle  fascia blunt dissected  c r y s t a l wires  external  to  a p p r o x i m a t e l y 10 cm from the  EO muscle  the  the  position.  the  technique  i n c i s i o n was of  stage o f  and c a u d a l l y .  s e p a r a t e d and the  skin  The s k i n i n c i s i o n s  decubitus  dorso-laterally  the  prolene).  d i r e c t i o n of  below  under  from the  over  and the  a dog  dog to  torso retain  suit and  (Alice protect  Chatham A r t s ) the  wires.  All  antibiotic  was The  loosely site  of  27  placement  of  crystals  schematically i n Figure  and  EMG w i r e s  for  each  muscle  with  the  is  shown  4.  Measurements Abdominal transducers wires.  muscle  lengths  (crystals).  The  bared  ends  of  the  EMG  electrodes.  The  were  connected  exteriorized  piezoelectric  to  wires  isolated  were,  fine  in  turn,  s h i e l d e d c a b l e to a sonomicrometer (model  T r i t o n T e c h n o l o g y , San D i e g o , Abdominal muscle  measured  The c r y s t a l s  connected by m i n i g r a b b e r s and 120,  were  Cal.).  electromyograms were measured v i a bared  ends  of  the  the  EMG e l e c t r o d e  fine  wire  wires  were  connected to a m p l i f i e r s by m i n i g r a b b e r s and s h i e l d e d c o a x i a l c a b l e . electromyographic high  pass  signals  filtered  sonomicrometer  (30Hz  were and  amplified  (Grass,  lKHz)  recorded  and  model in  P511),  The  low and  tandem w i t h  the  signals.  The t e c h n i q u e o f sonomicrometry has been adapted to a l l o w a c c u r a t e measurement  of  diaphragm l e n g t h  changes,  and has a l s o been shown to be an e f f e c t i v e muscle  length  acute study of  each  changes  (8),  were  abdominal  muscle  variation of  each  compared,  an acute  described previously  (10)  method o f measuring abdominal  preparation  (8).  In  that  earlier  the c r y s t a l s were p l a c e d i n a p p r o x i m a t e l y the same a r e a  abdominal  placements  in  as  muscle  found  as  to  length  give  muscle  i n the p r e v i o u s  were  good  changes.  i n l e n g t h changes, abdominal  they  in  the  present  representative To  evaluate  study.  measurements possible  the  study  (8).  measurements  between  of  regional  c r y s t a l s were p l a c e d i n d i f f e r e n t  and  These  regions  regions  were  No s i g n i f i c a n t r e g i o n a l v a r i a t i o n  i n abdominal muscle l e n g t h changes was found.  T h e r e f o r e , the  crystals  Figure  4: Schematic diagram o f the canine abdomen showing p o s i t i o n s and f i b e r o r i e n t a t i o n s o f the f o u r abdominal muscles: r e c t u s abdominis ( A ) , external oblique (A), i n t e r n a l o b l i q u e ( O ) and t r a n s v e r s u s abdominis (•) . The symbols indicate the approximate placement of the p i e z o e l e c t r i c t r a n s d u c e r s and EMG w i r e s i n each o f the muscles.  29  were p l a c e d all  i n approximately  the same a r e a  o f the dogs i n the p r e s e n t The  length,  was  the  present,  shortening  or  and was  i f no a c t i v e , e x p i r a t o r y ( p h a s i c )  length  immediately  LRL  termed  The  i n d i c a t e d by the arrows  meant t o r e p r e s e n t muscle  activity  the t r u e  may  have  shortening  present,  active  regardless  o f the dog's p o s i t i o n .  expressed  plateau  coinciding  with  as a percentage change from the i n i t i a l  since  tonic  the b a s e l i n e  phasic  during  length  The LRL was n o t  Changes i n l e n g t h  or shortening,  phasic  o f the TA  5 i s LRL.  b u t was  shortening  active,  r e s t i n g l e n g t h o f the muscle,  been  e i t h e r lengthening  preceding  slight  i n Figure  preceding  length,  (Figure 4 ) .  r e s t i n g l e n g t h o f the abdominal muscles was d e f i n e d as e i t h e r  the e n d - e x p i r a t o r y  tracing  study  o f each abdominal muscle i n  EMG from  tidal  length  activity, the r e s t i n g  breathing,  were  (%LRL) .  r e s t i n g length  Muscle s h o r t e n i n g was f u r t h e r d e f i n e d as t o n i c o r a c t i v e .  A decrease i n  the  termed  baseline  from  shortening. EMGs.  the  The l e n g t h  Length  changes  initial  resting  measurements were  were matched  Active  which c o i n c i d e d w i t h  shortening  pressure  transducer  measured  with  (Validyne  by u s i n g  a  EMG t o the l e n g t h  to be p h a s i c  shortening  and which u s u a l l y  o f the downward d e f l e c t i o n o f the l e n g t h  t r a c i n g , a f t e r the r e s t i n g l e n g t h p l a t e a u was  raw EMG  o f the p h a s i c  was determined  tonic  i n tandem w i t h the  the raw e x p i r a t o r y EMG a c t i v i t y  corresponded w i t h the b e g i n n i n g  Airflow  was  recorded  t o the p h a s i c  s t r a i g h t edge t o l i n e up the b e g i n n i n g measurement.  length  a  MP45,  (Figure 5).  pneumotachograph Medfield,  Mass.)  (Fleisch attached  #1)  and  t o the  d i s t a l end o f the tracheostomy tube and i n t e g r a t e d t o g i v e t i d a l volume. Volume was c a l i b r a t e d w i t h experiment.  a 3 liter  calibration  syringe p r i o r  I n s p i r a t o r y (Ti) and e x p i r a t o r y d u r a t i o n ( T ) were E  t o each  30  Figure  5: A r e p r e s e n t a t i v e r e c o r d i n g from an awake dog (lying i n left l a t e r a l decubitus) showing t r a n s v e r s u s abdominis (TA) l e n g t h changes and TA EMG a c t i v i t y . The arrows i n d i c a t e the r e s t i n g l e n g t h ( L R L ) o f the muscle and the downward d e f l e c t i o n o f the l e n g t h t r a c e a f t e r the arrow ( c o i n c i d i n g w i t h i n i t i a t i o n o f EMG a c t i v i t y ) i s a c t i v e , phasic shortening (%LRL) .  31  LLD  32  determined from the a i r f l o w t r a c i n g on the s t r i p Model  8000S)  using  a digitizing  device  chart recorder  (Sigma-Scan,  Jandel  (Gould,  Scientific,  C o r t e Madera, C A ) .  Protocol The s t u d y p e r i o d began immediately a f t e r while that  the dog was s t i l l time,  resting  anesthetized  lengths  of  all  w i t h the dog l y i n g i n the l e f t three  days  following  different,  They  included  to 8 weeks.  muscle  of  samples  after  the  and  breathing  of a  tube  EMG w i r e s respectively  stabilized,  study  i n the f o l l o w i n g  A day.  chapters.  loading  and C O 2  f o r each dog v a r i e d from two the dogs were  crystals  were  s t a i n e d by Masson's  each experiment,  topical (#7)  the  anesthetic  euthanized  performed.  trichome  jacket  (2%  were  i n the  connected  (Figure  6).  to  The  method and  c o n t r o l measurements  of  removed and  xylocaine),  tracheotomy.  lateral  the  When the  was  viscous  was i n s e r t e d through the  p l a c e d on a p l a t f o r m , p o s i t i o n e d  amplifiers,  length,  of  the  Two to  began.  on each  threshold  recorded  (N=8).  protocols  followed  study  were  At  microscope.  beginning  c u f f e d tracheostomy  crystal  awake  expiratory  containing  were s e c t i o n e d ,  application  dog was  the  p r o t o c o l was  duration of  muscle  examined under a l i g h t At  abdominal muscles  A t the end o f the awake p r o t o c o l s ,  and b i o p s i e s  the j a c k e t ) .  l a t e r a l decubitus p o s i t i o n  changes,  The t o t a l  implantation surgery,  f i t t i n g of  are d e s c r i b e d i n d e t a i l  postural  rebreathing.  the  instrumentation,  randomly a s s i g n e d  The v a r i o u s p r o t o c o l s  (before  the  a The  decubitus  and  sonomicrometer  and  dog  was  relaxed  abdominal muscle  and  resting  l e n g t h changes and EMG a c t i v i t y and t i d a l volume were made..  All  F i g u r e 6:  Example o f the e x p e r i m e n t a l setup w i t h the dog the l e f t l a t e r a l d e c u b i t u s p o s i t i o n .  lying  in  34  measurements were r e c o r d e d  on  an  e i g h t channel,  thermal  chart  recorder  (Gould, Model 8000S).  Analysis Paired lengths  of  T-tests  were  used  i n d i v i d u a l muscles  awake dogs. When comparisons the  different  level were  significance differed  of  i n the of  the  made  level  P<0.05 using  of  a  for  differences  in  resting  a n e s t h e t i z e d dogs compared amounts o f  was  tidal  accepted.  Tukey  P<0.05  s i g n i f i c a n t l y , log  the ANOVAS  test  to  shortening  abdominal muscles were made, a one-way ANOVA was  significance comparisons  to  Post-hoc  multiple  accepted.  comparison  When  transformations  of  the  data  with  the  dogs  among  used.  A  multiple  test  standard  the  and  a  deviations  were made  and  repeated.  RESULTS  Immediately  following  r e s t i n g muscle l e n g t h s position  (LLD).  To  measured i n the no LLD  lengths  (Table  I).  on muscle the  ranging two  (LRL) were r e c o r d e d  awake dogs two  of  the  12% To  i n the l e f t  to f o u r days a f t e r LLD  anesthetized  longer  explore  at  the  TA,  dogs  rest  effects  10  from  dogs two  to  (LLD  position)  e i g h t weeks.  to f o u r days o f i m p l a n t a t i o n  and  lateral  (P<0.05) of chronic  at  regular  There were  the  the  the  RA  was  anesthetized  dog  implantation of  muscle  were  LRL compared to  However,  in  decubitus  lengths  surgery.  E0  (N=8).  l e n g t h , measurements o f r e s t i n g  awake  anesthetized,  compare awake to a n e s t h e t i z e d , muscle  c o n s i s t e n t d i f f e r e n c e s i n the  approximately  in  implantation,  lengths  intervals,  crystals  were  repeated  over  periods  Length measurements o b t a i n e d (awake dogs) compared c l o s e l y  to  within those  35  made over a p e r i o d o f two weeks (Table I) one  dog.  The  measurement to 0.12,  coefficient  (over  0.01  of  variation  a two week p e r i o d ) ,  to 0 . 1 5 ,  0.03  and even a f t e r  to 0.13  of  each  resting  w i t h i n each dog,  and 0.04  to 0.21  e i g h t weeks  in  length  ranged from  0.05  f o r the TA, 10, EO  and RA, r e s p e c t i v e l y . The amount o f a c t i v e awake  dogs  essentially  ( L L Dposition) zero  o f mean a c t i v e not  occur  in  i n the  all  the  tidal was  of  day  2-4  anesthetized  muscles  or  9  on a t  the  in  dogs,  l e a s t one  performed.  to  all  mean,  log  EO or RA (P<0.05) within  each  over the whole  either  study p e r i o d .  (Table I ) .  the  dog v a r i e d  from  the  the  which e x h i b i t e d an i n c r e a s e  it.  the T A , 10 5 out o f 7  standard d e v i a t i o n  among the  different  transformations  of  muscles  the  data  one  tidal  However,  there  to  always  was no  each  the  next  present  consistent  o f v a r i a t i o n o f each measurement 2.4,  0 to  were  taken  the  of  i n t i d a l s h o r t e n i n g over  ranged from 0 to  and  difference  shortening  recording session  in  were  TA and 10 s h o r t e n e d more than  or a decrease  The c o e f f i c i e n t  dogs  the  (over  2.0  a  and 0  f o r the TA, 10 and EO, r e s p e c t i v e l y . At  muscle  of  Active shortening of  Since  from  shortening d i d  None  A c t i v e s h o r t e n i n g was not  two week p e r i o d ) , w i t h i n each dog, to 2.6  dogs.  The amount o f  study p e r i o d .  i n those muscles trend of  the  active  The t r a n s f o r m e d d a t a demonstrated a s i g n i f i c a n t  i n s h o r t e n i n g among the muscles:  muscle  that  the  The s m a l l amount  study day i n 9 out o f 9,  respectively.  the  significantly  (Table I ) .  fact  shortening d i f f e r e d s i g n i f i c a n t l y proportional  increased  dogs  s h o r t e n i n g o f the RA.  and EO was p r e s e n t 2 out  at  shortening r e f l e c t e d  exhibited active  and  s h o r t e n i n g (%LRL) o f the TA, 10 and EO i n  termination of  around the  the  experiments,  transducers  and f i x e d  biopsies  i n formalin.  from  These were  the then  36  sectioned,  stained  histologically. sonomicrometer  by  Two  Masson's  trichome  method  and  x - s e c t i o n s from an 10 muscle b i o p s y ,  transducers  i n place,  are  shown  f i x e d with  i n Figure  s e c t i o n s shown i n F i g u r e 7 are p e r p e n d i c u l a r to the p l a n e fibers thick.  and The  reveal that technique  the t r a n s d u c e r s  the  10  i n this  of bluntly  example was  7.  the  The  x-  o f the muscle  approximately  s e p a r a t i n g the muscle  i n the muscle caused  examined  5  cm  fibers  to p l a c e  some l o c a l i z e d damage, as  shown by  the p u r p l e c o l o u r e d a r e a o f f i b r o s i s j u s t below the t r a n s d u c e r p o c k e t  in  F i g u r e 7.  to  F u r t h e r muscle damage due  to the  t r a n s d u c e r s was  s m a l l c a p s u l e s o f f i b r o s i s immediately  surrounding  muscle  pockets  tissue  healthy tissue  between like  the  fibrotic  the t r a n s d u c e r s .  appeared  t h a t s t a i n e d r e d i n F i g u r e 7.  limited  to  S i n c e the  be  normal,  transducers  were p l a c e d w i t h t h e i r l e n s e s p e r p e n d i c u l a r to the muscle f i b e r s , in  the  around pairs  direction  i n which the f i b e r s  them d i d n o t of transducers.  interfere  ran,  the  thin  w i t h muscle f i b e r  capsule  The  of  facing  fibrosis  l e n g t h changes between  37  T a b l e I : R e s t i n g b a s e l i n e l e n g t h s (RL) o f the abdominal muscles in anesthetized compared to awake dogs and a c t i v e shortening (%LRL) in awake dogs (left lateral decubitus p o s i t i o n ) .  RL (mm) Anesthetized  RL (mm) Awake (d2-4)  TA  10  EO  RA  9.71  10.3  8.89  9.92  ±0.92  ±0.96  ±0.61  ±0.60  9.24  10.0  8.21  ±0.95  ±0.79  ±0.31  * 8.72 ±0.83  RL (mm) Awake (2 wks)  9.38  8.80  9.50  8.49  ±0.82  ±1.17  ±0.60  ±0.82  0.38%*  0.04%  0%  ±0.15**  ±0.03  *  %LRL  LLD Awake  0.71% ±0.16**  d2-4 = f i r s t measurements o f r e s t i n g l e n g t h (RL) i n awake dogs 2-4 days a f t e r s u r g e r y 2 wks = measurements o f RL i n awake dogs 2 weeks a f t e r ^surgery V a l u e s are means ± SE Asterisks (*) indicate significantly different from anesthetized (P<0.05). * * i n d i c a t e s l o g transformed d a t a s i g n i f i c a n t l y g r e a t e r than EO and RA ( P < 0 . 0 5 ) .  38  Figure  7: Two x - s e c t i o n s o f i n t e r n a l o b l i q u e muscle s t a i n e d w i t h Masson's trichome. The muscle b i o p s y had been f i x e d i n f o r m a l i n w i t h the sonomicrometer transducer i n p l a c e . E i g h t weeks p o s t i m p l a n t a t i o n . Diameter o f pocket i s e q u a l to t h a t o f t r a n s d u c e r ( 2 . 5 m m ) . The p u r p l e area o f f i b r o s i s below each c a p s u l e which had c o n t a i n e d the transducer i s a r e s u l t o f the s e p a r a t i o n o f the muscle f i b e r s to form the pocket f o r the t r a n s d u c e r . The t r a n s d u c e r s were p l a c e d with t h e i r l e n s e s p e r p e n d i c u l a r to the muscle f i b e r s , i e . f a c i n g i n the d i r e c t i o n i n which the f i b e r s r a n . The r e d s t a i n e d t i s s u e i s h e a l t h y muscle.  39  DISCUSSION This  study  implantation  examined  the  o f sonomicrometer  effects  of  transducers  anesthesia  and s h o r t e n i n g .  The r e s u l t s  effect  t h e r e s t i n g tone  o f the TA, 10 o r EO muscles  i n the  lengthening conclusively  awake  o f t h e RA  shortening  dog.  therefore,  discounted.  active shortening nor  suggest  p o s i t i o n , s i n c e the r e s t i n g lengths  different  In  that  of  a change  i n muscle  anesthesia  significantly  over  does n o t  i n the l a t e r a l  these  anesthesia  i n a l l f o u r abdominal muscles. changed  anesthesia  However,  contrast,  chronic  on abdominal muscle r e s t i n g  length  decubitus  and  muscles was n o t did result tone  in  c a n n o t be  appears  to  reduce  Neither r e s t i n g length  a  fifteen  i n d i c a t i n g t h a t sonomicrometry i s a u s e f u l technique  day  period,  t o measure i n v i v o  abdominal muscle l e n g t h changes i n c h r o n i c animal models. Anesthesia  the  response  depends on the type o f a n e s t h e t i c agent and may a l s o be s p e c i e s  specific  (15).  effects  I n the present  respiratory  study,  Anesthetic  muscle  r e l a x a t i o n v i a depression  include dogs  (17,19).  tone,  and dogs (17,19).  but  a r e thought  of spinal reflexes  t o induce  (9).  There  l o s s o f tone o f c h e s t w a l l  abdomen and diaphragm) muscles,  F o r example,  p a r t l y by muscle (15)  such as h a l o t h a n e  t h a t h a l o t h a n e causes r i b cage,  tone  the i n h a l a t i o n a n e s t h e t i c , halothane,  used.  evidence  agents  muscle  be  i n c r e a s e d d u r i n g halothane a n e s t h e s i a I n f a c t , diaphragm e n d - e x p i r a t o r y  man, s u g g e s t i n g  a b o l i s h e d by a n e s t h e s i a  a c t i v i t y was reduced w i t h  (15)  could and  c h e s t w a l l compliance, which i s determined  alone  (6).  that  i n humans  l e n g t h was t h e  same i n a n e s t h e t i z e d man compared to diaphragm e n d - e x p i r a t o r y paralysed-anesthetized  limb  i s also  (which  i n humans  was  diaphragm muscle  length i n tone may  Furthermore, diaphragm t o n i c EMG  i n d u c t i o n o f halothane a n e s t h e s i a  i n man  (9).  40  Consistent  with  anesthesia,  t h e r e was a decrease i n the a n t e r o p o s t e r i o r  in  the l a t e r a l  anteroposterior If  o f chest  wall  d i a m e t e r s b u t no change  t h e diaphragm  the present  i n the p r e s e n t  study,  halothane  on TA, 10 o r EO muscle  lengthening  o f t h e RA.  h a l o t h a n e has no e f f e c t resting  tone  i s not present  possible  lengthening  t o determine  o f t h e RA r e f l e c t s  muscle  lengths  one might  anesthesia lengths  these r e s u l t s  h a d no  a  length  consistent  but resulted  ina  suggest e i t h e r  that  tone o r t h a t  i n the q u i e t l y  results  difference  It is  whether  the  i n the e f f e c t o f  I t may be t h a t i n dogs,  coupled  breathing  decubitus p o s i t i o n .  the present  an a c t u a l  a r e n o t as t i g h t l y  predict  position.  lateral  a n e s t h e t i c on the d i f f e r e n t muscles.  (21,22).  diameters  The change i n r e s t i n g  i n those muscles  from  i n supine  an increase i n  on TA, 10 and EO abdominal muscle  awake dog, a t l e a s t n o t i n the l e f t not  and an i n c r e a s e  and abdomen,  study,  resting  Therefore,  halothane  tone, o r r e d u c e d tone and hence  would be dependent t o some degree on body  effect  during  i n lateral  change i n abdominal muscle r e s t i n g l e n g t h .  In  tone  and, i n the l a t e r a l d e c u b i t u s p o s i t i o n ,  a n e s t h e s i a r e d u c e d abdominal muscle  lengthened  muscle  d i a m e t e r s o f b o t h the r i b cage  (21,22)  subjects  loss  abdominal  t o l u n g volume change  below  FRC as they a r e above FRC (8) o r there may have been a l o s s o f abdominal muscle  tone  i n the a n e s t h e t i z e d  dog which was n o t apparent because o f  the dog's p o s i t i o n . I n the l a t e r a l d e c u b i t u s p o s i t i o n , muscle tone posterior the  diameter o f the abdomen (21,22)  abdominal  muscles position  might be expected t o r e s u l t  muscles,  (EO and RA) .  but particularly  l o s s o f abdominal  i n an i n c r e a s e and thus,  lengthening o f a l l  t h e more v e r t i c a l l y  The RA however, due t o i t s f i b e r  i n the midline  o f the a n t e r i o r  i n the antero-  abdominal w a l l  oriented  o r i e n t a t i o n and would  be most  41  a f f e c t e d by outward displacement most, as was found. during  anesthesia  decrease  o f the a n t e r i o r w a l l and would  The f i n d i n g  compared  t h a t the RA was s i g n i f i c a n t l y  t o the awake  state,  i n RA muscle tone d u r i n g a n e s t h e s i a .  a c t i v i t y was p r e s e n t and EO as w e l l . wakefulness,  lengthen  suggests  longer  there  was. a  I t follows that i f tonic  i n the RA, i t would l i k e l y be p r e s e n t  i n the TA, 10  O v e r a l l , t h e r e may simply be more tone i n the RA d u r i n g  o r the p a s s i v e  r e l a x a t i o n o f tone  i n a l l the abdominal  muscles was m a n i f e s t most i n the RA. There does n o t appear t o be any o t h e r muscle  resting  length  However, a study diaphragm  o f the e f f e c t s  resting  length  diaphragm ( l a t e r a l dog  i n a n e s t h e t i z e d dogs  the  tone  during  diaphragm. showed  a  anesthesia  Furthermore, decrease  in  FRC  resting  length  p o s i t i o n ) t o be l o n g e r  compared t o the awake dog (4).  muscle  i s compared  abdominal  t o awake  dogs.  o f p e n t o b a r b i t a l sodium a n e s t h e s i a  found  decubitus  s t u d i e s i n which  was  during (19)  the  that a reduction i n  f o r lengthening  halothane  anesthesia,  presumably  in  crural  i n the a n e s t h e t i z e d  I t was concluded responsible  of  o f the  supine  conjunction  dogs  with  l e n g t h e n i n g o f the diaphragm, perhaps as a r e s u l t o f a l o s s i n tone. the  lateral  crural  position  diaphragm  (as i n the p r e s e n t  might  lead  to a  study),  slight  muscles  on the dependent  result  of  gravitational  s i d e would forces.  In  measurements were made on the nondependent  side  the dependent s i d e f o r the EO and RA and except no  significant  shortening  o f the  likely  this  the abdominal  to lengthen  study,  resting  (Table I ) .  Therefore,  as a length  f o r the TA and 10 and f o r the RA,  d i f f e r e n c e s between the a n e s t h e t i z e d l e n g t h s  the awake l e n g t h s  In  o f the  Conversely,  be more  a  lengthening  passive  abdominal muscles on the nondependent s i d e .  on  the p r e s e n t  t h e r e were compared t o  study does n o t show  42  convincing  evidence  of a  anesthesia  i n the l a t e r a l  f a c t o r , s i n c e although  decrease decubitus  than  tone  The p o s i t i o n  may be a  (4),  (19),  dogs  In addition, lengthening  t o l o s s o f diaphragm tone) o c c u r r e d  anesthesia  with  which may have  different  during effects  halothane. All  t h e abdominal  shortening  muscles  i n the awake  than  showed  compared  s h o r t e n i n g was n e g l i g i b l e  (LLD  internal  (8,12)  dogs  abdominal  external  muscles.  activity  at rest  than one p e r c e n t and EO  than  these  (8).  differed  elastic  recoil)  active  shortening  anesthetized  of active  dog, i n which  supporting active  reports  from  the h y p o t h e s i s i n breathing  more  supine, that the  than  had s i g n i f i c a n t l y  the  greater  the EO o r RA, the amount o f s h o r t e n i n g was l e s s  than  that  The amount o f s h o r t e n i n g i n the  reported  i n some  studies  b u t g r e a t e r than t h a t observed of active shortening  of  supine,  by L e e v e r s and reported  among  s t u d i e s c o u l d be due t o f a c t o r s such as d i f f e r e n c e s i n  measurement technique shortening  previous  the TA and 10  V a r i a t i o n i n degree  previous  amount  The TA and 10 s h o r t e n e d  with  o f the r e s t i n g l e n g t h .  i s less  greater  t o the a n e s t h e t i z e d  a r e more  Although  a n e s t h e t i z e d dogs (12,13), Road  and thus,  muscles  a  position).  t h e EO o r RA, i n agreement  anesthetized  TA  diaphragm  i n FRC i n supine  i n prone dogs (17).  o f t h e diaphragm ( a t t r i b u t e d sodium  position.  t h e r e was a decrease  no change i n FRC was found  pentobarbital  i n FRC o r  or l e v e l of anesthesia.  between the s t u d i e s , i n t h a t b o t h  and a c t i v e  dogs  The methods f o r measuring  in  (EMG p r e s e n t )  the  (12,13).  studies This  shortening  reporting  measurement  passive were  more  technique  (due  to  i n c l u d e d as  shortening would  in  lead to  r e p o r t s o f a g r e a t e r amount o f s h o r t e n i n g than one i n which j u s t a c t i v e (EMG)  shortening  was measured  (8).  In addition, b a r b i t u a t e s ,  such as  43  pentobarbital activation sodium  i n a dose  anesthesia  expiratory "lightly  resting  appear related  resulted  abdominal  of  the  TA  at  disparity (12,13)  reflects  between  the  a  reduce (15).  manner  dose  activity  supine  abdominal muscle  perhaps  to  in a  nerve  anesthetized"  shortening  (8),  sodium,  was  difference of  supine  i n position.  i n the  posture  i s not  a  level  shortening  Unlike  the  natural  study may  f o r the dog  muscle  activity  underestimated  i n comparison  upper  is  airway  thought  to  to  a  tracheostomy,  the  phasic,  reports  of  reports  and  that  no  preparation  of anesthesia.  The  anesthetized  dogs  a l s o have been due a  and  posture, may  the  therefore,  l e v e l s or p a t t e r n s .  i n the p r e s e n t  study may  have  been  awake n o n - t r a c h e o s t o m i z e d dogs.  produce  expiratory  c o n t r i b u t e to abdominal muscle a c t i v a t i o n through  in  activity  decubitus  r e s u l t i n d i f f e r e n t abdominal muscle r e c r u i t m e n t Abdominal  to  i n the  lateral  one  EMG  found i n a s i m i l a r  and the awake dogs i n the p r e s e n t  difference  Thus,  phasic  i n contrast  shortening  amount  with  muscle  pentobarbital  reduction  (5).  i n cats  (12),  abdominal  For example,  dependent  dogs  rest  phasic,  upper  (16).  braking  Since  airway was  and  The hence  the dogs b r e a t h e d  bypassed  and  expiratory  b r a k i n g may have been reduced. At  two  ( T a b l e 1). which  weeks,  Alternatively,  surgery.  effects  of chronic  implantation  were  There c o u l d have been s c a r r i n g (as a f o r e i g n body  would  operative  the  have  changed  shortening  period  because  However, c h r o n i c  muscle  might have of  reflex  resting  length  and  studied  reaction)  shortening.  i n c r e a s e d from the immediate  consequent  to  i m p l a n t a t i o n o f sonomicrometer t r a n s d u c e r s  in  the abdominal muscles d i d n o t e f f e c t  inhibitory  effects  post-  abdominal muscle r e s t i n g l e n g t h o r  s h o r t e n i n g over the two week e x p e r i m e n t a l  period.  These r e s u l t s  differ  44  from  previous  diaphragm tidal  reports  (1,20).  gradually  day  chronic  sheep  were 28  increased  However, was  In  shortening  postoperative  of  (20), on  and  dogs  and  in  not  due  and a thoracotomy  a  activity  abdominal  muscle  decrease  in  in  via  a  but  three  weeks  of  the  length  and  compared  tidal  after  resting had  an  study,  implantation  implantation.  or  studies of  the  in  damage the  laparotomy  could  per  muscle In  se  tissue.  did  not  method f o r  the  measuring  c h r o n i c animal models.  require  would not  a be  acute  i m p a i r diaphragm  (10).  Therefore,  not  thin  in  However,  effect  the  abdominal  muscle  sections  fibrotic  capsules  Similar findings  conclusion,  a  the  Examination of revealed  in  transducers  result.  does  effect  (3).  activity  damage  to  EO EMG a c t i v i t y  the  which  (1)  effect  resulting  diaphragm d i d not  transducers,  (1).  in  the  i n h i b i t i o n of  shown  dogs,  of  approach  shortening.  a useful  changes i n l o n g - t e r m ,  a  been  on abdominal muscle  implantation  of healthy  is  increase  some l o c a l muscle f i b e r  diaphragm  sonomicrometry  or  tissue  length  also  to  shortening  implantation  procedure:  change  effects  contained  between areas  surgical  superficial  that  of  anesthetized  transducers  suggest  effect  in  minor  shortening despite  the  diaphragm  Laparotomy has  no  similar  implantation  for  one  I t was more l i k e l y a r e f l e x  activation  present  was  expected,  which  day  in  s i n c e both procedures have been shown to  (3).  TA b u t  the  laparotomy,  muscle  (1),  direct  from the  (20),  diaphragm  results  diaphragm r e s t i n g  postoperative  stabilized  to  diaphragm r e s u l t i n g  muscles  implantation  the diaphragm d y s f u n c t i o n which o c c u r r e d i n b o t h t h e s e  probably  Since  both  reduced  t r a n s d u c e r s on the diaphragm. the  sonomicrometer  results in vivo  were  reported  indicate muscle  that length  45  REFERENCES 1.  E a s t o n , P . A . , J . W . F i t t i n g , R. Arnoux, A . Gueraty and A . G r a s s i n o . Recovery o f diaphragm f u n c t i o n a f t e r laparotomy and c h r o n i c sonomicrometer i m p l a n t a t i o n . J . A p p l . P h v s i o l . 6 6 ( 2 ) : 613-621, 1989.  2.  F a r k a s , G . A . , R . E . B a e r , M. Estenne and A . De T r o y e r . M e c h a n i c a l r o l e o f e x p i r a t o r y muscles d u r i n g b r e a t h i n g i n u p r i g h t dogs. J . A p p l . P h v s i o l . 6 4 ( 3 ) : 1060-1067, 1988.  3.  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Ninane, V . , J . J . G i l m a r t i n and A . De T r o y e r . Changes i n abdominal muscle l e n g t h d u r i n g b r e a t h i n g i n supine dogs. R e s p i r . P h v s i o l . 73: 31-42, 1988.  13.  O l i v e n , A . and S . G . K e l s e n . E f f e c t o f h y p e r c a p n i a and PEEP on e x p i r a t o r y muscle EMG and s h o r t e n i n g . J . A p p l . P h y s i o l . 6 6 ( 3 ) : 1413, 1989.  14.  P a v l i n , E . G . , and T . F . H o r n b e i n . A n e s t h e s i a  and the c o n t r o l  of  1408-  46  v e n t i l a t i o n . I n : Handbook o f P h y s i o l o g y S e c t i o n 3 : The R e s p i r a t o r y System. V o l . I I I . P . T . Macklem, and J . Mead (eds). Williams & W i l k i n s , B a l t i m o r e , MD, 1 9 8 6 , 15.  Rehder, K . , and H . M . Marsh. R e s p i r a t o r y mechanics d u r i n g a n e s t h e s i a and m e c h a n i c a l v e n t i l a t i o n . In: Handbook o f P h y s i o l o g y S e c t i o n 3 : The R e s p i r a t o r y System. 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K i m b a l l , J . Q v i s t , e t a l . Sonomicrometric r e g i o n a l d i a p h r a g m a t i c s h o r t e n i n g i n awake sheep a f t e r t h o r a c i c s u r g e r y . J . Appl.  21.  Phvsiol.  67(6):  2357-2368,  1989.  V e l l o d y , V . P . , M. N a s s e r y , K. B a l a s a r a w a t h i , N . B . G o l d b e r g and J . T . S h a r p . Compliances o f human r i b cage and diaphragm-abdomen pathways i n r e l a x e d v e r s u s p a r a l y s e d s t a t e s . Am. Rev. R e s p i r . P i s . 1 1 8 : 4 7 9 491,  22.  1980.  1978.  ,  V e l l o d y , V . P . , M. N a s s e r y , W.S. Pruz and J . T . Sharp. E f f e c t s o f body p o s i t i o n change on thoracoabdominal m o t i o n . J . A p p l . P h y s i o l . 4 5 : 581-589,  1978.  47  I I I . EFFECTS OF POSTURE ON ABDOMINAL MUSCLE LENGTHS  INTRODUCTION The  f o u r muscles o f the v e n t r a l abdominal w a l l (TA,  10, EO and RA)  are thought t o be the p r i m a r y c o n t r i b u t o r s t o e x p i r a t i o n and the of  l u n g volume. I t has been suggested t h a t  activation diaphragm increase  i n upright (17)  length  i n passive  (14,16).  postures and a l s o  to  tidal  anesthetized  dogs  o f the chest  increases  from  FRC (13),  inspiration  supine  muscle  optimize  by p r o d u c i n g  an  wall a t end-expiration  i s i n d i r e c t evidence  volume  a r e moved  i n c r e a s i n g abdominal  to maintain  assists  outward r e c o i l  I n a d d i t i o n , there  contribution  helps  defence  to  t h a t abdominal muscle more  to upright  than  50%  (14).  when  Increased  abdominal muscle a c t i v a t i o n f o l l o w i n g assumption o f u p r i g h t p o s t u r e s i s thought  t o be mediated  segmental r e f l e x e s (6) The  abdominal  by v a g a l  reflexes  muscles  e x h i b i t both  i n upright postures  (9,18)  dogs  expiratory  abdominal  electromyography pressure  (5,17)  and abdominal  muscle  due t o g r a v i t a t i o n a l e f f e c t s on the c h e s t w a l l .  expiratory a c t i v i t y and awake  (9,13)  (8,17).  muscle  (8,9,18)  activity  diameters  tonic  i n man (7,11)  However,  or i n d i r e c t l y  o r abdominal  increased  both  were via  and p h a s i c ,  and a n e s t h e t i z e d  tonic  and  generally  assessed  measurements  (11).  A  phasic, by  of gastric  limitation  o f these  methods i s t h a t they do not a l l o w i n t e r p r e t a t i o n o f m e c h a n i c a l events i n terms o f abdominal muscle r e s t i n g l e n g t h and s h o r t e n i n g .  In particular,  abdominal  muscle  by  activity,  since  tonic tonic  activity  EMG a c t i v i t y  i s poorly  described  i s measured  by i n f e r e n c e  degree o f background n o i s e . I n a d d i t i o n , a l t h o u g h described  by  t h e EMG,  increases  i n phasic  t o n i c EMG from the  p h a s i c a c t i v i t y may be  EMG a c t i v i t y  w i l l not  48  necessarily  produce i n c r e a s e d t i d a l l e n g t h changes because the amount o f  shortening afterload  will on  be  the  influenced  muscle.  by  the  Indeed,  abdominal  postures.  F u r t h e r m o r e , abdominal muscle  in  tonic  i n the  activity  might  l e n g t h as a r e s u l t effects  of  length  and  dogs.  The use  afterload  gravitational be  initial  gravitational  increase  orientation  muscle  muscle's  and  field  forces  initial  tonic  activity  is  by  a decrease  in  has  differentially  been  previously  sonomicrometry p r o v i d e s  abdominal muscle r e s t i n g Analysis  not  of  reveals  that  relationships  to the  orientations  compartment differential active,  of  as w e l l each  muscle.  However,  the  mechanical  in  vivo  muscles  differential  and to  are  attachments  the abdominal  consequences  of  r e c r u i t m e n t i n terms o f abdominal muscle r e s t i n g l e n g t h and  hypothesized  phasic  expiratory  fours)  (STAND) p o s i t i o n s  on  the d i f f e r e n t  awake  e x p i r a t o r y s h o r t e n i n g have not been p r e v i o u s l y r e p o r t e d . We  that  as  in  (3,19,23).  This  r e c r u i t m e n t may be r e l a t e d to the d i s t i n c t  the  (initial)  measure  abdominal  (8,18).  muscle  However,  investigated  the  r e c r u i t e d i n upright postures  r i b cage,  initial  l e n g t h and t i d a l l e n g t h changes  EMG d a t a  by  An i n c r e a s e  resting  a method to  to  upright  influenced  o f a c t i v a t i o n o f muscle p r o p r i o c e p t o r s .  shortening  the  tend  in  and hence p o s t u r e .  reflected  and  would  length  changing body p o s i t i o n on abdominal muscle  of  length  the  resting  individual  abdominal  wall  hypothesized  lengths  abdominal and  that  be more a c t i v e  activity  the  that  the  in  the  abdominal sitting  compared to the i n the muscle  relative  (SIT)  orientation,  contribution  to  external  muscle  layer  show  and s t a n d i n g  positions  i n t e r n a l abdominal muscle  than the  would  l a t e r a l decubitus  different fiber  muscles  layer  (on  all  position  and  would be  dependent  position  breathing.  We  (TA and 10)  (EO and R A ) .  more  in  the  further would  Therefore,  49  the  objectives  phasic  and  of  tonic  this  study were  muscle  measuring s h o r t e n i n g  to  activity  and r e s t i n g  of  assess  the  effects  individual  length  of  posture  on  abdominal  muscles  by  in different  postures  in  awake  dogs.  METHODS Five tracheotomized, w i t h sonomicrometer  female mongrel dogs were s u r g i c a l l y i m p l a n t e d  t r a n s d u c e r s and f i n e w i r e  the f o u r abdominal muscles  EMG e l e c t r o d e s  as d e s c r i b e d i n Chapter I I  i n each  of  (Figure 4 ) .  Mea surement s Abdominal muscle r e s t i n g l e n g t h s and s h o r t e n i n g were measured w i t h the  sonomicrometer  transducers  Chapter I I ,  the  either  end-expiratory  the  shortening  was  resting  of  dog's p o s i t i o n ,  the  front  (STAND). positions  was  resting  was  expressed in  or  the  and was  length,  that  As  if  no  active,  described was  immediately  termed LRL(LLD),  The t h r e e  sitting  (SIT)  as  a percent  lengthening  a percentage  position.  change  preceding  change  Active  c o i n c i d i n g w i t h raw e x p i r a t o r y EMG  from the  shortening activity.  active,  regardless  positions  on a l l  studied  was  during t i d a l initial  four  legs  Change from breathing,  resting  determined  with  SIT o r STAND  from LLD L R L .  or s h o r t e n i n g ,  as  (phasic)  on the r e a r haunches  and s t a n d i n g  in  defined  expiratory  i n LRL between the LLD p o s i t i o n and the  expressed  as  II).  abdominal muscles  length  and c h e s t v e r t i c a l  The change  the  (%LRL)  length,  l a t e r a l decubitus  legs  the  Chapter  ( p l a t e a u i n d i c a t e d by arrows i n F i g u r e 8 ) ,  shortening  were the l e f t  length of  present,  phasic the  (see  to  length be  that  50  Figure  8: A r e p r e s e n t a t i v e r e c o r d i n g from an awake dog l y i n g i n l e f t l a t e r a l d e c u b i t u s p o s i t i o n (top p a n e l ) and s t a n d i n g on a l l f o u r s (bottom p a n e l ) showing t r a n s v e r s u s abdominis (TA) l e n g t h changes and TA EMG a c t i v i t y . The arrows i n d i c a t e the r e s t i n g l e n g t h (LRL) o f the muscle and the downward d e f l e c t i o n o f the l e n g t h t r a c e a f t e r the arrow ( c o i n c i d i n g w i t h i n i t i a t i o n o f EMG a c t i v i t y ) i s a c t i v e , p h a s i c s h o r t e n i n g (%LRL) . The LRL i n the s t a n d i n g p o s i t i o n i s 26% s h o r t e r than LRL i n the L L D p o s i t i o n . Note the background EMG a c t i v i t y i n the s t a n d i n g position, perhaps r e f l e c t i n g t o n i c EMG a c t i v i t y (bottom p a n e l ) .  5  sec.  52  The  electromyographic  signals  from  the  implanted  fine  e l e c t r o d e s were a m p l i f i e d and f i l t e r e d below 30Hz and above lKHz model  P511).  muscle  The  EMG s i g n a l s  was  measured  were  recorded  in  pairs  with  wire (Grass,  abdominal  length. Airflow  pressure to the  transducer  distal  volume.  (±lcmH 0,  end o f  the  flow  (Sigma-Scan,  pneumotachograph  tracheostomy  (Ti)  tracing  a  V a l i d y n e MP45,  2  Inspiratory  from the  with  chart  Jandel S c i e n t i f i c ,  Medfield,  duration  and  attached  to g i v e  ( T E ) were  recorder using  #1)  Mass.)  tube and i n t e g r a t e d  and e x p i r a t o r y  on the  (Fleisch  tidal  determined  a digitizing  device  C o r t e Madera, C A ) .  Protocol Each dog was testing  for  each  randomly a s s i g n e d protocols C0  2  studied dog  included  in  postural  detail  tube  (#7)  platform,  the  the  positioned  tidal  position  relaxed  and  of  to  eight  expiratory  threshold  loading  following  each  awake  i n the  were made.  length,  and C 0  The v a r i o u s loading  and  rebreathing  are  The  protocol  for  a  tracheostomy  The dog was p l a c e d on a  respectively.  control  changes  then  cuffed  and c r y s t a l and EMG w i r e s  stabilized,  stabilized,  different,  chapter.  protocol,  length  2  duration of A  threshold  and a m p l i f i e r s ,  The dog was  breathing  weeks.  chapters.  l a t e r a l decubitus  and b r e a t h i n g  total  on each study day.  through the tracheotomy.  resting  once  two  followed  to the sonomicrometer  muscle  volume  the  times and the  d e s c r i b e d i n the p r e s e n t  was i n s e r t e d  dog was  abdominal  in  beginning  were connected  from  changes,  Expiratory  p o s t u r a l changes i s At  varied  p r o t o c o l was  rebreathing.  described  a number o f  and  moved to  measurements  When  measurements EMG a c t i v i t y  the  SIT or  were  of and  STAND  repeated.  53  Tidal  volume and t i m i n g parameters i n a l l t h r e e  from o n l y position  three  dogs,  due to  dislodging of  positions  the  were  obtained  pneumotachograph d u r i n g  changes.  Analysis Measurements  of  abdominal muscle  tidal  shortening  over f i v e b r e a t h s f o r each p o s i t i o n ,  f o r each t r i a l  Individual  all  averaged  muscle  shortening  and t h e n  each p o s i t i o n ,  the  from  mean t i d a l  was d e r i v e d .  To t e s t  performed.  differences  in  A the  abdominal m u s c l e s , accepted. multiple  amount  ANOVA of  Post  hoc  comparison  multiple test.  also  i n the  the  were  made  of  for  different  o f P<0.05 was using  a  deviations  Tukey  in  the  the mean,  t r a n s f o r m a t i o n s o f the data were made and the ANOVAs r e p e a t e d .  lengths.  A  randomly, change resting  shift  in  i n the LLD p o s i t i o n were used as the  the  b u t the change  when moving from  dog's  LLD to  length with s h i f t  position,  for  all  the  position  to  SIT  or  i n r e s t i n g l e n g t h was always SIT or  in position  was determined f o r each t r i a l ,  LLD to  and the average  trials,  was  t i m i n g parameters were  also  was  for  made  The change  SIT o r LLD to  change  calculated  reference  c a l c u l a t e d as  STAND.  from LLD to  STAND  i n LRL w i t h each  the mean change i n LRL p e r p o s i t i o n change was d e t e r m i n e d . and  test  the  level  standard  in  amounts  to  among  A significance  When  was  a one-way ANOVA  performed  shortening  comparisons  dog  abdominal m u s c l e ,  three p o s i t i o n s , was  each  s i g n i f i c a n t l y d i f f e r e n t and p r o p o r t i o n a l to  The r e s t i n g l e n g t h s  in  for  for differences  tidal  i n each p o s i t i o n .  measurements were log  one-way  per  averaged  o f p o s t u r a l changes.  trials  shortening  abdominal muscle t i d a l shortening i n the was  the  were  the in  STAND shift  dog and  then  Tidal  volume  compared between LLD and S I T ,  and LLD  54  and  STAND i n t h r e e  dogs.  STAND were made u s i n g  Comparisons between LLD and S I T , and LLD and  the  Student's  T-test  and a s i g n i f i c a n c e  level  of  P<0.05.  RESULTS Both muscles,  phasic  tonic  r e f l e c t e d by degree  resting length i n posture. are  and  respiratory of active  (LRL) r e s p e c t i v e l y ,  The  effects  activity  shortening  of  the  (%LRL)  and changes  shortening of  in  were a f f e c t e d by movement and changes  o f moving from LLD to  STAND on TA %LRL and LRL  demonstrated by a t y p i c a l t r a c i n g shown i n F i g u r e 8.  tidal  abdominal  each muscle v a r i e d between t r i a l s .  The amount o f However,  there  was no c o n s i s t e n t  change over the d u r a t i o n o f each study p e r i o d and the  abdominal muscles  a l l showed the same t r e n d from one t r i a l  that i s ,  shortening either  to the  next:  i n c r e a s e d o r decreased i n a l l the muscles  which s h o r t e n i n g was p r e s e n t ) .  Active,  (in  e x p i r a t o r y s h o r t e n i n g i n each o f  the abdominal muscles except the RA was s i g n i f i c a n t l y g r e a t e r i n the SIT and STAND p o s i t i o n s  The c o e f f i c i e n t  of  v a r i a t i o n i n s h o r t e n i n g p e r muscle, w i t h i n each dog, ranged from 0.4  to  2.4,  0.07  to 2.0 TA,  to 2.0  compared to the LLD ( F i g u r e 9 ) .  and 0 to 2.5  i n the L L D , from 0 to 1.4,  i n SIT and from 0 to 0 . 6 ,  10 and E0, r e s p e c t i v e l y .  position, postures  and 0  i n STAND f o r  The RA showed no p h a s i c  activity  the  i n any  shortening i n a l l  three  than the E0 ( F i g u r e 9 ) .  from  were the  changes  a  longer  in  LLD p o s i t i o n  ( F i g u r e s 10 and 11) . changes;  and 0 to 2.0  and the TA and 10 had g r e a t e r a c t i v e  There moving  0 to 1.1  0 to 1.1  the to  resting either  length the  SIT  The TA was most c o n s i s t e n t l y  resting  length  of or  each  muscle  STAND  effected  when moving from LLD to  when  positions  by p o s i t i o n the  sitting  Figure  9: Bar graph showing a c t i v e s h o r t e n i n g o f the T A , 10 and EO i n the l e f t l a t e r a l d e c u b i t u s ( L L D ) , sitting (SIT) and s t a n d i n g (STAND) p o s t u r e s . The s h o r t e n i n g i s e x p r e s s e d as a percentage o f the r e s t i n g l e n g t h i n each p o s i t i o n . A s t e r i s k s (*) i n d i c a t e s i g n i f i c a n t l y l e s s s h o r t e n i n g o f EO than TA and 10 i n a l l three p o s i t i o n s (P<0.05). N=5.  56  p o s i t i o n and a s h o r t e r The  other  postural  three  change  muscles however,  Moving from LLD to 5 dogs  ( 1 5 to  had  shorter  a  length (4.7  to  22.5%)  ( 1 4 to  STAND,  their  consistent  3/5  (.9  to  8.6%) and  resting  length  resting  in  two  i n 3 out  of  5%); the EO  longer  resting  resting  length  (12.6%).  i n 3 out o f ( 6 to  dog.  7.6%);  3/5  Moving  5 dogs the  (4  EO a  25.8%)  to  length  a significantly  5 ( 4 to 24.6%)  each  to  ( 3 % ) ; and the RA a l o n g e r r e s t i n g l e n g t h i n 4 o f 5 ( 1 . 7 to resting  i n 4 of  length  a  i n one dog  1 0 a longer r e s t i n g length  shorter  within  i n 2 / 5 ( 3 to  2 5 % ) ; and the RA had a s h o r t e r  the  responses  length  was  i n one  longer  to LLD ( l e n g t h e n e d by 9 . 2 ± 4 . 6 % Tidal positions  volume  were  three  compared  but  duration  duration to  significantly  The mean change  i n the  T  measurements  and were  Inspiratory  different in  in  STAND).  the  i n EO LRL  s t a n d i n g p o s i t i o n compared  (mean ± S E ) ) .  VT was  (Ti)  (TI/T OT)  LLD.  SIT and 2 2 1 ± 1 2  length  in  There was no d i f f e r e n c e  positions  inspiratory  (15.7%).  and t i m i n g parameters measured i n the  compared to  dogs ( T a b l e I I ) .  in  in  standing.  and s h o r t e r r e s t i n g  shorter  breath  variable  1 0 had a s h o r t e r r e s t i n g l e n g t h  and a l o n g e r  and a  and  the  more  changes were  length  longer r e s t i n g length i n one  the  S I T , the  resting  12.3%)  from LLD to  were  25%) and a l o n g e r r e s t i n g l e n g t h  in 2/5  to  r e s t i n g l e n g t h when moving from LLD to  the  significantly  three  as  in  three E  inspiratory  drive  LLD p o s i t i o n ,  i n e x p i r a t o r y d u r a t i o n (T )  significantly  the  SIT and STAND  greater  in  STAND  fraction  of  the  total  and  STAND  greater  in  SIT  reflected  by  V /Ti  positions  in  (256±17  T  was  and  not  i n LLD, 2 5 4 ± 1 0  SIT 30  r  TA  Q 20  io RA  10  -10  -20  -30  Figure  10: Box p l o t s o f the change i n r e s t i n g l e n g t h (LRL) w i t h s h i f t i n p o s t u r e from l e f t l a t e r a l d e c u b i t u s ( L L D ) to s i t t i n g ( S I T ) . The l e n g t h i s expressed as a p e r c e n t o f the L L D l e n g t h (100%). The boxes are the 95% c o n f i d e n c e interval, vertical lines indicate the range and h o r i z o n t a l l i n e s are the mean. A s t e r i s k s (*) indicate s i g n i f i c a n t l y d i f f e r e n t from L L D LRL ( P < 0 . 0 5 ) . N=5.  58  Figure  11: Box p l o t s o f the change i n r e s t i n g l e n g t h (LRL) w i t h s h i f t i n p o s t u r e from l e f t l a t e r a l d e c u b i t u s (LLD) to s t a n d i n g (STAND). The l e n g t h i s expressed as a p e r c e n t o f the LLD l e n g t h ( 1 0 0 % ) . The boxes are the 95% c o n f i d e n c e interval, vertical lines indicate the range and h o r i z o n t a l l i n e s are the mean. A s t e r i s k s (*) indicate s i g n i f i c a n t l y d i f f e r e n t from LLD LRL ( P < 0 . 0 5 ) . N = 5 .  59  T a b l e I I : T i d a l volume and t i m i n g parameters  Position  i n three  postures.  LLD  SIT  Ti(secs)  1.251.02  1.4711.0*  T (secs)  3.331.35  2.751.04  2.751.15  TI/TIOT  0.281.02  0.351.02*  0.391.01*  V (mls)  297125  E  T  Asterisks N-3.  (*)  indicate  348126  significantly  different  STAND  1.671.06*  374114*  from LLD ( P < 0 . 0 5 ) .  60  DISCUSSION The  results  expiratory  this  shortening  (STAND) p o s i t i o n s , addition,  of  is  study  show  greater  in  that  the  abdominal  sitting  (SIT)  compared to the l a t e r a l d e c u b i t u s ,  the r e s u l t s  s u p p o r t the h y p o t h e s i s  muscle l a y e r ( t r a n s v e r s u s  muscle and  active standing  i n awake dogs.  In  t h a t the i n t e r n a l abdominal  abdominis and i n t e r n a l o b l i q u e )  i s more a c t i v e  i n b r e a t h i n g than the e x t e r n a l muscle l a y e r ( e x t e r n a l o b l i q u e and r e c t u s abdominis).  Furthermore,  transversus STAND  abdominis  suggests  importance  of  an  the c o n s i s t e n t  (TA) to increase  the  TA  in  change i n r e s t i n g l e n g t h o f  the  a s h o r t e r l e n g t h when moving from LLD to in  tonic  defending  activity  and  end-expiratory  indicates,  lung  the  volume  and  m a i n t a i n i n g diaphragm l e n g t h . The postures have  three  positions  f o r awake dogs.  used  similar  examined  Other s t u d i e s  SIT  and  STAND  p o s i t i o n was prone i n one  study  other  LLD i n  (17),  changes  compared  i n studies  to  of  or  shifting  (16).  from the  in  decubitus  present  of postural effects whereas  anesthetized is  dogs close  this  study.  dogs  In  generally  (14,20,24)  thus,  LLD i s  a reasonable  awake  dogs  is  similar  to  dogs,  and  the  sitting  and  i n awake dogs the  reference  contrast, involve  standing  the  postural  or headdown p o s i t i o n s  (24)  diaphragm  position.  tilted  in  from  o r prone-suspended of  anesthetized  However,  length  in  supine FRC diaphragm l e n g t h  reference the  natural  tilting  u t i l i z e d i n studies  that to  are  and r i g h t l a t e r a l d e c u b i t u s  and man makes comparisons d i f f i c u l t .  position  study  supine to p r o n e - c r a d l e d (21,24)  The v a r i e t y o f p o s t u r e s  awake dogs, shown  the headup  the  positions,  (8)  anesthetized  the supine p o s i t i o n to  in  headup positions  The s i t t i n g position in  man.  in  it the  has  and been  lateral  (21,24) position  and in  anesthetized The  standing  61  p o s i t i o n of  awake dogs approximates  dogs and man, to some degree,  the prone p o s i t i o n s  o f the p e l v i s  abdominal muscle l e n g t h and a c t i v a t i o n .  i n posture  among the v a r i o u s s t u d i e s makes comparisons  awake  dogs  would  the  sitting  increase  c o n t e n t s and hence,  (SIT)  the  effect  Although  and s t a n d i n g  gravitational  girdle  differences  difficult,  (STAND)  effects  chest  In a d d i t i o n ,  and s h o u l d e r  may e f f e c t  both  on the  l i k e l y be g r e a t e r .  c o n t r a c t i o n o f the s t a b i l i z i n g muscles  that  anesthetized  but the g r a v i t a t i o n a l e f f e c t s  w a l l and abdominal c o n t e n t s would most  clear  of  on  it  positions the  is of  abdominal  abdominal muscle l e n g t h and a c t i v i t y compared  to the LLD p o s i t i o n . The i n c r e a s e the  sitting  consistent upright (8).  and with  i n abdominal muscle a c t i v e , standing  previous  anesthetized  More  positions reports  dogs  demonstrate  that  mechanical  effect  expiratory  shortening  compensatory  the in  of  (9,13)  significantly  found  the  phasic  terms  abdominal  of  the  mechanism to  the  sitting  the  detrimental  that  was  unchanged  standing  dogs  contrast, reductions (13,24).  from  and s l i g h t l y  prone in  lateral  and  The r e l a t i v e  decubitus reduced  upright  diaphragm  diaphragm r e s t i n g  measurable  an  important upright  (20,21,24).  Indeed,  end-expiratory  dogs  sitting dogs  length  Active  that  awake  end-expiratory of  a  length  anesthetized  preservation  has  end-expiratory  in  had  dogs  convincingly  effects  it  reported  in  would be  have on diaphragm l e n g t h  recently  EMG a c t i v i t y  shortening.  and p r o n e - c r a d l e d p o s t u r e s was  is  results  muscle  in  study  and s t a n d i n g  EMG a c t i v i t y  abdominal muscles  counter  present  phasic  present  increased of  in  increased  and awake,  however,  expiratory shortening  in  awake  (17).  much  (compared  length  to  diaphragm e n d - e x p i r a t o r y  In greater supine) length  i n the awake dogs was a t t r i b u t e d to p h a s i c e x p i r a t o r y c o n t r a c t i o n o f  the  62  abdominal addition and  muscles,  preserving  abdominal  muscles  expiration. abdominal  muscles  abdominal p r e s s u r e  pressure  assist  it  has  in  been  contributed  support f o r  the  than  Different lines  muscle a c t i v i t y . vagotomy  in  in  inspiratory  Firstly,  intact  of  evidence  the  sitting  since  T  tidal  inspiratory  VJ/TJ  also  V  is  of  suggest t h a t the  there the  with  was same  no  the abdominal The g r e a t e r  increase  Thus r e l a x a t i o n o f  i.e.  phasic  in V  T  i n expiratory  tilting  apparent  i n the  compared to  the  a  three  to  upright,  i n VT  (14).  increase  in  positions  l a t e r a l decubitus  greater  c o n t r i b u t i o n to  l a t e r a l decubitus.  positions  d u r a t i o n not  passive  in  w i t h p r e v i o u s r e p o r t s i n awake  decreased  T  was  provide  and s t a n d i n g flow  the  volume  a c t i v i t y may not o n l y be p a r t i a l l y r e s p o n s i b l e may  end-  and  diaphragm EMG d i d not change s i g n i f i c a n t l y  shown i n awake s t a n d i n g dogs (19%)  at  (14).  a r e s u l t o f an i n c r e a s e  and s t a n d i n g p o s i t i o n s  , but  sitting  is  study  s t a n d i n g p o s i t i o n compared to  flow  the  the  mechanism o f  t h e r e was a t r e n d to an i n c r e a s e  present  drive,  Abdominal muscle V  dogs,  dogs  i n another s i m i l a r s t u d y ,  the  of  length  when abdominal muscle a c t i v i t y was reduced by  anesthetized  i n the  Secondly,  larger  50%  this  In  (21,24),  relaxing  important p o s t u r a l r o l e  when moving to u p r i g h t p o s t u r e s  the  (17).  i s p r o v i d e d by the t i d a l volume and t i m i n g r e s u l t s .  (17).  whereas  by  suggested t h a t  i n the s t a n d i n g p o s i t i o n i s c o n s i s t e n t  dogs  ability  inspiration  more  swings  a similar operating  generating  dogs t i l t e d towards u p r i g h t  Further  T  its  also  Indeed,  anesthetized  V  from  to m a i n t a i n i n g diaphragm l e n g t h a t  hence,  muscles  assessed  compared to  a significant  precedes  the  onset  e x p i r a t o r y muscle  T  (17).  for  the  in  the  T i was g r e a t e r  the  LLD b u t  n e u r a l T i (EMG a c t i v i t y ) . that  V  It  in  this has  in was  been  portion of i n s p i r a t o r y of  diaphragm EMG  activity  (25).  can c o n t r i b u t e  to  63  V  T  by p r o d u c i n g p a s s i v e  outward r e c o i l  of  the  chest w a l l before  active  inspiration. The  greater  amount  abdominal  muscles  is  from  the  increased  man (7,12,27) abdominal changes  afterload  on  necessarily  afterload,  (1).  muscle  is  resulted  in  but  the  i n shortening  In the  considerably. in  the  influence  generation  present  Indeed,  standing  could  a decrease  upright there  was and a  to  L  0  anesthetized  was  reported  maximal  although there  dogs, to  or  with  tilting  (22).  an  the  is  not when  In  increase  initial  in  corresponding  in parasternal  shortening  by  an i n c r e a s e  amount  depending (L )  on  for  0  of  decrease the  the  in  length TA.  at  (20). towards  intercostal that  study,  in  initial  length  varied  be  initial  length  which  tension  Unfortunately,  a v a i l a b l e d a t a on abdominal muscle c o n t r a c t i l e p r o p e r t i e s supine,  effected  a muscle  dogs,  abdominal muscle  That  shortening, be  upright  TA i n i t i a l l e n g t h decreased by a p p r o x i m a t e l y 12%  position.  would  increase  the  expected  F o r example,  length  anesthetized  associated  study,  all  i n diaphragm EMG a c t i v i t y  i n phasic was  for  EMG a c t i v i t y  towards  of  be  be  of  shortening.  a progressive  but  length.  length  of  However, b o t h  will  increased  no change  might  reported  increased  study  EMG a c t i v i t y decrease  that  afterload  i n diaphragm i n i t i a l  another  shortening  dogs (9,13).  initial  changed,  with  shortening, in  and  When the  a decrease  Conversely, upright  length  dogs were t i l t e d  in  consequence  and a n e s t h e t i z e d  initial  a  expiratory  abdominal EMG a c t i v i t y  (8)  associated  anesthetized  decrease  phasic  posture  active,  mechanical  and awake  muscle  in  a  of  is  limited.  the In  the i n v i v o r e s t i n g l e n g t h a t FRC i n r e l a t i o n 83% f o r  the  EO and 105% f o r  the  are no p u b l i s h e d data on TA Lo, TA supine  found to be a p p r o x i m a t e l y 74% o f L  0  (G. F a r k a s ,  personal  RA (15)  FRC l e n g t h  and was  communication).  64  The EO and TA would t h e r e f o r e , length-tension positions.  curves  As was  if  LRL  found,  be  on a more o p t i m a l p o r t i o n o f  were  longer  i n 4 of  in  the  sitting  or  5 dogs EO LRL lengthened  their  standing  when moving  from LLD to STAND ( F i g u r e 11)  and TA LRL lengthened when moving from LLD  to SIT ( F i g u r e 10).  assumed t h a t the  would o p t i m i z e  If  muscle  it  is  length,  then  the l a t e r a l d e c u b i t u s p o s i t i o n similar  to  position,  supine  EO (15)  the  increase  inference  is  i n EO and TA LRL  that  their  LRL  i s a t a s h o r t e r l e n g t h i n r e l a t i o n to  and  TA l e n g t h .  However,  TA LRL was c o n s i d e r a b l y reduced.  in  the  would  then  therefore,  be  TA  compromised.  at  an  tension  even  shorter  generating  Based on these wide  LQ,  standing  Such s h o r t e n i n g o f TA LRL  the s t a n d i n g p o s i t i o n i s not c o n s i s t e n t w i t h o p t i m i z i n g TA l e n g t h , it  in  length  capacity  than  i n LRL,  since  LLD TA LRL and  would  fluctuations  in  presumably it  is  be  clear  that  EMG d a t a may not be an a c c u r a t e r e f l e c t i o n o f mechanical e v e n t s . If have  the  would  position  of  all  also due  insertions  on  trend length  to  to the  explained  by  i n tonic  relaxed, of  the  be  As was  and a l t h o u g h not of  i n the  to  the  10  when moving the  found,  the  EMG a c t i v i t y .  This  from i n d i r e c t measurements.  as  tonic  the  wall  there 11).  In  shortening  which p r e v i o u s l y has  (10  and  standing and  their in  appeared to  The decrease  r e s u l t provides  should  and hence  EO d i d l e n g t h e n  and RA ( F i g u r e  it  to  abdominal  significant,  considering  position  The o b l i q u e muscles  standing p o s i t i o n .  activity  standing  abdominal compartment  lengthened  orientation  pelvis.  t o n i c abdominal muscle  the  abdominal muscles.  their  lengthening  decreased  increase  the  presumably  standing p o s i t i o n  be  was  produced outward movement  lengthening EO)  abdominal w a l l  the be  contrast,  a TA  i n TA LRL may reflecting  d i r e c t evidence o n l y been  an of  inferred  The t o n i c s h o r t e n i n g o f the TA found i n  the  65  present in  study i s  awake  tonic  c o n s i s t e n t w i t h r e p o r t s o f t o n i c TA and RA EMG a c t i v i t y  sitting  dogs  EMG a c t i v i t y  abdominal  muscle  compared to  (8).  was  found  activity  activity  That  in  in  in  the  sitting  difficult  to  the  the  study  does, n o t  standing  sitting  present  determine  or standing p o s i t i o n s  the  specify  position.  and  prone p o s i t i o n .  was abdominal muscle a c t i v i t y make i t  same  In  standing  It  is  whether addition,  positions  possible  that  was there  i n the prone p o s i t i o n which would presence  of  tonic  activity  in  the  when compared to p r o n e .  T o n i c s h o r t e n i n g o f the TA i n the s t a n d i n g p o s i t i o n would s e r v e defend  end-expiratory  anesthetized was  dogs,  decreased  lung  FRC was  (21)  volume  and  increased  compared to  the  diaphragm  (16)  supine  In  prone,  and diaphragm i n i t i a l  length  position.  muscle a c t i v a t i o n was found to p r e v e n t a g r e a t e r prone, for  anesthetized  the  Since  preservation of  diaphragm i n i t i a l  dogs (21,24), less to  dogs  it  position.  the  diaphragm l e n g t h length  was  less  i n standing than L  0  s t a n d i n g awake dog,  TA  effects  tonic  if on  shortening  abdominal  i n FRC i n  and was a l s o c o n c l u d e d to be  gravitational  Therefore,  However,  increase  the  responsible  awake  i n prone,  i s p r o b a b l e t h a t diaphragm i n i t i a l  than o p t i m a l i n the counteract  (16)  length.  to  dogs  (17).  anesthetized  l e n g t h would a l s o be  t h e r e were no mechanism the  diaphragm  (decrease  p r e v e n t i n g a decrease i n diaphragm e n d - e x p i r a t o r y l e n g t h ,  in  in  that  LRL),  would h e l p  by to  o p t i m i z e diaphragm l e n g t h . Increased muscles to  activation,  w i t h change  gravitational  i n posture  effects  phasic  and/or  tonic,  of  the  from supine to u p r i g h t i s most l i k e l y due  on the  chest  wall  (abdomen-diaphragm and r i b  cage).  The p r i m a r y mechanism c o n t r o l l i n g abdominal muscle  changes  in  posture  appears  abdominal  to  be  a  vagal  reflex  from  response lung  to  stretch  66  receptors. the  increased  produce (6). to  It  is  thought  that  FRC a s s o c i a t e d  a vagally  mediated  pulmonary a f f e r e n t s  with  reflex  assumption activation  of of  increased vagotomy  when l i g h t l y more  when  (13).  It  upright posture  the  is  decreased  and r a b b i t s muscle  reflexes.  Indeed,  (6)  rabbits,  muscle a c t i v i t y was g r e a t e r  the  proprioceptors. u p r i g h t man,  is  when  lung  following  anesthetized response.  also  augmented  by  was  increased  by  volume  during upright t i l t i n g  the  abdominal muscle  i n upright  likely  and  increased i n  f i n d i n g that  most  found  upright  p r e s s u r e b r e a t h i n g and t i l t i n g ,  abdominal  the  tonic  than those  of  greater distension It  has  (6).  abdominal  I n the  upright  the  has  techniques  were  been  measured abdominal muscle  anesthetized  of  the muscles  dogs  that  during  as  i n the  on the  is  this  reflects  a  causing  (26). expiratory  to  the  a single  expiratory  abdomen  lower abdomen  underestimated  abdominal  lower  Presumably,  the  limited  movement  individual  muscle in  generally  either  stimulating  supported by the o b s e r v a t i o n t h a t  upper abdomen.  suggested  thus,  is  o f the lower abdomen  been  which  activity  and  pressure being exerted  abdominal muscles  measured  muscles  This hypothesis  greater hydrostatic  have  to  muscles  was  decreased  t h a t FRC i s  vagotomy  it  to  g r a v i t y would tend to cause the abdominal w a l l to move outward,  stretching  greater  activity  the  after  activation In  study,  would support a v a g a l l y mediated  s i m i l a r amounts w i t h p o s i t i v e  posture,  muscle  by  posture  abdominal  dogs were t i l t e d  also well established  i n man (2).  Abdominal segmental  expiratory  is  expiratory a c t i v i t y dogs (9,13)  anesthetized  stimulated  upright  A l t h o u g h FRC was not measured i n the p r e s e n t increase  are  muscle  activity due  to  (7).  muscles Studies  shortening  threshold  the  measurement  superficial unit  of  loading  in (19)  or that  supine and  67  h y p e r c a p n i c hyperpnea (3) (TA  and  10)  external findings  tend  layer  to  (EO  be  recruited  and  of variable  postural  have shown t h a t the  RA).  amounts  differences.  earlier  The  of  i n t e r n a l abdominal muscles and  present  shorten  results  abdominal muscle  Evidence  of  more  than  extend  shortening  differential  the  previous  to  include  abdominal  muscle  r e c r u i t m e n t w i t h changes i n p o s t u r e has p r e v i o u s l y been demonstrated by EMG a c t i v i t y .  Anesthetized  supine to headup (18) the  EO.  awake  from supine  to  prone  had g r e a t e r amounts o f EMG a c t i v i t y  G r e a t e r TA EMG a c t i v i t y  standing,  versus  dogs moved  sitting  compared to  and prone  EO and RA EMG a c t i v i t y  dogs  EO has  (8).  a l s o been  sitting  and  i n the TA than  Similar  were found f o r  (16)  shown  results  in  o f TA  man (7).  There  does n o t appear to be any p o s t u r a l d a t a a v a i l a b l e f o r 10 EMG, b u t the 10 was r e c r u i t e d e a r l i e r and a t  lower l e v e l s o f v e n t i l a t i o n  man d u r i n g h y p e r c a p n i c hyperpnea (27). shortening  of  the  internal  t h a n the  T h e r e f o r e , the g r e a t e r amount o f  abdominal muscles  shown  in  this  c o n s i s t e n t w i t h the d i f f e r e n t i a l a c t i v a t i o n r e p o r t e d i n o t h e r What f a c t o r s internal  abdominal  activation. than  the  could  muscle  Conversely,  preferentially tension  muscle  EO or RA (19).  activity.  1.  layer?  There  Greater lengthening spindles  and  descending  activate  the  characteristics  of  may  be  lead  output  to  of  reflex  from c e n t r a l 2.  i n t e r n a l muscles. the  the  individual  was  tension  significantly  generated when the muscles greater  for  the  TA than  inflation  internal  muscles  facilitation controllers  muscles T  the  differential  The p a s s i v e  abdominal  is  studies.  lung  i m p o r t a n t i n terms o f abdominal muscle c o n t r i b u t i o n to V . the p a s s i v e  study  c o u l d account f o r the p r e f e r e n t i a l r e c r u i t m e n t o f  The TA and 10 are lengthened more by p a s s i v e  activate  EO i n  of may  lengthmay  be  I n hamsters,  were s t r e t c h e d beyond Lo the  EO (4).  The  greater  68  passive the  t e n s i o n o f the TA f o r a g i v e n change  EO suggests  that  it  may c o n t r i b u t e  i n f i b e r l e n g t h compared to  more to  the  the abdominal w a l l and hence s h o r t e n more than the operating  length  of  the  i n d i v i d u a l muscles  Thus,  the  internal  abdominal  pressure.  contribute  more  increasing  the  to  i n l e n g t h was g r e a t e r muscles  This V  T  by  may be  would  appositional  are  the  of  the  the  tension  generators muscles  of  preferential  recruitment  When s t i m u l a t e d s e p a r a t e l y ,  the  r i b cage  volume Thus,  increases  contraction of  effective  at  abdominal w a l l would make them e f f e c t i v e results  at  emphasize  the  the TA and  whereas the EO,  abdominal the  of  pressure,  EO has  opposing  d e f e n d i n g diaphragm l e n g t h .  the o r i e n t a t i o n and p o s i t i o n o f the i n t e r n a l muscles  These  to  assist  inflates  positions.  of  diaphragm c o n t r a c t i o n ,  and  upright  in  and by  decreases  Furthermore,  the range  l u n g volume  it  less  in  internal  although  which may make i t  important  is  effective  abdominal p r e s s u r e ,  (10).  in  (10).  advantages  lung  of  f o r the TA t h a n the EO  10 decrease l u n g volume and i n c r e a s e  actions  be  hamsters  end-expiratory  component  i n t e r n a l abdominal muscle l a y e r ?  more  enable  decreasing  the diaphragm d u r i n g i n s p i r a t i o n What  In  3_. The range  the TA was s m a l l e r than the EO, t h a t  g e n e r a t e d by a g i v e n change (4).  EO.  may a l s o  terms o f abdominal muscle c o n t r i b u t i o n to Vx. operating length of  r e c o i l pressure  compressing the  muscle l a y e r o f the abdominal w a l l i n b r e a t h i n g .  role  the of  in  abdomen  the  the in  internal  69  REFERENCES  1.  A g o s t o n i , E . , and E . J . M . Campbell. The abdominal m u s c l e s . I n : The R e s p i r a t o r y M u s c l e s : Mechanics and N e u r a l C o n t r o l . E . J . M . C a m p b e l l , E A g o s t o n i , and J . Newsom-Davis ( e d s ) . Saunders, P h i l a d e l p h i a , PA, 1970,  175-180.  2.  A g o s t o n i , E . , and R . E . H y a t t . S t a t i c b e h a v i o r o f the r e s p i r a t o r y system. I n : Handbook o f P h y s i o l o g y S e c t i o n 3 : The R e s p i r a t o r y System. V o l . I I I . W i l l i a m s & W i l k i n s , B a l t i m o r e , MD, 1 9 8 6 , 1 1 3 - 1 3 0 .  3.  A r n o l d , J . S . , M . A . H a x h i u , N . S . C h e r n i a c k and E . van L u n t e r e n . T r a n s v e r s e abdominis l e n g t h changes d u r i n g eupnea, h y p e r c a p n i a and airway o c c l u s i o n . J . A p p l . P h y s i o l . 6 4 ( 2 ) : 6 5 8 - 6 6 5 , 1 9 8 8 .  4.  A r n o l d , J . S . , A . J . Thomas and S . G . K e l s e n . L e n g t h - t e n s i o n r e l a t i o n s h i p o f abdominal e x p i r a t o r y muscles: e f f e c t o f emphysema. J.  APPI.  Phvsiol.  62:  739-745,  1987.  5.  C a m p b e l l , E . J . M . and J . H . Green. The v a r i a t i o n s i n i n t r a - a b d o m i n a l p r e s s u r e and the a c t i v i t y o f the abdominal muscles d u r i n g b r e a t h i n g ; a study i n man. J . P h y s i o l . 1 2 2 : 2 8 2 - 2 9 0 , 1 9 5 3 .  6.  D a v i e s , A . , F . B . Sant'Ambrogio and G . Sant'Ambrogio. C o n t r o l o f p o s t u r a l changes o f end e x p i r a t o r y volume (FRC) by airways s l o w l y a d a p t i n g mechanoreceptors. R e s p i r . P h y s i o l . 4 1 : 2 1 1 - 2 1 6 , 1 9 8 0 .  7.  De T r o y e r , A . , M. Estenne, V . Ninane, D. van Gansbeke and M. G o r i n i . T r a n s v e r s u s abdominis muscle f u n c t i o n i n humans. J . A p p l . P h y s i o l . 68(3):  8.  1010-1016,  De T r o y e r , A . , J . J . G i l m a r t i n and V . Ninane. Abdominal muscle use d u r i n g b r e a t h i n g i n u n a n e s t h e t i z e d dogs. J . A p p l . P h y s i o l . 6 6 ( 1 ) : 20-27,  9.  10.  1989.  De T r o y e r , A . and V . Ninane. E f f e c t o f p o s t u r e on e x p i r a t o r y muscle use d u r i n g b r e a t h i n g i n the dog. R e s p i r . P h y s i o l . 6 7 : 3 1 1 - 3 2 2 , 1 9 8 7 . De T r o y e r , A . , M. Sampson, S. S i g r i s t and S. K e l l y . How the abdominal muscles a c t on the r i b cage. J . A p p l . P h y s i o l . 5 4 : 4 6 5 469,  11.  1990.  1983.  D r u z , W.S. and J . T . Sharp. A c t i v i t y o f r e s p i r a t o r y muscles i n u p r i g h t and recumbent humans. J . A p p l . P h y s i o l . 5 1 ( 6 ) : 1 5 5 2 - 1 5 6 1 , 1981.  12.  Estenne, M . , V . Ninane and A . De T r o y e r . T r i a n g u l a r i s s t e r n i muscle use d u r i n g eupnea i n humans: e f f e c t o f p o s t u r e . R e s p i r . P h y s i o l . 7 4 : 151-162,  13.  1988.  F a r k a s , G . A . , R . E . B a e r , M. Estenne and A . De T r o y e r . M e c h a n i c a l r o l e o f e x p i r a t o r y muscles d u r i n g b r e a t h i n g i n u p r i g h t dogs. J__  70 Appl.  Phvsiol.  64(3):  1060-1067,  1988.  14.  F a r k a s , G . A . , M. Estenne and A . De T r o y e r . E x p i r a t o r y muscle c o n t r i b u t i o n to t i d a l volume i n head-up dogs. J . A p p l . P h v s i o l . 67(4): 1438-1442, 1989.  15.  F a r k a s , G . A . and D . F . R o c h e s t e r . C h a r a c t e r i s t i c s and f u n c t i o n a l s i g n i f i c a n c e o f c a n i n e abdominal muscles. J . A p p l . P h y s i o l . 6 5 ( 6 ) : 2427-2433, 1988.  16.  F a r k a s , G . A . and M . A . Schroeder. M e c h a n i c a l r o l e o f e x p i r a t o r y muscles d u r i n g b r e a t h i n g i n prone a n e s t h e t i z e d dogs. J . A p p l . P h v s i o l . 6 9 ( 6 ) : 2137-2142, 1990.  17.  F i t t i n g , J . W . , P . A . E a s t o n , R. Arnoux, A . G u e r r a t y and A . G r a s s i n o . Diaphragm l e n g t h adjustments w i t h body p o s i t i o n changes i n the awake dog. J . A p p l . P h v s i o l . 66(2): 870-875, 1989.  18.  G i l m a r t i n , J . J . , V . Ninane and A . De T r o y e r . Abdominal muscle use d u r i n g b r e a t h i n g i n the a n e s t h e t i z e d dog. R e s p i r . P h y s i o l . 70: 159171, 1987.  19.  L e e v e r s , A . M . and J . D . Road. M e c h a n i c a l response to h y p e r i n f l a t i o n o f the two abdominal muscle l a y e r s . J . A p p l . P h y s i o l . 6 6 ( 5 ) : 21892195, 1989.  20.  L e e v e r s , A . M . and J . D . Road. E f f e c t o f lung i n f l a t i o n and u p r i g h t p o s t u r e on d i a p h r a g m a t i c s h o r t e n i n g i n dogs. R e s p i r . P h y s i o l . 85: 29-40, 1991.  21.  Newman, S . L . , J . D . Road and A . G r a s s i n o . In v i v o l e n g t h and s h o r t e n i n g o f c a n i n e diaphragm w i t h body p o s t u r a l change. J . P h v s i o l . 6 0 ( 2 ) : 661-669, 1986.  Appl.  22.  Ninane, V . and A . De T r o y e r . Mechanics of p a r a s t e r n a l s and t r i a n g u l a r i s s t e r n i i n u p r i g h t v s . supine dogs. J . A p p l . P h v s i o l . 65(1): 452-459, 1988.  23.  Ninane, V . , J . J . G i l m a r t i n and A . De T r o y e r . Changes i n abdominal muscle l e n g t h d u r i n g b r e a t h i n g i n supine dogs. R e s p i r . P h y s i o l . 73: 31-42, 1988.  24.  Road, J . , S. Newman, J . P . Derenne and A . G r a s s i n o . In v i v o l e n g t h f o r c e r e l a t i o n s h i p o f canine diaphragm. J . A p p l . P h v s i o l . 6 0 ( 1 ) : 6370, 1986.  25.  Smith, C . A . , D . M . A i n s w o r t h , K . S . Henderson and J . A . Dempsey. D i f f e r e n t i a l t i m i n g o f r e s p i r a t o r y muscles i n response to c h e m i c a l s t i m u l i i n awake dogs. J . A p p l . P h y s i o l . 66(1): 392-399, 1989.  26.  S t r o h l , K . P . , J . Mead, R . B . B a n z e t t , S . H . L o r i n g and P . C . K o s c h . R e g i o n a l d i f f e r e n c e s i n abdominal muscle a c t i v i t y d u r i n g v a r i o u s maneuvers i n humans. J . A p p l . P h y s i o l . 51: 1471-1476, 1981.  71  27. Wakai, Y . , M.M. Welsh, A . M . Leevers and J . D . Road. The e f f e c t o f c o n t i n u o u s p o s i t i v e airway p r e s s u r e and h y p e r c a p n i a on e x p i r a t o r y muscle a c t i v i t y d u r i n g wakefulness and s l e e p . Am. Rev. R e s p i r . P i s . 141(4): A125, 1 9 9 0 . ( A b s t r a c t )  72  IV.  ABDOMINAL MUSCLE A C T I V A T I O N BY EXPIRATORY THRESHOLD LOADING  INTRODUCTION The (RA) ,  f o u r muscles  external  oblique  abdominis  (TA), are  expiration  (1)  positive load  o f the v e n t r a l abdominal w a l l : (EO) ,  known  to  be  end-expiratory pressure  (ETL) t o  the  due t o  recruitment  abdominal muscles  (18).  system  However,  in  recruitment  studies  of  abdominal  g e n e r a l l y employed a n e s t h e t i z e d known t o responses  influence in  the  awake a n i m a l .  reflexes,  muscles,  animal  dog and may a l s o e f f e c t factors.  Indeed,  p a r t i c u l a r l y the  muscle  by  to  E T L have  anesthesia  is  reflexes  (25,26),  the  extrapolated  to  animals  the often  i s n o t n a t u r a l f o r the  abdominal muscle response  independently o f other  discussed  in  Chapter  that  activated  but l o c a l  Since  can n o t be  in  and have  response  (6,18,21).  on changes i n p o s t u r e .  uniformly  (2-4)  is  one t h a t  as  dogs,  i n FRC i s  (3,24).  a c t i v a t i o n i s dependent anesthetized  in  characteristics  studies involving anesthetized  have the a n i m a l i n the supine p o s i t i o n ,  threshold  o f the abdominal muscles  p a r t i c u l a r l y vagal  anesthetized  In a d d i t i o n ,  animals  forced  increase  the i n c r e a s e  pressure-volume  the e x p i r a t o r y  r e f l e x e s may a l s o be i n v o l v e d  Previous  during  an  thought t o be due p r i m a r i l y to v a g a l l y mediated r e f l e x e s segmental  transversus  The a p p l i c a t i o n o f  and r e s u l t s  from p a s s i v e  This  and  recruited  (2,8,20,21).  (FRC) (8).  of  (10)  abdominis  (PEEP) p r e s e n t s an e x p i r a t o r y  respiratory  l e s s than would be expected  oblique  strongly  or expiratory loading  functional residual capacity  (23),  internal  rectus  different  expiratory  the  abdominal  relative  threshold  III,  muscle  We have p r e v i o u s l y  muscles  contributions loading  abdominal  are  r e c r u i t e d non-  to e x p i r a t i o n  (ETL) (18).  shown  when  Therefore,  73  a c t i v a t i o n of reflex  the  i n d i v i d u a l abdominal muscles  lateral  decubitus  abdominal  that  position  muscles  uniform a c t i v a t i o n  and  in  Therefore,  the the  the  o f the  the  same  awake  as  of  recruitment,  l e n g t h and s h o r t e n i n g ,  awake  dog  (TA and 10)  dog,  loading,  in  the  left  would produce a s t r o n g r e c r u i t m e n t resulting  abdominal muscles,  objectives  abdominal muscle  threshold  We a l s o h y p o t h e s i z e d  i n t e r n a l muscle l a y e r RA)  expiratory (LLD),  of  e x p i r a t o r y l u n g volume.  the  involve  pathways. We h y p o t h e s i z e d  the  may not  that  defence  there  with greater  of  end-  would be nonactivation  of  than the e x t e r n a l muscle l a y e r (EO  was  this  in  of  found  study  in  were  the to  as measured by the  anesthetized identify  individual  differences  d u r i n g e x p i r a t o r y l o a d i n g i n awake  dog.  in  resting  dogs.  METHODS Eight  tracheotomized,  implanted with  female  sonomicrometer  mongrel  transducers  i n each o f the f o u r abdominal muscles  dogs  and f i n e  were  wire  surgically  EMG e l e c t r o d e s  as d e s c r i b e d i n Chapter I I .  Three dogs were s u r g i c a l l y i m p l a n t e d w i t h femoral a r t e r y c a t h e t e r s ( v a s c u l a r a c c e s s p o r t , model GPV, Access T e c h n o l o g i e s , arterial  b l o o d sampling from a subcutaneous  port  I L ) which a l l o w e d  located  i n the  dorsal  changes  were  lumbar r e g i o n .  Measurements Abdominal muscle measured  with  the  resting baseline left  lateral  end-expiratory  sonomicrometer  length  decubitus  of  the  lengths  transducers  and l e n g t h (see  abdominal muscles,  position,  was  termed  LRL.  Chapter  with  the  Changes  II).  dog in  in  The the  muscle  74  length  during  expiratory resting  tidal  breathing,  shortening,  length  coinciding  (%LRL) .  with  l e n g t h from the percentage  were  of  raw  either  expressed  Active  inspiratory  as  initial  resting  tonic  than  LRL and t h e r e f o r e ,  length.  was  of  the  determined  to  be  A change  in  baseline  The  length  considered  electromyographic  electrodes  new  baseline  to  be  a  were  Airflow pressure  amplified  was  signals  (Grass,  measured  transducer  from  the  model P511)  with  a  implanted  fine  and f i l t e r e d  pneumotachograph  ( V a l i d y n e MP45,  opposite  end  of  the  non-rebreathing valve loads  of  6,10,  expiratory attached  of  Medfield,  (band w i d t h  the  via  a  (ETL),  expired  PEEP  expiratory  side  of  Mass.).  the  control when  expiratory  (Pao)  change  to  two-way  valve.  the  t i d a l volume. to  a  Expiratory  (Medigas,  and  two-way, threshold  Model  end-  BE-142)  End-expiratory  i n the two-way v a l v e  and r e c o r d e d  ( d i f f e r e n t i a l p r e s s u r e t r a n s d u c e r , V a l i d y n e MPDuring  the  application of  i n l u n g volume  parameters.  the  valve  the  was measured v i a a p o r t h o l e  Medfield,  #1)  attached  connected  (Hans Rudolph, model 2600).  (PEEP)  as airway p r e s s u r e  the  pneumotachograph was  signals.  (Fleisch  Mass.)  wire  14 and 18 C111H2O were produced by a p p l y i n g p o s i t i v e  pressure  to  pressure  to  a  usually  reflection  d i s t a l end o f the tracheostomy tube and i n t e g r a t e d to g i v e  load  as  length  ( L A B L ) • LABL was  100-10,000 Hz) and r e c o r d e d i n p a i r s w i t h the sonomicrometer  45,  that  activity. The  The  or  initial  l e n g t h was a l s o e x p r e s s e d  d u r i n g ETL was termed the a c t i v e b a s e l i n e shorter  was  EMG a c t i v i t y .  i n i t i a l resting baseline the  a percentage  shortening  expiratory  lengthening  expiratory  ( T E ) d u r a t i o n were  The  6V0I  l o a d was  (6V0I)  was  was measured  determined  released.  determined  expiratory  from the  from  threshold  in the  Inspiratory flow  addition volume  (Ti)  and  t r a c i n g on  the  75  chart recorder u s i n g a d i g i t i z i n g device  (Sigma-Scan, J a n d e l  Scientific,  C o r t e Madera, C A ) . One access  ml  port,  protocol, Blood  arterial  PC0 ,  during  and a t  samples  three  were  samples  resting levels  analyzed  p H , and P 0 , and  2  blood  breathing, of  PEEP  obtained, before  (6,10  (Corning,  168  via  and  and 14  the  after  cmH 0) gas  the  ETL  during ETL.  2  pH/Blood  vascular  analyzer)  for  determined by e x t r a p o l a t i o n .  HCO3"  2  were  Protocol The  eight  the  other  C0  rebreathing  2  dogs used  protocols  the  on d i f f e r e n t  (Chapter  chapter describes (ETL).  in this  V)  study days:  and  vagal  a l s o underwent  one  p o s t u r a l changes blockade  o r more  (Chapter  (Chapter  of  III),  VI) .  This  the p r o t o c o l f o l l o w e d f o r e x p i r a t o r y t h r e s h o l d l o a d i n g  Repeat s t u d i e s o f ETL were performed on d i f f e r e n t  r e p r o d u c i b i l i t y of  the  results.  A l l the  studies  days to  assess  f o r each dog were  performed over p e r i o d s r a n g i n g from two to e i g h t weeks. At (#7)  the  was  inserted  platform, EMG  beginning  each  through  positioned  wires  of  were  the left  connected  to  The two-way  distal  the  breathing length, An  of  and PEEP v a l v e and when  c o n t r o l measurements  load  allowed  for  was  then  applied  of  the  a l l o w e d to  placed  and the and  on  a  amplifiers,  were c o n n e c t e d dog  tube  c r y s t a l and  was  to  the  relaxed  and  abdominal muscle  resting  Pao and t i d a l volume were made. and  a  short  a regular breathing pattern  A f t e r E T L , b r e a t h i n g was  tracheostomy  The dog was  sonomicrometer  l e n g t h changes and EMG a c t i v i t y ,  expiratory  minutes)  the  valve  cuffed  l a t e r a l decubitus  pneumotachograph  stabilized,  a  tracheotomy.  i n the  respectively. end  ETL t r i a l ,  to  time be  period  (1-2  reestablished.  r e t u r n to c o n t r o l v a l u e s  before  the  76  next  load.  The  awake  dogs  were  exposed  a p p l i e d e x p i r a t o r y t h r e s h o l d loads were not a b l e to t o l e r a t e  to  three  or  four  ( 6 , 1 0 , 1 4 and 18 cmH 0).  randomly  (Four  2  dogs  a PEEP o f 18 cmH 0) . 2  Analysis Measurements PEEP,  for  between  each s t u d y  studies,  means  ±  averaged  day.  dog,  then  at  test.  were  each  compare the  of  the  results  made  data  at  used and a s i g n i f i c a n c e  for  using  were  different level  each  no c o n s i s t e n t  level  for  level  When s i g n i f i c a n t h e t e r o g e n e i t y  transformations  breaths  were  different  ANOVA was used and a s i g n i f i c a n c e comparisons  there  calculated  comparisons were made among the  multiple  five  from each PEEP study were  means p e r  SE were  over  Since  the means  each dog and the The  were  of  each  level  differences  then averaged  PEEP were  a  variable.  Whenever a  P<0.05 a c c e p t e d . Tukey's  multiple  one-way Post  hoc  comparison  of standard d e v i a t i o n e x i s t e d ,  made  and  levels  the  of  ANOVAs  PEEP,  o f P<0.05 a c c e p t e d .  comparison t e s t was used to t e s t f o r d i f f e r e n c e s  for  obtained.  abdominal m u s c l e s ,  of  of  log  repeated.  To  a one-way ANOVA was A Dunnett's m u l t i p l e  from c o n t r o l measures.  RESULTS All  eight  dogs were  easily  able  l o a d s up to 14 cmH 0 but o n l y f o u r o f 2  airway p r e s s u r e agitated  at  the  of  18  cmH 0.  higher  2  to the  The other  Pao.  tolerate eight four  Expiratory  V T , the  change  on RA a c t i v i t y .  i n volume  (SVol),  dogs c o u l d a d j u s t to an  dogs  became  threshold  r e c r u i t m e n t o f t h r e e o f the abdominal muscles measurable e f f e c t  expiratory threshold  The e f f e c t  restless  loading  and  produced  (TA, 10 and EO) b u t had no of  abdominal muscle  a PEEP o f (10)  10 cmH 0 on  active  2  baseline  77  (LABL)  length tracing is  the  the  length  phasic  preceding of  the  expiratory  the  phasic  resting baseline  the  downward  length  a  of  d e f l e c t i o n of  the  Pao=0).  The  the  onset  of  shortening.  immediately  shortening The  following  (%LRL) and  upward  d e f l e c t i o n of  i s i n s p i r a t o r y lengthening.  (LRL)  muscle.  and  muscle  the  The  active baseline  activity.  t o n i c muscle  d i f f e r e n c e between  An  shortening.  expiratory shortening three  active  and  length  tidal  Total tidal  shortening)  but  d i d not  the  EO  of  length  downward  is  the  active,  initiation  end-expiratory length  length  excursion  resting baseline  length  assumed to r e f l e c t shorter  tonic  LRL  implied  active  phasic,  than  length excursions,  the  changes i n b a s e l i n e l e n g t h -(tonic a c t i v i t y )  length  expiratory  (LABL) was  baseline  abdominal muscles d u r i n g ETL Total  the  LABL  length  t r a c i n g above  the e n d - i n s p i r a t o r y l e n g t h comprise the t o t a l t i d a l the  before  the The  with  the  The  is  the  coincides  muscle (LRL)  tracing  LABL  (when  active  representative  the  PEEP  tracing  EMG.  resting baseline and  The  preceding of  (%LRL) i s shown by  shortening  12.  application  deflection  of  tidal  i n Figure  immediately  of  and  are shown i n F i g u r e  excursions the  TA  and  (inspiratory 10  change s i g n i f i c a n t l y  increased ( F i g u r e s 13  13. lengthening  with and  of  increasing 14).  plus Pao  78  Figure  12: A r e p r e s e n t a t i v e t r a c i n g from an awake dog ( l e f t l a t e r a l d e c u b i t u s p o s i t i o n ) showing (from top to bottom) t i d a l volume (V ) , airway p r e s s u r e (Pao), i n t e r n a l oblique (10) length changes and EMG a c t i v i t y . The l e f t s i d e o f the t r a c i n g i s w i t h a PEEP o f 10 cmH 0. The r i g h t s i d e i s a f t e r r e l e a s e o f the l o a d . The 10 r e s t i n g l e n g t h (LRL) i s the l e n g t h immediately p r e c e d i n g the downward d e f l e c t i o n o f the l e n g t h t r a c e when Pao=0. The downward d e f l e c t i o n o f the l e n g t h t r a c e c o i n c i d i n g w i t h i n i t i a t i o n o f EMG a c t i v i t y i s a c t i v e p h a s i c s h o r t e n i n g e x p r e s s e d as %LRL. T  2  10 S e c  80  Figure 13: Length changes (%LRL) of three abdominal muscles (TA, 10 and EO) at control (Pao=0) and four levels of PEEP (Pao=6, 10, 14 and 18 CH1H2O) during expiratory threshold loading. The 0 l i n e i s the i n i t i a l , r e s t i n g baseline length of the muscles ( L R L ) , the p o s i t i v e length changes are inspiratory lengthening and the negative changes are shortening below the r e s t i n g baseline length. Active shortening i s represented by the black part of the bars and tonic shortening by the unshaded portion of the negative length changes. Values are means ± SE.  81  82  The  amount o f a c t i v e  i n c r e a s e d as the l e v e l  expiratory shortening  2  and  0.05±0.03  1.8±0.31%  changes effect  the  resting  i n the b a s e l i n e  baseline  length  that  length  increase  to an u n d e r e s t i m a t i o n  i n baseline  length  f o r the 10  SE) when  (fractional  occurred with  the c a l c u l a t i o n o f s h o r t e n i n g .  would l e a d  different  Pao was  S i n c e s h o r t e n i n g was e x p r e s s e d  2  of  ±  muscle  %LRL i n c r e a s e d  to 6 . 4 ± 1 . 2 9 %  f o r the EO (means  i n c r e a s e d from c o n t r o l to 14 cmH 0. percentage  13 and 1 5 ) .  to 4 . 9 ± 0 . 9 6 % f o r the TA, 0 . 5 ± 0 . 1 8 to  f o r each  o f PEEP i n c r e a s e d and was s i g n i f i c a n t l y  from c o n t r o l a t a PEEP o f 10 cmH 0 ( F i g u r e s from 1 . 0 ± 0 . 1 6  (%LRL)  shortening),  i n c r e a s i n g Pao c o u l d  A decrease i n the b a s e l i n e  of fractional  would l e a d  as a  shortening,  length  whereas an  to an o v e r e s t i m a t i o n .  However,  s h o r t e n i n g was e x p r e s s e d  i n terms o f the r e s t i n g b a s e l i n e  reasons:  study was concerned w i t h s h o r t e n i n g r e l a t i v e to  (1) the p r e s e n t  shortening at rest be s u f f i c i e n t ETL  of  At  2  the o v e r a l l  effected  the  LABL  of  i n baseline  the  t h a n LRL a t each  10  and EO ( F i g u r e  muscles  i n anesthetized  o f Pao ( F i g u r e s  i n tonic  i n t e r n a l and e x t e r n a l muscles  activity  (Figure 13).  than  o f PEEP ( F i g u r e 1 3 ) .  dogs  (18),  the i n t e r n a l  (TA and 10) p h a s i c a l l y s h o r t e n e d more than the e x t e r n a l  was a d i f f e r e n c e  The LABL  10 LABL was l o n g e r  2  and E0) a t a l l l e v e l s  there  13).  l e v e l of PEEP up to a Pao o f 14  18 cmH 0 Pao, measured i n f o u r dogs,  was found p r e v i o u s l y  was n o t c o n s i d e r e d t o  results.  The E0 LABL was l o n g e r than LRL a t each l e v e l As  (RA  to e f f e c t  the 10 was s h o r t e r  cmH 0. LRL.  also  and (2) the change  l e n g t h f o r two  13 and 1 5 ) . (change  i n LABL)  muscles  In addition, between the  83  12  Pao  Figure  15  (cmhLO)  14: T o t a l t i d a l l e n g t h e x c u r s i o n s of three abdominal muscles (TA, 10 and EO) expressed as a p e r c e n t a g e o f the i n i t i a l b a s e l i n e r e s t i n g l e n g t h (%LRL) p l o t t e d a g a i n s t increasing airway pressure (Pao) during expiratory t h r e s h o l d l o a d i n g . The a s t e r i s k s (*) 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 i n t o t a l t i d a l l e n g t h changes between the TA and 10 compared to the EO (P<0.05).  18  84  P a o (cmH  0)  Figure 15: Active, phasic expiratory shortening of three abdominal muscles (TA, 10 and EO) expressed as a percentage o f the i n i t i a l b a s e l i n e r e s t i n g l e n g t h (%LRL) p l o t t e d a g a i n s t i n c r e a s i n g airway p r e s s u r e (Pao) during e x p i r a t o r y t h r e s h o l d l o a d i n g . The a s t e r i s k s (*) 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 i n a c t i v e s h o r t e n i n g between the TA and 10 compared to the EO (P<0.05).  85  As in and  the  level  l u n g volume, breathing  o f PEEP i n c r e a s e d ,  there was a s i g n i f i c a n t  i n d i c a t i n g an i n c r e a s e frequency  (1/T OT) T  i n FRC ( F i g u r e 16).  were  unchanged  t h e r e was a h y p o v e n t i l a t i o n a t the h i g h e s t Although  TTOT  during  2  E  increased at  and T  1.15±0.07  sec  to  0.93+0.05  3.35±0.33  sec  at  Pao=0 and 14 cmH 0, r e s p e c t i v e l y .  The  mean  effects values  increased  However,  (significant  a t Pao  Ti decreased  from 2 . 5 6 ± 0 . 2 3  2  was l i n e a r l y r e l a t e d to the i n c r e a s e The  E  ETL. 2  14 cmH20 ( F i g u r e 17).  sec  T i d a l volume  l o a d o f 18 cmH 0 ( T a b l e I I I ) .  d i d not change d u r i n g ETL, T i d e c r e a s e d  10 cmH 0) and T  increase  sec  The i n c r e a s e  i n lung volume ( F i g u r e  from to  in T  E  18).  o f ETL on a r t e r i a l b l o o d gases are shown i n T a b l e I V . for  three  dogs  at  each  level  of  PEEP  indicate  h y p e r c a p n i a d i d not develop d u r i n g ETL up to a PEEP o f 14 cmH 0. 2  that  Table I I I : V e n t i l a t i o n and t i m i n g parameters  v  Pao (cm H 0)  V  E  during E T L .  T  T OT  T  T  E  (ml "min" )  (ml)  (sec)  (sec)  0  5981 ±842  292 ±23  3.61 ±.29  2.56 ±.23  6  4960 ±662  283 ±20  3.99 ±.31  3.05 ±.27  10  4648 ±651  266 ±23  4.11 ±.32  3.26 ±.28  14  4627 ±837  258 ±21  4.18 ±.37  3.35 * ±.33  18  3529 * ±585  240 ±12  4.59 ±.44  3.70 * ±.40  1  2  Pao=airway p r e s s u r e ( c o n t r o l = 0 cmH 0) V a l u e s are means ± S E N=8 (N=4 a t Pao=18 cmH 0) A s t e r i s k (*) i n d i c a t e s s i g n i f i c a n t l y d i f f e r e n t Pao=0 cmH 0 (P<0.05). 2  2  2  from c o n t r o l ,  Table IV: A r t e r i a l b l o o d gas v a l u e s d u r i n g ETL.  Pao (cm H 0)  PC0 mmHg  P0 mmHg  pH  0 (pre)  37.6 ±2.6  104.7 ±12.2  7.36 ±.005  6  38.2 ±2.4  97.9 ±6.1  7.36 ±.011  10  37.1 ±1.6  92.9 ±8.2  7.37 ±.011  14  39.5 ±0.8  83.9 ±5.0  7.35 ±.004  35.0 ±1.2  86.8 ±7.0  7.38 ±.007  2  0  (post)  2  2  Pao=airway p r e s s u r e ( c o n t r o l = 0cm H 0; c o n t r o l b e f o r e and a f t e r ETL) N=3 2  p r e and p o s t a r e  0  3  6  9  Pao (cm  Figure  12  15  H 0) 2  16: The change i n l u n g volume ( 6 V o l ) produced by ETL p l o t t e d a g a i n s t airway p r e s s u r e (Pao). V a l u e s a r e means ± SE. A s t e r i s k s (*) i n d i c a t e significantly different from c o n t r o l (P<0.05).  18  0.00 ^ 4.0  1  1  1  1  1  -  3.5 O  (0 UJ  3.0  2.5  6  9  12  18  Pao (cm H.O) Figure  17: Inspiratory air flow duration (Ti) (top) and expiratory duration ( T ) (bottom) plotted against airway p r e s s u r e (Pao) d u r i n g E T L . V a l u e s a r e means ± SE. T is significantly different from c o n t r o l at Pao=18cmH 0 (P<0.05). E  E  2  90  4.0  F i g u r e 18: E x p i r a t o r y d u r a t i o n ( T ) p l o t t e d a g a i n s t the change i n volume (6"vol) d u r i n g ETL. Values a r e means ± SE E  91  DISCUSSION T h i s s t u d y shows t h a t awake dogs a c t i v e l y  recruit  muscles i n response t o e x p i r a t o r y t h r e s h o l d l o a d i n g (18),  p r e v i o u s l y i n a n e s t h e t i z e d dogs  their  (ETL).  abdominal  As was found  t h e i n t e r n a l l a y e r o f muscles (TA  and 10) i s r e c r u i t e d p r e f e r e n t i a l l y and appears t o be more important i n the  defence  of  lung  volume  that  results  from  abdominal  muscle  activation. Abdominal  muscle  mechanisms employed are  exposed  abdominal capacity  i s one o f t h e l o a d  by the r e s p i r a t o r y  t o ETL  muscles  activation  (2-4,20).  helps  (FRC) and hence,  system when a n e s t h e t i z e d animals  Phasic,  prevent  compensating  expiratory  the increase  the r e s u l t i n g  shortening  i n functional  of  the  residual  decrease i n diaphragm  initial  l e n g t h which would compromise the mechanical e f f i c i e n c y o f the diaphragm (22).  In anesthetized  dependent  primarily  effectively  animals t h e abdominal muscle  on v a g a l l y  eliminates  phasic  (2-4),  mediated r e f l e x e s abdominal muscle  mechanisms i n t h e abdominal muscle  response t o ETL i s  activity  since  vagotomy  (6,24).  Other  response t o ETL may be i n v o l v e d i n  awake a n i m a l s .  The responses o f awake animals ( o t h e r than humans) have  not  investigated.  been  abdominal compared  well  muscles  would  to anesthetized  However,  be more animals.  i t  active  might  during  Greater  be e x p e c t e d ETL i n awake  abdominal muscle  of  2  found d u r i n g ETL i n a n e s t h e t i z e d animals (8),  expiratory  decreased  by  neurons  (17),  anesthesia  anesthetized  animals  chemoreflexes  (8)  because (12).  and thus  chemoreceptor  Therefore,  i s not considered  load  t o be  animals  activation  might be e x p e c t e d i n the awake animal i n s p i t e o f the i n c r e a s e d PC0  that the  arterial  stimulation  responsiveness compensation  very  b u t chemoreflexes may be more r e l e v a n t  dependent  is in on  i n t h e awake  92  dog.  I n a d d i t i o n , p e n t o b a r b i t a l a n e s t h e s i a has been shown t o i n h i b i t  abdominal  motoneuron  phasic  discharge  r a i s i n g the t h r e s h o l d f o r a c t i v a t i o n . be  involved  conscious  thus  presumably  Moreover, CNS mechanisms t h a t may  i n t h e r e s p i r a t o r y response  goats  (11)  i n cats  to v e n t i l a t o r y  loading i n  (15).  Therefore,  appeared t o be a f f e c t e d by a n e s t h e s i a  i t would appear t h a t more p o t e n t i a l , n e u r a l pathways t o abdominal muscle activation reflexes these  are present  i n awake  may be so enhanced  inhibiting  effects  animals.  On the o t h e r  i n anesthetized  o f anesthesia  animals  hand,  vagal  (7,10,25),  on chemoreceptor  that  mediation  of  abdominal muscle a c t i v a t i o n may be c o u n t e r a c t e d . In  the p r e s e n t  shortening  study,  (18),  dogs.  b u t the p h a s i c  differences  phasic  14  2  plus  (12.4±0.5%).  I f total active),  lateral  However,  effects  i n the supine  activation  (see  position  decubitus  operating  by ETL was  total  i n t h e awake  be a r t i f a c t u a l  shortening  shortening  shortening  between  due t o t h e two  was measured,  which  i s c a l c u l a t e d i n the present  10 s h o r t e n i n g  increases  cmH 0) which i s c l o s e r t o the amount found  postural  expiratory  t o n i c (change i n the b a s e l i n e l e n g t h from LRL) and a c t i v e  shortening. (tonic  could  of active  study,  elicited  o f the 10 was l e s s  i n 10 s h o r t e n i n g  I n the e a r l i e r  study  muscles  phasic  i n a n e s t h e t i z e d dogs i n an e a r l i e r  shortening  i n the a n a l y s i s  i n c l u d e d both  be  t o t h a t found  The d i f f e r e n c e  studies.  of active,  o f t h e TA and EO abdominal  quantitatively similar study  the amount  there  Chapter (18)  could  be  t o 9.0±1.3%  i n the a n e s t h e t i z e d  less  10  shortening  I I I ) : the a n e s t h e t i z e d dogs were  dogs  due t o studied  and the awake dogs were s t u d i e d i n t h e l e f t  p o s i t i o n . A l t e r n a t i v e l y a stronger vagal  i n the a n e s t h e t i z e d  o f the abdominal  (Pao =  dog  muscles.  (7,10,25)  Since  reflex  generating  the 10 h a d a  could  greater  relatively  93  greater  activation  reasonable reflexes C0  2  is  to  during  expect  it  ETL i n to  be  reduced i n anesthetized (8)  and  relatively  muscle  activation  increased  during  the  increase  during  which  was measured  it  stimulation the awake An  of  ETL (up  the  provides  phases  to  (12),  (17).  early  by  it if  is  vagal  although s e n s i t i v i t y  loading,  however  cmH 0) 2  in  its  may  the  it  was  have  did  three  2  for  well  not  dogs  questionable  chemoreflexes  to C 0  stimulus  PC0  2  to  in  whether  a factor  in  dogs. interesting  aspect  of  been p r e v i o u s l y r e p o r t e d , was reflected  by  the  shorter  which o c c u r r e d w i t h  the p r e s e n t the presence  active  most l i k e l y t h a t t o n i c increases  FRC (8)  i n c r e a s i n g Pao.  (18).  Thus,  length  would  require  therefore,  would  just  be  length  An LABL  expected  increase had  to  in  tonic  10  a c t i v i t y because  its'  LABL was s h o r t e r than L R L ,  Tonic  shortening  significant  the  not  i n the  10,  compared than  the  Indeed,  the  in  LRL is  abdominal baseline  It  follows  tonic  muscle  and i n a d d i t i o n ,  i n tonic a c t i v i t y since  it  to  s i n c e ETL  resting  activity.  increase  the TA  i t maintained  its'  13). of  the  abdominal  muscles  e x p i r a t o r y s h o r t e n i n g , h e l p prevent an i n c r e a s e length.  shorter  lengthen  LABL a t  the  LABL e q u a l to LRL ( F i g u r e  (LABL)  has  underestimated,  that  p r o b a b l y a l s o had an i n c r e a s e  a  that  i n tonic a c t i v i t y .  m a i n t a i n i n g the  an  and one  of tonic a c t i v i t y  a c t i v i t y was a c t u a l l y  and  muscles  study,  baseline  was c o n s i d e r e d to i n d i c a t e an i n c r e a s e  diaphragm  activated  Arterial  14  (18),  additional  Therefore,  abdominal muscles  dog  ETL g e n e r a l l y l e a d s  an  of  a PEEP o f  (Table I V ) .  less  Lastly,  animals  therefore  abdominal  LRL,  anesthetized  are reduced i n the awake dog.  retention  as  the  Furthermore,  tonic  would,  like  i n FRC and thus  abdominal  muscle  phasic optimize  contraction  94  during  inspiration  would  reduce  the compliance  of  the  abdominal  compartment and hence, i n c r e a s e the i n f l a t i o n a r y a c t i o n o f t h e diaphragm on  (19).  t h e r i b cage  suggests  There i s both d i r e c t  expiratory  activity.  In a  loading  study  e x h i b i t e d continuous (2).  efferent,  breathing  increase  o f anesthetized  abdominal 20  cats,  gamma  i s provided  by the o b s e r v a t i o n  motoneurons  and t h e f r e q u e n c y  discharged  o f the t o n i c  gamma motoneuron d i s c h a r g e  sensitivity  of  consequently,  the  discharge  lung  abdominal w a l l muscle  volume  and e x c i t e  spindles,  t h e motoneuron  passive  pool  was  of  i s c l e a r from  abdominal  vagal  muscle  abdominal  during  quiet  the r e s p o n s e . t o  abolish  tonic  suggests  that  gamma  afferents  r a t e and (14)  and  In a d d i t i o n , the increase i n  by  ETL  (8)  would  s t r e t c h the  i n t h e abdominal  the abdominal muscles  i s supported  during  by t h e d e m o n s t r a t i o n  i n humans, when t h e e x c i t a b i l i t y by s u s t a i n e d  stretch  o f the  (16).  activity  discussion that, i s most l i k e l y  ETL.  motoneuron  The o b s e r v a t i o n discharge  supraspinal proprioceptor  a d d i t i o n a l pieces  with  An i n c r e a s e i n  although  control  l a r g e l y mediated by.  r e f l e x e s , s u p r a s p i n a l and segmental p r o p r i o c e p t i v e r e f l e x e s  facilitate  Two  spindle  facilitated  the p r e c e d i n g  tonic  breathing  the d i s c h a r g e  s t r e t c h responses  stretch reflex  abdominals induced by s t a n d i n g It  produced  Such a p o s s i b i l i t y  o f an abdominal muscle of  muscle  thus p o s s i b l y a c t i v a t i n g  (24).  inspiration  abdominal  tonic  increased  (24).  that  o f the cats  that  tonically  would i n c r e a s e  r e f l e x l y s h o r t e n t h e muscle.  end-inspiratory  muscle  percent  i n c r e a s i n g Pao, d u r i n g p o s i t i v e p r e s s u r e b r e a t h i n g tonic  evidence  EO EMG a c t i v i t y d u r i n g p o s i t i v e p r e s s u r e  I n d i r e c t evidence  muscle  can  and i n d i r e c t  o f evidence  t h a t vagotomy d i d n o t  during  expiratory  loading  pathways c a n be i n v o l v e d  suggest  could  supraspinal  (24).  and segmental  95  r e f l e x involvement i n the abdominal muscle response t o ETL: spinal  transection  thoracic  eliminated  and upper  lumbar  rhizotomy  and (2) b i l a t e r a l  with  spinal  dogs (13,18).  is  intact  also  p r e f e r e n t i a l a c t i v a t i o n o f the i n t e r n a l abdominal muscle l a y e r  ( T A and 10) by ETL i s c o n s i s t e n t w i t h p r e v i o u s  tidal  cord  lower  (3).  e l i m i n a t e d the response The  the response  (1) t h o r a c i c  As was concluded  r e p o r t s from  anesthetized  i n these e a r l i e r s t u d i e s , d i f f e r e n c e s i n  l e n g t h changes between the i n t e r n a l and e x t e r n a l abdominal muscles  likely  related  orientation  to differences  and compliance  i n origin  and  insertion,  o f the i n d i v i d u a l muscles.  Such  fiber  anatomical  d i f f e r e n c e s c o u l d have mechanical e f f e c t s on t h e l o a d on t h e muscle and its  p o s i t i o n on i t s l e n g t h - t e n s i o n  shortening. lengthened  In addition, more by p a s s i v e  curve,  the f a c t  that  lung i n f l a t i o n  leading  to differences i n  the i n t e r n a l  (18),  muscles a r e  might r e s u l t  i n greater  a c t i v a t i o n v i a proprioceptor afferents. E x p i r a t o r y t h r e s h o l d l o a d i n g i n awake dogs produced an i n c r e a s e i n FRC  b u t the increase  compensating mechanisms not  initiated  was  V  E  volume  until  a PEEP  i s generally  however result  (18,23).  there of a  compared  tends greater  was  Despite  in V  T  and B  f  would  be  the i n c r e a s e d FRC, V 2  also  maintained  t o be a g r e a t e r reduction  expected  i f load  abdominal muscle a c t i v a t i o n ) were  o f 18 cmH 0, a t which p o i n t  t o what was found  decreased  than  (particularly  mediated by s t r o n g e r v a g a l was  less  V  T  E  was m a i n t a i n e d , as decreased.  i n anesthetized reduction  i n breathing  i n the awake  dogs  Tidal  d u r i n g ETL,  i n V , p r i m a r i l y as a E  frequency  dogs.  (Bf)  The slower  a c t i v i t y under a n e s t h e s i a  (26).  (21,23),  Bf may be  Ventilation  a t a Pao o f 18 cmH 0 because o f a n o n s i g n i f i c a n t decrease 2  ( i n c r e a s e i n T T ) a t PEEP 18 cmH 0. T O  2  96  The in  trend  towards an i n c r e a s e d T T  (and  T O  t u r n due t o an i n c r e a s e d TE ( s i g n i f i c a n t  Expiratory prolongation  thus a d e c r e a s e d  a t Pao = 14 and 18 C111H2O). o f ETL (8)  i s an expected r e s u l t  shown i n a n e s t h e t i z e d dogs (21)  and c a t s  (5,10)  and has been  exposed t o ETL.  the response i s p r i m a r i l y mediated by v a g a l r e f l e x e s (5,6). was  l i n e a r l y r e l a t e d t o t h e i n c r e a s e i n FRC ( F i g u r e In  during  contrast  ETL.  to the increased  A initial  decrease  Bf) was  Again,  In fact, T  E  18).  T , T i was s i g n i f i c a n t l y  reduced  E  i n T i would be c o n s i s t e n t w i t h  vagal  i n h i b i t i o n o f i n s p i r a t i o n due t o the Hering-Breuer i n f l a t i o n r e f l e x  (9).  Indeed, an i n h i b i t i o n o f i n s p i r a t i o n was observed i n the awake dogs w i t h the  onset  o f ETL, which  Hering-Breuer r e f l e x  would  i n the  awake dogs.  study was measured from t h e flow therefore,  i s probably  certainly  support  the p r e s e n c e  However, the T i i n t h e p r e s e n t  tracing after breathing  not representative  o f neural  s t a b i l i z e d and  Ti.  Because ETL  l o a d s t h e i n s p i r a t o r y muscles as w e l l as the e x p i r a t o r y muscles, airflow  can begin,  t h e i n s p i r a t o r y muscles  airway p r e s s u r e  to zero.  remain c o n s t a n t  or increase to maintain  the  present  study,  As a r e s u l t ,  the  must  neural  Ti  contract  before  to return  T i would have  to e i t h e r  S i n c e VT was m a i n t a i n e d i n  Vj.  measured  o f an  most  likely  considerably  underestimated i n s p i r a t o r y d r i v e . In summary, the  abdominal  abdominal  expiratory  muscles.  muscles  diaphragm i n i t i a l  helps  threshold  Both prevent  loading  tonic  and p h a s i c  an i n c r e a s e  l e n g t h and m a i n t a i n i n g  abdominal  muscle  layer  recruited  and hence,  i n awake dogs a c t i v a t e s  VT.  i n FRC, thus  e x t e r n a l l a y e r (EO and RA).  effective  o f the  preserving  In a d d i t i o n , the i n t e r n a l  (TA and 10) appears  more  shortening  i n load  t o be  preferentially  compensation  than t h e  97  REFERENCES 1.  A g o s t o n i , E . , and E . J . M . Campbell. The abdominal m u s c l e s . I n : The R e s p i r a t o r y M u s c l e s : Mechanics and N e u r a l C o n t r o l . E . J . M . C a m p b e l l , E A g o s t o n i , and J . Newsom-Davis ( e d s ) . Saunders, P h i l a d e l p h i a , PA, 1970, 175-180.  2.  B i s h o p , B. 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ABDOMINAL MUSCLE ACTIVITY DURING HYPERCAPNIA  INTRODUCTION The hyperpnea activation abdominal  abdominal  muscles  produced  by  o f dogs  have  been  (3,18,20).  hypercapnia  shortening  demonstrated  There  a r e r e c r u i t e d by  (3,15,19,32).  hypercapnia  (EMG) and i n c r e a s e d muscles  and humans  Both  increased  (sonomicrometry)  i n anesthetized  do n o t appear  o f the  dogs  t o be any r e p o r t s  during o f the  s i m u l t a n e o u s response o f the f o u r muscles o f the v e n t r a l abdominal w a l l : r e c t u s abdominis transversus  (RA),  abdominis  external oblique (TA)  (EO),  to hypercapnia  has been p r e v i o u s l y shown i n a n e s t h e t i z e d IV)  dogs,  the four  have d i f f e r e n t expiratory  abdominal muscles  relative  threshold  by  loading  (16,20)  Recent  CO2 rebreathing.  are d i f f e r e n t i a l l y  the i n t e r n a l  muscle  studies  length  (28)  found  The r e s u l t s  changes  (TA and 10)  is  i n the p a t t e r n and  i n anesthetized  from  the EMG d a t a  the greatest  s t u d i e s , b u t evidence  (20).  indicated that  blood  r e b r e a t h i n g i n a n e s t h e t i z e d dogs. i n these  layer  stimulation  dogs  (3,18,20)  and l e n g t h changes o f t h e abdominal muscles  t h a n the EO and RA d u r i n g h y p e r c a p n i a al.,  r e c r u i t e d and  f o u r abdominal muscles w i t h  the TA was the l e a s t a c t i v a t e d by h y p e r c a p n i a abdominal  However, as  and awake (see Chapter  Whether d i f f e r e n c e s e x i s t  examined b o t h EMG a c t i v i t y during  (ETL);  o f these  C O 2 i s unclear.  i n awake dogs.  (10) and  c o n t r i b u t i o n s t o e x p i r a t i o n , when a c t i v a t e d by  preferentially recruited. degree o f r e c r u i t m e n t  i n t e r n a l oblique  (3,18). flow  suggested  that  However, a n a l y s i s o f  t h e TA s h o r t e n e d  more  I n a d d i t i o n , Robertson e t was t o t h e TA d u r i n g  C0  2  Shortening  o f the 10 was not  analyzed  from ETL (16)  suggests t h a t the  10 would  have a response s i m i l a r t o the TA.  100  Hypercapnia and c e n t r a l reflexes  abdominal muscle  chemoreflexes  (10).  thought  produces  to  (21)  In c o n t r a s t ,  be  mediated  with possibly  primarily  via  via  peripheral  some involvement  abdominal muscle  activation  vagal  m o d i f i e d by s p i n a l and s u p r a s p i n a l r e f l e x e s differences  activation  vagal  d u r i n g ETL i s  reflexes  (14).  of  and  possibly  We h y p o t h e s i z e d  that  i n the mechanisms o f a c t i v a t i o n c o u l d produce d i f f e r e n c e s  in  degree o f a c t i v a t i o n and p a t t e r n o f r e c r u i t m e n t o f the abdominal muscles d u r i n g h y p e r c a p n i a , compared to E T L . The  majority  of  studies ^ of  abdominal  h y p e r c a p n i a have used supine a n e s t h e t i z e d may a l t e r (10)  the  effects  and r e s p i r a t o r y muscle  influence  animals.  C O 2 on v e n t i l a t i o n  of  abdominal muscle  activity  (14).  recruitment  muscle  However,  (21),  may  Therefore,  effect  to  assess  abdominal muscles) activation left  the  were  to  recruitment  the  pattern  of  hypercapnia,  measured  l a t e r a l decubitus  response  the  Chapter I I I )  of  the  2  and  rebreathing  in  can  clearly,  These c o n f o u n d i n g abdominal  muscles.  major e x p i r a t o r y muscles  abdominal muscle  d u r i n g C0  pattern  Furthermore, posture  (see  to  anesthesia  breathing  the supine p o s i t i o n i s n o t p h y s i o l o g i c a l f o r the dog. factors  response  length awake  changes dogs  in  (the and the  position.  METHODS Five studied.  tracheotomized  female,  mongrel  The dogs were t r a i n e d to l i e  a c u f f e d tracheostomy  tube,  dogs  quietly,  (weight  23-29  kg)  were  w h i l e b r e a t h i n g through  d u r i n g the e x p e r i m e n t a l  protocols.  Instrumentation One  pair  of  2.5mm  double-lensed,  piezoelectric  transducers  101  (crystals)  (10-15mm  surgically  implanted  apart)  and  bipolar, fine  i n each o f the  wire  EMG  electrodes  f o u r abdominal muscles as  were  described  Chapter I I .  in  Two  dogs were s u r g i c a l l y  implanted  ( v a s c u l a r a c c e s s p o r t , model GPV, a r t e r i a l blood  sampling  with  femoral  artery  catheters  I L ) which  Access T e c h n o l o g i e s ,  allowed  from a subcutaneous p o r t l o c a t e d i n the  dorsal  lumbar r e g i o n .  Measurements Abdominal crystals. bared  The  ends  minigrabbers Technology, the dog  muscle crystals  and  s h i e l d e d cable  in or  shortening, initial  f u r t h e r d e f i n e d as  2  the  hypercapnia  The  was  termed  and  electromyographic  were  resting  from  tidal  resting  length  the  (LRL) .  A  active  (model of  the  resting was  (%LRL) .  tonic.  120,  by  Triton  muscle,  length,  w i t h «•  either  expressed  Muscle  EMG  The  termed L R L (as  Active  raw  wires. connected  p o s i t i o n , was  length or  fine turn  breathing,  o f t e n a decrease  the  in  piezoelectric  as  shortening  shortening  activity.  was  During  i n the b a s e l i n e l e n g t h new  baseline  baseline length  a  length (LABL)  from  during and  was  tonic shortening.  bared  minigrabbers  The  during  length  the  to a sonomicrometer  Change  FRC  with  isolated  that c o i n c i d i n g with phasic  resting  c o n s i d e r e d to be  wires  a c t i v e phasic  r e b r e a t h i n g , t h e r e was initial  to  l a t e r a l decubitus  I I ) .  Chapter  determined to be C0  Cal.).  i n the l e f t  p e r c e n t a g e o f the was  exteriorized  Diego,  measured  connected  the  San  lengthening  were  were  of  lying  described  lengths  ends  of  the  shielded  EMG  electrode  coaxial  wires  cable  s i g n a l s were a m p l i f i e d and  to  filtered  were  connected  amplifiers. (Grass model  by The  P511,  102  band w i d t h 100-10,000 Hz)  and  recorded  i n p a i r s w i t h the  sonomicrometer  signals. Ventilation attached  to  integrated  the to  was  measured  distal  give  end  tidal  with  of  the  volume.  a  pneumotachograph  tracheostomy  tube  (Fleisch  and  I n s p i r a t o r y (Ti) and  #1)  airflow  was  expiratory  (T ) E  d u r a t i o n were d e t e r m i n e d from the flow t r a c i n g on the c h a r t r e c o r d e r . two-way v a l v e to set by  (#2600 Hans-Rudolph Inc.,  the pneumotachograph, and up  as  the  gas  sampled  attachment  dogs  mixture  at  w i t h a C0  the to  rebreathe of  7%C0 , 2  the  before  was  2  10  liter  and  balance  a  needle  via  and  attached  expiratory airflow  bag N. 2  was  attained  containing  a  E n d - t i d a l C0  inserted  concentration  (%)  was  five 2  through  was the  determined  (model IL-200, F i s h e r S c i e n t i f i c L t d . ) .  and  blood  (Corning,  temperature.  168  samples  after  the r e b r e a t h i n g p e r i o d .  rectal  50%0  a  pneumotachograph,  milliliter  breathing,  Mo.)  Progressive hypercapnia  from  tracheostomy,  analyzer  2  One  analyzer  i n s p i r a t o r y and  a rebreathing c i r c u i t .  having  liter,  the  Kansas C i t y ,  A  the  PC0 , pH 2  were  obtained  during  r e b r e a t h i n g p r o t o c o l , and and P0  2  twice  resting during  were measured w i t h a b l o o d  gas  pH/Blood gas a n a l y z e r ) and c o r r e c t e d to the dog's  103  Protocol The other  protocols  expiratory VI) .  f i v e dogs used i n t h i s study a l s o underwent one o r more o f the on  different  days:  loading  (Chapter  threshold  This chapter  postural  changes  IV) and v a g a l  (Chapter I I I ) ,  blockade  d e s c r i b e s the p r o t o c o l f o l l o w e d f o r C0  Repeat  studies  o f C0  rebreathing  assess  the r e p r o d u c i b i l i t y o f the r e s u l t s .  2  were performed  (Chapter  rebreathing.  2  on d i f f e r e n t  days t o  A l l the s t u d i e s f o r each dog  were performed over p e r i o d s r a n g i n g from two t o e i g h t weeks. The in  r e b r e a t h i n g p r o t o c o l s began w i t h  the l e f t  lateral  decubitus  connected and the tracheostomy  position. tube was  control period of quiet breathing and  breathing  containing minutes.  a  The awake  mixture  C0  7%  After  and  2  on a p l a t f o r m  a l l the w i r e s  inserted, a five  followed,  to s t a b i l i z e . of  the dog l y i n g  to allow  dog then 50%  0, 2  were  t o t e n minute  the dog t o r e l a x  rebreathed  from a bag  f o r approximately  A l l s i g n a l s were r e c o r d e d on an e i g h t channel  recorder  five (Gould,  model 8000S).  Analysis For for  each  experimental  the c o n t r o l v a l u e s .  During  progressively,  therefore  three  around  breaths  analysis,  from 5.8-6.2%, mid C0 to and  7.6%.  2  2  was  level  of  C0  2  was three  To  levels.  was  mean v a l u e s  2  analyzed increased  the mean o f aid in  Low C 0 2  2  were  data  ranged  ranged from  from one o r more t r i a l s  individual  as mean ± SE.  and  used.  ranged from 6.8-7.0% and h i g h C0  mean o f these  Data a r e p r e s e n t e d  d i d not s t a b i l i z e  grouped i n t o  F o r each dog, the data  the o v e r a l l  a mean o f s i x b r e a t h s  the r e b r e a t h i n g , e n d - t i d a l C0  breathing  each  e n d - t i d a l C0  trial,  7.4  averaged  was c a l c u l a t e d .  whenever comparisons were made among  104  the  different  significance  abdominal  level  were made u s i n g heterogeneity  muscles,  a  one-way  o f P<0.05 accepted.  a Tukey's m u l t i p l e  o f standard  levels  used  comparison  test.  C0 , 2  When  one-way  o f P<0.05 accepted.  ANOVA  a  significant  To compare a l l t h e  a  and  comparisons  deviation existed, l o g transformations  of end-tidal  significance level  was  Post hoc m u l t i p l e  d a t a were made and t h e ANOVAs repeated. different  ANOVA  was  o f the  results at used  A Dunnett's m u l t i p l e  and a  comparison  t e s t was used t o t e s t f o r d i f f e r e n c e s from c o n t r o l measures.  RESULTS  The  arterial  implanted  with  hypercapnia Arterial  blood  gases  the v a s c u l a r  access  was a t t a i n e d d u r i n g  PC0  2  and pH  obtained  ports  the C0  from  confirms  the two  that  progressive  rebreathing protocol  2  i n c r e a s e d and pH decreased  as e n d - t i d a l C 0  dogs  ( T a b l e V) .  concentration  2  increased. Ventilation rebreathing transversus  C0 . 2  and A  abdominis  abdominal  muscle  representative (TA) EMG  activity  tracing  activity  of  were  stimulated  tidal  and TA l e n g t h  volume changes  by  (V ) , T  during  c o n t r o l and towards the end o f the r e b r e a t h i n g p e r i o d i s shown i n F i g u r e 19.  The TA l e n g t h e n e d  tracing)  and s h o r t e n e d  phasically rebreathing.  with  i n s p i r a t i o n (upward d e f l e c t i o n o f t h e volume  both  (corresponding  tonically  t o TA  EMG  (change activity)  i n baseline with  length)  expiration /  and  during  T a b l e V : A r t e r i a l b l o o d gas and pH v a l u e s d u r i n g CO2 r e b r e a t h i n g .  PaC0 (mmHg)  PETC02  2  Pa0 (mmHg) 2  pH  a  Control  37.5±0.5  95±2  7.36±0.03  Low C 0  2  43.8±0.5  88±2  7.34±0.01  Mid C 0  2  44.4±0.5  130±2  7.29±0.01  106  Figure  19: A r e p r e s e n t a t i v e r e c o r d i n g from an awake dog ( l e f t l a t e r a l decubitus position) showing t r a n s v e r s u s abdominis (TA) length changes, TA E M G a c t i v i t y and t i d a l volume (VT) d u r i n g C O 2 rebreathing. The left panel is control quiet breathing (normocapnia) and the r i g h t p a n e l i s d u r i n g C O 2 r e b r e a t h i n g . The downward d e f l e c t i o n o f the l e n g t h t r a c e c o i n c i d i n g w i t h i n i t i a t i o n o f EMG a c t i v i t y i s a c t i v e s h o r t e n i n g .  108  The  effects  of  breathing  pattern  are  levels, 1/min  V  T  was  (mean  809±66  16.5±2.37 increase  SE).  With  increasing  The i n c r e a s e  rather  to  minute  T  20  and  3.63±0.19  T O  decreased  V ,  Figure  T T was  TTOT  T  in  mis,  1/min. in V  shown  on  290±11  ±  mis,  hypercapnia  ventilation  Table V I . sec  and V  end-tidal  3.08±.21  sec  in ventilation  than b r e a t h i n g frequency  C0 , 2  and  was (Bf)  V V  E  T  E  since  However,  although Bf d i d not change,  significantly  highest  level  the  of  d u r a t i o n (Ti) d i d n o t change s i g n i f i c a n t l y  end-tidal  was  E  C0 . 2  and  control 5.0±0.44  increased  to  increased  to  due p r i m a r i l y  change s i g n i f i c a n t l y . at  At  (V )  to  TTOT d i d T  E  an not  decreased  Inspiratory  ( F i g u r e 21 and T a b l e VI) .  109  F i g u r e 20: Vj p l o t t e d as a f u n c t i o n o f e x p i r e d minute v e n t i l a t i o n (VE) d u r i n g C 0 r e b r e a t h i n g . V and V increased with increasing end-tidal C 0 concentrations. N=5. Values are means ± S E . A s t e r i s k s (*) indicate significantlyd i f f e r e n t from c o n t r o l ( P < 0 . 0 5 ) . 2  T  2  E  110  Figure  21: V p l o t t e d a g a i n s t T and T i d u r i n g C 0 r e b r e a t h i n g . N=5. V a l u e s are means ± SE. A s t e r i s k s (*) i n d i c a t e significantly d i f f e r e n t from c o n t r o l (P<0.05). T  E  2  T a b l e V I V e n t i l a t o r y Parameters f o r r e s t i n g a i r b r e a t h i n g and t h r e e l e v e l s o f e n d - t i d a l C O 2 .  V (mls)  PETC02  T  TTOT  (sec)  T (sec) E  control  Ti(sec)  Control  290±11  3.631.19  2.60±.21  1.03±.15  Low C 0  2  447±57  3.43±.28  2.26±.28  1.17±.23  Mid C0  2  660±71*  3.18±.23  1.85±.13  1.33±.18  809±66*  3.081.21  1.69±.ll*  1.39±.15  High C0  2  N=5. V a l u e s a r e means ± S E . Asterisks  (*)  indicate  significantly  different  from c o n t r o l  (P<0.05)  112  The  length  changes  (%LRL)  of  three  abdominal  muscles  r e s t i n g c o n t r o l b r e a t h i n g and a t three  levels of e n d - t i d a l C0  in  was  Figure  22.  The r e c t u s  negligible  changes  (LRL) ,  positive  the  negative  i n length.  changes  Active  length are  shortening  shortening  by  abdominis  changes  are  shortening  is  the  The 0 l i n e  unshaded  is  by  portion  i n c l u d e d because  the  resting  the  of  any o f the abdominal muscles,  tonic  and a c t i v e  high C0 was  2  level,  shortening  i n the  stimulated  (inspiratory expiratory  by  shaded  the  shortening  (Figures  23  increase  in total  as  V  increased  E  shortening the  and  was  Both greater  As  to  were  increased  plotted can  length  due  ( F i g u r e 24).  TA i n c r e a s e d  expiratory  24).  and  and  length  from c o n t r o l shown.  tonic  changes.  total  be  against seen  tidal  values  change  primarily  to  For example,  12.8±2.4%LRL  of  each the  the  two  the  tidal  (V ) E  figures,  abdominal in  the  phasic,  ventilation  increase  total  at  changes  and a c t i v e  these of  Both  ventilation  length  minute  from  values  Since  the  length.  from c o n t r o l  and e x p i r a t o r y s h o r t e n i n g )  were  tidal  portion  had  length  d u r i n g the s t i m u l a t e d b r e a t h i n g .  hypercapnia,  lengthening  it  baseline  negative  t h r e e abdominal muscles the  shown  the r e s t i n g b a s e l i n e  I n s p i r a t o r y l e n g t h e n i n g d i d not change s i g n i f i c a n t l y for  are  2  i n s p i r a t o r y lengthening  below  represented  not  during  muscles  active  length  the  phasic  change  o f which a p p r o x i m a t e l y 70% was  of  active  shortening. the  extent  internal than  the  oblique  (10)  external  increasing l e v e l s of e n d - t i d a l C0  2  and  oblique (Figure  TA a c t i v e l y (EO) 24).  as  V  shortened E  increased  to  a  with  113  Figure  22: Length changes o f the t r a n s v e r s u s abdominis ( T A ) , i n t e r n a l oblique (10) and e x t e r n a l oblique (EO) d u r i n g a i r - b r e a t h i n g c o n t r o l and a t t h r e e l e v e l s o f e n d - t i d a l C 0 . The 0 l i n e i s the r e s t i n g l e n g t h o f the muscles d u r i n g normocapnia, the positive length changes are i n s p i r a t o r y lengthening and the negative changes are s h o r t e n i n g below the r e s t i n g b a s e l i n e l e n g t h . Active shortening i s r e p r e s e n t e d by the b l a c k e n e d p o r t i o n and t o n i c s h o r t e n i n g by the unshaded p o r t i o n o f the n e g a t i v e l e n g t h changes. V a l u e s are means ± S E . 2  115  5  7  9  11  13  15  Ventilation (l/min)  F i g u r e 23: T o t a l t i d a l l e n g t h changes o f the TA, 10 and EO (%LRL) p l o t t e d a g a i n s t i n c r e a s i n g minute v e n t i l a t i o n d u r i n g C O 2 r e b r e a t h i n g . N=5. V a l u e s are means ± S E . A s t e r i s k (*) i n d i c a t e s s i g n i f i c a n t d i f f e r e n c e between EO compared to TA and 10 ( P < 0 . 0 5 ) .  17  Figure  24: A c t i v e s h o r t e n i n g o f the TA, 1 0 and EO (%LRL) p l o t t e d against increasing minute ventilation during C0 r e b r e a t h i n g . N=5. Values are means ± S E . A s t e r i s k s (*) i n d i c a t e s s i g n i f i c a n t d i f f e r e n c e between EO and TA and 1 0 2  (P<0.05).  117  DISCUSSION This  study  shows  hypercapnia with  that  the  an i n c r e a s e  means o f an i n c r e a s e  awake  dog  i n minute  i n t i d a l volume  responds  ventilation  (V ) .  to  (V ) ,  progressive p r i m a r i l y by  E  The abdominal muscles  T  are  a c t i v a t e d and e x h i b i t b o t h t o n i c and p h a s i c e x p i r a t o r y s h o r t e n i n g d u r i n g C0  rebreathing.  2  and  10)  is  In a d d i t i o n ,  preferentially  the i n t e r n a l abdominal muscle  r e c r u i t e d and shortens  to  l a y e r (TA  a greater  extent  t h a n the e x t e r n a l l a y e r (RA and E O ) . Hypercapnia patterns.  can  Breathing  increased  V  T i (6,10).  number  of  measuring  timing  such  observed  of  in  various  (Bf)  (23);  i n breathing as  the  parameters,  PC0  2  E  levels)  range  species  results  have  been  (10) and dogs (1) decreased PC0  2  ratio  of  PC0  T OT T  attributed  also to  different  the e f f e c t s  of  and thus  transition  to  a  new l e v e l  the  V  and  T  anesthesia  study,  This  2  of  and the  rebreathing C0  2  from c o n t r o l a t the h i g h e r  response  Similar  o f awake  the T i / T  that  cats  In those two s t u d i e s , T  divergence  PC0 ,  a  A l t h o u g h Bf (TTOT) d i d n o t  rebreathing versus  of  from  method  ratio  E  increased  to what was found i n the  I t has been shown i n awake human s u b j e c t s of  result  increased during hypercapnia.  i n contrast  decreased.  used,  differences,  to s t e a d y - s t a t e h y p e r c a p n i a .  However,  could  2  r e p o r t e d f o r the v e n t i l a t o r y  b u t T i was unchanged,  increased.  study,  E  increased  patterns  I n the p r e s e n t  (significantly  and the T i / T  include:  E  i n c r e a s e d v e n t i l a t i o n by i n c r e a s i n g VT a l o n e . T decreased  breathing  studies  T  method o f p r o d u c i n g h y p e r c a p n i a .  change,  different  and i n c r e a s e d V , decreased T and no change  Differences  factors  variety  frequency  (22,29);  E  a  patterns  and b r e a t h i n g  T  d e c r e a s e d T i and T in  generate  in  results  i n the f i r s t  T i and T  E  tend  to  as  present  could  steady-state  E  be  methods.  2-3  minutes  change  in  118  opposite  directions  Such was  the  case  with consequently, i n the  present  little  study;  d u r i n g r e b r e a t h i n g , whereas TE decreased Breathing decreased of  dogs,  methodological  also  which  among the  reported  in  using  differences  that  E  V  T  Ti actually  increased  increased  and  r e p o r t e d from two  steady-state  Smith et  i n TTOT  (9) .  slightly  (Table V I ) .  could explain  studies.  apparatus and T i and T Ti  in  d u r i n g h y p e r c a p n i a were  awake  results  patterns  o r no change  T  both  E  studies  (22,29).  Again,  the  discrepancies  in  used a flow  through hood  were measured from flow r e c o r d i n g s .  The c o n t r o l  study  was  greater  (29),  and  additional  methods  some o f  al.  Tj  than t h a t  found  in  the  present  study and i n o t h e r s t u d i e s from the same l a b o r a t o r y , i n which awake dogs breathed  through  parameters were reported  it  variability  Ti as in  from  appears  and two o f  and t h e r e f o r e ,  four  a decrease  that the  i n T i , the  studies.  it  much l i k e humans (6,10);  difference  anesthetized  (present  be  E  the  dogs  timing  al.  but  (22),  gave  no  However, upon c l o s e e x a m i n a t i o n o f Bf  and  Ti  had  dogs had a much slower  Ti/T  that  P h i l l i p s o n et  increase  a  wide  range  Bf and g r e a t e r  of  Ti at  i n Bf and d e c r e a s e  in  o f whether o r not h y p e r c a p n i a r e s u l t e d  ratio  increased with  increasing results  PCO2  in  and those  appears t h a t awake dogs respond to h y p e r c a p n i a p r i m a r i l y by i n c r e a s i n g V  Bf r e s u l t from a decrease  dogs  may  T h e r e f o r e , based on the p r e s e n t  from p r e v i o u s s t u d i e s ,  awake  it  tracheotomized  control  Regardless  2  The  awake,  a r e l a t i v e l y greater  PC0 i n c r e a s e d .  b o t h these  Therefore,  f o r the h y p e r c a p n i a d a t a .  data,  rest  (1).  a l t e r e d by the hood a p p a r a t u s .  results  statistics the  masks  i n T , with l i t t l e E  i n breathing results  animal s u p p o r t s  and  pattern (1))  T  and any i n c r e a s e s  in  or no change i n T i . response  and c a t s  the c o n c l u s i o n t h a t  (10)  to  hypercapnia compared  anesthesia  in  to  the  effects  the  119  breathing pattern response. (10,35)  VT  Unlike  awake  responded  increase (TI/T  response  to  to h y p e r c a p n i a , animals,  increases  during  by  (32)  stimulated  by  anesthetized  (3,20).  hypercapnia.  dogs  with phasic,  that  that  The p r e s e n t  (19,27) T  and Bf;  the  i n b o t h T i and T E  potentiation  of  and awake dogs  abdominal muscle In  addition,  shortening  study  V  and c a t s  the d e c r e a s e i n T i , as  a  (19,34)  abdominal muscle  expiratory  ventilation  vagal  (24,36).  i n anesthetized  demonstrated  the  both  that  reflects  i n h i b i t o r y r e f l e x e s by a n e s t h e s i a  humans  dogs  increasing  I t i s thought  hypercapnia,  Previous studies  as  from a p r o p o r t i o n a l decrease  r a t i o d i d n o t change).  e  anesthetized  hypercapnia  i n Bf r e s u l t i n g  as w e l l  expiratory it  has  activation  extends  these  activity  been  is in  associated  during hypercapnia  findings  to  awake  shows t h a t abdominal muscle a c t i v a t i o n by h y p e r c a p n i a r e s u l t s e x p i r a t o r y s h o r t e n i n g and i n a d d i t i o n ,  shown  (EMG) i s  (sonomicrometry)  (29) and  dogs and i n phasic,  t o n i c s h o r t e n i n g o f the abdominal  muscles. It  is  difficult  to  compare  s h o r t e n i n g found i n the p r e s e n t anesthetized  dogs  because  b r e a t h i n g p a t t e r n response of analyzing active length the This  decrease method  result the  changes  of  parameters  the  shortening.  include  (20).  tonic  differences  (3,20) length  in  ventilation  analyzed phasic below  shortening,  of active,  In addition,  Despite  muscle  and  i n methods  Two s t u d i e s r e p o r t i n g abdominal muscle  i n abdominal muscle  study.  abdominal  to h y p e r c a p n i a and the d i f f e r e n c e s  i n an o v e r e s t i m a t i o n  present  phasic  studies with that reported i n studies of  during hypercapnia  would  the a c t i v e ,  only  phasic  the r e l a x e d which  if  when EO t o t a l  would  as d e f i n e d  detailed  as  FRC l e n g t h .  present,  shortening  one study  these d i f f i c u l t i e s ,  shortening  in  ventilatory tidal  length  120  changes  were  12.81/min  compared  (Figure  Furthermore, produce (3,20), can  if  at  23)),  it  is  they  V E in  comparable  similar  ventilation  were  assumed  that  similar  both  a  study  found (3),  to  750  (5.1%),  position likely  (tonic  quite  for  (12). that  comparable  follows  therefore,  is  the  compared  awake  positions)  awake  No o t h e r it  study.  to  that  dogs  lying  studies the  in  describe  same  reported  the  abdominal muscle  right  The  dog  (at  s h o r t e n i n g has Clearly,  a direct  to  VT.  occurs  addition,  of  below  the the  there  increase muscle's  abdominal muscle  would  be  muscles  an  significant  The p r e s e n t  general  a VT of  decubitus it  is  conclusion  is  least  similar  in  the  at  passive  active,  initial  in  lying  in  recoil  end-expiration. component  of  indirect  an  effects  (LRL).  resulted  This  the  chest  recoil  a  which  That  is,  One r e s u l t  wall may  i n s p i r a t o r y mechanical  as  i n a decrease  (LEE) (Figure 22). of  increase  shortening  length  abdominal muscles  outward  is  effects  expiratory contribution  expiratory  resting  important  effect  a number o f  end-expiratory length  increase  relaxed  are  in  h y p e r c a p n i c s t i m u l a t i o n o f the in  earlier  changes b u t  several  e x p i r a t o r y flow r e s u l t i n g i n a g r e a t e r a c t i v e in  the  lateral  10 l e n g t h  in  But  shortening)  those r e p o r t e d a t  trend.  anesthetized  d u r i n g h y p e r c a p n i c hyperpnea.  consequence  in  respectively.  the  (3)  i s n o r m a l i z e d to V E .  when i t  Phasic,  dogs  When TA s h o r t e n i n g  t h a t abdominal muscle e x p i r a t o r y s h o r t e n i n g to  would  anesthetized  s h o r t e n i n g and a c t i v e p h a s i c  TA % L R L a l s o compare f a v o u r a b l y to  of  of  and  4.0%LRL.  PCO2  end-tidal  preparations  a p p r o x i m a t e l y 8.0%LRL and 10.5%LRL,  results ml  be  (20)  approximately  similar  be compared to those found i n the p r e s e n t  was  (12.41/min  o f TA l e n g t h changes d u r i n g CO2 r e b r e a t h i n g  then the r e s u l t s  below FRC was c a l c u l a t e d it  a  when produce  flow,  the a  despite  121  increasing  inspiratory  muscle  activation  Evidence  support  proposal  is  to  studies  of  awake  between  onset  of  this  dogs  (1,30).  It  inspiratory  diaphragm EMG a c t i v i t y  and  inspiratory  p r o v i d e d by o b s e r v a t i o n s  was  shown  that  there  flow  (Ti)  and  mechanical  EMG a c t i v i t y  of  inspiratory  reflects  active  flow  passive.  was  reported that p a r a s t e r n a l i n t e r c o s t a l a c t i v i t y patterns awake  dogs  and  s i m i l a r to thus,  the  would  not  be  (12).  abdominal  muscle  to  utilizing  the  (30)  from the  awake s t a n d i n g dogs, i n end-expiratory contrast, the  would  be  expiratory reserve  estimated  by  decrease  in  l u n g volume  Indeed,  responsible  allow  V T to  abdominal  (EELV)  Finally, excursion L E E  of  when  capability  crural  sterni since  than  of  inspiration  a decrease  in  partially  by  Smith et  al., in  and T A ) , EELV i n c r e a s e d  by  the  curve  Therefore,  the  no  In of  the  was  c r u r a l diaphragm i s costal  would presumably  diaphragm  length-tension (26).  recently  recruitment  diaphragm  (7),  a  crural  dogs c r u r a l diaphragm r e s t i n g  length  generating  LEE would p l a c e and i n c r e a s e  lengthen  more  the  to be 93% o f LQ ( o p t i m a l p r e s s u r e  its  was  any  In f a c t ,  there  is  of  significant  approximately 0 . 1 6 l i t e r s .  In supine a n e s t h e t i z e d  part  that  i n end-expiratory p l e u r a l pressure  (triangularis  0.27 liters.  increasing  for  increase  (ERV).  diaphragm.  Thus,  of  and 23%  assuming a  it  Another e f f e c t  hypoxia,  abdominal muscle  estimated  onset  that hypercapnic s t i m u l a t i o n r e s u l t e d i n a decrease  e x p i r a t o r y muscles  effected  inspiration,  delay  diaphragm d u r i n g h y p e r c a p n i a i n  volume  increase  during hypocapnic  an e s t i m a t e d  the  a  i n s p i r a t o r y muscles had t i m i n g and  costal  p r e c e d i n g diaphragm a c t i v a t i o n LEE  was  Thus,  2  portion  from two  t h a t was a p p r o x i m a t e l y 19% o f T i a t r e s t  o f T i d u r i n g h y p e r c a p n i c ( 6 . 5 % C 0 ) hyperpnea (30). diaphragm  flow.  its  overall effects  it  length)  on a more o p t i m a l  pressure of  (26).  generating  abdominal muscle  122  phasic the  s h o r t e n i n g would be  to  distribute  i n s p i r a t o r y and e x p i r a t o r y muscles  efficiency The  the  work o f b r e a t h i n g between  and to  increase  the  o f the diaphragm. present  study  appears  to  be  the  first  to  demonstrate  abdominal muscle s h o r t e n i n g d u r i n g h y p e r c a p n i c h y p e r p n e a . slight  indirect  studies of gastric tonic  evidence  awake dogs  pressure  in  the  of  tonic  (1,30).  abdominal muscle  A t r e n d towards  r e p o r t e d by A i n s w o r t h et  abdominal muscle  studied  mechanical  activity.  standing  However,  position,  activity  (1)  since  any change  There i s  an i n c r e a s e  al.,  in  was  the tonic  abdominal muscle  from  the  same  expiratory  allow  the  muscle  and would  change  in  tonic  activity  position  (see  have  1.  be It  (PEEA) It  to  awake  dogs  would  tonic  be  difficult  been  the is  potential  possible  effects  that  both  increased.  the  diaphragm to  (26),  2.  insertional  expand the  and a p p o s i t i o n a l  of  by a l l o w i n g  of  its  to  study  showed  post-  that  into  PEEA would  resting  baseline  Again,  determine,  due  to  posture  to  the  any since  standing  tonic  abdominal  muscle  the  diaphragm to  begin  the m e c h a n i c a l advantage  Tonic  d e c r e a s e abdominal w a l l compliance.  enables  due  Another  shortening.  present  were  TA e x t e n d i n g  possible  to  III).  diaphragm would be  would  is  baseline  activity  dogs,  the  as  s h o r t e n i n g from a more o p t i m a l l e n g t h the  of  r e l a x back to  manifest  already  standing  two  attributed  Chapter I I I ) .  using  (30).  enough time  EMG a c t i v i t y may  (see  EMG a c t i v i t y  therefore  Chapter  What would shortening?  also  during hypercapnia  length  tonic  activity  laboratory,  expiratory  inspiration, not  tonic  some  from  in  h y p e r c a p n i c s t i m u l a t i o n may have been obscured by the e f f e c t s on  tonic  abdominal muscle  of  activity  Reduced abdominal compliance  r i b cage  components  more e f f e c t i v e l y (17).  3.  It  through  may be  that  123  tonic in  abdominal muscle  much  (PIIA)  the  is  same  thought  activity  manner to  that  "track"  contraction of antagonistic to  retard  decrease (6). The  inspiratory  enables  TE to  tracking  that  increase  tripled that  in  inflation  did  to  T  not  produced an  turn  is,  simultaneous  would  help  to  during progressive  CO2 d r i v e  to  reduces  indirectly  prevent  a  hypercapnia study.  (30),  PIIA  support  be  muscles  and  abdominal in V  T  length  predicted (16).  the abdominal muscles  responsible be  for  the  involved  parasternal  might  has  this  which  inspiratory  be  in  expected  intercostal  a  are  anesthetized  greater  to  the  increase LEI of  muscle  the  in  agreement  shortening  dogs  muscles  dogs (3,20).  of  with  in  was the  those  The f a c t  i n s p i t e o f an i n c r e a s e  cage  lung  abdominal  characteristics  cage c o n t r i b u t i o n to  rib  (33)  muscle  anesthetized  that EILV,  inspiration  was  Mechanisms  that  i n c r e a s e d EILV d u r i n g h y p e r c a p n i a . in  shown  d u r i n g h y p e r c a p n i a and  passive  results  d i d not l e n g t h e n  VT almost  Considering that passive  from c o n t r o l  in rib  intercostal  However,  from the  since  p r e v i o u s l y been  lengthening  (LEI).  These  an i n c r e a s e  it  (EILV),  parasternal  muscle  found i n two s t u d i e s o f s u p i n e ,  that  volume  In a d d i t i o n ,  significantly  than might  lung  during hypercapnia.  increase  change  abdominal  could  That  as PCO2 i n c r e a s e d i n the p r e s e n t  tends  (27)  end-inspiratory  implies  in  increase  end-inspiratory  diaphragm  such  less  (25).  activity  f o r a decrease i n EELV, there would c l e a r l y a l s o be  shortening increases  muscle  This  during rebreathing.  both  (16),  inspiratory  hypothesis.  Even a l l o w i n g an  inspiration  e x p i r a t o r y and i n s p i r a t o r y muscles would a c t  increasing  decrease,  "track" or brake  post-inspiratory  T i d i d not change  observation  to  expiration  flow.  i n T i and a l l o w V  Indeed,  serves  contribution  are  or a p r o g r e s s i v e  increased  increase  in  124  diaphragmatic compliance although  (produced  by  diaphragmatic  mechanical rib  shortening,  action  is  in  association  tonic  with  abdominal  shortening  muscle  progressively  t r a n s f e r r e d to  reduced activity).  increases  displacement  abdominal  of  the  Thus,  (8,27),  more  its  compliant  cage (17) . The  length,  lack  of  increase  d e s p i t e an i n c r e a s e  activity  in  abdominal  i n EILV,  mediated by segmental  the abdominal muscles shortening  of  the  muscle.  end-inspiratory  a l s o suggests the p r e s e n c e  reflexes.  and a c t i v a t e  muscle  Increasing  This  hypothesis  is  of  EILV would  muscle s t r e t c h r e f l e x e s ,  (EI) tonic  stretch  resulting  consistent  with  in the  o b s e r v a t i o n t h a t the muscles which are the most s t r e t c h e d d u r i n g p a s s i v e lung i n f l a t i o n  (TA and 10)  (16)  are  the  ones which showed  t o n i c shortening during hypercapnia (Figure Abdominal muscle to  be  a  function  E  of  (13),  central  of  the  hyperpnea  are  e x p i r a t o r y muscle r e c r u i t m e n t C0  abdominal  motoneurons  evidence  has  2  an  22).  which  produced.  Although  excitatory (15).  thought  (31). effect  However,  to be  In the on  the  primary  on  mediators  absence o f p r o p r i o c e p t o r  expiratory  there  is  also  neurons  (4)  a  body  large  and of  to s u p p o r t the c o n c l u s i o n t h a t abdominal muscle a c t i v i t y d u r i n g  hypercapnia  is,  at  least  partially,  In a d d i t i o n ,  t h a t segmental  r e f l e x e s may a l s o p l a y a r o l e .  Although recruitment  the  are  loading  control  different (ETL-see  the  results  mediated  (2,5,11,19).  threshold  is  appears  might be i n v o l v e d i n d i r e c t l y , v i a i n f l u e n c e s  chemoreflexes  feedback,  greatest  r e c r u i t m e n t by h y p e r c a p n i a i n awake dogs  p e r i p h e r a l chemoreflexes V  the  mechanisms during  from the  involved  hypercapnia  Chapter I V ) ,  the  by  vagal  present  in  afferents  study  suggest  abdominal  compared  recruitment  to  muscle  expiratory  pattern  which  125  was  observed,  not  differ  predominantly  from the  therefore, the  of  some  differences,  abdominal  muscle  hypercapnia  despite  to  be  hypercapnia  abdominal  10  could muscle  is  less  muscles, ETL;  making  In shortening  of  shortening  summary, of  the  effects  e x p i r a t o r y muscles  layer  more  these  during  concluded  increase  in  compared  to  less  reflexes  than  it the  effect  in  redistribute  and  increase  the  thus,  also  What  differences to  to  in  hypercapnia?  may be  that  other  the  abdominal  the  activation  and the  muscle  increasing  their  afferents.  awake  some o f  would have advantages  w i t h l u n g volume  There  on abdominal  h y p e r c a p n i a produces  and to  tonic  s m a l l e r amount o f s h o r t e n i n g d u r i n g  excitable  muscles  TA  similar.  apparent  (1)  There  ETL compared  ETL compared  a direct  The p r e f e r e n t i a l  (TA and 10)  these muscles  to  be  were  explanations:  vagal  progressive  would be  to  shortening  for  changes  abdominal  does  alone.  13)  during  to a c t i v a t i o n by muscle s p i n d l e  diaphragm.  muscle  TA  two p o s s i b l e  them  be  greater  (Figure  appeared  EO p h a s i c  by  cannot  TA e n d - i n s p i r a t o r y l e n g t h .  o r h y p e r c a p n i a may have  susceptibility  the  to  length  responsible  influenced  motoneurons  the  greater  length  activation,  CO2 s t i m u l a t i o n  to  there  phasic  It  ETL produced a  which c o u l d account f o r i t s  (2)  overall  yet  and  be  Speculation leads TA  the  less  but  mechanisms  comparison  however.  22)  layer  a l t e r the g e n e r a l r e c r u i t m e n t p a t t e r n o f  end-inspiratory  (Figure  shortening, appeared  in  muscle  seen d u r i n g E T L .  that vagal afferents  abdominal muscles  were  to  pattern  internal  tonic  dog,  the  and  of  phasic  which  work o f  breathing  mechanical e f f i c i e n c y of  the  internal  i n terms o f  greater  the  mechanical  the  of  abdominal coupling advantage  produced by v i r t u e o f t h e i r o r i e n t a t i o n to the abdominal compartment.  126  REFERENCES 1.  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(Abstract)  13.  Heeringa,  J . , A . Berkenbosch,  J . De Goede and C N . O l i e v i e r .  127  R e l a t i v e c o n t r i b u t i o n o f c e n t r a l and p e r i p h e r a l chemoreceptors to the v e n t i l a t o r y response to C02 d u r i n g h y p e r o x i a . R e s p i r . P h v s i o l . 37: 365-379, 1979. 14.  I s a z a , G . D . , J . D . Posner, M.D. A l t o s e , S . G . K e l s e n and N . S . C h e r n i a c k . Airway o c c l u s i o n p r e s s u r e s i n awake and a n e s t h e t i z e d g o a t s . R e s p i r . P h y s i o l . 27: 87-98, 1976.  15.  L e d l i e , J . F . , A . I . Pack and A . P . Fishman. E f f e c t s o f h y p e r c a p n i a and h y p o x i a on abdominal e x p i r a t o r y nerve a c t i v i t y . J . A p p l . P h y s i o l . 55(5): 1614-1622, 1983.  16.  L e e v e r s , A . M . and J . D . Road. M e c h a n i c a l response to h y p e r i n f l a t i o n o f the two abdominal muscle l a y e r s . J . A p p l . P h y s i o l . 6 6 ( 5 ) : 21892195, 1989.  17.  Macklem, P . T . , D . M . Macklem and A . De T r o y e r . A model o f i n s p i r a t o r y muscle mechanics. J . Appl. Phvsiol. : Respirat. Environ. E x e r c i s e P h v s i o l . 55: 547-557, 1983.  18.  Ninane, V . , J . J . G i l m a r t i n and A . De T r o y e r . Changes i n abdominal muscle l e n g t h d u r i n g b r e a t h i n g i n supine dogs. R e s p i r . P h v s i o l . 73: 31-42, 1988.  19.  O l i v e n , A . , E . C . D e a l , J r . , S . G . K e l s e n and N . S . C h e r n i a c k . E f f e c t s o f h y p e r c a p n i a on i n s p i r a t o r y and e x p i r a t o r y muscle a c t i v i t y d u r i n g e x p i r a t i o n . J . A p p l . P h y s i o l . 59(5): 1560-1565, 1985.  20.  O l i v e n , A . and S . G . K e l s e n . E f f e c t o f h y p e r c a p n i a and PEEP on e x p i r a t o r y muscle EMG and s h o r t e n i n g . J . A p p l . P h y s i o l . 6 6 ( 3 ) : 1413, 1989.  1408-  21.  P a v l i n , E . G . , and T . F . H o r n b e i n . A n e s t h e s i a and the c o n t r o l o f v e n t i l a t i o n . I n : Handbook o f P h y s i o l o g y S e c t i o n 3: The R e s p i r a t o r y System. V o l . I I I . P . T . Macklem, and J . Mead ( e d s ) . W i l l i a m s & W i l k i n s , B a l t i m o r e , MD, 1986,  22.  P h i l l i p s o n , E . A . V a g a l c o n t r o l o f b r e a t h i n g p a t t e r n independent o f l u n g i n f l a t i o n i n c o n c i o u s dogs. J . A p p l . P h y s i o l . 37(2): 183-189, 1974.  23.  P h i l l i p s o n , E . A . , R . F . H i c k e y , C R . B a i n t o n and J . A . N a d e l . E f f e c t o f v a g a l b l o c k a d e on r e g u l a t i o n o f b r e a t h i n g i n c o n c i o u s dogs. J . A p p l . P h v s i o l . 2 9 ( 4 ) : 475-479, 1970.  24.  P h i l l i p s o n , E . A . , R . F . H i c k e y , P . D . G r a f and J . A . N a d e l . H e r i n g Breuer i n f l a t i o n r e f l e x and r e g u l a t i o n o f b r e a t h i n g i n c o n c i o u s dogs. J . A p p l . P h v s i o l . 31(5): 746-750, 1971.  25.  Remmers, J . E . and D\ B a r t l e t t , J r . . R e f l e x c o n t r o l o f e x p i r a t o r y a i r f l o w and d u r a t i o n . J . A p p l . P h v s i o l . 4 2 ( 1 ) : 80-87, 1977.  26.  Road, J . , S. Newman, J . P . Derenne and A . G r a s s i n o . I n v i v o l e n g t h f o r c e r e l a t i o n s h i p o f canine diaphragm. J . A p p l . P h y s i o l . 6 0 ( 1 ) : 63-  128  70, 1986. 27.  Road, J . D . , S . L . Newman and A . G r a s s i n o . Diaphragm l e n g t h and b r e a t h i n g p a t t e r n changes d u r i n g h y p o x i a and h y p e r c a p n i a . R e s p i r . P h v s i o l . 65: 39-53, 1986.  28.  R o b e r t s o n , C . H . , M . A . Pagel and R . L . Johnson. The d i s t r i b u t i o n o f b l o o d f l o w , oxygen consumption and work output among the r e s p i r a t o r y muscles d u r i n g u n o b s t r u c t e d h y p e r v e n t i l a t i o n . J . C l i n . I n v e s t . 59: 43-50, 1977.  29.  S m i t h , C . A . , D . M . A i n s w o r t h , K . S . Henderson and J . A . Dempsey. D i f f e r e n t i a l responses o f e x p i r a t o r y muscles to c h e m i c a l s t i m u l i awake dogs. J . A p p l . P h y s i o l . 66(1): 384-391, 1989.  in  30.  S m i t h , C . A . , D . M . A i n s w o r t h , K . S . Henderson and J . A . Dempsey. D i f f e r e n t i a l t i m i n g o f r e s p i r a t o r y muscles i n response to c h e m i c a l s t i m u l i i n awake dogs. J . A p p l . P h y s i o l . 6 6 ( 1 ) : 392-399, 1989.  31.  S t . J o h n , W.M. R e s p i r a t o r y neuron responses to h y p e r c a p n i a and c a r o t i d chemoreceptor s t i m u l a t i o n . J . A p p l . P h y s i o l . 5 1 ( 4 ) : 816-822, 1981.  32.  T a k a s a k i , Y . , D. O r r , J . P o p k i n , A . X i e and T . D . B r a d l e y . E f f e c t o f h y p e r c a p n i a and h y p o x i a on r e s p i r a t o r y muscle a c t i v a t i o n i n humans. J . A p p l . P h v s i o l . 6 7 ( 5 ) : 1776-1784, 1989.  33.  v a n L u n t e r e n , E . and N . S . C h e r n i a c k . E l e c t r i c a l and m e c h a n i c a l a c t i v i t y o f r e s p i r a t o r y muscles d u r i n g h y p e r c a p n i a . J . A p p l . P h v s i o l . 6 1 ( 2 ) : 719-727, 1986.  34.  van L u n t e r e n , E . , M . A . H a x h i u , N . S . C h e r n i a c k and J . S . A r n o l d . R i b cage and abdominal e x p i r a t o r y muscle responses to C02 and esophagel d i s t e n s i o n . J . A p p l . P h v s i o l . 64(2): 846-853, 1988.  35.  Widdicombe, J . G . and A . Winning. E f f e c t s o f h y p o x i a , h y p e r c a p n i a and changes i n body temperature on the p a t t e r n o f b r e a t h i n g i n c a t s . R e s p i r . P h v s i o l . 21: 203-221, 1974.  36.  Younes, M . K . , and J . E . Remmers. C o n t r o l o f T i d a l Volume and R e s p i r a t o r y Frequency. I n : The R e g u l a t i o n o f B r e a t h i n g . M a r c e l Dekker, I n c . , New Y o r k , 1981, 621-671.  129  VI.  EFFECTS OF VAGAL BLOCKADE ON ABDOMINAL MUSCLE ACTIVATION  INTRODUCTION The loading The  abdominal muscles  are  (ETL) and h y p e r c a p n i a as has  mechanisms  of activation  inflation  reflexes  hypercapnia. previously  in  activated  by  the  following  inspiratory timing  recruitment  effects  In  of  in  Chapters  muscles  of  the for  has  recently  removal  Such d i f f e r e n c e s  may  mechanisms  variable  in  may  indirectly  that the  effect  of  muscle  unanesthetized significantly  the  TA i s  vagally  effects  of  degrees  abdominal  shown  of  and  when  via  suggests  and V ,  expiration  (TA) EMG a c t i v i t y was not which  during  non-  example  been  IV  lung  recruited  potential  activation  addition,  (8)  are  contributions'to  i n h i b i t o r y and e x p i r a t o r y e x c i t a t o r y parameters  chemoreflexes  (13,18,19,21).  (9),  on  under  mediated  ventilation  abdominal  muscle  patterns. s t u d i e s have p r e d o m i n a n t l y u t i l i z e d a n e s t h e t i z e d  Since anesthesia  anesthesia animals.  vagotomy  shown  muscles;  abdominis  influences.  Previous (13,18,19).  it  peripheral  relative  reflex  Indeed,  transversus  extravagal  and  abdominal  shown i n Chapters IV and V .  to be p r i m a r i l y v i a a v a g a l l y -  these  contributions  supraspinal  proprioceptors. dogs t h a t  been  ETL o r h y p e r c a p n i a  of  or  and  dogs,  different  differing  spinal  has  anesthetized  and have  activation  as  threshold  d u r i n g ETL and v i a v a g a l l y - m e d i a t e d  central  However,  uniformly  reflect  and  during expiratory  been  are thought  mediated l u n g i n f l a t i o n r e f l e x  reduced  recruited  vagotomy and  in  differ  Therefore,  i s known to i n f l u e n c e  anesthetized from  the  the  animals  effects  objectives  of  of this  reflexes  may be vagal study  animals  (12,29)  confounded blockade were  to  the  by  in  the  awake  identify  130  individual awake  abdominal muscle  dogs b e f o r e  what degree the  recruitment  and a f t e r  reversible  i n d i v i d u a l muscles  d u r i n g ETL and h y p e r c a p n i a vagal blockade  are under v a g a l  to  in  determine  to  influence.  METHODS Six tracheotomized, implanted with  female mongrel dogs (22-29kg) were c h r o n i c a l l y  sonomicrometer  transducers  i n each o f the f o u r abdominal muscles In a d d i t i o n , the  cervical  reversible cuffs x  region  blockade  consisted  5/16  in.  silastic  the dogs had c u f f s  of  O.D.  topical  ports  of  the  cuff  to  facilitate  cuffs  cuffs  implantation surgery. c a r o t i d sheath,  and  nerve.  separately.  The  and  inner  one  (14)  Midland,  ends.  (Figure  tubing,  The c a t h e t e r s  enclosed  and  nerve.  EMG wires  A  (see  50% o f  s u t u r e d c l o s e d around the c u f f s muscle  layers  40cm  long  two  holes  as  inlet  sterile  of  Three  The  inside  The n e r v e s  to  were  cuff seal  the  other  a week a f t e r  the  a  surgical  i n which  were p l a c e d around the nerve  and  I.D.  circulation  implanted.  surgery,  approximately  in.  acted  same s u r g e r y  were  The  Chapter I I ) .  catheters directed l a t e r a l l y .  fascial  two  for  25).  3/16  MI) w i t h  application  in  developed  i n . O.D.) penetrating  p l a c e d i n a separate  and o c c u p i e d  The c a r o t i d s h e a t h was  from  of s i l a s t i c  p l a c e d d u r i n g the  The c u f f s  w i t h the  diameter  the  modified  .085  the  EMG e l e c t r o d e s  p l a c e d around b o t h vagus n e r v e s  described previously  transducers  t h r e e dogs had the  the  wire  as d e s c r i b e d i n Chapter I I .  motoneurons  Corp.,  I.D. x  near  around  dogs had the  in  in.  f o l l o w e d as  sonomicrometer  2-3mm  peripheral  (.04  anesthetic  procedure was  method  (Dow C o r n i n g  catheters  outlet  a  o f a 2.5cm l o n g p i e c e  punched through the and  using  and f i n e  the the were  volume. the  cuff  then  sutured  The c a t h e t e r s were t u n n e l l e d under s k i n and e x i t e d  through  131  the were  s k i n o f the d o r s a l neck r e g i o n . flushed  every  2-3  h e p a r i n (50 u n i t s / m l ) Three  of  the  artery catheters IL)  which  located  implanted  the  dogs  p l a c e d i n three  were  1 ml o f  the  also  sterile  blood  lumbar  separate  o f the  surgically  access p o r t ,  arterial  dorsal  during  with  the  catheters  solution  of  sodium  i n lactated Ringers.  (vascular  allowed  in  days  To p r e v e n t p l u g g i n g ,  implanted  model GPV, A c c e s s  sampling  region.  from  The  surgery  in  a  femoral  Technologies,  subcutaneous  arterial  which  with  the  port  catheters  vagal  were  cuffs  were  dogs.  Measurements Abdominal muscle measured resting left  with  baseline  lateral  length  the  expiratory resting  length  tidal  l e n g t h from the  raw  transducers  was  termed  either  expressed  Active  of  the  termed the  active  as  LRL and t h e r e f o r e ,  a  (LABL)•  dog  Changes  percentage was  the  signals  e l e c t r o d e s were a m p l i f i e d and f i l t e r e d i n p a i r s w i t h the sonomicrometer  of  in  the  muscle or  initial  to  be  A change  in  baseline  LABL was  the  the  determined  The new b a s e l i n e  from  usually  implanted  ( G r a s s , model P511)  signals.  in  The  lengthening  length  shorter  was c o n s i d e r e d to be a r e f l e c t i o n o f t o n i c  electromyographic  II) .  l e n g t h was a l s o e x p r e s s e d  length.  length  with  LRL.  EMG a c t i v i t y .  i n i t i a l resting  Chapter  inspiratory  shortening  expiratory  baseline  (see  abdominal m u s c l e s ,  i n i t i a l resting baseline  percentage  The  the  position,  were  (%LRL) .  with  of  breathing,  shortening,  length  coinciding  sonomicrometer  decubitus  during  e n d - e x p i r a t o r y l e n g t h s and l e n g t h changes were  that  as  a  was than  activity. fine  wire  and r e c o r d e d  Figure  25:  Photograph showing placement o f a s i l a s t i c c u f f around the r i g h t c e r v i c a l vagus nerve i n one o f the dogs. The l e f t s i d e o f the p i c t u r e i s the head end o f the dog.  133  Expiratory  Threshold  Airflow pressure distal  Loading  was  measured  transducer end  volume.  of  the  tracheostomy end o f  non-rebreathing  threshold loads  a  pneumotachograph  ( V a l i d y n e MP45,  The o p p o s i t e  two-way,  with  o f 6,  tube,  the  valve  Medfield,  (PEEP) v i a a PEEP v a l v e  expiratory  was measured v i a a p o r t h o l e (Pao)  Medfield, Mass.). l u n g volume  parameters.  The S V o l  expiratory  load  side  was  of  the  2600).  i n the  (differential D u r i n g the  expiratory  (<SVol)  measured  was  was  determined  released.  valve.  Inspiratory  and r e c o r d e d  (Ti)  V a l i d y n e MP-  load  addition volume  positive  End-expiratory  threshold  from the  to  (ETL), the  the  control  e x p i r e d when  and  a  Model BE-142)  transducer,  in  to  Expiratory  two-way v a l v e  pressure  the  tidal  connected  (Medigas,  two-way  and  to  give  2  pressure  in  to  was  (Hans Rudolph, model  to  change  attached  integrated  pneumotachograph  attached  45,  Mass.),  #1)  10 and 14 cmH 0 were produced by a p p l y i n g  end-expiratory pressure  as airway p r e s s u r e  and  (Fleisch  expiratory  the (T ) E  d u r a t i o n were determined from the flow t r a c i n g on the c h a r t r e c o r d e r . One  ml  arterial  access p o r t , and  each  level  CO2  of  PEEP  (6,10  were  and 14 cmH 0) 2  ( C o r n i n g , 168 p H / B l o o d gas  was e x t r a p o l a t e d  H C O 3 "  samples  during r e s t i n g breathing before  were a n a l y z e d The  blood  from known  obtained, and a f t e r  via  vascular  the ETL p r o t o c o l ,  during ETL.  analyzer)  the  B l o o d samples  f o r PC0 , 2  pH and P 0 . 2  equations.  Rebreathing  Ventilation attached  to  integrated  the to  was distal  give  were determined  measured  tidal  from the  end  of  volume. flow  with the  a  pneumotachograph  tracheostomy Inspiratory  tube  (Fleisch  #1)  airflow  was  and  and e x p i r a t o r y  t r a c i n g on the c h a r t r e c o r d e r .  duration A two-way  134  valve  (#2600 Hans-Rudolph I n c . ,  pneumotachograph, as  a  and the  rebreathing  h a v i n g the  gas m i x t u r e o f  (model I L - 2 0 0 ,  2  Fisher Scientific  breathing,  before  after  during  rebreathing  pH/Blood  determined by  and  gas  was  (%)  a five  sampled to  the  2  analyzer  during  resting  Ltd.).  samples the  period.  analyzer)  a C0  by  liter,  2  determined w i t h  the  setup  attained  E n d - t i d a l C 0 was  2  and c o n c e n t r a t i o n  blood  168  a i r f l o w was  hypercapnia  and balance N .  to  v i a a n e e d l e i n s e r t e d through the attachment  milliliter  the  attached  from a 10 l i t e r bag c o n t a i n i n g  2  pneumotachograph,  One  Progressive  7% C 0 , 50% 0  a t the tracheostomy,  Mo.) was  i n s p i r a t o r y and e x p i r a t o r y  circuit.  dogs r e b r e a t h e  Kansas C i t y ,  were  obtained  rebreathing  protocol,  B l o o d samples were for  PC0 ,  pH,  2  and  and  two  analyzed  P0 , 2  times  (Corning,  and  HC0 "  was  3  extrapolation.  Protocol A total experiments: three of  to  the  C0  2  six  six 2  rebreathing.  experiments  position,  began  quiet  were with  tube  breathing  stabilize.  the  i n the pre and p o s t v a g a l  The  was  in  two  dogs p r e v i o u s l y underwent  the  preceding  different  on d i f f e r e n t  the  lying  dog After  inserted,  all  in  followed  to  allow  the  awake  dog  was  then  t h r e s h o l d l o a d i n g or C0  2  rebreathing.  days.  the  the  a five  chapters.  experimental  followed  on a p l a t f o r m .  tracheostomy  A l l the  described  rebreathing)  protocol  dogs were used  blockade  were exposed to e x p i r a t o r y t h r e s h o l d l o a d i n g  protocols  blockade C0  of  wires  to  left were  t e n minute  dog  to  exposed  relax to  (ETL) and one  For  the  protocols Every  or  all  vagal  (ETL and  experimental  lateral  decubitus  connected  and  the  control period  of  and b r e a t h i n g  to  either  expiratory  135  ETL The  two-way n o n - r e b r e a t h i n g v a l v e and PEEP v a l v e were connected  the d i s t a l  end o f  breathing length, An  the pneumotachograph and when the  stabilized,  c o n t r o l measurements  l e n g t h changes and EMG a c t i v i t y ,  expiratory  minutes)  load  was  then  applied  of  expiratory  The awake threshold  dogs  loads  were  (6,10  a  short  exposed 14  to  period  on the l o a d ,  CI11H2O) .  to be r e -  randomly Between  (1-2  applied  each  load,  values.  Rebreathing R e s t i n g c o n t r o l measurements  length The  time  three  b r e a t h i n g was a l l o w e d to r e t u r n to q u i e t b a s e l i n e  CO2  resting  Pao and t i d a l volume were made. and  and  dog was r e l a x e d and  abdominal muscle  allowed f o r a regular breathing p a t t e r n ,  established.  to  changes and EMG a c t i v i t y ,  r e b r e a t h i n g c i r c u i t was  bag c o n t a i n i n g minutes.  a mixture  of  o f abdominal muscle  t i d a l volume  then a t t a c h e d  and  resting  PCO2  length,  were r e c o r d e d .  and the dog r e b r e a t h e d from a  7% C O 2 and 50% O 2 , f o r  Measurements were made c o n t i n u o u s l y  approximately  throughout the  five  rebreathing  protocol.  Vagal  Blockade Another c o n t r o l p e r i o d f o l l o w e d  to a l l o w had  the  dog to  stabilized,  i n j e c t i o n of the c u f f The  the  r e t u r n to p r e v i o u s  ETL o r r e b r e a t h i n g  resting  levels.  protocols,  When b r e a t h i n g  the vagus nerves were r e v e r s i b l y b l o c k e d b i l a t e r a l l y by  t o p i c a l anesthetic  (4% x y l o c a i n e )  into  the v a g a l c u f f s  via  catheters. correct  procedure to  follow  dosage to  of  achieve  anesthetic blockage  of  required the  and  nerve was  the  optimum  determined  in  136  three vagal  pilot cuffs.  xylocaine decrease vagus  studies Two  into  applications  each c u f f  studies.  were  cut  via  withdrawing l - 2 c c , later.  repeated.  the  chronic implantation of  minutes  apart)  r e s u l t e d i n an i n c r e a s e  after  The a n e s t h e t i c  simultaneously,  to  (5  i n b r e a t h i n g frequency.  nerves  5 minutes  conducted p r i o r  was  one  the  d i d not  xylocaine  each  cuffs'  other catheter  Fresh anesthetic  2.5cc  in tidal  blockade,  catheter  in  4%  when the  into  and  from each c u f f ,  of  volume and a  change  a p p l i e d by i n f u s i n g 2 . 5 c c  of  v i a the  The r e s u l t s  of  the  pilot  each  then  the  cuff  slowly  approximately  was then r e a p p l i e d and the p r o c e d u r e  T h i s p r o c e d u r e a l l o w e d the a n e s t h e t i c  nerve and was found to be the most e f f e c t i v e  to c i r c u l a t e around the  to produce b l o c k a g e o f  the  nerve. Vagal  blockade  was  reduction  or  following  end-inspiratory  bilateral  Horner's  assessed  elimination  of  The  syndrome;  (3)  the  following  Hering-Breuer of  the  increased  The vagus  criteria:  inflation  tracheostomy tidal  protocol  was  then  (1) reflex  tube;  volume;  and  nerves were c o n s i d e r e d to  b l o c k e d i f a t l e a s t three out o f f o u r c r i t e r i a were  experimental  blocked.  the  occlusion  decreased b r e a t h i n g frequency. effectively  by  repeated  with  the  (2) (4) be  present.  vagus  nerves  A l l s i g n a l s were r e c o r d e d on an e i g h t channel r e c o r d e r ( G o u l d ,  model 8000S).  Analysis  ETL Measurements PEEP,  for  each  were  study  averaged  day.  Since  over there  five were  breaths  for  each  no c o n s i s t e n t  level  of  differences  137  between s t u d i e s ,  the  each dog and the  means  The  means  effects  means  p e r dog,  ± SE were then  of  from each PEEP study were then averaged at  each  calculated  ETL on each v a r i a b l e ,  for  level  of  PEEP,  were  each v a r i a b l e .  a one-way  analysis  level  o f PEEP any d i f f e r e n c e  o f P<0.05 was a c c e p t e d .  different  abdominal  of variance  were made u s i n g  significant  heterogeneity  transformations  CO2  A  (ANOVA)  determine  significance  a  one-way  ANOVA  was  a Tukey's m u l t i p l e of  standard  used  and  comparison  deviation  o f the d a t a were made and the ANOVAs  the  multiple  test.  When  existed,  log  repeated.  Rebreathing For  for  may have o c c u r r e d .  the  Whenever comparisons were made among  muscles,  comparisons  obtained.  To a s s e s s  was performed and a D u n n e t t ' s m u l t i p l e comparison t e s t used to a t what l e v e l  for  each  experimental  the c o n t r o l v a l u e s .  progressively,  trial,  a mean o f  six  breathing  d i d not  stabilize  three breaths  around each l e v e l  o f C 0 was u s e d .  from  more  meaned  one  or  trials  i n d i v i d u a l mean v a l u e s  were  ± SE was  different  l e v e l s of PC0 . 2  differences  Multiple  significant  transformations Differences  heterogeneity of  the  data  analyzed  the  overall  mean  Analysis of  mean the of  of  data these  variance  among the v a r i a b l e s and a t  comparisons were made u s i n g e i t h e r  Tukey o r D u n n e t t ' s m u l t i p l e comparison t e s t When  the  then c a l c u l a t e d .  was used to determine s i g n i f i c a n t  and  F o r each dog,  2  and  was  e n d - t i d a l CO2 i n c r e a s e d  D u r i n g the r e b r e a t h i n g ,  therefore  breaths  of were  a  (whichever was a p p r o p r i a t e ) .  standard made  were c o n s i d e r e d to be s i g n i f i c a n t  deviation  and,, the at  existed,  ANOVAs  P<0.05.  log  repeated.  138  Vagal  blockade All  the  analyses  vagal blockade data. tests  were  variable.  used  were  performed s e p a r a t e l y  To a s s e s s the e f f e c t s  to  compare  Differences  results  pre  on  the  pre  and  of vagal blockade, and p o s t  paired T-  blockade,  were c o n s i d e r e d to be s i g n i f i c a n t  at  post  for  each  P<0.05.  RESULTS  Effects  o f V a g a l Blockade on C o n t r o l  All assess  the  reflex, or  the  dogs  effectiveness  increased  bilateral  determined protocols, blockade.  exhibited  in by  of  at  least  three  the  vagal  block:  t i d a l volume  Horner's one  results  There was no change  in V  T  at of  the  the  c r i t e r i a used  decreased  of  end  cutting  the  the of  block  the  vagi  or t i m i n g parameters  to  Hering-Breuer  b r e a t h i n g frequency  Completeness  anesthetized  comparing the  of  (VT) , decreased  syndrome.  dog,  Parameters  (Bf)  was  also  experimental to  anesthetic  after  vagotomy  compared to b l o c k a d e . B i l a t e r a l v a g a l blockade of  20 to  73%)  and TTOT  (range 5 to 123%) 30) .  Although  before  and a f t e r  changes;  two  increased V  T  by a p p r o x i m a t e l y 30%  (decreased b r e a t h i n g frequency)  (range  by a mean o f  20%  d u r i n g r e s t i n g b r e a t h i n g (Table V I I and F i g u r e s 29 and there  was  no  significant  v a g a l blockade  dogs  decreased  difference  between  (Table V I I ) , i n d i v i d u a l dogs V  E  and  four  dogs  increased  m'ean V E exhibited V  E  after  blockade. Control nerve.  a r t e r i a l blood  When the  control  gases were  values  from  also  effected  the  ETL and  by b l o c k i n g C0  2  the  rebreathing  139  experiments  were  (mean±SE);  combined,  significantly  (37.6±1.7mmHg)  4.5  dogs,  to 4.1  lower  (Tables  and 4.4  to  a  and  i n two  e n d - t i d a l C0  P C0  after  2  blockade  (P<0.05) than  VIII  measurements were made these two  the  X).  dogs,  In  at  the  a l s o decreased  2  the  was  P C0 a  before  2  addition, same  33.5±1.4mmHg blockade  end-tidal  time  as  C0  2  P C0 .  For  a f t e r vagal blockade,  from  a  2  3.8%.  ETL S i x dogs were exposed to e x p i r a t o r y t h r e s h o l d l o a d i n g b e f o r e a f t e r blockade results  of  however  only  chapter. and  EO  o f the vagus n e r v e s .  the the  Before as  eight  was  dogs  results  v a g a l blockade, discussed  in  % L R L of  the  TA  was  ETL  o f PEEP ( F i g u r e 26).  i n FRC)  produced by ETL was  it  the  is  increase  in  abdominal muscle a c t i v i t y , the change i n l u n g volume.  Since  10 a c t i v i t y and V  T  discussed  dogs  are  in  produced r e c r u i t m e n t IV.  (%LRL)  in  lung  Following  vagal  to  ETL,  at  which  is  ( F i g u r e 27) .  this  TA,  thought  to  10  reduced  comparable (increase  ( F i g u r e 32)  abdominal muscle s h o r t e n i n g was  10  IV,  blockade,  o f the 10 and EO was  response  When % L R L was  in  o f the  the change i n l u n g volume  volume  (TA,  Chapter  presented  g r e a t e r a f t e r v a g a l blockade  l u n g volume, a l l t h r e e muscles l e s s a f t e r v a g a l blockade  ETL  six  Chapter  unchanged  levels  to  these  a c t i v e , phasic expiratory shortening but  A l l s i x dogs were i n c l u d e d i n the  exposed  from  and  and  stimulate  normalized  to  compared a t the same change i n and  The  EO)  shortened  significantly  e f f e c t s of v a g a l blockade  are shown by the r e p r e s e n t a t i v e t r a c i n g i n F i g u r e  on 28.  140  0 I 0  i  l 2  i  l 4  i  J 6  i  l 8  i  l 10  i  I  12  i  I  14  Pao ( c m H 0 ) 2  Figure  26: Abdominal muscle a c t i v e p h a s i c s h o r t e n i n g v e r s u s airway p r e s s u r e (Pao) d u r i n g E T L . Asterisks (*) indicate significant difference between p r e and p o s t vagal b l o c k a d e s h o r t e n i n g (P<0.05).  I  .  0  I  .  50  I  I  100  150  200  i  250  I  300  i  L_  350  Volume Change (ml) Figure  27:  Abdominal muscle a c t i v e p h a s i c s h o r t e n i n g v e r s u s the change i n volume d u r i n g ETL. Asterisks (*) indicate significant difference between p r e and p o s t vagal b l o c k a d e s h o r t e n i n g a t the same change i n volume (P<0.05).  142  Figure  28:  R e p r e s e n t a t i v e r e c o r d i n g from an awake dog ( l e f t lateral decubitus position) showing tidal volume (V ) , airway p r e s s u r e ( P a o ) , i n t e r n a l o b l i q u e (10) l e n g t h changes and 10 EMG a c t i v i t y d u r i n g e x p i r a t o r y t h r e s h o l d l o a d i n g . The l e f t p a n e l (Pre) i s b e f o r e v a g a l blockade and the r i g h t p a n e l (Post) i s a f t e r v a g a l b l o c k a d e . The downward d e f l e c t i o n o f the l e n g t h t r a c e c o i n c i d i n g w i t h i n i t i a t i o n o f EMG a c t i v i t y i s a c t i v e , p h a s i c s h o r t e n i n g . 10 EMG a c t i v i t y and s h o r t e n i n g are e f f e c t i v e l y e l i m i n a t e d f o l l o w i n g v a g a l b l o c k a d e . T  144  Ventilatory maintained  parameters are g i v e n  during  significantly  ETL b o t h  greater  ETL b e f o r e  blockade  and  (Figure  30).  during after during  was As  ETL when vagal  greater a  at  result,  was  a l l levels there  ETL, the i n c r e a s e  due in  was  a l l levels  increased,  of  there  PEEP was  compared an  of a  PEEP  Arterial  blood  gases  was  to  increase  compared  The  to  intact  hypoventilation increase  greater  in  in  TE  but  (Figure  after  vagal  blockade  the  level  of  end-expiratory  lung  intact.  As  PEEP  volume,  There was a g r e a t e r i n c r e a s e  a t a l l l e v e l s o f PEEP ( F i g u r e 32). were  obtained  during  ETL b e f o r e  and  after  There were no s i g n i f i c a n t d i f f e r e n c e s between PC0  pH a t a l l l e v e l s  o f PEEP p r e and p o s t blockade  dogs had a  before  (Table  lower  VIII) .  P0  2  TTOT  Ti at rest  due to an i n c r e a s e  in  after  vagal blockade.  the  was  was unchanged  TTOT  significant  to a  i n d i c a t i n g an i n c r e a s e i n FRC ( F i g u r e 32) . i n FRC a f t e r v a g a l b l o c k a d e  but  i n c r e a s i n g Pao  were b l o c k e d .  primarily  TTOT  volume was  blockade  In contrast,  but increased with  the vagus nerves  blockade  vagal  Tidal  o f PEEP when the vagus n e r v e s were  ( F i g u r e 29).  blockade  after  VII.  Both T i and T E were s i g n i f i c a n t l y d i f f e r e n t  31). at  vagal  and  at a l l levels  b l o c k e d compared t o i n t a c t by  before  i n Table  during  There was  ETL a f t e r also  w i t h i n c r e a s i n g Pao a f t e r v a g a l blockade  (Table V I I I ) .  vagal  a trend (P=.08)  blockade  or  2  However,  compared t o  to an i n c r e a s e  i n P C0 a  2  Table  VII:  V e n t i l a t i o n and t i m i n g parameters b e f o r e and a f t e r v a g a l b l o c k a d e .  Pre  during  E T L  V a g a l Blockade  Pao (cm H 0)  v (ml "min" )  V (ml)  TTOT  T  (sec)  (sec)  0  6486 ±1033  288 ±28  3.21 ±.53  2.23 ±.41  6  5669 ±946  287 ±25  3.68 ±.58  2.77 ±.50  10  5333 ±866  257 ±29  3.50 ±.63  2.72 ±.56  14  5503 ±1175  251 ±28  3.53 ±.67  2.76 ±.59  2  E  1  T  ..-  E  Post V a g a l Blockade  v  Pao (cm H 0)  v (ml 'min" )  (ml)  0  6441 ±789  371 ±28  6  5255 ±636  2  10  14  E  1  4618 ±558  **  ±448 4099  T  *  TTOT  T  (sec)  (sec)  3.84 ±.44  *  ±25 355  ±.41 4.45  *  * * *  ±24 336  ±.42 4.68  321*  4.97*  **  **  E  2.60 ±.33 3.33  *  ±.38 3.61  3.90* ±.38**  ±25 ±.42 Pao=airway p r e s s u r e ( c o n t r o l = 0cm H 0) V a l u e s a r e means ± S E N=6 A s t e r i s k (*) i n d i c a t e s s i g n i f i c a n t d i f f e r e n c e between b e f o r e and a f t e r vagal blockade (P<0.05). * * i n d i c a t 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 c o n t r o l ( P < 0 . 0 5 ) . 2  146  400 - F  o Pre-vagotomy • Post—vagotomy  375  350 co vZ>  325  E -§ >  300  "5 5-  275  250  6  8  10  12  Pao (cm hLO)  Figure 29: T i d a l volume v e r s u s airway p r e s s u r e (Pao) d u r i n g ETL b e f o r e and a f t e r v a g a l b l o c k a d e . Asterisks (*) indicate significant difference between p r e and p o s t v a g a l blockade (P<0.05).  _l 14  147  Figure  30:  T OT v e r s u s airway p r e s s u r e (Pao) d u r i n g E T L b e f o r e and a f t e r v a g a l blockade. A s t e r i s k s (*) 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 between p r e and p o s t v a g a l blockade (P<0.05). T  v Pre—vagotomy • Post—vagotomy  6  8  10  Pao (cm H.O)  Figure 31: Ti and T E versus airway pressure (Pao) during ETL before and after vagal blockade. S o l i d symbols are post and open symbols are pre vagal blockade. Asterisks (*) indicate significant difference between pre and post vagal blockade (P<0.05).  149  o Pre—vagotomy  0  •  Post—vagotomy  2  4  6  8  10  12  Pao ( c m H 0) 2  F i g u r e 32: Change i n l u n g volume ( f i v o l ) v e r s u s airway p r e s s u r e (Pao) d u r i n g ETL b e f o r e and a f t e r v a g a l b l o c k a d e . Asterisks (*) indicate significant difference between p r e and p o s t v a g a l b l o c k a d e (P<0.05).  14  150  Table V I I I :  A r t e r i a l b l o o d gases d u r i n g ETL b e f o r e and a f t e r v a g a l blockade. Pre Vagal  Blockade  Pao (cm H 0)  PC0 mmHg  P0 mmHg  0  37.6 ±2.6  104.7 ±12.2  7.36 ±.005  6  38.2 ±2.4  .97.9 ±6.1  7.36 ±.011  10  37.1 ±1.6  92.9 ±8.2  7.37 ±.011  14  39.5 ±0.8  83.9 ±5.0  7.35 ±.004  2  2  Post Vagal Pao (cm H 0) 2  0  PC0 mmHg 2  33.5 ±1.6  *  2  pH  a  Blockade P0 mmHg 2  pH  a  95.8 ±5.0  7.39 ±.013  6  38.1 ±2.6  87.9 ±15.5  7.37 ±.010  10  37.0 ±3.1  84.5 ±7.9  7.37 ±.010  14  39.3 ±2.1  76.3 ±7.0  7.36 ±.006  N=3 Pao=airway p r e s s u r e A s t e r i s k (*) i n d i c a t 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 b l o c k a d e c o n t r o l (P<0.05).  pre-vagal  151  CC>2 R e b r e a t h i n g Three dogs f o l l o w e d v a g a l blockade. and V in  Figure  active,  33.  2  rebreathing, before  shortening  e n d - t i d a l PC0  10 and EO was s i g n i f i c a n t l y compared  Since  blocking  ventilation  t h e vagus  increased %LRL  reduced  three  Figures  i n resting V 36  progressive after  vagal  greater  muscles  i n those  V  hypercapnia  both  (P<0.05)  V, T  compared  (Table IX and F i g u r e s  2  2  This  increased  % L R L was  rebreathing  was post  significantly after  and V  E  increased  p r e and p o s t T T,  V ,  to before  36 and 37).  three  the vagus and T  vagal  T I and T  T O  E  were a l s o  s i x dogs, these  T  T  (Table I X ) ,  vagal  (Figure 35).  and 3 7 ) .  blockade,  parameters and  (TA, 10 and EO)  and T OT a f t e r b l o c k i n g  T  2  (Figure 34).  t o minute v e n t i l a t i o n .  dogs i n v o l v e d i n the C 0  to ETL and as demonstrated increase  ventilatory  At isoventilation,  i n a l l three  b l o c k a d e compared t o i n t a c t The  affected  e n d - t i d a l C0  was the same  as the v e n t i l a t o r y response t o C 0  ( s e e below).  (P<0.05)  shortening o f  a t the h i g h e s t  b u t TA % L R L  was n o r m a l i z e d  muscle  progressive  a f t e r v a g a l blockade,  2  nerves  with  l i n e a r l y with progressive hypercapnia  p a r t i c u l a r l y important blockade  i s shown  When abdominal muscle % L R L was  reduced  t o p r e blockade,  abdominal muscle  vagal  increased  (%LRL)  2  level  o f TA l e n g t h changes and EMG  and a f t e r v a g a l b l o c k a d e ,  produced by r e b r e a t h i n g C0 .  compared a t s i m i l a r the  and a f t e r  As was shown p r e v i o u s l y i n Chapter V, abdominal  expiratory  hypercapnia  rebreathing protocol before  2  A representative tracing  during C0  T  the C 0  E  blockade  E  dogs had an  (Table  decreased  blockade.  were  all  E  during  significantly of  may i n d i c a t e  the v e n t i l a t o r y response t o C0 i n c r e a s e d when t h e v a g i were 2  IX and  However,  a t any l e v e l  The i n c r e a s e i n V  exposed  PC0  2  that  blocked.  152  Figure  33:  R e p r e s e n t a t i v e r e c o r d i n g from an awake dog (left lateral decubitus p o s i t i o n ) showing V T , TA phasic shortening (%LRL) and TA EMG during moderate hypercapnia before (left panel) and after (right p a n e l ) v a g a l blockade.  153  Pre  7.2% P  E T  C0  Post  2  7.2%  P  E T  C0  2  154  Figure  34:  Abdominal muscle a c t i v e p h a s i c s h o r t e n i n g p l o t t e d a g a i n s t e n d - t i d a l PC0 d u r i n g r e b r e a t h i n g , b e f o r e and a f t e r v a g a l blockade. 2  155  4  v •  EO pre-vagotomy EO post-vagotomy  •  10 pre-vagotomy  •  10 post—vagotomy  2 0 12 10 8 _l  6  cn c *c  4  o  CO  0 14  CD >  12  o  10  CD -+-»  <  2  O TA pre-vagotomy •  TA post—vagotomy  8 6  8  10  12  14  16  18  20  22  Ventilation ( l / m i n )  Figure  35:  Abdominal muscle active phasic shortening plotted a g a i n s t minute v e n t i l a t i o n d u r i n g r e b r e a t h i n g , b e f o r e and after vagal blockade. Asterisks (*) indicate s i g n i f i c a n t d i f f e r e n c e i n s h o r t e n i n g at the same l e v e l of ventilation before and after vagal blockade (P<0.05).  156 T a b l e IX: V e n t i l a t o r y Parameters f o r r e s t i n g a i r b r e a t h i n g c o n t r o l and t h r e e l e v e l s o f e n d - t i d a l C0 . 2  Pre V a g a l Blockade V (mls)  PETC02  T  TTOT  (sec)  T (sec) E  Ti(sec)  Control  288±21  4.271.72  3.051.69  1.221.15  Low C0  2  359115  4.121.72  2.211.74  1.911.23  Mid C0  2  631+91  3.511.34  2.031.21  1.481.18  767±93  3.481.16  1.891.18  1.581.15  High C0  2  Post V a g a l Vi(mls)  PETC02  TTOT  (sec)  Control  455186*  5.001.93  Low C0  2  7791203*  4.271.51  Mid C0  2  10661210*  13291229*  High C0  2  Blockade T (sec) E  3.341.69  Tj(sec)  1.661.15*  2.351,32  2.921.23  4.131.28*  2.331.39*  1.801.18  3.931.41  2.151.48*  1.781.15  N=5. V a l u e s a r e means 1 SE. A s t e r i s k s (*) 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 between b e f o r e and a f t e r v a g a l blockade (P<0.05)  157  Figure  36:  T i d a l volume (V ) p l o t t e d a g a i n s t minute v e n t i l a t i o n during C0 rebreathing, before and after vagal blockade. Asterisks (*) indicate. significant d i f f e r e n c e between V pre and p o s t v a g a l b l o c k a d e . T  2  T  Figure 37:  T o t a l a i r f l o w d u r a t i o n ( T O T ) p l o t t e d a g a i n s t minute v e n t i l a t i o n d u r i n g C 0 r e b r e a t h i n g , b e f o r e and a f t e r vagal blockade. A s t e r i s k s (*) 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 between T T O T pre and p o s t v a g a l b l o c k a d e . T  2  159  Arterial rebreathing  blood  before  gases  and a f t e r  d i f f e r e n c e s between PC0 , P0 2  blockade  (Table X ) .  were  2  obtained  from  vagal blockade.  two There  o r pH a t a l l l e v e l s  dogs were  o f PC0  2  during no  CO2  apparent  p r e and p o s t  T a b l e X: A r t e r i a l Blood Gas and pH v a l u e s Pre V a g a l Blockade  PaC0 (mmHg)  PETC02  2  Control  Pa0 (mmHg) 2  95±2  37.5±0.4  pH  a  7 36±0.03  Low C 0  2  43.8±0.5  88±2  7.34±0.01  Mid C 0  2  44.4±0.5  130±2  7. 2 9 ± 0 . 0 1  Post V a g a l  PETC02  PaC0 (mmHg)  Control  33.5±3.5  2  Blockade  Pa0 (mmHg) 2  86±11  pH  a  7.37±0.02  Low C 0  2  42.8±2.5  78±6  7 .33±0.01  Mid C 0  2  47.7±2.3  150+16  7. 2 9 ± 0 . 0 1  (N-2)  161  DISCUSSION  E f f e c t s o f V a g a l Blockade The  approximately  which o c c u r r e d a f t e r nerves,  are  Anesthetic  application  consistent  afferents)  with  inspiratory  inhibitory  (lung  remove a f f e r e n t  the i n s p i r a t o r y f a c i l i t a t o r y  (8).  of this  unlike  results  blockade  T  i n awake  s t u d i e s were from the  other  (22,23).  were  r e p o r t e d by K e l s e n  variability  i n t h e change i n V  in  t h r e e and d e c r e a s e d  the p r e s e n t the mean V The agreement  E  study,  Therefore,  V  E  complete  i n f o r m a t i o n from  both  lung  inflation  lung i r r i t a n t  receptors  t h e r e was no change i n V , E  i n which  V  However,  several  E  increased after  t h e same l a b o r a t o r y and appeared  same t h r e e dogs  study  studies  (22,23).  dogs  afferents)  (8).  i n c r e a s e d and Bf decreased,  from  (lung  study a r e c o n s i s t e n t w i t h r e d u c t i o n o f b o t h  i n h i b i t o r y and e x c i t a t o r y i n f l u e n c e s Although V  blockade.  myelinated  and e x p i r a t o r y e x c i t a t o r y  r e c e p t o r s and from The r e s u l t s  vagal  irritant  (10).  differential  would  of  the large  myelinated  i n Bf,  a n e s t h e t i c t o t h e vagus  attainment  shown t o e f f e c t  no s i z e  nerves  of a topical the  and s m a l l  equally, with  b l o c k o f the vagus the  30% i n c r e a s e i n V? and the 20% decrease  b l o c k has been  inflation fibers  on C o n t r o l Parameters  E  o f these  t o those  et  They  (16).  o f the present  found  considerable  produced by v a g a l b l o c k a d e : V  i n two dogs b u t the mean V  earlier  t o be conducted on  Results similar al.,  vagal  E  E  increased  was unchanged.  i n c r e a s e d i n f o u r and d e c r e a s e d  In  i n two dogs b u t  was unchanged.  control with  p r e v a g a l blockade  a previous  study  arterial  which  "normal" b l o o d gases f o r awake dogs (36).  b l o o d gas v a l u e s  specifically  are  in  i n v e s t i g a t e d the  F o r example, r e s t i n g  arterial  162  PC0  (P C0 )  2  P C0 a  a  of  2  was  2  37.6  mmHg i n the p r e s e n t  35.9mmHg  (36).  Following  d e c r e a s e d by a s m a l l b u t s i g n i f i c a n t in  or  are  available  alveolar  PC0  conflicting  (PAC0 )  2  results.  a  (23).  2  An e a r l y  topical  were b l o c k e d by c o o l i n g  vagal  P C0 a  blockade  surprising  same  cooling that  the  effects  of  three  of  increase  in  V  T  are,  dogs,  in  P C0 a  vagi  change  dogs whose in  P C0 a  p r o d u c e d by  PAC0  in  vagi  2  (16).  rabbits  after  would  2  2  present  whose  found no  awake  2  Few  on e i t h e r  i n anesthetized  A decrease  a  In a d d i t i o n ,  that  awake  five  P C0  also decreased.  (tetracaine),  study  (17).  vagal  not  be  blockade  ventilation.  expiratory  shortening  discussed  in  prevent  diaphragm l e n g t h  occurred lung  abdominal muscle Abdominal  of  loading  (ETL) on  abdominal  IV.  The  increase and Vf.  curves  in  recruitment  FRC p r o d u c e d by  Indeed,  much l e s s (26),  of  the than  change would  indicating  abdominal  ETL and  hence,  i n volume  (6"Vol)  be  the  the  the  predicted  effectiveness  from of  recruitment. muscle  mediated  elimination  the  d u r i n g ETL was inflation  threshold  (%LRL) , .V? and FRC p r e v a g a l b l o c k a d e were  Chapter  defends  vagally  2  and those  of  decrease  alveolar  helps  passive  (Table V I I I ) .  0 ° C r e p o r t e d a mean d e c r e a s e  found to  muscles  that  a later to  i n greater  phasic  as  was  study  control  vagal blockade  animals  the "normal"  o f V a g a l Blockade d u r i n g ETL  The muscle  by  given  could result  Effects  2  of  anesthetic  In c o n t r a s t ,  Furthermore,  awake  blockade,  e n d - t i d a l C0  effects  in  2  were b l o c k e d w i t h P C0  on the  vagal  amount  two dogs i n which i t was measured,  reports  s t u d y compared to  via  recruitment lung  pulmonary  by  inflation  stretch  ETL i s  thought  reflexes  receptor  to  (4-6).  afferent  be  primarily Therefore,  information  by  163  b l o c k i n g the vagus n e r v e s would be reduce abdominal muscle p h a s i c of anesthetized effectively  (27,28) of  results  after  although  (21)  dogs  anesthetized  a c t i v i t y but  dogs  only  abdominal  vagal  found  that  28) , t h e r e  muscles  with  is  in  still  PEEP  may  in  be  muscles.  The  blockade  and  finding  One  I t has the  other  sterni,  that  %LRL i s  the  TA  muscles,  one  demonstrate at  i t might  proposal,  appear  s i n c e the TA  that  the  shortening  before  a f t e r . v a g a l blockade  and  studies apparently of  normalizing  the  E  the  that,  similar  of  the  6Vol  abdominal  suggests  least  some  that  of  the  increased  in  reflex was  the  l u n g volume,  activation least  of  resulting the  abdominal  e f f e c t e d by  since  the  TA  the  vagal  i s the  most  (18).  closer  a different to  present  (%LRL) when %LRL was  no VT or V  EMG  of  that  of  results  i n p a r t i c u l a r d i d not  expiratory  a  This at  EO  p o s s i b l e mechanism i s a c t i v a t i o n  been p r o p o s e d t h a t the TA has  abdominal  dogs.  and  study  Similarly,  recruitment  t h i s .mechanism,  lung i n f l a t i o n  RA  (13).  study  for  cats  However, another  reduced  awake  studies  anesthetized  triangularis  (9,20).  would  At  first  support  this  show a r e d u c t i o n i n p h a s i c compared  ( F i g u r e 27).  at  a  similar  However, i n the  data were a n a l y z e d  abdominal muscle  i n n e r v a t i o n from the  and as such, i s not governed by v a g a l r e f l e x e s  glance,  means  by  supraspinal  i s consistent with  s t r e t c h e d by p a s s i v e  in  ETL  present  from  That i s , vagotomy  abolished  responsible  abdominal muscle p r o p r i o c e p t o r s (segmental)  reasoning.  during  significantly  Evidence  activity  significant  abdominal muscle r e c r u i t m e n t .  spinal  the  phasic  increasing  mechanisms  this  vagotomy  activity  blockade muscle  (Figure  EMG  ETL.  during pressure breathing.  r e d u c e d TA  abdominal  extravagal  %LRL d u r i n g  a n i m a l s would support  eliminated  and  expected to a b o l i s h or  and  thus,  activation  data  Pao,  previous  t h e r e was (which  no was  164  limited  t o EMG  activity).  Since  V  i s increased  T  by vagotomy,  the  abdominal muscles may be more s t r e t c h e d a t e n d - i n s p i r a t i o n , which might activate  muscle  proprioceptors,  muscle a c t i v a t i o n . on the TA (18), reduction vagal  reflexly  t o be e f f e c t e d .  would  be  one study  hours p r i o r t o the study have p r o f o u n d ventilatory  obscured  involved (9).  by  from  awake  overall  I n agreement  (2).  i s possible  standing  that  state  with  showed a decrease i n TA EMG a c t i v i t y  any  t o an  increase  i n P C0 a  a  2  as Pao  pH w i t h o u t changing the mean P C0 a  i n chemical  However, d e s p i t e  s h o r t e n i n g was s t i l l Finally, which case l u n g responsible  drive  a possible  2  (34).  increased  cooling  ETL p o s t  (Table  VIII).  t h e r e may have been  still  2  active  blockade.  n o t have been a c h i e v e d ,  in  have been o p e r a t i v e and  albeit  f o r accepting  d e c r e a s e d Bf, d e c r e a s e d Hering-Breuer  i t has  a  blockade may  o f the c r i t e r i a  In  i n arterial  i n d r i v e , abdominal muscle  reflexes could  was  n o t r e f l e c t e d by mean P C0 .  f o r abdominal muscle r e c r u i t m e n t ,  out o f f o u r  by  during  oscillations  Therefore,  to breathe,  increase  vagal  inflation  blocked  recent  i n d r i v e , since there  reduced compared t o p r e v a g a l  complete  study,  may not have changed s i g n i f i c a n t l y ,  2  likely  and i n p a r t i c u l a r on  the v a g i  been shown t h a t vagotomy induces w i t h i n - b r e a t h  increase  reflexes.  had been c u t 24  abdominal muscle r e c r u i t m e n t  a d d i t i o n , a l t h o u g h mean P C0  three  Therefore,  the present  v a g a l blockade was due i n p a r t t o an i n c r e a s e  an  inflation  C u t t i n g the vagus n e r v e s would most  with  trend  lung  i n segmental  awake dogs whose v a g i  e f f e c t s on the dogs  parameters.  increases  dogs  a  abdominal  i n abdominal muscle a c t i v a t i o n r e s u l t i n g from e l i m i n a t i o n o f  Furthermore,  It  increasing  Due t o the g r e a t e r e f f e c t o f p a s s i v e  i t would be more l i k e l y  reflexes  evidence  thus  reduced.  block  and b i l a t e r a l  However,  (increased  Horner's  V, T  syndrome)  165  were  found  in  all  the  dogs.  These  e l i m i n a t i o n o f v a g a l r e f l e x e s (23) did  criteria  and would suggest  indicative  that vagal  of  blockade  occur. Although  there  v a g a l blockade, inflation  and  (26).  until  a  could  be  was  i t was  curves  vagotomy  a  greater  less  than  less  Hence,  PEEP  of  V  than was  T  to  6"Vol pre  and  Therefore,  post  that  defended 33).  and  EMG  following  activity vagal  decrease  cooling  Some o f  There was in  the  vagotomy  (26).  difference.  awake A (1)  (awake v e r s u s  assume  a  load  dogs number  Vagal  of  %LRL  with  of  vagal  could  i n the higher  but  i t is  was  reduced. activation Indeed,  breathing in  i n awake dogs,  anesthetized  dogs,  be  (26).  dogs  involved  enhanced  r e f l e x e s would be (2) There may  be  TS  to  pre  blockade and  post  explain  during  this  anesthesia  consistent with an  affect  of  the  state  such t h a t the importance o f v a g a l mechanisms  awake s t a t e priority  be  ETL  (TS) , an e x p i r a t o r y r i b cage  anesthetized  f a c t o r s may  reflexes  anesthetized)  motoneurons may  sterni  to  after  compensation  shortening,  not e f f e c t e d by vagotomy  compared  lung  I n o t h e r words, f o r the same  Furthermore,  f i n d i n g s i n Chapter IV.  i s reduced  this  decrease  a s m a l l e r d i f f e r e n c e between pre and p o s t v a g a l  Enhancement  previous  phasic  d u r i n g eupneic  (2).  after  dogs  i n abdominal muscle a c t i v a t i o n .  increases  r e c r u i t m e n t d u r i n g ETL was  (11,29).  d i d not  abdominal muscle  been shown t h a t t r i a n g u l a r i s  muscle,  i n anesthetized  o t h e r e x p i r a t o r y muscles must have i n c r e a s e d t h e i r  to compensate f o r the i t has  blockade,  (6"Vol)  p r e d i c t e d from p a s s i v e  found  abdominal muscle  vagal  i n l u n g volume  would be  14cmH20 ( F i g u r e  attributed  change  apparent t h a t o t h e r f a c t o r s are i n v o l v e d .  6"Vol  are  in  (15). the  For example, segmental r e f l e x e s awake  state  be more s e n s i t i v e to chemical  or  central  may  expiratory  stimulation i n this state.  166  Despite  defending  hypoventilation  V  until  T  PEEP  14cmH 0,  d u r i n g ETL, post vagal blockade  neither V  T  post  effect  was  a  that  of  anesthesia  greater found  in  length-tension the d e c r e a s e  the  increase  i n volume  present  curve  in V  muscle  diaphragm  length  abdominal muscle  similar,  It to  was  a  the  less  thus  blockade,  ETL h e l p s  be  than  emphasizes  study,  there than  decrease  in  p o r t i o n of  its  responsible  for  i n Chapter I V ,  to  maintain  optimal  ETL.  Although  reduced  vagotomy can e x p l a i n the  TE.  prolongation  unexpected, lung  inflation  chest  wall  blockade. that  as  or  T E is  T E during  of  p r o l o n g e d by a c t i v a t i o n  (8).  Therefore,  abdominal  Support f o r  intercostal  ETL, after  (rib  non-vagal  muscles  this  may  hypothesis  cage)  and  vagal vagal  decrease  blockade, afferents  afferents  have is  of  the  in  The d e c r e a s e i n Bf a f t e r v a g a l blockade was due to a p r o l o n g a t i o n o f a  explain  reduction  Bf.  Such  does not  marked,  vagotomy,  resulting  to  This  in  T  occurred during ETL, i t  after  As d i s c u s s e d  V T during  defend  activation after  In that  favourable  considered  during  less  and a g a i n ,  tone.  occurred with ETL.  and  (26)  vagal  which was  activation  but  during loading,  study.  (25),  that  T  is  dogs p o s t vagotomy  and displacement  abdominal  that  The h y p o v e n t i l a t i o n  and Bf, whereas b e f o r e v a g a l  T  blockade  to  increase  diaphragm l e n g t h  V  vagal  found i n a n e s t h e t i z e d  the  indicates  o r Bf d e c r e a s e d s i g n i f i c a n t l y w i t h l o a d i n g ( T a b l e V I I ) .  hypoventilation that  significant  (Table V I I ) ,  t h a t l o a d compensating mechanisms were compromised. was due to b o t h a d e c r e a s e i n V  the  2  arising  prolonged  lumbar  nerve  during  from  T E after  p r o v i d e d by the  is  the  vagal  observation  (abdominal  muscle)  stimulation inhibits  d o r s a l r e s p i r a t o r y group  (DRG) i n s p i r a t o r y neurons  in  to  The i n h i b i t o r y a c t i o n  the  a manner s i m i l a r muscle  afferents  on  lung  inflation  (30).  i n s p i r a t o r y neuron a c t i v i t y  appears  to  have  of a  167  secondary e f f e c t  of prolonging  the d u r a t i o n o f e x p i r a t o r y a c t i v i t y when  the muscle a f f e r e n t s a r e s t i m u l a t e d d u r i n g e x p i r a t i o n (31). illustrate  the  recruitment  f o r l o a d compensation.  E f f e c t s of The  results in  V.  Chapter  hypercapnia,  has  That  is,  10)  and  a significant at  a  on  be  were  agreement  v a g a l blockade  that  the  few  of  these  reduced both  EO  studies TA  hypercapnia  (13),  TA (20).  EMG  related  as  (%LRL)  during  those  muscles  others  these  that  have  recruited  i n c r e a s e d and  vagal  are  %LRL would  vagotomy  (3)  be  but  not  were  enhances v a g a l  whereas another  muscles no  However, TA %LRL and  EO  thus, i t  reduced  i n v e s t i g a t e d the  abolished  blockade,  if  EMG  to be  in  effects  of  would seem  studies  clearly  by  internal  apparently  abdominal muscle a c t i v a t i o n these  in  of e l i m i n a t i n g vagal  activity  results  the  abdominal  There  effects  to EMG  discussed  were  Following  35) .  muscle  Therefore,  activity,  muscle  %LRL d u r i n g h y p e r c a p n i a .  abdominal  that  abdominal  shortening  same  PCO2  i n v e s t i g a t e d the  anesthesia  found  activity  and  the  VE ( F i g u r e  However,  a n e s t h e t i z e d dogs and  and  r e d u c t i o n i n %LRL o f a l l the  o r vagotomy on  (13,20).  hypercapnia  were  more a c t i v e .  linearly  decreased.  with  phasic  abdominal  was  abdominal muscle  expected  activity  the  nerve  results  Rebreathing  muscle  dogs  similar  been shown to be  might  vagus  i n c r e a s e d as e n d - t i d a l  s t u d i e s which have  reflexes  the  abdominal intact  (TA  when compared other  of  the  %LRL  layer  t h e r e was  of  V a g a l Blockade d u r i n g CO2  hypercapnia  muscle  importance  The  (EMG)  during  performed activity.  activity  but  in One only  study r e p o r t e d a r e d u c t i o n i n  elimination of  activity  during  1 0 a c t i v i t y does not appear to have been i n v e s t i g a t e d  i n previous studies.  168  The r e d u c t i o n i n abdominal muscle % L R L i n the vagal  blockade,  mediated  implies  component  that  involved  there  in  the  is  indeed  response  awake dog,  a  to  significant  PC0  2  i n response  (significant  to  at  C 0 , although  the  compared to p r e b l o c k a d e T  decreased  E  progressive vagal  and  highest  triangularis  may  sterni  hence,  have  T E was s t i l l  addition,  TS EMG a c t i v i t y  activity  might  stimulation, abdominal volume i n TE  with  was  activity  volume and t h e r e f o r e , found  elimination to  like  of  increase  in V  blockade,  a  increased  due  T  It will  increase  is  is  the  to  pattern  an i n c r e a s e  These r e s u l t s  to  levels  of  vagal  blockade  evidence is  diaphragm  vagal  inhibitory  more  for  the  the  action,  it  that  shorter  during  activity  by h y p e r c a p n i a  speculated  produce a  after  that  the  i n h i b i t e d by (33,35).  In  i n awake  dogs  reflexes,  same  effects  TS  degree of  reduced  end-expiratory may a l l o w  of  lung  reductions  a predominance o f diaphragm a t  any  rib lung  the i n s p i r a t o r y work o f b r e a t h i n g .  previously  and a decrease  similar  able  decreased)  Accordingly, since  h y p e r c a p n i a and the  increase  all  muscle  There  stimulated  activity.  during hypercapnia.  was  at  after  (TTOT  expiratory  would be defended by t h i s  cage e x p i r a t o r y  Ti).  cage  feedback,  expected  expiratory  progressive  increased  d u r i n g h y p e r c a p n i a and c o u n t e r a c t  (EELV)  As  P<0.05)  increased.  receptor  be  greater  ( T S ) , a r i b cage e x p i r a t o r y muscle,  stretch  Therefore,  level,  Bf  Rib  pulmonary  (32).  was  However,  (Table I X ) .  hypercapnia.  blockade  it  2  vagally  hypercapnia.  d e s p i t e the r e d u c t i o n i n abdominal muscle a c t i v i t y , decrease  following  in  Chapter  increase in T of  E  V,  V  i n V E was  and no  response  change was  E  during  due p r i m a r i l y  to  in Ti.  vagal  found  i n V T and a d e c r e a s e  increased  After  (Table  i n TE  (no  an  IX): V E change  would seem to c o n t r a d i c t the e a r l i e r c o n c l u s i o n  in that  169  there  is  a significant  vagal  component  to  the  response  to h y p e r c a p n i a .  I f v a g a l r e f l e x e s were i n v o l v e d i n the h y p e r c a p n i c response, expected and  to  decrease  following  during  vagal  h y p e r c a p n i a when  blockade,  E a r l i e r s t u d i e s o f the e f f e c t s in  awake  dogs  discussed  found  earlier,  same t h r e e  these  both  dogs.  Ti  would  is  clear  response  to  response  (22,23).  However,  as  appeared  to be  conducted on  the  earlier  study  (23),  the  i n the  blocked  differentially  results  are  cooling  to  whereas  difficult  agreement  (1).  to  with  cooling  awake  cats,  those  from  i n which a  study  the  decreased  the  results  T i d i d not  in  awake  confounding  since  are  dogs,  i n which  from  the  h y p e r c a p n i a was n o t a b o l i s h e d by v a g a l blockade concluded that altered  by  hypercapnia i s  increase  C02 in  V  blockade,  a  breathing  f i n d i n g i n the p r e s e n t  there E  was  was due  appears to be i n c o n t r a s t reported  the  the were  a  given  response. study  frequency  In  in  intact  (12)  in  and  response  Therefore,  pattern  and  to CO2,  hypercapnia  (33).  The  is  to  it  is  markedly  response  to  not.  An i n t e r e s t i n g end-tidal  are  although breathing during c o n t r o l conditions  vagal  vagi  response  ventilatory  during  on  temperatures.  ventilatory  decrease  protocols.  the  statistics  those  of  effects  (22),  study  no  two  hypercapnia  different  increased  present  the  second to  interpret  cooling the  have  In the  by  8°C a p p a r e n t l y  further  would  expected  results  expected  locomotion  hypercapnia  (7)  intact  o f v a g a l blockade on h y p e r c a p n i c  studies  be  were  change.  In addition,  that  vagi  to  these  not  dogs were w a l k i n g on a t r e a d m i l l throughout It  the  T i might be  reduction  in  a to  greater an  V  almost  to p r e v i o u s ventilatory  study was t h a t  after  vagal  doubling  of  E  f o r the  blockade. VT.  This  r e p o r t s i n awake dogs, response  after  vagal  same This  finding  which have blockade  170  (22,23). slope  However, or  position  i n awake r a b b i t s , of  the  vagal blockade  ventilatory  response  d i d not  curve  s u g g e s t i n g t h a t t h e r e was no r e d u c t i o n i n C 0 r e s p o n s e .  levels  of  rabbits,  PC0  following  2  v a g a l blockade  ventilation vagotomy  i n other  increased  (17).  It  i n awake dogs "may not reduce  degrees o f h y p e r c a p n i a " (23). present  was  response therefore,  to  C0  that  (17,22,23). post  2  In t h i s  vagal  a possible  (V /PC0 ) E  (24)  2  low  also  and  moderate  suggested  the response  of V  E  to  that mild  The l e v e l s o f h y p e r c a p n i a a t t a i n e d i n the  study c o u l d be c o n s i d e r e d moderate, studies  was  at  the  Furthermore, i n  2  anesthetized  change  study,  blockade,  was  based on the l e v e l s r e p o r t e d the  increase  marked.  in It  ventilatory is  believed  c o n c l u s i o n to be drawn from these r e s u l t s  is  t h a t a t low and moderate l e v e l s o f C 0 , v a g a l r e f l e x e s may be i n h i b i t o r y 2  to the v e n t i l a t o r y  response.  REFERENCES 1.  A i n s w o r t h , D.M. , C A . Smith, S.W. E i c k e r , K . S . Henderson and J . A . Dempsey. 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SUMMARY AND CONCLUSIONS  SUMMARY  (1)  OF MAJOR  The f i r s t  determine  FINDINGS  objective  whether  dog compared to measuring  the the  i  of this  study,  abdominal muscles anesthetized  abdominal  muscle  dog.  length  c h r o n i c a l l y i m p l a n t e d sonomicrometer found t h a t  c o n s i s t e n t measurements  changes c o u l d be any  inhibition  scarring  confined  transducer). compared to shortening. was  obtained of  over  muscle to  the  i n the  area  changes  awake  o f muscle of  or  muscle  dogs,  length  muscle  damage  It  and  shortening dog,  in  there  was  the  the  without local  implanted  awake  dog  significantly  to determine c o n c l u s i v e l y whether  tone  i n the  awake  dog,  but  it  was  length  (except  surrounding  of  from  was a s s e s s e d .  resting  to  awake  feasibility  two weeks and more,  immediately  anesthetized  abdominal muscle  the  in  was  i n the  In a d d i t i o n ,  periods  I t was n o t p o s s i b l e  greater  were more a c t i v e  transducers,  movement  When abdominal that  a d d r e s s e d i n Chapter I I ,  was more there  can not  be  of posture  on  discounted.  (2)  The second major o b j e c t i v e  abdominal  muscle  hypothesized the  tonic  and  was to a s s e s s the  phasic  shortening  effects  (Chapter  III).  It  was  t h a t the abdominal muscles would p h a s i c a l l y s h o r t e n more i n  upright postures be  compared to  shortening  might  present  in  hydrostatic  pressure  more i n the  s t a n d i n g and s i t t i n g  decubitus.  F u r t h e r m o r e , the  gradient.  the the  A l l of  lateral  decubitus  upright the  positions  and t h a t  postures,  due  abdominal muscles compared to  TA had a c o n s i s t e n t  shift  the in  tonic  to  the  shortened  left  lateral  its  resting  baseline  length  to a s h o r t e r length  i n the  c o n s i d e r e d to be an i n d i c a t i o n o f t o n i c  Based on r e s u l t s  (3) was  hypothesized  activated  by  This  internal  was  of  p r e v e n t i n g the  (4) in  threshold  shortening.  i n anesthetized  abdominal  i n d e e d what  muscles  loading  was  found  was  found to  the  abdominal muscles  increase  anesthetized  dogs (22)  was h y p o t h e s i z e d  by CO2 i n the activation different  awake  of  exhibit  the  (3,19-21)  dogs  the  study.  it  progressively  (ETL) and t h a t  (Chapter I V ) .  tonic  shortening  helped  and s i n c e  the  internal  to  during ETL.  The  defend  t i d a l volume  the abdominal  anesthesia  is  abdominal muscles  (Chapter V ) .  abdominal  Furthermore, i t  muscles  by  than ETL and t h e r e f o r e ,  For the  was  that  activated  thought  would the  two abdominal muscles  involve  from  of  the  muscles,  in  anesthetized  which has  present not  p r e v i o u s l y r e p o r t e d , was a l s o found d u r i n g p r o g r e s s i v e h y p e r c a p n i a . abdominal hypercapnia  muscles as  that  exhibited  the  same  pattern  found d u r i n g ETL; p r e f e r e n t i a l  of  the  (TA and EO) i n  o f s h o r t e n i n g were found i n the  shortening  that  recruitment  might v a r y and be d i f f e r e n t  measured  affect  to h y p e r c a p n i a ,  hypercapnia  d u r i n g h y p e r c a p n i a had been  tonic  by  muscles  known t o  would be more  the  comparable amounts  However,  the  that dog  awake  In a d d i t i o n ,  response  i n d i v i d u a l muscles  shortening (3,21),  be  and b r e a t h i n g p a t t e r n (12)  p a t t e r n found d u r i n g E T L . which  (13,14,20),  i n l u n g volume produced by E T L .  c o n t r o l pathways  pattern of  dogs  would  S i n c e h y p e r c a p n i a had been shown to a c t i v a t e  the v e n t i l a t o r y it  the  which was  (TA and 10) would be p r e f e r e n t i a l l y r e c r u i t e d , i n the  layer  recruitment  that  expiratory  muscle l a y e r dog.  from s t u d i e s  standing p o s i t i o n ,  response  recruitment  been The  during of  the  176  i n t e r n a l muscle l a y e r (TA and 10).  The  (5)  final  objective  contribution  of  muscles,  comparing  by  hypercapnia, Although,  similar  before  the  different  vagal  study  to  abdominal  and a f t e r  mechanisms  hypercapnia.  this  reflexes  abdominal  effect  of  the  was  vagus  thought  to  reducing  In a d d i t i o n ,  e l i m i n a t i o n o f the v a g a l  the  activation  assess  the  during  nerves  d u r i n g ETL and h y p e r c a p n i a ,  of  to  of  activation  b l o c k i n g the are  try  activation  muscle  muscles  to  be  the  abdominal ETL and  (Chapter V I ) . activated  vagal  blockade  during  both  via  had  ETL  a  and  the p a t t e r n o f r e c r u i t m e n t was n o t changed by reflexes.  CONCLUSIONS  There  are  several  conclusions  they w i l l be d i s c u s s e d  (1)  The r e s u l t s  recruited (5,9,15) layer,  at  a  expiratory  obtain  study  and  the abdominal muscles  are  ventilation  importance  an a c c u r a t e  have  recent  of  than  previously  measuring  reflection studies  demonstrated  E  expiration is  left  an a c t i v e  lateral process  decubitus even a t  muscle  abdominal  muscle  in  man,  utilizing  the  10 and TA  than found p r e v i o u s l y shortening i n  position rest.  proposed  deeper  in  activity  a t much lower l e v e l s o f V  the  of  The d e m o n s t r a t i o n o f abdominal muscle a c t i v e  awake dog l y i n g i n the that  of  Indeed,  electrodes,  ( i n t e r n a l muscle l a y e r ) (7,25).  the  activity.  intramuscular  study c o n f i r m t h a t  level  and emphasizes i n o r d e r to  drawn from t h i s  separately.  from t h i s lower  which can be  (LID),  the  suggests  Furthermore,  these  177  results  indicate  that  activity  from s u r f a c e  measurements  of  abdominal  muscle  EMG or abdominal d i s p l a c e m e n t  techniques  s e n s i t i v e t o p h a s i c e x p i r a t o r y a c t i v i t y and l e n g t h changes (TA and 10).  abdominal muscles muscle  length  changes  with  expiratory are  o f the  In a d d i t i o n ,  measurement  sonomicrometry  provides  not  deeper  of  abdominal  a  means  of  q u a n t i f y i n g t o n i c s h o r t e n i n g as w e l l as a c t i v e e x p i r a t o r y s h o r t e n i n g .  The g r e a t e r  (2)  upright occurs  postures and  increase in  is  the  excitability  and t h u s ,  the  (6).  muscle the  upright postures  (2).  postures  tonic  of  tonic  of  to g r e a t e r  in  vagal  afferents  via  in  the  FRC t h a t  (10).  i n p a r t , be due to  pressure  an  activation  activity study  in  (8),  activity  thought  the  appears  abdominal muscle  activated  gradient  This activation is  The increase  of  muscle  inspiration  of tonic  to  assumption  of  to be r e s p o n s i b l e  upright  to  to  clearly  be  the In  first  previous  an i n c r e a s e (4)  It  is  assessment  suggested  a c t i v a t i o n o f TA muscle p r o p r i o c e p t o r s compared to I t was  reasoned t h a t  the  p o s i t i o n of  in  o r abdominal  shortening allows  activity.  studies,  s h o r t e n i n g o f the TA, found i n the s t a n d i n g p o s i t i o n ,  abdominal m u s c l e s .  for  in  i n f e r r e d from  The d e m o n s t r a t i o n o f t o n i c  response  abdominal muscles  shortening.  has been  in  with  g a s t r i c p r e s s u r e measurements  the m e c h a n i c a l consequences  the t o n i c  increase  motoneurons  hydrostatic  This  EMG background n o i s e (9).  of  found  the  p r o p r i o c e p t o r s may be  abdominal muscle  diameters  given  excitation  spinal  tonic  (1,9,15).  demonstrate  surprising,  shortening  P h a s i c s h o r t e n i n g can produce p a s s i v e  in  appearance  expiratory  s h a r e d by i n s p i r a t o r y and e x p i r a t o r y m u s c l e s .  Abdominal  the  active  s h o r t e n i n g may a l s o ,  of  VT i s  increase  not  attendant  i n phasic  proprioceptors  the  amount o f  the  that  was  the  due  other  TA i n  the  178  abdominal w a l l and the make i t  more s u s c e p t i b l e  shortening reasons  transverse  of  just  to s t r e t c h i n g  abdominal  outlined),  and p r e v e n t postures  the  the  (10),  expansion.  Indeed,  i n the  muscles,  would s e r v e  increase and by  orientation of i t s  to  It  helps  is  with  assumption  r e d u c i n g abdominal compliance, diaphragmatic  TA  (for  of  it  length  is  effect,  increase  and  suggested  than  in  conclusion  is  shortening  during  enhanced,  V  (24).  T  as  that  the  In  c o n t r i b u t i o n to  the  segmental  V  has  T  (4)  It  VE,  probably  awake  dog,  by  ETL.  the In  dog.  abdominal  of  anesthetized  anesthesia  a greater  Evidence  presence  e v i d e n c e d by the g r e a t e r  have  amount o f  a  muscle  reflexes, modulating  support  abdominal  vagal  depressing  this muscle  reflexes  abdominal muscle  compared to t h a t  has  to  tonic  dogs,  defends  phasic  found i n the  effect  on  are  awake  segmental  (18).  is  functions in  cage  o f abdominal volume.  reflexes  anesthetized  provided  Furthermore,  reflexes  upright  i n FRC produced by ETL and hence,  s h o r t e n i n g found d u r i n g ETL (14,21) dogs.  (11)  improve r i b  a c t i v a t i o n appears to be i n f l u e n c e d to a l a r g e degree by v a g a l but  the  c o n c l u d e d t h a t the a c t i v a t i o n o f the abdominal muscles by ETL  to p r e v e n t the  diaphragm  the  Tonic  m a i n t a i n diaphragm l e n g t h  i n FRC a s s o c i a t e d  the  would  standing p o s i t i o n .  particularly  been u n d e r e s t i m a t e d by p r e v i o u s measurements  (3)  muscle f i b e r s  concluded t h a t . t h e to  optimize  distributes  expiratory  muscles.  the  a c t i v a t i o n o f the  diaphragm l e n g t h work o f The  and,  breathing  activation  of  abdominal muscles by CO2  i n response  between the  the  abdominal  to  an  increase  inspiratory  and  muscles  during  p r o g r e s s i v e h y p e r c a p n i a appears to be p r i m a r i l y v i a chemoreflexes  i n the  179  awake  dog.  again,  However,  suggests  activity  a  (22),  layer is,  compared  that  to  activation  under  Furthermore,  depresses  that vagal  preferential  what  the  reflexes.  muscles  The  shortening  during  respiratory  recruitment  are  considered  hypercapnia,  neuron  are more  found i n  involved  in  occurred  after vagal blockade. muscles  It  during  volume,  leads  earlier  activation  to  is  o f the  i n t e r n a l abdominal  i n posture, different  in  the same.  and  muscle  separate  differential  is  layer.  expiratory  patterns  not  is  mechanisms  dogs  greater In  the  of a c t i v a t i o n  to  phasic  addition,  project  (13,14)  of  central  and  blockade,  awake  the  to  all  accounts of  for the  i n d i v i d u a l abdominal  muscles  the  recruitment but,  evidence  the  support  mechanisms  o f segmental  of  abdominal  shortening  no  dogs,  to  of  is  or  which  the  persisted  stretching (14)  tonic  that  activation.  and  volume  reflexes,  there  preferential  reflexes  lung  segmental  innervation of  due  Although vagal  of  in  muscle  recruitment of  i n f e r r e d that p r e f e r e n t i a l  increases  neurons  Therefore,  probably  and  ETL and h y p e r c a p n i a ;  Preferential  anesthetized  activation  internal  (16,17).  the  abdominal  d u r i n g ETL and d u r i n g h y p e r c a p n i a and t h i s r e c r u i t m e n t p a t t e r n  and the  the  to CO2  response  v a g a l r e f l e x e s are e l i m i n a t e d by v a g a l  the p a t t e r n o f r e c r u i t m e n t  internal  tonic  and enable s h a r i n g o f  (3,21)  reflexes  d u r i n g changes  even a f t e r  layer  (23)  by  i n a n e s t h e t i z e d dogs than i n awake dogs.  (TA and 10)  internal  segmental  anesthetized  anesthesia  There i s  (5)  from  exhibited  The s m a l l e r amount o f p h a s i c  would suggest  muscle  shortening  may s e r v e to "track" i n s p i r a t i o n  dogs  reports  tonic  contribution  work o f b r e a t h i n g . awake  the  abdominal of  the  motoneurons  internal  rather  to  layer  different  reflexes.  may not  be  responsible  for  differential  180  activation  of  important f o r  the the  abdominal  muscles,  l o a d compensating  the  vagus  However,  and hence,  i n the awake  diaphragm l e n g t h dog,  l u n g volume,  even a f t e r  by n o n - v a g a l  mechanisms.  Although ventilatory a role  vagal  the  do  not  clearly  defended  T  is  defence o f  evidence o f  appear  to  be  vagotomy, (24).  end-expiratory the  role  required  played  for  the  and b r e a t h i n g p a t t e r n response to h y p e r c a p n i a , they may p l a y  i n abdominal muscle a c t i v a t i o n .  vagally  mediated  prevent  gas  defending  since after  and V , are not  persistence of  vagal blockade,  reflexes  is  f u n c t i o n o f the muscles d u r i n g E T L .  T h i s i s p a r t i c u l a r l y t r u e i n the a n e s t h e t i z e d dog, l u n g volume  nerve  augmentation  trapping  diaphragm  and length  an  of  2  abdominal  increase and  During C0 stimulated  in  allowing  muscle dynamic sharing  activity lung of  breathing, may  volume the  help thus,  work  of  breathing.  REFERENCES 1.  A g o s t o n i , E . , and E . J . M . C a m p b e l l . The abdominal m u s c l e s . I n : The R e s p i r a t o r y M u s c l e s : Mechanics and N e u r a l C o n t r o l . E . J . M . C a m p b e l l , E . A g o s t o n i , and J . Newsom-Davis ( e d s ) . Saunders, P h i l a d e l p h i a , PA, 1970, 175-180.  2. A g o s t o n i , E . , and R . E . H y a t t . S t a t i c b e h a v i o r o f the r e s p i r a t o r y system. I n : Handbook o f P h y s i o l o g y S e c t i o n 3: The R e s p i r a t o r y System. V o l . I I I . W i l l i a m s & W i l k i n s , B a l t i m o r e , MD, 1986, 113-130. 3. A r n o l d , J . S . , M . A . H a x h i u , N . S . C h e r n i a c k and E . van L u n t e r e n . T r a n s v e r s e abdominis l e n g t h changes d u r i n g eupnea, h y p e r c a p n i a and airway o c c l u s i o n . J . A p p l . P h y s i o l . 6 4 ( 2 ) : 658-665, 1988. 4.  Campbell, E . J . M . and J . H . Green. The v a r i a t i o n s i n i n t r a - a b d o m i n a l p r e s s u r e and the a c t i v i t y o f the abdominal muscles d u r i n g b r e a t h i n g ; a study i n man. J . P h y s i o l . 122: 282-290, 1953.  5.  Campbell, E . J . M . and J . H . Green. The e x p i r a t o r y f u n c t i o n o f the abdominal muscles i n man. An e l e c t r o m y o g r a p h i c s t u d y . J . P h y s i o l . 120: 409-418, 1953.  181  6.  D a v i e s , A . , F . B . Sant'Ambrogio and G. Sant'Arabrogio. C o n t r o l o f p o s t u r a l changes o f end e x p i r a t o r y volume (FRC) by airways s l o w l y a d a p t i n g mechanoreceptors. R e s p i r . P h y s i o l . 41: 211-216, 1980.  7.  De T r o y e r , A . , M. Estenne, V . Ninane, D. van Gansbeke and M. G o r i n i . T r a n s v e r s u s abdominis muscle f u n c t i o n i n humans. J . A p p l . P h v s i o l . 6 8 ( 3 ) : 1010-1016, 1990.  8.  De T r o y e r , A . , J . J . G i l m a r t i n and V . Ninane. Abdominal muscle use d u r i n g b r e a t h i n g i n u n a n e s t h e t i z e d dogs. J . A p p l . P h y s i o l . 6 6 ( 1 ) : 20-27, 1989.  9.  D r u z , W.S. and J . T . Sharp. A c t i v i t y o f r e s p i r a t o r y muscles i n u p r i g h t and recumbent humans. J . A p p l . P h y s i o l . 5 1 ( 6 ) : 1552-1561, 1981.  10.  F a r k a s , G . A . , R . E . B a e r , M. Estenne and A . De T r o y e r . M e c h a n i c a l r o l e o f e x p i r a t o r y muscles d u r i n g b r e a t h i n g i n u p r i g h t dogs. J . A p p l . P h v s i o l . 6 4 ( 3 ) : 1060-1067, 1988.  11.  F i t t i n g , J . W . , P . A . E a s t o n , R. Arnoux, A . G u e r r a t y and A . G r a s s i n o . Diaphragm l e n g t h adjustments w i t h body p o s i t i o n changes i n the awake dog. J . A p p l . P h v s i o l . 66(2): 870-875, 1989.  12.  G a u t i e r , H. P a t t e r n of breathing during hypoxia or hypercapnia o f the awake o r a n e s t h e t i z e d c a t . R e s p i r . 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Welsh, A . M . Leevers and J . D . Road. The e f f e c t o f continuous p o s i t i v e airway p r e s s u r e and h y p e r c a p n i a on e x p i r a t o r y muscle a c t i v i t y d u r i n g wakefulness and s l e e p . Am. Rev. R e s p i r . P i s . 141(4): A125, 1990.(Abstract)  

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