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The relationship between the hypoxic ventilatory response and arterial desaturation during heavy work Hopkins, Susan Roberta 1988

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THE RELATIONSHIP BETWEEN THE HYPOXIC VENTILATORY RESPONSE AND ARTERIAL DESATURATION DURING HEAVY WORK by SUSAN ROBERTA HOPKINS B.Med.Sci. Memorial University of Newfoundland, St. John's, 1978 M.D. Memorial University of Newfoundland, St. John's, 1980 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF PHYSICAL EDUCATION i n THE FACULTY OF GRADUATE STUDIES School of Physical Education and Recreation We accept this thesis as conforming to the required standards. THE UNIVERSITY OF BRITISH COLUMBIA February, 1988 © Susan Roberta Hopkins, 1988. 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 The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6(3/81) ABSTRACT A r t e r i a l d e s a t u r a t i o n i n f i t a t h l e t e s , d u r i n g e x e r c i s e a t an i n t e n s i t y g r e a t e r t h a n or e q u a l t o 90% of VO max has been 2 r e p o r t e d by a number of a u t h o r s y e t t h e e t i o l o g y o f t h e s e c h a n g e s r e m a i n o b s c u r e . I n a d e q u a t e p u l m o n a r y v e n t i l a t i o n due t o a b l u n t e d r e s p i r a t o r y d r i v e , or l u n g m e c h a n i c s has been i m p l i c a t e d as a f a c t o r i n t h e e t i o l o g y o f t h i s phenomenon. I t was t h e p u r p o s e of t h i s e x p e r i m e n t t o i n v e s t i g a t e t h e r e l a t i o n s h i p between a r t e r i a l d e s a t u r a t i o n and v e n t i l a t o r y r e s p o n s e t o h y p o x i a (HVR). T w e l v e h e a l t h y male s u b j e c t s ( age = 23.8 +_ 3.6 y r s . , h e i g h t = 181.6 +_ -1 5.6 cms., Weight = 73.7 + 6.2 k g . , VO max = 63,2 + 2.2 ml .kg . -1 2 .min ) p e r f o r m e d a f i v e m i n u t e e x e r c i s e t e s t on a t r e a d m i l l a t 100% of VO max. A r t e r i a l s a m p l e s f o r pH, PCO , P0 , and SaO 2 2 2 2 were w i t h d r a w n v i a an i n d w e l l i n g a r t e r i a l c a n n u l a a t r e s t and e v e r y 15s t h r o u g h o u t t h e e x e r c i s e t e s t . The b l o o d gas s a m p l e s were a n a l y z e d w i t h an I n s t r u m e n t L a b o r a t o r i e s 1306 b l o o d gas a n a l y z e r . V e n t i l a t i o n and VO were measured by a Beckman 2 m e t a b o l i c measurement c a r t . On a s e p a r a t e o c c a s i o n the v e n t i l a t o r y r e s p o n s e t o h y p o x i a (HVR) was d e t e r m i n e d by r e c o r d i n g VE as p r o g r e s s i v e h y p o x i a was i n d u c e d by a d d i n g N t o a m i x i n g 2 chamber. SaO was measured u s i n g a H e w l e t t - P a c k a r d e a r o x i m e t e r ; 2 t o m a i n t a i n i s o c a p n i a s m a l l ammounts of CO were added t o the 2 open c i r c u i t s y s t e m . ANOVA f o r r e p e a t e d measured was used t o e v a l u a t e c h a n g e s i n b l o o d g a s e s , v e n t i l a t i o n , and VO . S i m p l e 2 l i n e a r r e g r e s s i o n and m u l t i p l e l i n e a r r e g r e s s i o n was used t o e v a l u a t e t h e r e l a t i o n s h i p between t h e changes i n SaO and HVR 2 and t h e d e s c r i p t i v e v a r i a b l e s . S u b j e c t s showed a s i g n i f i c a n t d e c l i n e i n a r t e r i a l s a t u r a t i o n and PO o v e r t h e c o u r s e of t h e 2 t e s t (p < 0.01,and p < 0 . 0 1 ) . F o u r s u b j e c t s ( M i l d ) e x h i b i t e d modest d e c r e a s e s i n SaO t o (94.6 +_ 1 . 9 % ) , t h r e e ( M o d e r a t e ) 2 showed an i n t e r m e d i a t e r e s p o n s e (SaO 91.6 +_ 0.1%) and f i v e 2 ( M a r k e d ) d e m o n s t r a t e d a marked d e c r e a s e i n a r t e r i a l s a t u r a t i o n (SaO = 90.0 + 1 . 2 % ) . The d i f f e r e n c e s i n P0 and SaO between 2 2 2 M i l d and Marked g r o u p s were s i g n i f i c a n t ( p < 0.05, and p < 0 . 0 1 ) ; t h e r e 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 g r o u p s i n VE, VO , pH or PCO . T h e r e was no s i g n i f i c a n t c o r r e l a t i o n between 2 2 t h e l o w e s t • SaO r e a c h e d and HVR, or any of t h e d e s c r i p t i v e 2 v a r i a b l e s . N i n e s u b j e c t s d i d not r e a c h m a x i m a l VE ( a s d e t e r m i n e d by t h e VO max t e s t ) on t h e e x e r c i s e t e s t , two s u b j e c t s 2 e x h i b i t e d s i m i l a r v e n t i l a t i o n , and t h e r e m a i n i n g s u b j e c t e x c e e d e d m a x i m a l VE, but f e l l i n t o t h e M i l d group w i t h r e s p e c t t o d e s a t u r a t i o n . Oxygen u p t a k e e x c e e d e d t h a t r e c o r d e d f o r t h e VO 2 max d e t e r m i n a t i o n f o r f o u r o f t h e f i v e s u b j e c t s i n t h e Marked g r o u p ; t h e r e m a i n i n g s u b j e c t s d e m o n s t r a t e d l o w e r or s i m i l a r v a l u e s . I t was c o n c l u d e d t h a t a r t e r i a l d e s a t u r a t i o n was not r e l a t e d t o b l u n t e d h y p o x i c d r i v e . TABLE OF CONTENTS A b s t r a c t . . i i L i s t o f Symbols v L i s t o f T a b l e s . . v i L i s t of F i g u r e s „.. . v i i A c k n o w l e d g e m e n t s . v i i i I n t r o d u c t i o n 1 Methods 5 R e s u l t s .9 D i s c u s s i o n '. ...17 R e f e r e n c e s 2 8 A p p e n d i x A R e v i e w o f l i t e r a t u r e 34 V e n t i l a t i o n d u r i n g e x e r c i s e 34 R e s p i r a t o r y d r i v e s 36 R e s p i r a t o r y f a c t o r s l i m i t i n g p e r f o r m a n c e 39 Hypoxemia d u r i n g e x e r c i s e 42 H e m o g l o b i n a f f i n i t y f o r oxygen d u r i n g e x e r c i s e 45 A r t e r i a l d e s a t u r a t i o n d u r i n g heavy e x e r c i s e 46 B PO s a t u r a t i o n normogram % f o r whole b l o o d 51 2 C S u b j e c t p h y s i o l o g i c d a t a 52 D P u l m o n a r y f u n c t i o n t e s t s .53 E H y p o x i c v e n t i l a t o r y r e s p o n s e 54 F S u b j e c t d a t a 55 G Equip m e n t and s u p p l i e s 61 H C o n s e n t f o r m 62 i v L I S T OF SYMBOLS FEV f o r c e d e x p i r a t o r y volume i n one s e c o n d 1 FVC f o r c e d v i t a l c a p a c i t y 2,3-DPG 2 , 3 - d i p h o s p h o g l y c e r a t e + H h y d r o g e n i o n HVR h y p o x i c v e n t i l a t o r y r e s p o n s e HCVR h y p e r c a p n i c v e n t i l a t o r y r e s p o n s e PCO p a r t i a l p r e s s u r e o f c a r b o n d i o x i d e 2 pH n e g a t i v e l o g a r i t h m o f h y d r o g e n i o n c o n c e n t r a t i o n PO p a r t i a l p r e s s u r e o f oxygen 2 SaO a r t e r i a l oxygen s a t u r a t i o n . 2 VE e x p i r e d m i n u t e v e n t i l a t i o n VO max m a x i m a l oxygen c o n s u m p t i o n 2 L I S T OF TABLES T a b l e I T a b l e I I T a b l e I I I T a b l e IV T a b l e P h y s i o l o g i c a l c h a r a c t e r i s t i c s 9 15 s e c o n d i n t e r v a l measures f o r a r t e r i a l b l o o d v a l u e s , VO and v e n t i l a t i o n f o r 2 a l l s u b j e c t s 11 Anova r e s u l t s ......14 D i f f e r e n c e s i n v e n t i l a t i o n and maximal oxygen u p t a k e between VO max d e t e r m i n a - 2 t i o n and f i v e - m i n u t e e x e r c i s e t e s t 15 HVR and s p o r t f o r each s u b j e c t 16 v i L I S T OF FIGURES F i g u r e 1. Changes i n PO o v e r t i m e 12 2 F i g u r e 2. Changes i n SaO o v e r t i m e .13 2 v i i ACKNOWLEDGMENTS The f i n i s h e d p r o d u c t t h a t t h i s t h e s i s r e p r e s e n t s i s t h e combined e f f o r t o f many p e o p l e : my s u b j e c t s who d o n a t e d t h e i r t i m e , e f f o r t and b l o o d , my d a t a c o l l e c t i o n a s s i s t a n t s , who were a v a i l a b l e a t a l l h o u r s o f t h e day.and n i g h t , and my c o m m i t t e e members who r e v i e w e d and a d v i s e d . To a l l o f you I am s i n c e r e l y g r a t e f u l . I e x t e n d s p e c i a l a p p r e c i a t i o n t o Dr. Don M c K e n z i e , my a d v i s o r and f r i e n d who f r e e l y gave t i m e and e n e r g y t o me d u r i n g a l l p h ases o f t h i s p r o j e c t . T h i s t h e s i s i s d e d i c a t e d t o my p a r e n t s , Bob and B a r b a r a H o p k i n s who s e t t h e p r e c i d e n t f o r h i g h e r e d u c a t i o n . INTRODUCTION I n h e a l t h y i n d i v i d u a l s e x e r c i s i n g a t s e a l e v e l t h e p u l m o n a r y s y s t e m i s n o t g e n e r a l l y t h o u g h t t o be a l i m i t i n g f a c t o r t o p e r f o r m a n c e d u r i n g m a x i m a l a e r o b i c e x e r c i s e . H o w e v e r , r e c e n t r e s e a r c h ( D e m p s e y e t a l . , 1 9 8 4 ; P o w e r s e t a l . , 1 9 8 4 ; Y o u n g a n d W o l l c o c k , 1 9 7 8 ; W i l l i a m s e t a l . , 1 9 8 6 ) h a s d e m o n s t r a t e d a d e c l i n e i n a r t e r i a l o x y g e n t e n s i o n o f s u f f i c i e n t m a g n i t u d e t o c a u s e d e s a t u r a t i o n o f h e m o g l o b i n d u r i n g m a x i m a l e x e r c i s e t a s k s . T h i s s u g g e s t s t h a t t h e r e s p i r a t o r y s y s t e m may be c a p a b l e o f l i m i t i n g p e r f o r m a n c e , p a r t i c u l a r l y i n i n d i v i d u a l s c a p a b l e o f v e r y h i g h w o r k o u t p u t s . D u r i n g e x e r c i s e t h e c o m b i n e d e f f e c t o f i n c r e a s i n g t e m p e r a t u r e , d e c r e a s e d pH a n d a l t e r a t i o n s i n 2,3-DPG, c o m b i n e t o p r o d u c e a r i g h t w a r d s h i f t i n t h e o x y g e n h e m o g l o b i n d i s s o c i a t i o n c u r v e , r e s u l t i n g i n a d e c l i n e i n s a t u r a t i o n f r o m a n o r m a l v a l u e o f 97 t o 9 8 % s a t u r a t e d t o a p p r o x i m a t e l y 94 t o 9 5 % s a t u r a t e d ( T h o m p s o n a n d D e m p s e y , 1 9 7 4 ) . The e f f e c t o f t h i s r i g h t w a r d s h i f t on 0 c o n t e n t o f b l o o d i s m i n i m a l a t t h e l u n g w h e r e t h e p a r t i a l 2 p r e s s u r e o f o x y g e n i s h i g h . H o w e v e r , a t t h e w o r k i n g m u s c l e w h e r e o x y g e n p a r t i a l p r e s s u r e s a r e l o w , t h e n e t e f f e c t i s i n c r e a s i n g r e l e a s e o f o x y g e n , p r e s e r v i n g t h e d i f f u s i o n g r a d i e n t i n t o t h e m u s c l e c e l l m i t o c h o n d r i a ( T h o m p s o n a n d Dempsey, 1 9 7 4 ) . A r t e r i a l d e s a t u r a t i o n , g r e a t e r t h a n t h a t e x p e c t e d f r o m t h e c h a n g e s d e s c r i b e d a b o v e h a s b e e n r e p o r t e d d u r i n g v e r y i n t e n s e e x e r c i s e , d a t i n g f r o m . 1 9 1 9 , when H a r r o p o b s e r v e d a d e c l i n e i n a r t e r i a l s a t u r a t i o n t o 8 5 % i m m e d i a t e l y f o l l o w i n g h e a v y e x e r c i s e . 1 i n v e r y h i g h l y t r a i n e d i n d i v i d u a l s w i t h a h i g h a e r o b i c c a p a c i t y e x e r c i s i n g a t an e x e r c i s e i n t e n s i t y g r e a t e r t h a n 90% of m a x i m a l (Dempsey e t a l . , 1984; Powers e t a l . , 1984; W i l l i a m s e t a l . , 1986) . M a x i m a l oxygen c o n s u m p t i o n (VO max), and hence maximal 2 a e r o b i c p e r f o r m a n c e i s l i m i t e d by a number of f a c t o r s ( D i P r a m p e r o , 1 9 8 5 ) . As VO max i s o b s e r v e d t o i n c r e a s e w i t h 2 i n c r e a s i n g p a r t i a l p r e s s u r e o f oxygen ( B a n n i s t e r and Cunningham, 1954; K a i s j e r , 1970; and o t h e r s ) and w i t h r e d c e l l i n f u s i o n ( B u i c k e t a l . , 1980) and d e c r e a s e w i t h h y p o x i a ( S q u i r e s and B u s k i r k , 1982; W e l s h , 1987 f o r r e v i e w ) and a c u t e anemia (Woodson e t a l . , 1 9 7 8 ) , t h e main l i m i t a t i o n t o a e r o b i c p e r f o r m a n c e has been c o n s i d e r e d t o be t h e oxygen t r a n s p o r t s y s t e m . C l e a r l y , o t h e r f a c t o r s s u c h as m i t o c h o n d r i a l oxygen u t i l i z a t i o n , p e r i p h e r a l c i r c u l a t i o n and oxygen d i f f u s i o n a t t h e w o r k i n g m u s c l e can a l s o e x e r t some c o n s t r a i n t . In two l e g g e d e x e r c i s e , a p p r o x i m a t e l y 75% of VO max i s s e t by oxygen t r a n s p o r t w i t h the r e m a i n i n g 25% 2 b e i n g e q u a l l y a c c o u n t e d f o r by m i t o c h o n d r i a l c a p a c i t y and p e r i p h e r a l d i f f u s i o n and p e r f u s i o n ( D i p r a m p r o , 1 9 8 5 ) . Thus i t can be seen t h a t a r t e r i a l d e s a t u r a t i o n l e a d i n g t o d e c r e a s e d oxygen d e l i v e r y and d e c r e a s e d d i f f u s i o n g r a d i e n t a t t h e m u scle can s i g n i f i c a n t l y e f f e c t VO max. The l e v e l of d e s a t u r a t i o n a t w h i c h 2 a l i m i t t o VO max can be o b s e r v e d has not been e s t a b l i s h e d , 2 " a l t h o u g h some a u t h o r s ( S q u i r e s and B u s k i r k , 1982) f e e l t h a t i t may be on t h e o r d e r of f o u r p e r c e n t . In the e l i t e a t h l e t e p e r f o r m i n g a t maximal l e v e l s any d e crement i n maximal a e r o b i c p e r f o r m a n c e may be s i g n i f i c a n t . 2 A v a r i e t y of mechanisms have been p r o p o s e d t o a c c o u n t f o r t h e s e o b s e r v a t i o n s i n c l u d i n g v e n o a r t e r i a l s h u n t i n g , v e n t i l a t i o n p e r f u s i o n i n e q u a l i t y , h y p o v e n t i l a t i o n and d i f f u s i o n l i m i t a t i o n ( P o w e r s and W i l l i a m s , 1 9 8 7 ) . C u r r e n t t h i n k i n g s u g g e s t s t h a t t h e l a t t e r two e x p l a n a t i o n s may be t h e most l i k e l y . Thus two main i s s u e s may be c o n s i d e r e d : 1. p u l m o n a r y v e n t i l a t i o n i s not a d e q u a t e e i t h e r as a r e s u l t of b l u n t e d r e s p i r a t o r y d r i v e or of a m e c h a n i c a l i n a b i l i t y of t h e p u lmonary s y s t e m t o meet t h e h i g h l e v e l s o f v e n t i l a t i o n r e q u i r e d (Dempsey e t a l . , 1 9 8 4 ) . 2. p u l m o n a r y v e n t i l a t i o n i s a d e q u a t e but d i f f u s i o n of oxygen i s l i m i t e d by s h o r t e n e d r e d c e l l t r a n s i t t i m e or i n c r e a s e d d i f f u s i o n d i s t a n c e due t o l o c a l i z e d edema a t v e r y h i g h l e v e l s of p u lmonary b l o o d f l o w (Dempsey e t a l . , 1984; Powers and W i l l i a m s , 1987) . I t has been s u g g e s t e d t h a t t h e f a c t o r s d e t e r m i n i n g e x e r c i s e v e n t i l a t i o n r e p r e s e n t t h e i n t e g r a t i o n of the c h e m i c a l s t i m u l u s t o b r e a t h e w i t h t h e m e c h a n i c a l c o n s t r a i n t s imposed by t h e work of b r e a t h i n g (Dempsey e t a l . , 1 9 8 5 ) . B o t h a d e c r e a s e i n e x e r c i s e v e n t i l a t i o n ( M a r t i n e t a l . , 1978a; M a r t i n e t a l . , 1979.) and a low h y p o x i c v e n t i l a t o r y r e s p o n s e ( M a r t i n e t a l . , 1979) have been d e m o n s t r a t e d i n e n d u r a n c e a t h l e t e s compared w i t h n o n - e n d u r a n c e a t h l e t e s . T h e r e f o r e i t i s l o g i c a l t o c o n s i d e r t h a t i f h y p o v e n t i l a t i o n i s a f a c t o r i n a r t e r i a l d e s a t u r a t i o n d u r i n g i n t e n s e e x e r c i s e t h a t d e s a t u r a t i o n may be more l i k e l y i n t h o s e i n d i v i d u a l s w i t h a b l u n t e d r e s p o n s e t o h y p o x i a . Thus t h e p u r p o s e of t h i s s t u d y was t o examine t h e r e l a t i o n s h i p between the h y p o x i c v e n t i l a t o r y r e s p o n s e and c hanges i n a r t e r i a l oxygen s a t u r a t i o n i n h e a l t h y e n d u r a n c e and n o n - e n d u r a n c e t r a i n e d a t h l e t e s d u r i n g h i g h i n t e n s i t y e x e r c i s e a t sea l e v e l . 4 METHODS A n o n - p r o b a b i l i t y sample of 12 h e a l t h y male s u b j e c t s was s e l e c t e d f rom a t o t a l o f 16 i n d i v i d u a l s who v o l u n t e e r e d f o r t h e s t u d y . C r i t e r i a f o r p a r t i c i p a t i o n i n c l u d e d n o r m a l c a r d i o v a s c u l a r and r e s p i r a t o r y f u n c t i o n , n o r m a l a r t e r i a l c i r c u l a t i o n t o the hand -1 -1 and m a x i m a l oxygen c o n s u m p t i o n (VO max) _> 60 ml.kg .min . Of 2 the s i x t e e n v o l u n t e e r s , t h r e e f a i l e d t o meet the e l i g i b i l i t y r e q u i r e m e n t s and i n one s u b j e c t i n s e r t i o n o f t h e a r t e r i a l c a t h e t e r was u n s u c c e s s f u l . A l l s u b j e c t s gave i n f o r m e d c o n s e n t and t h e e x p e r i m e n t was a p p r o v e d by t h e U n i v e r s i t y of B r i t i s h C o l u m b i a Committee on Human E x p e r i m e n t a t i o n . A t o t a l of s i x e l i t e e n d u r a n c e and s i x e l i t e n o n - e n d u r a n c e a t h l e t e s were r e c r u i t e d . I t was p r e d i c t e d t h a t t h e d i v i s i o n o f s u b j e c t s between p r e d o m i n a n t l y e n d u r a n c e and n o n - e n d u r a n c e s p o r t s would g i v e a r a n g e of v e n t i l a t o r y r e s p o n s e s t o h y p o x i a . B a s e l i n e D a t a D e s c r i p t i v e p h y s i c a l c h a r a c t e r i s t i c s and VO max were 2 d e t e r m i n e d f o r each s u b j e c t one t o two weeks p r i o r to t e s t i n g . P u l m o n a r y f u n c t i o n t e s t i n g i n c l u d i n g FVC, % p r e d i c t e d FVC, FEV , 1 and peak f l o w r a t e , was c a r r i e d out f o r e ach s u b j e c t u s i n g an a u t o s p i r o m e t e r ( M i n t o M e d i c a l S c i e n c e Co. L t d . , model A S - 7 0 0 ) . M a x i m a l oxygen u p t a k e was d e t e r m i n e d u t i l i z i n g a c o n t i n u o u s g r a d e d t r e a d m i l l ( Q u i n t o n 24-72 t r e a d m i l l ) t e s t . The s t a r t i n g -1 -1 speed was 3.08 m.sec and t h i s was i n c r e a s e d by 0.22 m.sec per m i n u t e u n t i l v o l i t i o n a l f a t i g u e . A n a l y s i s of e x p i r e d r e s p i r a t o r y g a s e s was p e r f o r m e d (Beckman M e t a b o l i c Measurement C a r t ) and measurements were t a b u l a t e d e v e r y 15 s e c o n d s by a H e w l e t t P a c k a r d 3052A d a t a a c q u i s i t i o n s y s t e m . VO max was d e t e r m i n e d by t h e 2 a v e r a g e of t h e f o u r h i g h e s t c o n s e c u t i v e 15 s e c o n d measures of oxygen u p t a k e . T h i s r e s u l t was used t o c a l c u l a t e a t r e a d m i l l v e l o c i t y w h i c h r e p r e s e n t e d 100% of VO max. 2 Exercise Test S u b j e c t s were a s k e d t o r e t u r n a g a i n a p p r o x i m a t e l y one week l a t e r h a v i n g r e f r a i n e d f rom e a t i n g i n t h e l a s t two h o u r s and from e x e r c i s i n g i n t h e l a s t 24 h o u r s . The e x e r c i s e p r o t o c o l c o n s i s t e d -1 of a f i v e m i n u t e t r e a d m i l l warm-up a t 3.08-3.52 m.sec f o l l o w e d by a f i v e m i n u t e r u n a t a speed t h a t c o r r e s p o n d e d t o 100% of V0 2 max . Data Collection P r i o r t o t h e e x e r c i s e t e s t , an i n d w e l l i n g a r t e r i a l c a n n u l a ( A r r o w , # 20 gauge, or J e l c o #22 gauge) was i n s e r t e d p e r c u t a n e o u s l y i n t h e r i g h t r a d i a l a r t e r y , a f t e r i n f i l t r a t i o n w i t h l o c a l a n a e s t h e t i c ( 1 % X y l o c a i n e H y d r o c h l o r i d e ) and u s i n g s t e r i l e t e c h n i q u e . Each s u b j e c t was c h e c k e d f o r a d e q u a t e c o l l a t e r a l c i r c u l a t i o n v i a the u l n a r a r t e r y ( A l l e n ' s t e s t ) b e f o r e the c a n n u l a was i n s e r t e d . A minimum volume (1.2 c c ) e x t e n s i o n t u b e ( C u t t e r ) and and two way s t o p c o c k (PVB) f i l l e d w i t h n o r m a l s a l i n e was a t t a c h e d . C a n n u l a p a t e n c y was m a i n t a i n e d by f r e q u e n t f l u s h i n g w i t h n o r m a l s a l i n e t o w h i c h h e p a r i n sodium (2000 u/1) had been added. At t h e o n s e t of s a m p l i n g t h e s a l i n e was w i t h d r a w n and t h e a r t e r i a l s a m p l e s were a n a e r o b i c a l l y 6 c o l l e c t e d i n p r e - h e p a r i n i z e d p l a s t i c s y r i n g e s . The f r e q u e n c y of s a m p l i n g (15 s) d i d not a l l o w f o r r e i n f u s i o n of h e p a r i n i n s a l i n e between s a m p l e s , nor was i t r e q u i r e d . A l l c a n n u l a s r e m a i n e d p a t e n t u n t i l t h e end of t h e s a m p l i n g p e r i o d . A r t e r i a l b l o o d s a m p l e s were w i t h d r a w n i m m e d i a t e l y p r i o r t o t h e o n s e t of t h e e x e r c i s e t e s t and a t 15 s e c o n d i n t e r v a l s a f t e r t h e s t a r t of t h e t e s t f o r a t o t a l o f 21 s a m p l e s . The b l o o d s a m p l e s were a n a e r o b i c a l l y capped and m a i n t a i n e d on i c e u n t i l t h e t e s t s e s s i o n was c o m p l e t e and b a t c h a n a l y s i s c o u l d be p e r f o r m e d . Each 2 ml sample was a n a l y z e d w i t h i n .90 m i n u t e s of c o l l e c t i o n u s i n g a I n s t r u m e n t L a b o r a t o r i e s 1306 a u t o m a t e d B l o o d Gas/ pH A n a l y z e r . T h i s machine was c a l i b r a t e d u s i n g a two p o i n t c a l i b r a t i o n p r i o r t o b a t c h a n a l y s i s and one p o i n t c a l i b r a t i o n was a u t o m a t i c a l l y peformed a f t e r e v e r y s a m p l e . The s a m p l e s were a n a l y z e d f o r pH, PCO , and PO ; oxygen s a t u r a t i o n (SaO ) was 2 2 2 c a l c u l a t e d a u t o m a t i c a l l y . The s a m p l e s were not c o r r e c t e d f o r t e m p e r a t u r e as c o r e t e m p e r a t u r e was not measured d u r i n g the d a t a c o l l e c t i o n . E x e r c i s e v e n t i l a t i o n and e x p i r e d gas c o n c e n t r a t i o n were measured a t 15 s e c o n d i n t e r v a l s by the s y s t e m d e s c r i b e d p r e v i o u s l y f o r VO max d e t e r m i n a t i o n . 2 The s u b j e c t s r e t u r n e d a t h i r d t i m e and h y p o x i c v e n t i l a t o r y r e s p o n s e s were measured u s i n g a m o d i f i c a t i o n of the method of W e i l e t a l . , ( 1 9 7 0 ) . B a s i c a l l y t h e s u b j e c t s b r e a t h e d room a i r f r o m a m i x i n g chamber (volume = 13.5 1 ) , t h r o u g h a two-way R u d o l p h v a l v e . Under c o n t i n u o u s c a r d i a c m o n i t o r i n g , p r o g r e s s i v e h y p o x i a was i n d u c e d by t h e a d d i t i o n of 100% n i t r o g e n gas i n t o the m i x i n g chamber. Oxygen s a t u r a t i o n was measured v i a a H e w l e t t - P a c k a r d 47201A e a r o x i m e t e r and t h e amount of n i t r o g e n was i n c r e a s e d a t one m i n u t e i n t e r v a l s u n t i l an oxygen s a t u r a t i o n o f 80% was r e a c h e d . End t i d a l PCO was measured (Beckman LB-2) and 2 i s o c a p n i a was m a i n t a i n e d _+ 2 t o r r by t h e a d d i t i o n of v e r y s m a l l amounts o f 100% CO gas d i s t a l t o t h e m i x i n g chamber. V e n t i l a t i o n 2 was measured v i a a low r e s i s t a n c e pneumotach and and t h e d a t a was r e c o r d e d and t a b u l a t e d e v e r y 15 s e c o n d s v i a an IBM d a t a a c c q u i s i t i o n s y s t e m . A BMDP P:1R, s i m p l e l i n e a r r e g r e s s i o n , program was used t o d e t e r m i n e t h e s l o p e of the l i n e a r r e l a t i o n s h i p between SaO and v e n t i l a t i o n . S u b j e c t s were t e s t e d 2 u n t i l i s o c a p n i a was m a i n t a i n e d w i t h i n t h e ra n g e s p e c i f i e d above and u n t i l 70% of t h e v a r i a t i o n i n v e n t i l a t i o n c o u l d be e x p l a i n e d 2 on t h e b a s i s o f cha n g e s i n SaO (R _> 0.7) or u n t i l c o n s i s t a n t 2 v a l u e s were o b t a i n e d . S t a t i s t i c a l A n a l y s i s BMDP s t a t i s t i c a l s o f t w a r e , P:2V, ANOVA f o r r e p e a t e d measures was used t o s t a t i s t i c a l l y t e s t c h a n g e s i n b l o o d gas p a r a m e t e r s , v e n t i l a t i o n , and V0 o v e r t i m e . P:1R, S i m p l e L i n e a r R e g r e s s i o n , 2 and P:2R, M u l t i p l e L i n e a r R e g r e s s i o n were used t o d e t e r m i n e t h e r e l a t i o n s h i p between c h a n g e s i n SaO and d e s c r i p t i v e v a r i a b l e s , 2 i n c l u d i n g HVR. RESULTS B a s e l i n e M e a s u r e s Mean v a l u e s f o r the p h y s i o l o g i c c h a r a c t e r i s t i c s of the t w e l v e s u b j e c t s a r e r e p o r t e d i n T a b l e I . Pulmonary f u n c t i o n r e s u l t s were w i t h i n n o r m a l l i m i t s f o r a l l s u b j e c t s . TABLE I . PHYSIOLOGICAL CHARACTERISTICS Means + S.D. AGE ( y r s ) 23.8 + 3.6 HEIGHT (cms) 1 8 1 . 6 + 5 . 6 WEIGHT (Kg) 73.7 + 6.2 VO max ( m l . k g .min ) 63.2 +_ 2.2 2 The s u b j e c t s i n c l u d e d two t r i a t h l e t e s , t h r e e l o n g d i s t a n c e r u n n e r s (10 km, m a r a t h o n ) , two oarsmen (one c o l l e g i a t e and one O l y m p i c m e d a l i s t ) , t h r e e m i d d l e d i s t a n c e r u n n e r s (400, 800 m), one c o m p e t i t i v e c y c l i s t and one member of Canada's Pan-Am f i e l d hockey team. A l l s u b j e c t s were a c t i v e l y t r a i n i n g f o r t h e i r r e s p e c t i v e s p o r t s a t the t i m e of the i n v e s t i g a t i o n . - Changes i n A r t e r i a l B l o o d Gases W i t h E x e r c i s e E l e v e n of the t w e l v e s u b j e c t s c o m p l e t e d the f u l l f i v e m i n u t e s of e x e r c i s e . The r e m a i n i n g s u b j e c t was u n a b l e to c o m p l e t e the f u l l t e s t i n g t i m e and t e r m i n a t e d the t e s t a f t e r f o u r m i n u t e s and f i f t e e n s e c o n d s . The d a t a from t h i s s u b j e c t were e x c l u d e d from s t a t i s t i c a l a n a l y s i s , but were r e t a i n e d f o r d e s c r i p t i v e p u r p o s e s . Means and s t a n d a r d d e v i a t i o n s f o r the 15 second 9 i n t e r v a l measures of pH, PCO , PO and SaO i n t h e e l e v e n 2 2 2 s u b j e c t s who c o m p l e t e d t h e f u l l t e s t a r e r e p o r t e d i n T a b l e I I . R e s t i n g v a l u e s f o r pH, PCO , PO , and SaO , were w i t h i n 2 2 2 n o r m a l l i m i t s f o r a l l s u b j e c t s . As would be e x p e c t e d f r o m i n t e n s e e x e r c i s e a s i g n i f i c a n t (F - 141, p < 0.001) m e t a b o l i c a c i d o s i s o c c u r e d ; pH d e c l i n e d f r o m a r e s t i n g v a l u e of 7.43+0.03 t o 7.21+0.06 a t t h e end of f i v e m i n u t e s o f e x e r c i s e . A v e r a g e d o v e r a l l s u b j e c t s t h e r e was a s i g n i f i c a n t d e c l i n e i n P0 (F == 26.1, p 2 < 0.001) and SaO (F =64.8, p < 0 . 0 0 1 ) . S u b j e c t s f e l l i n t o t h r e e 2 g r o u p s w i t h r e s p e c t t o changes i n PO and SaO ; f u r t h e r a n a l y s i s 2 2 was d i r e c t e d t o w a r d s c h a r a c t e r i z i n g d i f f e r e n c e s between t h e s e g r o u p s . As o n l y t h r e e s u b j e c t s f e l l i n t o t h e group of i n t e r m e d i a t e ( M o d e r a t e ) r e s p o n d e r s , F i g u r e s 1 and. 2 r e p o r t d a t a from M i l d and Marked g r o u p s o n l y . F o u r s u b j e c t s ( M i l d ) showed l i t t l e d e c l i n e i n PO and 0 s a t u r a t i o n , w i t h r e s t i n g v a l u e s o f 2 2 PO a t 105.8+12.6 t o r r (SaO 98.2+0.6%) d e c l i n i n g t o 87.5+5.7 2 2 t o r r (SaO 94.6+. 1.9%) a f t e r t h e f i v e m i n u t e e x e r c i s e t a s k . T h r e e 2 s u b j e c t s ( M o d e r a t e ) d e m o n s t r a t e d an i n t e r m e d i a t e d e c l i n e i n PO 2 and SaO , w i t h r e s t i n g P0 102.5+3.5 (SaO 98.2+0.1%) d e c l i n i n g 2 ' 2 2 to 76.5+_2.1 t o r r (SaO 91.6+ 0 . 1 % ) . The r e m a i n i n g f i v e s u b j e c t s 2 ( M a r k e d ) d e m o n s t r a t e d a marked d e c l i n e i n s a t u r a t i o n w i t h r e s t i n g PO d e c l i n i n g f r o m 111.0+8.9 t o r r (SaO 98.5+0.4%) t o 2 2 • 71.4+3.5 t o r r (SaO 90.1+ 1 . 2 % ) . AN0VA f o r mixed model d e s i g n was 2 used t o d e t e r m i n e d i f f e r e n c e s between m i l d and marked g r o u p s f o r P0 , SaO , pH, PCO , V0 , and VE. The r e s u l t s of t h e s e 2 2 . 2 2 s t a t i s t i c a l a n a l y s e s a r e p r e s e n t e d i n T a b l e I I I . As would be e x p e c t e d d u r i n g i n t e n s e e x e r c i s e , a v e r a g e d o v e r a l l 10 TABLE II 15 SECOND INTERVAL MEASURES FOR ARTERIAL BLOOD VALUES,VO , AND VENTILATION FOR ALL SUBJECTS: 2 (Mean + SD.) TIME (rain) R 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00 2:15 2:30 2:45 3:00 3:15 3:30 3:45 4:00 4:15 *4:30 *4:45 *5:00 pH 7.43 0.03 7.45 0.02 7.45 0.02 7.43 0.02 7.42 0.03 7.40 0.03 7.37 0.03 7.36 0.03 7.34 0.03 7.33 0.03 7.32 0.04 7.31 0.04 7.29 0.04 7.28 0.05 7.27 0.05 7.25 0.05 7.25 0.05 7.25 0.06 7.23 0.05 7.23 0.06 7.21 0.06 PQ02 (torr) 36.3 4.3 35.9 3.5 37.8 2.7 37.3 2.5 38.1 2.0 38.4 2.7 38.3 2.0 38.6 2.2 38.5 2.2 38.0 2.3 38.2 2.8 38.0 2.1 37.4 2.5 37.5 2.2 38.4 2.6 36.9 2.5 37.2 2.6 36.9 2.6 36.6 3.0 36.2 2.7 36.4 3.3 P02 (torr) 107 9.2 112 14.4 102 11.5 93 8.9 89 7.5 89 7.8 89 6.8 89 9.0 88 8.6 86 9.3 85 9.2 83 9.2 83 10.1 82 9.0 81 9.6 82 9.9 80 9.6 79 7.5 79 8.5 78 7.5 78 8.6 Sa02 (%) 98.3 0.44 98.4 0.9 98.0 0.9 97.2 1.0 96.9 0.9 96.8 0.9 96.6 0.9 96.3 1.2 96.0 1.2 95.9 1.4 95.3 1.3 94.9 1.5 94.6 1.6 94.3 1.7 93.7 2.1 93.8 2.1 93.1 2.2 92.8 1.9 92.6 2.2 92.3 2.2 92.0 2.5 V02(l/min) - 1.53 0.56 2.36 0.51 3.78 0.62 4.13 0.48 4.08 0.43 4.17 0.39 4.27 0.46 4.29 0.48 4.29 0.39 4.31 0.50 4.38 0.45 4.41 0.44 4.31 0.34 4.44 0.49 4.50 0.42 4.57 0.42 4.44 0.51 4.61 0.44 4.56 0.43 4.43 0.51 YECl/ndn BTR 57.8 19.5 78.4 16.5 102.1 20.5 115.2 21.3 120.9 18.4 127.5 17.1 134.5 17.6 139.2 18.9 138.2 18.2 141.2 18.6 143.7 17.8 143.9 16.7 142.6 17.6 145.3 17.4 145.7 17.0 148.0 13.0 145.8 17.4 149.8 15.3 149.1 13.6 148.0 17.3 * N = 11 subjects  100 s u b j e c t s , t h e r e were s i g n i f i c a n t d i f f e r e n c e s i n a l l v a r i a b l e s o v e r t i m e . The group by t i m e i n t e r a c t i o n , w h i c h r e f l e c t s t h e degree t o w h i c h b o t h g r o u p s e x h i b i t e d t h e same change o v e r t i m e r e v e a l e d s i g n i f i c a n t d i f f e r e n c e s f o r PO and SaO . V a l u e s f o r 2 2 t h e s e two measures were s i m i l a r f o r b o t h g r o u p s u n t i l one m i n u t e , t h e n t h e Marked group d e m o n s t r a t e d a s t e e p e r r a t e of d e c l i n e i n PO t h a n 9 t h e M i l d g r o u p . 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 z between g ro u p s f o r pH, PCO , 2 VE, and V0 . 2 TABLE I I I . AN0VA RESULTS VARIABLE GROUP F ( p ) TIME F ( p ) GROUP x TIME F ( p ) PO 9 10.1 (<0.05) 22.4 (<0.001) 2 . 7 (<0.001) SaO 2 20. 1 (<0.01) 64.8 (<0.001) 9.8 (<0.001) pH 1 .0 O 0 . 0 5 ) 96.0 (<0.001) <1 .0 PCO 9 <1 .0 2 . 1 (<0.01) 1 . 1 O0.05) VE 1 . 1 O 0 . 0 5 ) 91.4 (<0.001) <1 .0 VO <1 .0 83 . 2 (<0.001) <1 .0 Changes i n VE and V0 2 F i f t e e n s e c o n d r e c o r d i n g s f o r VE and V0 f o r t h e t w e l v e 2 s u b j e c t s a r e p r e s e n t e d i n T a b l e I I . M a x i m a l v e n t i l a t i o n and V0 2 d u r i n g t h e t h e f i v e m i n u t e e x e r c i s e t e s t a r e c o n t r a s t e d w i t h v a l u e s o b t a i n e d d u r i n g t h e V0 max d e t e r m i n a t i o n i n T a b l e I I I . I t 2 can be seen t h a t n i n e o f the t w e l v e s u b j e c t s a c h i e v e d h i g h e r v e n t i l a t i o n d u r i n g t h e V0 max d e t e r m i n a t i o n t h a n d u r i n g the f i v e 2 m i n u t e t e s t . I n two, t h e v e n t i l a t i o n was s i m l i a r on t h e two t e s t s and i n one s u b j e c t peak v e n t i l a t i o n was h i g h e r d u r i n g t h e f i v e 14 m i n u t e e x e r c i s e t e s t . Four s u b j e c t s a c h i e v e d h i g h e r VO on t h e 2 f i v e m i n u t e e x e r c i s e t e s t t h a n on the VO max d e t e r m i n a t i o n . These 2 i n d i v i d u a l s a l l f e l l i n f o t h e marked group w i t h r e s p e c t to d e s a t u r a t i o n . TABLE IV DIFFERENCES IN VENTILATION AND MAXIMAL OXYGEN UPTAKE BETWEEN V02 MAX DETERMINATION AND FIVE MINUTE EXERCISE TEST GROUP SUBJECT OXYGEN CONSUMPTION VENTILATION ( l i t e r s / min) ( l i t e r s / min BTPS) V02MAX 5 min % VEmax VE 5min % MILD 1 . 4.78 4 .78 100.0 186.4 169.0 90. 2 . 4.58 4. 18 91.3 127.2 140.8 111. 3. 4.46 4.12 92.4 166.0 135.8 81 . 4. 4.99 4.67 93.6 178.2 140.5 78. MOD 5 . 4.51 4.30 95.3 145.1 142.0 97 . 6. 4.13 4.11 99 . 5 142.4 132.0* 92 . 7 . 5.17 5.08 98.3 148. 2 149.3 100. MARKED 8 . 4.39 4.01 92 . 7 158. 2 143.1 90. 9. 5.45 5.51 101 . 1 191.8 182 . 7 9 5 . 10. 4 .10 4.32 , 105.3 148.6 151.9 102 . 11 . 4.58 4.82 105 . 2 162 . 7 154.9 98. 12 . 4.54 4.60 101.3 143. 2 137.9 96. * o b t a i n e d a t 4:15 H y p o x i c v e n t i l a t o r y r e s p o n s e The measured h y p o x i c v e n t i l a t o r y r e s p o n s e and s p o r t f o r each s u b j e c t i s r e c o r d e d i n T a b l e V. The r e a p p e a r e d t o be two d i s t i n c t g r o u p s w i t h i n our sample o f s u b j e c t s . S i x s u b j e c t s were c l a s s i f i e d as n o r m a l (N) r e s p o n d e r s and s i x as h a v i n g a d i m i n i s h e d r e s p o n s e ( B ) . D i v i s i o n i n t o t h e s e g r o u p s was based on a n a l y s i s of d a t a p u b l i s h e d by F l e e t h a m e t a l . , ( 1 9 8 0 ) ; G r i n d l a y - Moore e t a l . , ( 1 9 8 2 ) ; Rebuck and C a m p b e l l , (1974) and Rebuck and W o o d l e y , ( 1 9 7 5 ) . The mean s l o p e of the l i n e d e s c r i b e d by change i n -1 v e n t i l a t i o n per 1% change i n SaO was found t o be 1.08 1 .min .1% 2 15 -1 -1 -1 ASaO ; standard deviation was 0.97 l.min. .1% ASaO 2 2 refle c t i n g the positively skewed distribution of values. TABLE V HVR AND SPORT FOR EACH SUBJECT (n = 12) SUBJECT SPORT HVR (A VE/l%ASa02) N or B (l.min. l%ASa02) 1. Field hockey 0.43 B 2. 400 m, 800 m 0.43 B 3. rowing 0.78 N 4. 800 m 1.12 N 5. marathon 1 .05 N 6. marathon 1 .03 N 7 . triathlon 0.22 B 8. 400 m 0.22 B 9 . rowing 1.22 N 10. triathon 0.87 N 11 . 10 k 0.43 B 12. cycling 0.26 B -1 -1 ' MEAN (l.min .l%ASa02 )+ S .D normal diminished a l l 1 .02 + 0.15 0.33+0.10 0.67+0.36 Relationship of HVR to a r t e r i a l desaturation Correlation analysis was performed to determine the relationship between... the hypoxic ventilatory response and the lowest observed SaO . This analysis yielded a correlation 2 coefficient of 0.06, which was non-significant (F<1.0). A multiple regression analysis revealed no significant relationship between the degree of a r t e r i a l desaturation and the dependant variables age, height, weight, V0 max, or treadmill speed of each 2 subject. 16 DISCUSSION A r t e r i a l d e s a t u r a t i o n o c c u r e d t o some e x t e n t i n a l l o f the s u b j e c t s t e s t e d . The t r a d i t i o n a l v i e w of changes i n b l o o d gas p a r a m e t e r s d u r i n g e x e r c i s e has h e l d t h a t PO i s r e l a t i v e l y s t a b l e 2 and a l t e r a t i o n s d u r i n g i n t e n s e e x e r c i s e a r e of i n s u f f i c i e n t m a g n i t u d e t o c a u s e d e s a t u r a t i o n of h e m o g l o b i n . The s m a l l c hanges o b s e r v e d i n t h e l i t e r a t u r e ( d e c l i n e t o 94-98% s a t u r a t e d ) have been a t t r i b u t e d t o t h e combined e f f e c t s of d e c r e a s i n g pH, i n c r e a s i n g t e m p e r a t u r e (Thompson and Dempsey, 19 74) and a l t e r a t i o n s i n 2,3-DPG ( K l e i n e t a l . , 1 9 8 0 ) . A r t e r i a l d e s a t u r a t i o n has been r e p o r t e d as e a r l y as 1919 ( H a r r o p , 1 9 1 9 ) , but was g e n e r a l l y i g n o r e d by t h e s c i e n t i f i c c ommunity, p o s s i b l y b e c a u s e o f d i f f i c u l t y i n o b t a i n i n g a r t e r i a l s a m p l e s d u r i n g m a x i m a l e x e r c i s e o r b e c a u s e o f t h e p r e p o n d e r a n c e of e v i d e n c e o b t a i n e d d u r i n g l e s s i n t e n s e e x e r c i s e , w h i c h does not d e m o n s t r a t e any changes i n PCO or PO ( B j u r s t e d t and 2 2 W i g e r t z , 1971; 0 - B a r r e t a l . , 1964; S u s k i n d e t a l . , 1 9 5 0 ) . P e r h a p s t h e most c o m p l e t e s t u d y i n v e s t i g a t i n g c h a n g e s i n PO 2 and SaO i s f o u n d i n the work o f Dempsey e t a l . , ( 1 9 8 4 ) . I n t h i s 2 s t u d y , s i x t e e n e n d u r a n c e a t h l e t e s , c a p a b l e of s u s t a i n i n g v e r y -1 -1 h i g h m e t a b o l i c r a t e s (VO max = 72+_2 ml.kg .min ) p e r f o r m e d a 2 p r o g r e s s i v e e x e r c i s e t e s t t o maximum on a t r e a d m i l l . H e m o g l o b i n s a t u r a t i o n was measured by means of an e a r o x i m e t e r , and a r t e r i a l pH, PCO ,and PO were measured by means of an i n d w e l l i n g a r t e r i a l 2 2 c a n n u l a . I t was f o u n d t h a t e i g h t o f the s i x t e e n s u b j e c t s d e m o n s t r a t e d a d e c r e a s e i n a r t e r i a l oxygen c o n t e n t o f 21-35 t o r r , t o an PO of l e s s t h a n 75 t o r r . The most s e v e r e h ypoxemia was 2 17 a s s o c i a t e d w i t h l i t t l e or no a l v e o l a r h y p e r v e n t i l a t i o n . When h e l i u m b r e a t h i n g was used t o r e d u c e t u r b u l e n t f l o w and t h u s u n l o a d t h e r e s p i r a t o r y m u s c l e s e x e r c i s e v e n t i l a t i o n i n c r e a s e d s u b s t a n t i a l l y . The mechanisms a c c o u n t i n g f o r a r t e r i a l d e s a t u r a t i o n d u r i n g heavy work have not been e l u c i d a t e d , however s p e c u l a t i o n as t o t h e p o s s i b l e c a u s e s c o n s i d e r s t h e f o l l o w i n g a r e a s : 1. veno- a r t e r i a l s h u n t . 2 . v e n t i l a t i o n - p e r f u s i o n i n e q u a l i t y . 3. d i f f u s i o n l i m i t a t i o n 4. h y p o v e n t i l a t i o n . V e n o - a r t e r i a l s h u n t : At r e s t i n the h e a l t h y i n d i v i d u a l s m a l l ( a p p r o x i m a t e l y 1-1.5% of c a r d i a c o u t p u t ( B a c h o f e n e t a l . , 1 9 7 3 )) volumes of b l o o d a r e s h u n t e d v i a t h e t h e b e s i a n v e i n s and b r o n c h i a l venous b l o o d s u p p l y d i r e c t l y i n t o t h e s y s t e m i c c i r c u a t i o n and t h e r e f o r e do not p a r t i c i p a t e i n gas e x c h a n g e . The i n t r o d u c t i o n of t h i s p o o r l y o x y g e n a t e d b l o o d r e s u l t s i n a s m a l l d e c l i n e i n oxygen t e n s i o n i n a r t e r i a l b l o o d . I f s h u n t i n g were t h e c a u s e of t h e d e c l i n e i n PO no change would be e x p e c t e d i n 2 oxygen t e n s i o n w i t h t h e i n t r o d u c t i o n of a h y p e r o x i c gas m i x t u r e . In f a c t t h i s i s not t h e c a s e , as r e p o r t s e x i s t of h y p e r o x i a c o r r e c t i n g t h e h y poxemia seen d u r i n g e x e r c i s e a t sea l e v e l (Dempsey e t a l . , 1984; G a l e e t a l . , 1985; T o r r e - B u e n o e t a l . , 1985) and a t a l t i t u d e ( G a l e e t a l . , 1985; T o r r e - B u e n o e t a l . , 1 9 8 5 ) . Thus some o t h e r . m e c h a n i s m must a c c o u n t f o r t h i s phenomena. V e n t i l a t i o n - p e r f u s i o n i n e q u a l i t y : G e n e r a l l y v e n t i l a t i o n and p e r f u s i o n of t h e l u n g a r e n o n - u n i f o r m : due t o t h e e f f e c t s of g r a v i t y t h e base of t h e l u n g r e c e i v e s a g r e a t e r b l o o d f l o w t h a n does t h e apex. I f v e n t i l a t i o n and p e r f u s i o n i n e q u a l i t y i n c r e a s e d d u r i n g m a x i m a l e x e r c i s e t h e n a r t e r i a l h y p oxemia would a l s o 18 i n c r e a s e as b l o o d p a s s e d t h r o u g h a p o o r l y v e - n t i l a t e d segment of t h e l u n g . D u r i n g low i n t e n s i t y e x e r c i s e t h e r e i s an i n c r e a s e i n b o t h a p i c a l v e n t i l a t i o n and p e r f u s i o n w i t h t h e o v e r a l l r e s u l t t e n d i n g t o g r e a t e r h o m o g e n i t y w i t h i n d i f f e r e n t a r e a s of t h e l u n g . At more i n t e n s e l e v e l s of e x e r c i s e o n l y m i n o r changes i n v e n t i l a t i o n - p e r f u s i o n i n e q u a l i t y have been f o u n d ( G a l e et a l . , 1985) w h i c h a r e n o t s u f f i c i e n t i n m a g n i t u d e t o a c c o u n t f o r .the c h anges i n PO seen d u r i n g m a x i m a l e x e r c i s e . 2 D i f f u s i o n l i m i t a t i o n : A n o t h e r p o s s i b l e e t i o l o g y of a r t e r i a l h y p oxemia d u r i n g heavy e x e r c i s e r e l a t e s t o d i f f u s i o n l i m i t a t i o n . I n t h e s e d e n t a r y i n d i v i d u a l d u r i n g heavy e x e r c i s e t h e t r a n s i t t i m e f o r t h e r e d b l o o d c e l l t h r o u g h t h e p u l m o n a r y c i r c u l a t i o n i s w e l l w i t h i n t h e t i m e r e q u i r e d f o r c o m p l e t e e q u i l i b r a t i o n ( a b o u t 0.25 s e c o n d s ) . I n t h e a t h l e t e c a p a b l e of r e a c h i n g v e r y h i g h work l e v e l s , mean t r a n s i t t i m e may be r e d u c e d to 0.40 s e c o n d s or l e s s , s e c o n d a r y t o i n c r e a s e s i n p u l m o n a r y b l o o d f l o w . I f t h e b l o o d i s a l s o d i r e c t e d t o u n d e r v e n t i l a t e d a r e a s of t h e l u n g , t r a n s i t t i m e s may be f u r t h e r r e d u c e d t o l e s s t h a n 0.25 s e c o n d s (Dempsey e t a l . , 1 9 8 2 ) . D i f f u s i o n d i s t a n c e c o u l d a l s o be i n c r e a s e d i f h i g h i n t r a v a s c u l a r p r e s s u r e s w i t h i n t h e p u l m o n a r y c a p i l l a r y l e a d t o f l u i d l e a k and an i n c r e a s e i n f l u i d i n t h e i n t e r s t i t i a l s p a c e . Thus d i f f u s i o n l i m i t a t i o n may a l s o e x p l a i n t h e c hanges i n a r t e r i a l s a t u r a t i o n o b s e r v e d (Dempsey e t a l . , 1 9 8 2 ) . H y p o v e n t i l a t i o n : T hat h y p o v e n t i l a t i o n p l a y s a r o l e i n t h e g e n e s i s of a r t e r i a l h y p o x e m i a seems l i k e l y , but t o what e x t e n t i s u n c e r t a i n . I n t h e s t u d y of Dempsey e t a l . , ( 1 9 8 4 ) , the 19 i n d i v i d u a l s d e m o n s t r a t i n g the g r e a t e s t d egree of a r t e r i a l h ypoxemia e x h i b i t e d the l o w e s t v e n t i l a t o r y r e s p o n s e t o e x e r c i s e . Our d a t a i n d i c a t e t h a t our s u b j e c t s were w e l l - t r a i n e d i n d i v i d u a l s engaged i n h i g h l e v e l c o m p e t i t i o n . T h e i r mean VO max 2 i s l o w e r t h a n t h a t r e p o r t e d f o r s u b j e c t s i n some d e s a t u r a t i o n s t u d i e s (Dempsey e t a l . , 1984; W i l l i a m s e t a l . , 1986) but i s h i g h e r t h a n t h a t r e p o r t e d i n s t u d i e s u s i n g l e s s e l i t e , a t h l e t e s (Thompson and Dempsey, 1974).' The b l o o d gas d a t a i n d i c a t e s t h a t t h i s was a d i f f i c u l t e x e r c i s e t a s k to p e r f o r m ; our s u b j e c t s i n c u r r e d a s i g n i f i c a n t m e t a b o l i c a c i d o s i s w i t h t h e a v e r a g e end of e x e r c i s e pH f o r the e l e v e n s u b j e c t s who c o m p l e t e d the f u l l f i v e m i n u t e t e s t r e c o r d e d a t 7.. 21+0.06. The s u b j e c t who was u n a b l e to c o m p l e t e the t e s t o b t a i n e d a pH of 7.13. An i n c r e a s e i n pH was o b s e r v e d i n t e n of t w e l v e s u b j e c t s d u r i n g the f i r s t t h i r t y s e c o n d s of e x e r c i s e . T h i s c o r r e s p o n d e d t o a r e l a t i v e h y p e r v e n t i l a t i o n as P0 l e v e l s i n c r e a s e d f o r the f i r s t 2 15 s e c o n d s . Changes i n PCO ( s e e T a b l e I I ) were v a r i a b l e and d i d 2 2 not c o r r e l a t e w i t h the pH change (R =0.05). I t i s p o s s i b l e t h a t t h e i n c r e a s e i n pH may r e f l e c t the c o n s u m p t i o n of a hydrogen i o n w i t h i n the w o r k i n g m u s c l e d u r i n g the h y d r o l y s i s of c r e a t i n i n e p h o s p h a t e , a b u f f e r i n g p r o c e s s w h i c h has r e s u l t e d i n a l k a l o s i s w i t h i n the w o r k i n g m u s c l e ( Hultman and S a h l i n , 1 9 8 0 ) . S i m i l a r changes have been r e p o r t e d by o t h e r i n v e s t i g a t o r s d u r i n g e x e r c i s e of s i m i l a r i n t e n s i t y (Dempsey e t a l . , 1984.) however t h e s e changes were a t t r i b u t e d to d e c l i n e s i n PCO . 2 The g r e a t e s t d e c l i n e i n P0 o c c u r e d w i t h i n the f i r s t 45 t o 2 60 s e c o n d s of e x e r c i s e , w h i c h c o r r e s p o n d e d t o the p e r i o d of g r e a t e s t r i s e i n V0 and VE ( s e e T a b l e I I ) . Changes were s i m i l a r 2 20 f o r a l l s u b j e c t s f o r t h e f i r s t 45 s e c o n d s , t h e n t h o s e i n the M i l d g roup showed some l e v e l i n g w h i l e ' s u b j e c t s i n t h e Marked group showed a g r e a t e r r a t e of d e c l i n e ( F i g u r e 1 ) . S i m i l a r o b s e r v a t i o n s were t r u e of t h e c hanges on SaO ( F i g u r e 2 ) , however b o t h the 2 M i l d and Marked g r o u p s c o n t i n u e d t o show a d e c l i n e i n s a t u r a t i o n r e f l e c t i n g t h e e f f e c t s of i n c r e a s i n g a c i d o s i s on t h e o x y g e n - h e m o g l o b i n d i s s o c i a t i o n c u r v e . Our r e s u l t s a r e i n agreement w i t h t h o s e of Dempsey e t a l . , (1984) who showed s i m i l a r p a t t e r n s of d e c l i n e i n PO and SaO . The mean s a t u r a t i o n a t t h e end o f f i v e m i n u t e s f o r a l l s u b j e c t s , (91.9+_0.6%) i s a l s o c l o s e t o t h e f i na 1 s a t u r a t i o n o b s e r v e d (92.0+2 .5%) i n t h i s s t u d y . A n o t h e r s t u d y ( W i l l i a m s e t a l . , 1986) d e m o n s t r a t e d g r e a t e r d e c l i nes i n s a t u r a t i o n t o 87.0+0.2% i n t r a i n e d s u b j e c t s and 92.6+0 . 7% i n u n t r a i n e d s u b j e c t s . These v a l u e s were o b t a i n e d u s i n g an e a r o x i m e t e r (B i o x I I ) , and t h u s u n r e l i a b i l i t y of t h i s method of d a t a c o l l e c t i o n may a c c o u n t f o r o b s e r v e d d i f f e r e n c e s i n SaO (Sm y t h e 2 e t a l . , 1986) . .-. T e m p e r a t u r e measurements were not made i n our s u b j e c t s and t h e r e f o r e i t i s l i k e l y t h a t t h e d e g r e e of d e s a t u r a t i o n i s u n d e r e s t i m a t e d i n our s u b j e c t s . A s s u m i n g a r i s e i n t e m p e r a t u r e of one d e g r e e c e l c i u s t h e e x p e c t e d d e c r e a s e i n s a t u r a t i o n would be i n t h e o r d e r of 0.5%. T h i s i s r e l a t i v e l y s m a l l compared t o the d e c r e a s e s as a r e s u l t of hypoxemia and a c i d o s i s . A r t e r i a l d e s a t u r a t i o n has been shown to be more l i k e l y i n i n d i v i d u a l s c a p a b l e of v e r y h i g h work o u t p u t s (Dempsey e t a l . , 1984; Powers and W i l l i a m s , 1 9 8 7 ) , e x e r c i s i n g a t g r e a t e r t h a n 90% of V0 max. V0 , VE, pH, and PCO were s i m i l a r between M i l d , 2 2 2 21 M o d e r a t e and Marked d e s a t u r a t i o n g r o u p s , t h e r e f o r e t h e d i f f e r e n c e s i n f i n a l SaO c a n o t be e x p l a i n e d on the b a s i s of 2 d i f f e r e n c e s i n f i t n e s s or d i f f e r i n g work i n t e n s i t y i n t h e group who showed t h e g r e a t e s t d e c l i n e i n s a t u r a t i o n . G e n e r a l l y our s u b j e c t s showed l i t t l e r e s p i r a t o r y c o m p e n s a t i o n f o r t h e m e t a b o l i c a c i d o s i s of e x e r c i s e . In most s u b j e c t s t h e r e s t i n g sample w h i c h was t a k e n j u s t p r i o r t o t h e o n s e t of e x e r c i s e showed a d e p r e s s e d PCO (mean = 36.0+_4.4 t o r r ) . 2 T h i s i s not s u r p r i s i n g as the s a mples were t a k e n as t h e s u b j e c t was s t r a d d l i n g t h e t r e a d m i l l w i t h t h e m o u t h p i e c e f o r m e a s u r i n g e x p i r e d gas i n p l a c e . PCO t h e n i n c r e a s e d t o a mean v a l u e of 37- 2 38 t o r r and d e c l i n e d t o l e s s t h a n 37 t o r r o n l y i n t h e l a s t m i n u t e of e x e r c i s e . The changes i n PCO a r e l e s s t h a n t h a t r e p o r t e d by 2 Dempsey e t a l . , ( 1 9 8 4 ) , even when h y p e r v e n t i l a t i o n p r i o r t o the o n s e t of e x e r c i s e was c o n s i d e r e d . Dempsey e t a l . , ( 1 9 8 4 ) f e l t t h a t the r e l a t i v e h y p o v e n t i l a t i o n s e c o n d a r y t o m e c h a n i c a l c o n s t r a i n t i n t h e i r s u b j e c t s m i g h t have c o n t r i b u t e d t o a r t e r i a l d e s a t u r a t i o n and the l a c k o f c o m p e n s a t i o n f o r t h e r e s p i r a t o r y a c i d o s i s of e x e r c i s e . P r e l i m i n a r y e v i d e n c e f o r t h i s was g i v e n by d a t a o b t a i n e d d u r i n g s t u d i e s i n v o l v i n g t h e r e p l a c e m e n t of room a i r w i t h h e l i u m - o x y g e n m i x t u r e s . T h i s l e d t o an i n c r e a s e i n t h e v e n t i l a t i o n and p a r t i a l c o r r e c t i o n of t h e b l o o d gas a b n o r m a l i t i e s (Dempsey e t a l . , 1 9 8 4 ) . T h i s p o s s i b i l i t y does not seem l i k e l y i n our s u b j e c t s s i n c e n i n e of t h e t w e l v e s u b j e c t s showed g r e a t e r VE on the VO max d e t e r m i n a t i o n t h a n on the f i v e m i n u t e e x e r c i s e 2 t e s t . One s u b j e c t e x h i b i t e d g r e a t e r v e n t i l a t i o n on t h e f i v e m i n u t e e x e r c i s e t e s t t h a n t h e VO max d e t e r m i n a t i o n , but f e l l i n t o 2 t h e M i l d group w i t h r e s p e c t t o d e s a t u r a t i o n . The r e m a i n i n g 22 s u b j e c t s had s i m i l a r v e n t i l a t i o n i n b o t h s i t u a t i o n s ; one was i n t h e M o d e r a t e group , t h e o t h e r was i n t h e Marked g r o u p . I t i s p o s s i b l e t h a t s e c o n d a r y m o d i f i e r s o f e x e r c i s e v e n t i l a t i o n s u c h as t e m p e r a t u r e and c a t h e c h o l a m i n e p r o d u c t i o n (Wasserman e t a l . , 1981) may have c o n t r i b u t e d t o t h e i n c r e a s e d v e n t i l a t i o n i n t h e VO max d e t e r m i n a t i o n f o r t h e m a j o r i t y o f t h e s u b j e c t s . C e r t a i n l y 2 i t would seem t h a t i n t h i s i n s t a n c e t h a t m e c h a n i c a l f a c t o r s per s e , a r e n o t s i g n i f i c a n t . I t i s p o s s i b l e t h a t r e s p i r a t o r y m u s c l e oxygen c o n s u m p t i o n (Bye e t a l . , 1983) may be r e s p o n s i b l e f o r the l i m i t e d r e s p i r a t o r y c o m p e n s a t i o n f o r t h e m e t a b o l i c a c i d o s i s d u r i n g heavy e x e r c i s e . At -1 v e n t i l a t i o n s g r e a t e r t h a n 100 l . m i n t h e VO of r e s p i r a t o r y 2 . -1 m u s c l e (VO r e s p ) has been e s t i m a t e d t o be 2-8 ml 0 .1 VE~ 2 2 (McKerrow and O t i s , 1956; B r a d l e y and L e i t h , 1 9 7 8 ) . T h e r e f o r e i n -1 our s u b j e c t s whose mean peak v e n t i l a t i o n was 149.8 l . m i n , VO -1 2 r e s p c o u l d r a n g e f r o m 0.3 t o 1.2 l . m i n , r e p r e s e n t i n g 6 t o 26% of VO max. I t has been a r g u e d t h a t t h e c r i t i c a l v e n t i l a t i o n where 2 any i n c r e a s e i n VO would go e n t i r e l y t o r e s p i r a t o r y muscles- i s -1 2 140 l . m i n ( O t i s , 1 9 5 4 ) . Our s u b j e c t s e x c e e d e d t h i s l e v e l of v e n t i l a t i o n , t h u s i t may be t h a t optimum v e n t i l a t i o n i s l i m i t e d due t o oxygen d e l i v e r y . The amount of l a c t a t e p r o d u c e d by r e s p i r a t o r y m u s c l e s i s not t r i v i a l , and a s i m i l a r arguement can be a p p l i e d t o CO e x c r e t i o n 2 and r e s p i r a t o r y c o m p e n s a t i o n . A s s u m i n g no l a c t a t e c o n s u m p t i o n and d i s t r i b u t i o n t h r o u g h o u t body w a t e r , l a c t a t e p r o d u c t i o n from -1 r e s p i r a t o r y m u s c l e c o u l d r e a c h as h i g h as 10 mmol.l ( R o u s s o s , 1982) . I t i s p o s s i b l e t h a t a t maximal e x e r c i s e , p a r t i c u l a r l y i n a 23 s i t u a t i o n where oxygen d e l i v e r y may be c o n s t r a i n e d , a s i t u a t i o n c o u l d be r e a c h e d where any i n c r e a s e i n v e n t i l a t i o n t o i n c r e a s e CO e x c r e t i o n would be b a l a n c e d by an i n c r e a s e i n r e s p i r a t o r y 2 m u s c l e l a c t a t e p r o d u c t i o n l e a d i n g i n an i n c r e a s i n g a c i d o s i s . Thus i t may be t h a t t h e l e v e l of v e n t i l a t i o n r e a c h e d d u r i n g maximal e x e r c i s e may r e p r e s e n t an optimum v e n t i l a t i o n , b a l a n c i n g 0 2 d e l i v e r y t o t h e w o r k i n g m u s c l e and r e s p i r a t o r y c o m p e n s a t i o n f o r t h e a c i d o s i s of e x e r c i s e w i t h t h e i n c r e a s i n g m e t a b o l i c demands of th e r e s p i r a t o r y m u s c l e s . The mean h y p o x i c v e n t i l a t o r y r e s p o n s e f o r our s u b j e c t s - 1 - 1 (0.67+0.36 l . m i n .l%ASaO ) i s l e s s t h a n t h a t r e p o r t e d f o r t h e 2 -1 -1 n o r m a l p o p u l a t i o n (1.09+0.9 7 l . m i n .l%ASaO ; F l e e t h a m e t a l . , 2 1980; G r i n d l e y - M o o r e e t a l 1984; Rebuck e t a l . , 1976; Rebuck and Woodley, 1975) and p o s s i b l y r e f l e c t s t h e l o w e r HVR r e p o r t e d f o r a t h l e t i c i n d i v i d u a l s ( B y r n e - Q u i n n e t a l . , 1982; M a t h e r e t a l . , 1982; M a r t i n e t a l . , 1 9 7 8 b ) . The c u r v e of the n o r m a l p o p u l a t i o n i s n ot b e l l - s h a p e d but i s p o s i t i v e l y skewed . W h i l e a l l our v a l u e s f e l l w i t h i n t h e n o r m a l range of v a l u e s e x p e c t e d f o r t h e g e n e r a l p o p u l a t i o n i t was a p p a r e n t t h a t t h e r e were two d i s t i n c t r e s p o n s e s t o h y p o x i a . S i x s u b j e c t s (N) showed HVRs t h a t were c l o s e t o t h e mean r e p o r t e d f o r t h e n o r m a l p o p u l a t i o n a b o v e , w h i l e s i x s u b j e c t s (B) showed r e s p o n s e s t h a t were a p p r o x i m a t e l y -1 -1 one t h i r d o f t h o s e v a l u e s (N = 1.02+0.15 l . m i n . l % A S a 0 vs B = -1 -1 2 0.33+0.10 l . m i n . l % A S a 0 ). T h e r e was no r e l a t i o n s h i p between 2 , s p o r t and HVR. That i s , i n our s u b j e c t s who were s i m i l a r i n V0 2 max, t h e r e was no d i f f e r e n c e between e n d u r a n c e t r a i n e d (mean HVR -1 -1 = 0.64+0.35 l . m i n .l%ASa0 ) and n o n - e n d u r a n c e t r a i n e d (mean -1 2 -1 HVR = 0.70+0.37 l . m i n .l%ASaO ) a t h l e t e s . I n t h i s a n a l y s i s t h e 2 24 two oarsmen were c o n s i d e r e d t o be n o n - e n d u r a n c e a t h l e t e s s i n c e t h e r a c e d i s t a n c e i s 2000m and t a k e s a p p r o x i m a t e l y 6 m i n u t e s t o c o m p l e t e . At t h e t i m e of t e s t i n g (May) t h e s e a t h l e t e s were i n s p e c i f i c t r a i n i n g f o r t h i s e v e n t . T h i s d a t a i s i n c o n t r a s t t o M a r t i n e t a l . , ( 1 9 7 9 ) , who f o u n d b l u n t e d HVRs i n e n d u r a n c e t r a i n e d a t h l e t e s compared t o a c o n t r o l group of n o n - e n d u r a n c e a t h l e t e s and non a t h l e t i c n o r m a l s . In t h e s e s u b j e c t s VO max was 2 s i g n i f i c a n t l y h i g h e r i n the e n d u r a n c e a t h l e t e s t h a n n o n - e n d u r a n c e a t h l e t e s and n o n - a t h l e t e s and d i f f e r e n c e s i n f i t n e s s may a c c o u n t f o r t h e d i f f e r e n c e s between g r o u p s . S i n c e e n d u r a n c e a t h l e t e s have a l o w e r e x e r c i s e v e n t i l a t i o n a t any g i v e n work i n t e n s i t y , ( M a r t i n e t a l . , 1979; M a r t i n e t a l . , 1978a; M a r t i n e t a l . , 1978b; S t o c k l e y , 1978 ) and e x e r c i s e v e n t i l a t i o n i s r e l a t e d t o HVR ( M a r t i n e t a l . , 1978b; S t o c k l e y , 1 9 7 8 ) , i t was p r e d i c t e d t h a t t h a t h y p o v e n t i l a t i o n s e c o n d a r y t o b l u n t e d r e s p i r a t o r y d r i v e s m i g h t be c a u s e of t h e a r t e r i a l d e s a t u r a t i o n . I t t h e n would be e x p e c t e d t h a t some e v i d e n c e o f b l u n t e d r e s p o n s e t o h y p o x i a would be e v i d e n t i n our s u b j e c t s . The a d v a n t a g e t o t h e i n d i v i d u a l o f b e i n g a b l e t o " i g n o r e " h y poxemia would be a r e d u c t i o n i n r e s p i r a t o r y work, and p o s s i b l y a more e f f i c i e n t p a t t e r n o f v e n t i l a t i o n . T h i s was not o b s e r v e d i n our s u b j e c t s ; t h e r e was no s i g n i f i c a n t r e l a t i o n s h i p between HVR and l o w e s t SaO r e a c h e d . Thus i t seems u n l i k e l y t h a t b l u n t e d 2 r e s p i r a t o r y d r i v e p l a y s a r o l e i n t h e d e s a t u r a t i o n seen i n t h e s e i n d i v i d u a l s . The r e m a i n i n g p o s s i b i l i t y t o be c o n s i d e r e d i s d i f f u s i o n l i m i t a t i o n and t h e r e i s some i n d i r e c t e v i d e n c e t o s u p p o r t t h i s as 2 5 a mechanism f o r t h e a r t e r i a l d e s a t u r a t i o n o b s e r v e d i n our s u b j e c t s . E i g h t s u b j e c t s -did not r e a c h VO max on t h e f i v e m i n u t e 2 e x e r c i s e t e s t . W i t h one e x c e p t i o n t h e s e s u b j e c t s f e l l i n t o t h e M i l d or M o d e r a t e group w i t h r e s p e c t t o a r t e r i a l d e s a t u r a t i o n . Of t h e s u b j e c t s who d e v e l o p e d marked d e s a t u r a t i o n f o u r of t h e f i v e s c o r e d h i g h e r s c o r e s f o r VO on t h e f i v e m i n u t e e x e r c i s e t e s t . . . 2 t h a n on t h e i r VO max d e t e r m i n a t i o n . T h i s d i f f e r e n c e r a n g e d from 2 1.1 t o 5.0 p e r c e n t i n c r e a s e . A l t h o u g h s p e c u l a t i v e , t h e only- l o g i c a l e x p l a n a t i o n f o r t h i s i n c r e a s e i s t h a t a g r e a t e r c a r d i a c o u t p u t was a c h i e v e d by t h e s e s u b j e c t s due t o d e c r e a s e d p e r i p h e r a l p o o l i n g of b l o o d . T h i s w o u l d be e x p e c t e d s i n c e t h e d u r a t i o n of t h e e x e r c i s e t e s t was much l e s s t h a n d u r i n g t h e VO max 2 d e t e r m i n a t i o n (13-18 m i n u t e s ) . Thus s u b j e c t s would have l e s s p e r i p h e r a l p o o l i n g of b l o o d due t o t h e r m o r e g u l a t i o n d u r i n g t h e f i v e m i n u t e t e s t and g r e a t e r venous r e t u r n . S i n c e l i m i t s t o VO max can be c o n s i d e r e d t o be a b o u t 75% due t o l i m i t a t i o n s 2 oxygen t r a n s p o r t ( D i P r a m p e r o , 1984) any i n c r e a s e i n c a r d i a c o u t p u t w o u l d be e x p e c t e d t o i n c r e a s e VOmax. I f d i f f u s i o n 2 l i m i t a t i o n due t o s h o r t e n e d , red. c e l l t r a n s i t t i m e were t h e c a u s e of a r t e r i a l d e s a t u r a t i o n , any f a c t o r w h i c h i n c r e a s e d c a r d i a c o u t p u t and t h e r e f o r e s h o r t e n e d t r a n s i t t i m e , would be e x p e c t e d t o r e s u l t i n a i n c r e a s e i n a r t e r i a l d e s a t u r a t i o n . . I f t h e c hanges i n c a r d i a c o u t p u t were c o n s i d e r e d t o be t h e c a u s e of t h e i n c r e a s e i n VO i t c o u l d a l s o e x p l a i n t h e o b s e r v e d changes i n SaO i n f o u r of 2 -2 t h e f i v e s u b j e c t s who d e v e l o p e d marked d e s a t u r a t i o n . I n summary a r t e r i a l d e s a t u r a t i o n was o b s e r v e d i n a l l of our s u b j e c t s r a n g i n g from M i l d (SaO = 94.6%) , M o d e r a t e ( 9 1 . 6 % ) t o 2 Marked ( 9 0 . 1 % ) . T h e r e was no d i f f e r e n c e s between g r o u p s i n VE, 26 VO max, pH and PCO , and i t seems u n l i k e l y t h a t m e c h a n i c a l 2 . 2 f a c t o r s l i m i t i n g v e n t i l a t i o n a r e s i g n i f i c a n t s i n c e o n l y two s u b j e c t s a p p r o a c h e d or e x c e e d e d m a x i m a l v e n t i l a t i o n d e t e r m i n e d d u r i n g t h e VO max t e s t . T h e r e was no r e l a t i o n s h i p between t h e 2 d e g r e e o f d e s a t u r a t i o n and h y p o x i c v e n t i l a t o r y r e s p o n s e . I n d i r e c t e v i d e n c e s u g g e s t s t h a t d i f f u s i o n l i m i t a t i o n due t o s h o r t e n e d r e d c e l l t r a n s i t time- i s t h e most l i k e l y e x p l a n a t i o n f o r t h i s phenomena. 27 REFERENCES Anholm J.D., H o u s t o n , C.S., H e y e r s , T.M. The r e l a t i o n s h i p between A c u t e M o u n t a i n S i c k n e s s and p u l m o n a r y v e n t i l a t i o n a t 2,835 m. 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Aerobic capacity during acute exposure to simulated altitude 914-2286 M. Med. S c i . Sports exercise 14(l):36-40, 1982. Suskind.M., Bruce R.A., McDowe 11,M.E., Yu, P.N., Lovejoy, F.W. Normal variations in end-tidal air and a r t e r i a l blood carbon dioxide and oxygen tensions during moderate exercise. J . Appl. Physiol. 3:282-290, 1950. Sutton J.R., Gray, G.W. Pathophysiology of high-altitude i l l n e s s . Exercise Sport S c i . Rev. 11: 210-231, 1983. Stockley, R.A. The contribution of the reflex hypoxic drive to the hyperpnoea of exercise. Respirat. Physiol. 3 5:78-79, 1978. Tammling, G.J., Quanger P.H. Contours of Breathing 2. Boehringer Ingelheim, Ingelheim am Rein, West Germany p.226, 1983. Thompson,J.M., Dempsey, J.A. Chosy L.W., Shandi, N . T „ , Reddan, W.G. Oxygen transport and oxyhemoglobin dissociation during prolonged muscular work. J . Appl. Physiol.: Respirat.. Environ. Exercise Physiol. 37(5):658-664, 1974. Torre-Bueno, J.R., Wagner,P.D., Saltzman,H.A., Gale, G.E., Reddan, W.G. Diffusion limitation in normal humans during exercise at sea level and simulated a l t i t u d e . J . Appl. Physiol.: Respirat. Environ. Exercise Physiol. 58(3 ): 989-995, 1985. 32 Wasserman, K., Whipp. B . J . , D a v i s . R e s p i r a t o r y p h y s i o l o g y of e x e r c i s e : m e t a b o l i s m , gas e x c h a n g e , and v e n t i l a t o r y c o n t r o l . I n t e r n a t i o n a l R eview of P h y s i o l o g y . R e s p i r a t o r y P h y s i o l o g y 111, ed. John G. Widdicomb, U n i v e r s i t y P a r k P r e s s , B a l t i m o r e , 1981. Wasserman, K., Whipp, B . J . , K o y a l , S.N.-, C l e a r l y , M.G. E f f e c t of c a r o t i d body r e s e c t i o n on v e n t i l a t o r y and a c i d base c o n t r o l d u r i n g e x e r c i s e . J . A p p l . P h y s i o l . : R e s p i r a t . E n v i r o n . E x e r c i s e P h y s i o l . 39 ( 3 ) : 354-358, 1975. W e i l , J.V., B r y n e - Q u i n n , E., S o d a l . I . E . , F r i e s e n , W.O., U n d e r h i 11,B., F i l l e y , G.F., G r o v e r , R.F. H y p o x i c v e n t i l a t o r y d r i v e i n n o r m a l man. J . C l i n . I n v e s t . 49:1061-1072, 1970. W e i l , J.V., W h i t e , D.P., D o u g l a s , N . J . , Z w i l l i c h C.W. V e n t i l a t o r y c o n t r o l d u r i n g s l e e p i n n o r m a l humans. i n H i g h a l t i t u d e and Man. ed. West, J.B., L a h i r i , S.K., A m e r i c a n P h y s i o l o g i c a l S o c i e t y , B e t h e s d a , M a r y l a n d , 1984. W e l s h , H.G. E f f e c t s of h y p o x i a and h y p e r o x i a on human p e r f o r m a n c e . E x e r c i s e and S p o r t s S c i e n c e R e v i e w s . 15:191-221, 1987. West, J.B. V e n t i l a t i o n / b l o o d - f l o w and gas e x c h a n g e . B l a c k w e l l S c i e n t i f i c Pub. O x f o r d . . 1977 . Whipp, B . J . T e n e t s o f t h e e x e r c i s e h y p e r p n e a and t h e i r d e g r e e o f c o r r o b o r a t i o n . C h e s t 73: 274-276, 1978. W i l l i a m s , J.H., Power s , S.K., S t e w a r t , M.K. H e m o g l o b i n d e s a t u r a t i o n i n h i g h l y t r a i n e d a t h l e t e s d u r i n g heavy e x e r c i s e . Med. S c i . S p o r t s . E x e r . 18(2 ) : 1 68-1 73 , 1986. Woodson, R.D., W i l l s R.E., L e n f a n t , C. E f f e c t o f a c u t e and e s t a b l i s h e d anemia on 02 t r a n s p o r t a t r e s t , s u b m a x i m a l and ma x i m a l work. J . A p p l . P h y s i o l . : R e s p i r a t . E n v i r o n . E x e r c i s e P h y s i o l . 4 4:36-43, 1978. Young, I.H., W o l l c o c k , A . J . Changes i n a r t e r i a l b l o o d gas t e n s i o n s d u r i n g u n s t e a d y - s t a t e e x e r c i s e . J ; A p p l . P h y s i o l . : R e s p i r a t . E n v i r o n . E x e r c i s e P h y s i o l . 4 4 ( l ) : 9 3 - 9 6 , 1978. 33 APPENDIX A REVIEW OF LITERATURE VENTILATION DURING E X E R C I S E The v e n t i l a t o r y r e s p o n s e t o m u s c u l a r e x e r c i s e i s commonly d e s c r i b e d i n t h r e e p h a s e s . I n phase I a r a p i d i n c r e a s e o c c u r s , b e g i n n i n g b e f o r e any m e t a b o l i t e o f m u s c u l a r work c o u l d r e a c h a known a r e a of c h e m o r e c e p t i o n . The e x t e n t t h a t VE i n c r e a s e s w i t h t h e f i r s t b r e a t h v a r i e s f rom a l m o s t no change up t o 100% of t h e s t e a d y s t a t e r e s p o n s e . I n a n i m a l s , t h i s i s a c c o m p a n i e d by an i n c r e a s e i n P0 and d e c r e a s e i n PCO ; t h u s i t i s a r g u e d t h a t t h e 2 2 i n i t i a l i n c r e a s e i n v e n t i l a t i o n c a n n o t r e f l e c t t h e a c t i o n , of h y d r o g e n i o n a t t h e c h e m o r e c e p t o r (Whipp, 1 9 7 8 ) . The use of n e u r a l b l o c k i . n g a g e n t s i n a n i m a l s has . d e m o n s t r a t e d as much as a f i f t y p e r c e n t d e c r e a s e i n v e n t i l a t o r y r e s p o n s e t o h i n d l i m b m o t i o n when a f f e r e n t f i b e r s a r e b l o c k e d s u g g e s t i n g t h a t t he l i k e l y s o u r c e of n e u r o g e n i c d r i v e t o e x e r c i s e v e n t i l a t i o n i s t h e s m a l l m y e l i n a t e d and n o n m y e l i n a t e d f i b e r s . The e v i d e n c e s u r r o u n d i n g t h i s i s s u e i s c o n f l i c t i n g as s i m i l a r s t u d i e s i n man have d e m o n s t r a t e d t h a t v e n t i l a t i o n i s i n d e p e n d a n t of h i n d l i m b m o t i o n and v a r i e s w i t h m e t a b o l i c r a t e (Wasserman e t a l . , 1981),. F o l l o w i n g t h i s i n i t i a l i n c r e a s e t h e r e i s a s l o w r i s e ( p h a s e I I ) i n v e n t i l a t i o n u n t i l s t e a d y s t a t e ( p h a s e I I I ) i s r e a c h e d . B e c a u s e of t h e d e l a y i n phase I I r e s p o n s e f o l l o w i n g t h e o n s e t of e x e r c i s e t h i s i s g e n e r a l l y t h o u g h t t o be c o n s i s t a n t w i t h t h e t r a n s i t o f some m e d i a t o r t o t h e c h e m o r e c e p t o r s (Whipp, 1 9 7 8 ) . The t o t a l v e n t i l a t i o n seen i n s t e a d y s t a t e i s t h e n t h e summation of 34 t h e h u m o r a l and c o n t i n u i n g n e u r o g e n i c s t i m u l i . E x e r c i s e v e n t i l a t i o n has been d e m o n s t r a t e d t o be l i n e a r l y r e l a t e d t o t h e + m i n u t e v e n t i l a t i o n o f c a r b o n d i o x i d e ; CO and H a r e g e n e r a l l y 2 c o n s i d e r e d t o be the o n g o i n g h u m o r a l s t i m u l i t o e x e r c i s e v e n t i l a t i o n ( F a v i e r e t a l . , 1 9 8 3 ) . Of i n t e r e s t i s work i n i n d i v i d u a l s who have u n d e r g o n e c a r o t i d body r e s e c t i o n . Phase I v e n t i l a t i o n does not a p p e a r t o be s i g n i f i c a n t l y a l t e r e d i n t h e s e i n d i v i d u a l s , however t h e y d e m o n s t r a t e an i n c r e a s e i n VE d u r i n g phase I I v e n t i l a t i o n d u r i n g e x e r c i s e t h a t i s a p p r o x i m a t e l y one h a l f t h a t of n o r m a l c o n t r o l s . They a l s o d e m o n s t r a t e a l o w e r a r t e r i a l pH s e c o n d a r y t o t h e i n a b i l i t y o f t h e s e s u b j e c t s t o d e v e l o p r e s p i r a t o r y c o m p e n s a t i o n f o r t h e m e t a b o l i c a c i d o s i s of e x e r c i s e . T h i s e v i d e n c e s u g g e s t s t h a t the c a r o t i d body c h e m o r e c e p t i o n i s i n t i m a t e l y r e l a t e d t o e x e r c i s e v e n t i l a t i o n (Wasserman et' a l . , 1 9 7 5 ) . T h i s n e u r o h u m o r a l t h e o r y of e x e r c i s e v e n t i l a t o r y c o n t r o l a c c o u n t s f o r the v e n t i l a t o r y r e s p o n s e s d u r i n g m u s c u l a r e x e r c i s e by s u g g e s t i n g t h a t t h e r e i s f i r s t a r a p i d n e u r o g e n i c component, f o l l o w e d by a s l o w e r h u m o r a l component. I n c l u d e d i n - t h e n e u r o g e n i c component a r e i m p u t s from t h e c e r e b r a l c o r t e x , i n c l u d i n g v o l u n t a r y i m p u t s , and from m u s c l e s p i n d l e s and j o i n t p r o p r i o c e p t o r a f f e r e n t s . Humoral mechanisms s u g g e s t e d i n c l u d e CO + 2 f l o w t o t h e l u n g s , a l t e r a t i o n s i n i n t r a m e d u l l a r y and CSF [H ] , i n c r e a s e i n p u l m o n a r y b l o o d f l o w , and o s c i l l a t i o n s of PCO 2 about an unchanged mean. S e c o n d a r y f a c t o r s a f f e c t i n g e x e r c i s e v e n t i l a t i o n a r e body t e m p e r a t u r e w h i c h would a p p e a r t o be a s l o w l y d e v e l o p i n g m o d i f i e r of p r i m a r y s t i m u l i and c i r c u l a t i n g c a t e c h o l a m i n e s w h i c h may p r o v i d e a d d i t i o n a l d r i v e t o 35 h y p e r v e n t i l a t e (Whipp, 1 9 7 8 ) . The r i s e i n v e n t i l a t i o n d u r i n g e x e r c i s e c o r r e l a t e s w i t h b o t h the v e n t i l a t o r y r e s p o n s e t o h y p o x i a as w e l l as t h e v e n t i l a t o r y r e s p o n s e t o h y p e r c a p n i a ( M a r t i n e t a l . , 1979; S t o c k l e y e t a l . , 1 9 7 8 ) . Thus t h e e n d u r a n c e a t h l e t e w i t h a documented b l u n t i n g o f t h e s e r e s p o n s e s c o u l d be e x p e c t e d t o have a l o w e r e x e r c i s e v e n t i l a t i o n f o r any g i v e n l e v e l of e x e r c i s e . T h i s has been c o n s i s t a n t l y documented i n t h e l i t e r a t u r e ( M a r t i n e t a l . , 1978a; M a r t i n e t a l . , 1979) and an i n v e r s e r e l a t i o n s h i p has been f o u n d between VO and t h e v e n t i l a t o r y r e s p o n s e t o e x e r c i s e ( M o r r i s o n e t 2 a l . , 1 9 7 3 ) . The use o f p r e s s u r e volume c u r v e s t o c a l c u l a t e t h e work of b r e a t h i n g , has d e m o n s t r a t e d t h e p h y s i o l o g i c a d v a n t a g e of a low e x e r c i s e v e n t i l a t i o n ( M i l i c - E m i l i e t a l . , 1 9 6 2 ) . S u b j e c t s who e x h i b i t a d e c r e a s e d e x e r c i s e v r e s p i r a t o r y work, and t h e r e f o r e d y s p n e a i s a p o w e r f u l l i m i t a t i o n t o t o e x p e c t t h a t a more e f f i c i e n f a c i l i t a t e a t h l e t i c p e r f o r m a n c e . RESPIRATORY DRIVES The h y p o x i c v e n t i l a t o r y r e s p o n s e The h y p o x i c v e n t i l a t o r y r e s s e n s i t i v i t y o f t h e c o r t i c a l and per h y p o x i c s t r e s s . The i n v e s t i g a t i o n where PO and PCO can be c o n t r o l l e 2 2 i s g r a d u a l l y l o w e r e d i n t h i s c i r c u i u n t i l a l v e o l a r oxygen t e n s i o n i s 1 a l . , 1978; H i r s h m a n e t a l . , 1975; 36 e n t i l a t i o n w i l l p e r f o r m l e s s e x p e r i e n c e l e s s d y s p n e a . As p h y s i c a l work, i t r e a s o n a b l e t v e n t i l a t o r y p a t t e r n would ponse i s a measure of t h e i p h e r a l r e g u l a t i n g c e n t e r s t o of t h e HVR i n v o l v e s a c i r c u i t d. The c o n c e n t r a t i o n of oxygen t by t h e a d d i t i o n o f n i t r o g e n owered t o 40 t o r r ( C o l l i n s e t S c o g g i n e t a l . , 197 8; Schoene e t a l . , 1982) w h i c h c o r r e s p o n d s t o a h e m o g l o b i n s a t u r a t i o n of ab o u t 80%. Changes i n t h e a l v e o l a r p a r t i a l p r e s s u r e of c a r b o n d i o x i d e s e c o n d a r y t o h y p e r v e n t i l a t i o n , a r e p r e v e n t e d by t h e a d d i t i o n o f c a r b o n d i o x i d e i n s m a l l q u a n t i t i e s t o the gas m i x t u r e . A r t e r i a l oxygen s a t u r a t i o n i s m o n i t o r e d by means of an e a r o x i m e t e r . The m i n u t e v e n t i l a t i o n i s t h e n r e c o r d e d i n t h e s u p i n e s u b j e c t and c o m p a r i s o n of m i n u t e v e n t i l a t i o n v e r s u s p a r t i a l p r e s s u r e o f oxygen o r p e r c e n t s a t u r a t i o n of h e m o g l o b i n (SaO ) i s made. Due t o t h e "S" shaped n a t u r e of the oxygen 2 h e m o g l o b i n d i s s o c i a t i o n c u r v e , t h e g r a p h o f SaO v e r s u s m i n u t e 2 v e n t i l a t i o n (VE) i s a l i n e a r f u n c t i o n , i n w h i c h t h e s l o p e of t h e l i n e v a r i e s as a f u n c t i o n o f an i n d i v i d u a l ' s s e n s i t i v i t y t o h y p o x i a ( T a m m l i n g , 1 9 8 3 ) . The g r a p h o f VE v e r s u s PaO i s a c u r v e . 2 w h i c h i s d e s c r i b e d by t h e h y p e r b o l i c f u n c t i o n VE = Vo + A/(PA0 2 3 2 ) , where VE i s t h e o b s e r v e d v e n t i l a t i o n ( B T P S ) , PAO i s 2 a l v e o l a r oxygen t e n s i o n i n t o r r and Vo i s the e x t r a p o l a t e d a s y m p t o t e . The A v a l u e d e s c r i b e s t h e shape of t h e c u r v e , w i t h a h i g h A v a l u e d e n o t i n g a b r i s k v e n t i l a t o r y r e s p o n s e t o h y p o x i a and a low A v a l u e a b l u n t e d r e s p o n s e t o h y p o x i a ( C o l l i n s e t a l . , 1 9 7 8 ) . S t a t i s t i c a l a n a l y s i s o f s e v e r a l s t u d i e s ( B r y n e - Q u i n n e t a l . , 1971; C o l l i n s e t a l . , 1978; H i r s h m a n e t a l . , 1975; G r i n d l a y - Moore e t a l . , 1974;) i n d i c a t e a skewed d i s t r i b u t i o n tov/ard l o w e r v a l u e s o f A m i t h a mean A v a l u e of 145 and s t a n d a r d d e v i a t i o n e q u a l t o 80. S i m i l a r a n a l y s i s o f s t u d i e s c o m p a r i n g VE to. SaO 2. ( F l e e t h a m e t a l . , 1980; G r i n d l a y - M o o r e e t a l . , 1984; Rebuck and C a m p b e l l 1975; Rebuck and Woodley 1975; Rebuck e t a l . , 1976) i n d i c a t e s a s i m i l a r skewed d i s t r i b u t i o n w i t h t h e mean s l o p e e q u a l 37 to 1.09+0.97 l . m i n . l%ASaO . When t h e h y p o x i c v e n t i l a t o r y 2 r e s p o n s e i s measured under c o n d i t i o n s where t h e CO t e n s i o n i s 2 a l l o w e d t o f a l l ( p o i k i l o c a p n i c h y p o x i a ) t h e o b s e r v e d r e s p o n s e i s l e s s t h a n under c o n d i t i o n s where c a r b o n d i o x i d e t e n s i o n r e m a i n s c o n s t a n t ( i s o c a p n i c h y p o x i a ) . T h i s r e f l e c t s t h e i n h i b i t o r y e f f e c t o f d e c r e a s i n g CO on v e n t i l a t i o n ( G r i n d l e y - M o o r e e t a l . , 2 1 9 8 4 ) . Some i n t e r e s t i n g o b s e r v a t i o n s have come t o l i g h t r e g a r d i n g t h e v e n t i l a t o r y r e s p o n s e t o h y p o x i a i n d i f f e r e n t a t h l e t i c g r o u p s . E l i t e m o u n t a i n e e r s c a p a b l e of a t t a i n i n g t h e e x t r e m e s of a l t i t u d e have been f o u n d t o have a g r e a t l y enhanced v e n t i l a t o r y r e s p o n s e t o h y p o x i a compared w i t h n o r m a l c o n t r o l s w h i l e e l i t e m i d d l e and l o n g d i s t a n c e r u n n e r s show a b l u n t e d r e s p o n s e ( B r y n e - Q u i n n e t a l . , 1971; C o l l i n s e t a l . , 1978; M a r t i n e t a l . , 1979, Schoene e t a l . , 1 9 8 2 ) . I n one s e r i e s , c l i m b e r s were f o u n d t o have an A v a l u e of 158.9+_29.9 (meant S.D.), w h i l e t h e c o r r e s p o n d i n g v a l u e f o r r u n n e r s was 49.3+7.1. Normal c o n t r o l s e x h i b i t e d a v a l u e of 109.9+21.0 (S c h o e n e e t a l . , 1 9 8 2 ) . Some i n t r i g u i n g q u e s t i o n s a r e r a i s e d as t o w h e t h e r t h e h y p o x i c v e n t i l a t o r y r e s p o n s e i s a g e n e t i c or a c q u i r e d t r a i t . C r o s s s e c t i o n a l s t u d i e s s u g g e s t t h a t t h e f o r m e r i s t r u e . E l i t e e n d u r a n c e a t h l e t e s show a b l u n t i n g o f HVR t h a t i s r e f l e c t e d i n t h e r e s p o n s e s of f i r s t d e g r e e r e l a t i v e s who a r e not engaged i n t h e same a c t i v i t i e s ( C o l l i n s e t a l . , 1 9 7 8 ) . T h i s would s u g g e s t t h a t . t h e o b s e r v e d d i f f e r e n c e s i n t h e c l i m b e r vs e n d u r a n c e r u n n e r p o p u l a t i o n r e p r e s e n t s s e l e c t i o n i n t h e s e g r o u p s ; t h e c l i m b e r who i s s u c c e s s f u l a t a l t i t u d e b e c a u s e of an a b i l i t y to c l i m b h i g h w i t h o u t s u c c u m b i n g t o a l t i t u d e i l l n e s s and the r u n n e r who i s a b l e 38 to r u n f a s t ,because o f d e c r e a s e d e x e r c i s e v e n t i l a t i o n , l e s s r e s p i r a t o r y work and l e s s d y s p n e a . I t i s i n t e r e s t i n g t o n o t e t h a t t h e v e n t i l a t o r y r e s p o n s e t o h y p o x i a i s b l u n t e d i n h i g h a l t i t u d e r e s i d e n t s as w e l l as e n d u r a n c e r u n n e r s . H y p e r c a p n i c v e n t i l a t o r y r e s p o n s e The s e n s i t i v i t y o f an i n d i v i d u a l t o c a r b o n d i o x i d e can be measured by m a i n t a i n i n g a c o n s t a n t PO and i n c r e a s i n g t h e 2 c o n c e n t r a t i o n o f c a r b o n d i o x i d e i n t h e r e b r e a t h i n g c i r c u i t . The g r a p h o f VE v e r s u s PCO i s a l i n e a r f u n c t i o n t h e s l o p e of w h i c h 2 v a r i e s as a f u n c t i o n o f i n d i v i d u a l s e n s i t i v i t y t o h y p e r c a p n i a . A wide range o f r e s p o n s e s t o CO i s seen among n o r m a l i n d i v i d u a l s 2 (Re a d , 1966; I r s i g l e r , 1976) w i t h women t e n d i n g t o be l o w e r r e s p o n d e r s t h e n men. The mean s l o p e of t h e r e s p o n s e l i n e has -1 -1 been r e p o r t e d t o be 2.60 l . m i n . t o r r i n c r e a s e i n PCO w i t h a -1 -1 . 2 s t a n d a r d d e v i a t i o n o f 1.2 l . m i n . t o r r ( I r g s i l e r , 1 9 7 6 ) . S i n c e i n d i v i d u a l v a r i a b i l i t y i s so g r e a t , i t may be more r e a s o n a b l e t o -1 -1 c o n s i d e r CO r e s p o n s e i n terms of low (<1.5 l . m i n . t o r r ) , 2 - 1 - 1 -1 -1 medium (1 . 5 - 5 . 0 l . m i n . t o r r ), and h i g h (>5.0 l . m i n . t o r r ) r e s p o n d e r s . RESPIRATORY FACTORS LIMITING PERFORMANCE I t was n o t u n t i l r e c e n t l y t h a t t h e pulm o n a r y s y s t e m has been c o n s i d e r e d t o e x e r t some c o n s t r a i n t on maximal e x e r c i s e p e r f o r m a n c e i n some i n d i v i d u a l s . S e v e r a l a u t h o r s have d e m o n s t r a t e d a d e c l i n e i n a r t e r i a l oxygen s a t u r a t i o n w i t h i n t e n s e e x e r c i s e w h i c h o f f e r s e v i d e n c e t o e n c o u r a g e t h i s l i n e of t h o u g h t . T h e r e a r e t h r e e p o s s i b l e mechanisms by w h i c h t h e r e s p i r a t o r y 39 s y s t e m c o u l d l i m i t m aximal e x e r c i s e p e r f o r m a n c e ( B y e , 1984; Dempsey, 1986; Dempsey and F r e g o s i , 198 5; Dempsey e t a l . , 1 9 8 2 ) : 1. l u n g m e c h a n i c s . 2. e n e r g e t i c s and 3. r e s p i r a t o r y , m u s c l e f a t i g u e . Lung m e c h a n i c s : I n n o r m a l i n d i v i d u a l s p e r f o r m i n g m o d e r a t e e x e r c i s e , t h e t i d a l f l o w v o l u m e . l o o p f a l l s w e l l w i t h i n t h e maxim a l f l o w volume l o o p , however, i n maxi m a l e x e r c i s e , t h e l i m i t s o f t h i s m a x i m a l f l o w volume l o o p may be a p p r o a c h e d or e x c e e d e d ( O l a f s o n and H y a t t , 1 9 6 9 ) . These l i m i t s a r e r e a c h e d on t h e e x p i r a t o r y s i d e where f l o w becomes i n d e p e n d e n t of e f f o r t ( H y a t t , 1983) t h u s e x c e e d i n g t h e maxi m a l volumes c o u l d be e x p e c t e d t o l e a d t o h y p e r i n f l a t i o n of t h e l u n g s r e s u l t i n g i n s h o r t e n i n g o f t h e i n s p i r a t o r y m u s c l e s and i n c r e a s e d e l a s t i c work of b r e a t h i n g . E n e r g e t i c s : I n a s i t u a t i o n where oxygen t r a n s p o r t i s l i m i t e d , s u c h as a t maxi m a l e x e r c i s e , i t i s p o s s i b l e t h a t any i n c r e a s e i n r e s p i r a t o r y m u s c l e VO (VO r e s p ) would d e c r e a s e t h e 2 2. a v a i l a b l e oxygen f o r n o n - r e s p i r a t o r y m u s c l e s . At low l e v e l s o f v e n t i l a t i o n , t h e p o r t i o n o f VO s u p p l y i n g r e s p i r a t o r y m u s c l e s i s 2 r e l a t i v e l y l o w . At l e v e l s of e x e r c i s e , v e n t i l a t i o n g r e a t e r t h a n -1 -1 100 l . m i n , VO r e s p may be as g r e a t as 2-8 ml 0 .1 VE 2 2 (McKerrow and O t i s , 1 9 5 6 ) . Some a u t h o r s have a r g u e d t h a t i t i s p o s s i b l e t o r e a c h a s t a t e where any i n c r e a s e i n VO would be 2 consumed e n t i r e l y by t h e r e s p i r a t o r y m u s c l e s ( O t i s , 195 4 ) . R e s p i r a t o r y m u s c l e f a t i g u e : R e s p i r a t o r y m u s c l e f a t i g u e can be d e f i n e d as t'he f a i l u r e of the r e s p i r a t o r y m u s c l e s t o g e n e r a t e t h e f o r c e t o p r o d u c e a g i v e n p l e u r a l p r e s s u r e . F o r t h e d i a p h r a g m , t h i s o c c u r s w i t h p r e s s u r e s t h a t a r e 40% of maximum 40 p r e s s u r e w h i l e , f o r t h e i n s p i r a t o r y m u s c l e s , f a t i g u e r e s u l t s i f the p l e u r a l p r e s s u r e r e q u i r e d i s g r e a t e r t h a n 50 - 70% of maximum ( B y e , 1 9 8 3 ) . The u n i q u e c h a r a c t e r i s t i c s o f d i a p h r a g m m u s c l e , w i t h a b i l i t y t o m a i n t a i n v e r y h i g h o x i d a t i v e c a p a c i t y , r e n d e r s t h i s m u s c l e r e l a t i v e l y r e s i s t a n t ' t o f a t i g u e compared w i t h s k e l e t a l m u s c l e (Wasserman e t a l . , 1981) However, s e v e r a l s t u d i e s have shown t h a t h i g h l e v e l s o f v e n t i l a t i o n c a n n o t be m a i n t a i n e d i n d e f i n i t e l y ( B e n d e r and M a r t i n , 1985; Bye e t a l . , 1984; M a r t i n e t a l . , 1 9 8 1 ) . A d e c l i n e i n t h e s t r e n g t h o f the v e n t i l a t o r y m u s c l e s a t t h e end of a marathon r a c e w i t h a f a l l i n maximum . i n s p i r a t o r y and e x p i r a t o r y mouth p r e s s u r e s and t r a n s d i a p h r a g m a t i c p r e s s u r e s s u g g e s t s t h a t t h e s e c o n s i d e r a t i o n s may be of p r a c t i c a l c o n c e r n ( L o k e e t a l . , 1 9 8 2 ) . Reduced t i m e t o e x h a u s t i o n has been shown d u r i n g s h o r t - t e r m m a x i m a l e x e r c i s e a f t e r 150 m i n u t e s of maxi m a l v e n t i l a t i o n ( M a r t i n e t a l . , 1 9 8 2 ) . T h i s r e d u c e d e x h a u s t i o n t i m e o c c u r r e d a t a s i g n i f i c a n t l y l o w e r h e a r t r a t e and v e n t i l a t o r y r a t e t h a n d u r i n g t h e c o n t r o l s i t u a t i o n where t h i s v e n t i l a t o r y work was not p e r f o r m e d . V e n t i l a t o r y e n d u r a n c e has been shown t o be g r e a t e r i n a t h l e t e s t h a n n o n - a t h l e t e s d e s p i t e i d e n t i c a l e n e r g y c o s t s o f b r e a t h i n g f o r t h e two g r o u p s i n v e s t i g a t e d ( M a r t i n e t a l . , 1 9 8 1 ) . T r a i n i n g s t u d i e s have shown an i n c r e a s e i n MVV and t h e p e r c e n t a g e of MVV t h a t can be s u s t a i n e d f o r 15 m i n u t e s of v o l u n t a r y h y p e r v e n t i l a t i o n i n s u b j e c t s i n v o l v e d i n an e n d u r a n c e t r a i n i n g p rogram when compared t o s t r e n g t h t r a i n i n g i n d i v i d u a l s and c o n t r o l s u b j e c t s ( L e i t h and B r a d l e y , 1 9 7 6 ) . T h i s s u g g e s t s t h a t v e n t i l a t o r y m u s c l e t r a i n i n g may o c c u r d u r i n g e n d u r a n c e e x e r c i s e 41 t r a i n i n g . HYPOXEMIA DURING EXERCISE H y p o x i a and a l t i t u d e C o n v e n t i o n a l wisdom has h e l d t h a t t h e a t h l e t e w i t h n o r m a l l u n g s i s e x p o s e d t o h y p o x i a under n o r m a l c i r c u m s t a n c e s o n l y w i t h t r a v e l t o h i g h a l t i t u d e . I t has become a p p a r e n t t h a t h y p o x e m i a of s u f f i c i e n t m a g n i t u d e t o c a u s e d e s a t u r a t i o n of h e m o g l o b i n can be f o u n d i n h e a l t h y a t h l e t e s e x e r c i s i n g n e a r maximal l e v e l s a t sea l e v e l (Dempsey e t a l . , 1984; Powers e t a l . , 1984; W i l l i a m s e t a l . , 1986; and o t h e r s ) . H y p o x i a i s the main s t i m u l u s t o t h e p h y s i o l o g i c a l t e r a t i o n s seen a t h i g h a l t i t u d e . An i n c r e a s e i n m i n u t e v e n t i l a t i o n p r e c e d e s o t h e r c h a n g e s , and i s m e d i a t e d t h r o u g h m e d u l l a r y c h e m o r e s p i r a t o r y c e n t r e s and t h r o u g h t h e c a r o t i d body s y s t e m . T h i s i n t u r n - a c t s t o d e c r e a s e a r t e r i a l PCO 2 w h i c h a c t s on p e r i p h e r a l c h e m o r e c e p t o r s and t o d e c r e a s e m i n u t e v e n t i l a t i o n . Thus t h e n e t v e n t i l a t i o n o b s e r v e d a t h i g h a l t i t u d e i s t h e sum of two c o n f l i c t i n g s t i m u l i . H y p o x i a has been shown t o be an i m p o r t a n t p u l m o n a r y v a s o c o n s t r i c t o r d u r i n g n o r m a l r e g u l a t o r y r e s p o n s e s . At sea l e v e l , t h i s p r o t e c t s a g a i n s t p e r f u s i o n of h y p o v e n t i l a t e d segment of l u n g , however, a t h i g h a l t i t u d e , t h e c hanges a r e more g e n e r a l i z e d , l e a d i n g t o p u l m o n a r y h y p e r t e n s i o n . I n t h e c e r e b r a l c i r c u l a t i o n , h y p o x i a a c t s as a v a s o d i l a t o r , a p r o t e c t i v e mechanism w h i c h o p t i m i s e s oxygen d e l i v e r y i n a s i t u a t i o n of d e c r e a s e d s u p p l y . T h i s e f f e c t i s c o u n t e r e d i n p a r t by t h e e f f e c t s of t h e a c c o m p a n y i n g h y p o c a p n i a w h i c h a c t s as a v a s o c o n s t r i c t o r of t h e c e r e b r a l v a s c u l a t u r e ( S u t t o n and G r e y , 1 9 8 2 ) . The i m p l i c a t i o n s of t h e s e c hanges a r e 42 i m p o r t a n t c o n s i d e r a t i o n s i n t h e p a t h o g e n e s i s of a l t i t u d e s i c k n e s s . A l t i t u d e i l l n e s s Many i n v e s t i g a t o r s b e l i e v e t h e u n d e r l y i n g p a t h o l o g i c mechanisms o f t h e d i f f e r e n t a l t i t u d e i l l n e s s e s t o be t h e same. G e n e r a l l y , a l t i t u d e i l l n e s s i s t h o u g h t t o r e s u l t f r o m a d i s o r d e r of w a t e r h a n d l i n g . E x p o s u r e t o a l t i t u d e l e a d s t o a s h i f t o f f l u i d f r om t h e i n t r a v a s c u l a r s p a c e t o t h e i n t e r s t i t i a l s p a c e . In th e l u n g , t h i s i s augmented by t h e i n c r e a s e i n i n t r a v a s c u l a r p r e s s u r e s e c o n d a r y t o t h e h y p o x i a - m e d i a t e d v a s o c o n s t r i c t i o n . In the b r a i n , an i n c r e a s e d c e r e b r a l b l o o d f l o w s e c o n d a r y t o t h e v a s o d i l a t o r y e f f e c t s o f h y p o x i a l e a d s t o i n c r e a s e d f i l t r a t i o n of f l u i d and edema f o r m a t i o n a c c o r d i n g t o S t a r l i n g ' s l a w . I t can t h e r e f o r e be a p p r e c i a t e d t h a t t h e i n d i v i d u a l who e x h i b i t s r e l a t i v e h y p o v e n t i l a t i o n a t a l t i t u d e w i l l have a g r e a t e r d e g r e e of h y p o x i a and h y p e r c a p n i a , l e a d i n g t o i n c r e a s e d v a s o d i l a t i o n and an e x a g e r a t i o n of t h e p a t h o l o g i c mechanisms d e s c r i b e d above ( S u t t o n and G r e y , 1 9 8 3 ) . T h i s l i n e of t h o u g h t s u g g e s t s t h a t a b r i s k v e n t i l a t o r y r e s p o n s e t o h y p o x i a s h o u l d o f f e r some p r o t e c t i o n a g a i n s t t h e d e v e l o p m e n t o f t h e a l t i t u d e i l l n e s s e s . S e v e r a l s t u d i e s s u p p o r t t h i s r e a s o n i n g . I t has been f o u n d t h a t t h e i n c i d e n c e of A c u t e M o u n t a i n S i c k n e s s (AMS) i s g r e a t e r i n t h o s e i n d i v i d u a l s who have th e g r e a t e s t i n c r e a s e i n m i n u t e v e n t i l a t i o n (Anholm et a l . , 1979).- I n c l i m b e r s t o e x t r e m e a l t i t u d e , i t was f o u n d t h a t t h e i n d i v i d u a l s who were a b l e t o c l i m b t h e h i g h e s t and s l e e p a t t h e h i g h e s t a l t i t u d e , had an e x a g e r a t e d r e s p o n s e t o h y p o x i a ( S c hoene 43 et a l . , 1 9 8 2 ) . T h i s s u g g e s t s t h a t t h o s e i n d i v i d u a l s w i t h a b r i s k r e s p o n s e t o h y p o x i a o p t i m i s e t h e i r o xygen u p t a k e i n an e n v i r o n m e n t where oxygen i s l i m i t e d and m a i n t a i n a low a r t e r i a l and a l v e o l a r PCO . The a d v a n t a g e s of t h i s a r e t h r e e f o l d : 2 f i r s t l y , a d e c r e a s e i n a l v e o l a r c a r b o n d i o x i d e a l l o w s a r e l a t i v e i n c r e a s e i n t h e a l v e o l a r p a r t i a l p r e s s u r e of o x y g e n . S e c o n d l y , t h e r e s p i r a t o r y a l k a l o s i s f a c i l i t a t e s t h e b i n d i n g of oxygen t o h e m o g l o b i n , t h u s a h i g h e r p r o t i o n of h e m o g l o b i n i s s a t u r a t e d f o r a g i v e n PO . T h i r d l y , a l o w e r c a r b o n d i o x i d e t e n s i o n m i n i m i s e s 2 t h e v a s o d i l a t o r y e f f e c t s of h y p o x i a . Exercise i n a hypoxic environment P e r f o r m a n c e i n c r e a s e s l i n e a r l y w i t h i n c r e a s i n g PO and d r o p s 2 o f f s h a r p l y w i t h d e c r e a s i n g PO ( s e e W e l s h , 1987 f o r r e v i e w ) . I n 2 m i l d h y p o x i a ( i n s p i r e d PO 120 t o r r ) t h e c hanges a r e s m a l l and 2 not s t a t i s t i c a l l y s i g n i f i c a n t , however, a t h i g h e r a l t i t u d e s i n c r e a s i n g d e s a t u r a t i o n of h e m o g l o b i n i s f o u n d p a r t i c u l a r l y w i t h e x e r c i s e ( S q u i r e s and B u s k i r k , 1 9 8 2 ) . M a x i m a l oxygen oxygen u p t a k e i s r e l a t e d t o oxygen d e l i v e r y , ( c a r d i a c o u t p u t and o x y g e n - h e m o g l o b i n . d i s s o c i a t i o n c u r v e ) p e r i p h e r a l b l o o d f l o w and d i f f u s i o n g r a d i e n t f o r o x y g e n , and t h e a b i l i t y of t h e m i t o c h o n d r i a t o u t i l i z e oxygen ( D i P r a m p e r o , 1 9 8 5 ) . Thus the a r t e r i a l d - e s a t u r a t i o n seen a t a l t i t u d e l i m i t s VO max by l i m i t i n g 2 t h e d i f f u s i o n o f oxygen i n t o t h e m u s c l e c e l l . The e f f e c t s of h y p o x i a on oxygen d e l i v e r y a r e c o m p l e x , however, as b l o o d f l o w t o a c t i v e m u s c l e i s a f f e c t e d by a r t e r i a l o xygen t e n s i o n (Hogan and W e l s h , 1 9 8 6 ) . D u r i n g s u b m a x i m a l e x e r c i s e , no e f f e c t i s seen on VO u n l e s s h y poxemia i s s e v e r e ( W e l s h , 1 9 8 7 ) . D u r i n g a c u t e 2 44 e x p o s u r e , l i t t l e e f f e c t i s seen on c a r d i a c o u t p u t d u r i n g m a x i m a l e x e r c i s e , a l t h o u g h v a s o d i l a t i o n i s seen i n a c t i v e beds ( W e l s h 1 9 8 7 ) . VE i s i n c r e a s e d f o r subrnaximal e x e r c i s e and l i t t l e or no change i s seen d u r i n g maximal e x e r c i s e . An i n c r e a s e i n pH i s o b s e r v e d d u r i n g subrnaximal e x e r c i s e r e f l e c t i n g t h e e f f e c t of h y p o x i a on p u l m o n a r y v e n t i l a t i o n ( W e l s h , 1 9 8 7 ) . HEMOGLOBIN AFFINITY FOR OXYGEN DURING EXERCISE D u r i n g e x e r c i s e , t h e combined e f f e c t s of d e c r e a s e d pH, i n c r e a s e d t e m p e r a t u r e and a l t e r a t i o n s i n 2,3 DPG s e r v e to p r o d u c e a r i g h t s h i f t i n t h e h e m o g l o b i n - o x y g e n (HbO ) d i s s o c i a t i o n c u r v e . 2 G e n e r a l l y , t h i s change i s r e l a t i v e l y m i n o r , s u c h t h a t h e m o g l o b i n r e m a i n s h i g h l y s a t u r a t e d w i t h oxygen ( 9 4 - 9 8 % ) . T h i s change f a c i l i t a t e s i n c r e a s e d oxygen d e l i v e r y t o t i s s u e s a t low oxygen t e n s i o n s ; d u r i n g e x e r c i s e i n t h e n o r m o x i c c o n d i t i o n , t h e d e c r e a s e d b i n d i n g i n t h e l u n g s i s more t h a n o f f s e t by t h e i n c r e a s e i n 0 d e l i v e r y a t t h e t i s s u e s . D u r i n g h y p o x i c e x e r c i s e , 2 e v e n t u a l l y t h e p o i n t i s r e a c h e d where any g a i n i n t i s s u e d e l i v e r y i s b a l a n c e d by l o s s i n oxygen l o a d i n g a t t h e l u n g s . A pH d e c r e a s e f r o m 7.4 t o 7.2 w i l l c a u s e a d e c r e a s e i n SaO 2 from 97% t o a p p r o x i m a t e l y 94% s a t u r a t e d a t a PO of 90 t o r r . o 2 o S i m i l a r l y , an i n c r e a s e i n t e m p e r a t u r e f r o m 37 C t o 38 C w i l l c a u s e a d e c r e a s e i n SaO from 97% t o 96.4%' ( s e e A p p e n d i x B ) . 2 D u r i n g e x e r c i s e , t h e combined e f f e c t s of t e m p e r a t u r e and pH a r e a d d i t i v e (Thompson and Dempsey, 1 9 8 4 ) . 2 , 3 - D i p h o s p h o g l y c e r a t e (2,3-DPG) i s an i n o r g a n i c p h o s p h a t e t h a t a c t s i n t h e r e d c e l l t o a l t e r i t s oxygen c a r r y i n g c a p a c i t y i n t h e f o l l o w i n g ways: 1. 2,3-DPG b i n d s d i r e c t l y t o h e m o g l o b i n , 45 c o m b i n i n g more r e a d i l y t o d e o x y h e m o g l o b i n and t e n d i n g t o h o l d i t i n t h i s s t a t e . 2. When s y n t h e s i s e d i n s i d e t h e r e d c e l l , t h i s m o l e c u l e i s u n a b l e t o c r o s s t h e r e d c e l l membrane. T h i s a l t e r s t h e Donnan e q u i l i b r i u m and a c t s t o d e c r e a s e i n t r a c e l l u l a r pH and t h u s a l t e r t h e HbO c u r v e t h r o u g h e f f e c t on pH ( K l o c h e , 1 9 7 2 ) . 2 S h o r t - t e r m e x h a u s t i v e e x e r c i s e has been show t o p r o d u c e a change i n h e m o g l o b i n a f f i n i t y f o r oxygen i n d e p e n d e n t of t e m p e r a t u r e and pH, t h a t can be a t t r i b u t e d t o c hanges i n 2,3-DPG. Ve r y i n t e n s e e x e r c i s e i s r e q u i r e d t o p r o d u c e t h e s e c h a n g e s ; a p p r o x i m a t e l y 30- 50% of t h e v a r i a b i l i t y i n s a t u r a t i o n can be a c c o u n t e d f o r by a l t e r a t i o n i n 2,3-DPG ( K l e i n e t a l . , 1 9 8 0 ) . A n o t h e r a d a p t i v e mechanism t h a t o c c u r s d u r i n g e x e r c i s e i s an i n c r e a s e i n oxygen c a r r y i n g c a p a c i t y as a r e s u l t o f s m a l l c h a n g e s i n h e m o g l o b i n c o n c e n t r a t i o n . The h e m o c o n c e n t r a t i o n seen a c c o u n t s f o r an i n c r e a s e of 1.0-1.5 g h e m o g l o b i n per 100 ml l e a d i n g t o an i n c r e a s e i n oxygen c o n t e n t of t h e o r d e r of a b o u t 2 ml per 100 ml + + (Thompson and Dempsey, 1 9 7 4 ) . I n a d d i t i o n , c hanges i n NA , K , and CI i o n s have been documented ( K l o c h e , 1972) w h i c h may c o n t r i b u t e t o t h e c hanges i n a r t e r i a l s a t u r a t i o n d u r i n g e x e r c i s e . ARTERIAL DESATURATION DURING HEAVY EXERCISE The d o c u m e n t a t i o n of a r t e r i a l d e s a t u r a t i o n d u r i n g heavy- work i s not new ( H a r r o p , 1 9 1 9 ) , however, t h i s phenomena was i g n o r e d a s i d e f r o m s c a t t e r e d r e p o r t s ( R o w e l l e t a l . , 1964; Thompson and Dempsey, 1974) u n t i l r e c e n t l y . The most l i k e l y e x p l a n a t i o n f o r t h i s l a c k of i n t e r e s t i n t h e p a r t of t h e s c i e n t i f i c community was t h e f o c u s on a r t e r i a l gas d a t a o b t a i n e d d u r i n g subrnaximal e x e r c i s e ( B j u r s t e d and W i g e r t z , 1971; 0 - B a r r e t a l . , 1964; 46 S u s k i n d e t a l . , 1950) w h i c h d i d not show any d e c l i n e i n h e m o g l o b i n s a t u r a t i o n t h a t c o u l d not be a c c o u n t e d f o r by t h e f a c t o r s p r e v i o u s l y d i s c u s s e d . P e r h a p s t h e most c o m p l e t e s t u d y i n v e s t i g a t i n g c h anges i n PO and SaO i s f o u n d i n t h e work of 2 2 Dempsey e t a l . , 1984. I n h i s s t u d y , s i x t e e n e n d u r a n c e a t h l e t e s c a p a b l e of s u s t a i n i n g v e r y h i g h m e t a b o l i c r a t e s (VO max = 7 2+_2 -1 -1 2 ml.kg min ) p e r f o r m e d a p r o g r e s s i v e e x e r c i s e t e s t on a t r e a d m i l l . H e m o g l o b i n s a t u r a t i o n was measured by means of an e a r o x i m e t e r , and a r t e r i a l pH, PCO , and PO were measured by means 2 2 of an i n d w e l l i n g a r t e r i a l c a n n u l a . I t was f o u n d t h a t e i g h t of t h e s i x t e n s u b j e c t s d e m o n s t r a t e d a d e c r e a s e i n a r t e r i a l oxygen c o n t e n t of 21-35 t o r r , t o a PO of l e s s t h a n 75 t o r r . The most 2 s e v e r e h y p o x e m i a was a s s o c i a t e d w i t h l i t t l e o r no a l v e o l a r h y p e r v e n t i l a t i o n . When h e l i u m b r e a t h i n g was used t o r e d u c e t u r b u l e n t f l o w , and t h u s u n l o a d t h e r e s p i r a t o r y m u s c l e s , e x e r c i s e v e n t i l a t i o n i n c r e a s e d s u b s t a n t i a l l y . The mechanisms a c c o u n t i n g f o r a r t e r i a l d e s a t u r a t i o n d u r i n g heavy work have not been e l u c i d a t e d , however, the s p e c u l a t i o n as t o p o s s i b l e c a u s e s p r o c e e d s a l o n g t h e f o l l o w i n g l i n e s : 1. veno- a r t e r i a l s h u n t . 2. v e n t i l a t i o n - p e r f u s i o n i n e q u a l i t y . 3. d i f f u s i o n l i m i t a t i o n . 4. h y p o v e n t i l a t i o n . V e n o a r t e r i a l s h u n t : At r e s t i n the h e a l t h y i n d i v i d u a l , t h e r e a r e s m a l l ( a p p r o x i m a t e l y 1-1.5% of c a r d i a c o u t p u t ( B a c h o f e n e t a l . , 1973) amounts of b l o o d t h a t a r e s h u n t e d v i a t h e t h e b e s b i a n v e i n s and b r o n c h i a l venous b l o o d s u p p l y d i r e c t l y i n t o t h e s y s t e m i c c i r c u l a t i o n and t h e r e f o r e do not p a r t i c i p a t e i n gas e x c h a n g e . The i n t r o d u c t i o n of t h i s p o o r l y o x y g e n a t e d b l o o d 47 c a u s e s a s m a l l d e c l i n e i n oxygen t e n s i o n i n a r t e r i a l b l o o d . I f s h u n t i n g were t h e c a u s e of t h e d e c l i n e i n PO , no change would be 2 e x p e c t e d i n oxygen t e n s i o n w i t h t h e i n t r o d u c t i o n of a h y p e r o x i c gas m i x t u r e . I n f a c t , t h i s i s not the c a s e w i t h r e p o r t s of h y p e r o x i a c o r r e c t i n g the h y p o x i a seen d u r i n g e x e r c i s e a t sea l e v e l (Dempsey e t a l . , 1984; G a l e , e t a l . , 1985; T o r r e - B u e n o e t a l . , 1 9 8 5 ) . Thus some o t h e r mechanism must a c c o u n t f o r t h i s phenomena. V e n t i l a t i o n - p e r f u s i o n i n e q u a l i t y : G e n e r a l l y v e n t i l a t i o n and p e r f u s i o n of t h e l u n g a r e . n o n - u n i f o r m : due t o t h e e f f e c t s of g r a v i t y t h e b a s e s of t h e l u n g r e c i e v e a g r e a t e r b l o o d f l o w t h a n do t h e a p i c e s . I f v e n t i l a t i o n and p e r f u s i o n i n e q u a l i t y i n c r e a s e d t h e n a r t e r i a l h y p oxemia c o u l d a l s o i n c r e a s e as b l o o d p a s s e d t h r o u g h a p o o r l y v e n t i l a t e d segment of t h e l u n g . D u r i n g low i n t e n s i t y e x e r c i s e t h e r e i s an i n c r e a s e i n b o t h a p i c a l v e n t i l a t i o n and p e r f u s i o n w i t h t h e o v e r a l l r e s u l t t e n d i n g t o g r e a t e r h o m o g e n i t y w i t h i n d i f f e r e n t a r e a s of the l u n g . At more i n t e n s e l e v e l s o f e x e r c i s e o n l y m inor c h a n g e s i n v e n t i l a t i o n - p e r f u s i o n unequai.i t.y,.. have been f o u n d ( G a l e e t a l . , 1985) w h i c h a r e not s u f f i c i e n t t o a c c o u n t f o r t h e c h a n g e s i n P 0 seen d u r i n g 2 m a x i m a l e x e r c i s e . D i f f u s i o n l i m i t a t i o n : A n o t h e r p o s s i b l e e t i o l o g y of a r t e r i a l h y p o x e m i a d u r i n g heavy e x e r c i s e r e l a t e s t o d i f f u s i o n l i m i t a t i o n . I n t h e s e d e n t a r y i n d i v i d u a l d u r i n g heavy e x e r c i s e t h e t r a n s i t t i m e f o r t h e r e d b l o o d c e l l t h r o u g h t h e p u l m o n a r y c i r c u l a t i o n i s w e l l t h e t i m e r e q u i r e d f o r c o m p l e t e e q u i l i b r a t i o n ( a b o u t 0.25 s e c o n d s ) . I n t h e a t h l e t e c a p a b l e of r e a c h i n g v e r y h i g h work l e v e l s , mean t r a n s i t t i m e may be r e d u c e d t o 0.40 s e c o n d s or l e s s , 48 s e c o n d a r y t o i n c r e a s e s i n p u l m o n a r y b l o o d f l o w . I f t h e b l o o d i s a l s o d i r e c t e d t o u n d e r v e n t i l a t e d a r e a s of t h e l u n g , t r a n s i t t i m e s may be f u r t h e r r e d u c e d t o l e s s t h a n 0.25 s e c o n d (Dempsey e t a l . , 1 9 8 2 ) . D i f f u s i o n d i s t a n c e c o u l d a l s o be i n c r e a s e d i f h i g h i n t r a v a s c u l a r p r e s s u r e s w i t h i n t h e •pulmonary c a p i l l a r y . l e a d to f l u i d l e a k and an i n c r e a s e i n f l u i d i n t h e i n t e r s t i t i a l s p a c e . Thus d i f f u s i o n l i m i t a t i o n may a l s o e x p l a i n t h e c hanges i n a r t e r i a l s a t u r a t i o n o b s e r v e d . H y p o v e n t i l a t i o n : T h at h y p o v e n t i l a t i o n p l a y s a r o l e i n the g e n e s i s of a r t e r i a l h y p o x e m i a seems l i k e l y , but t o what e x t e n t i s u n c e r t a i n . I n the s t u d y of Dempsey e t a l . , 1984, t h e i n d i v i d u a l s d e m o n s t r a t i n g t h e g r e a t e s t d e g r e e of a r t e r i a l h y p o x e m i a e x h i b i t e d the l o w e s t h y p e r v e n t i l a t o r y r e s p o n s e t o e x e r c i s e . W h i l e t h e s e s u b j e c t s d i d not r e t a i n CO above r e s t i n g l e v e l s , i t may be 2 c o n s i d e r e d i n t h e l i g h t of s i g n i f i c a n t m e t a b o l i c a c i d o s i s , t h a t n o r m a l l e v e l s of PCO may be i n a p p r o p r i a t e . 2 N o n - a p n e i c a r t e r i a l d e s a t u r a t i o n of 11% of more has been r e p o r t e d d u r i n g s l e e p i n p a t i e n t s w i t h c h r o n i c o b s t r u c t i v e p u l m o n a r y d i s e a s e . Some a u t h o r s ( L i t t n e r e t a l . , 1980) have d e s c r i b e d d i m i n i s h e d v e n t i l a t o r y , r e s p o n s e s t o h y p o x i a and h y p e r c a p n i a d u r i n g d a y t i m e w a k e f u l n e s s i n t h e s e i n d i v i d u a l s compared t o n o n - d e s a t u r a t i n g c o n t r o l s . In n o r m a l s u b j e c t s q u i e t or non-REM s l e e p i s a s s o c i a t e d w i t h d e c r e a s e d v e n t i l a t i o n , a l t e r a t i o n s i n b r e a t h i n g p a t t e r n and m i l d h y p o x i a and h y p e r c a p n i a ; t h e h y p o x i c and h y p e r c a p n i c v e n t i l a t o r y r e s p o n s e s show some d e c r e a s e . ( W e i l e t a l . , 1 9 8 4 ) . I n n o r m a l s u b j e c t s SaO 2 i s w e l l m a i n t a i n e d . Thus i t can be seen t h a t i n some 49 c i r c u m s t a n c e s d e s a t u r a t i o n i s a s s o c i a t e d w i t h d i m i n i s h e d r e s p i r a t o r y d r i v e s . T h i s r e v i e w has f o c u s e d on e x e r c i s e v e n t i l a t i o n and t h e p o s s i b l e mechanisms of a r t e r i a l d e s a t u r a t i o n d u r i n g heavy e x e r c i s e . Of t h e f o u r p o s s i b l e e x p l a i n a t i o n s f o r the d e c l i n e i n a r t e r i a l d e s a t u r a t i o n , d i f f u s i o n and i n a d e q u a c y of v e n t i l a t i o n e i t h e r due t o b l u n t e d r e s p i r a t o r y d r i v e o r m e c h a n i c a l c o n s t r a i n t s a r e t h e a r e t h e most l i k e l y . 50 A P P E N D I X B r c © 43 • 40 • M - 4 30- 2 5 - ^ 20-3 15- 10 0—=* P H © -6.6 -6.7 -6.8 -6.9 -7.0 -7.1 •7.2 •7.3 •7.4 •7.3 •7.6 • 7.7 • 7.8 •7.9 • 8.0 • 8.1 • 8.2 Po 2-OXYGEN SATURATIONS NOMOGRAM FOR WHOLE BLOOD C O R R E C T I O N S FOR TEMPERATURE AND pH Sundvd DfccKlaMon C***m *£X*&rq to 1. W. ScwvrtnQhevl. 1903 t n w i w i an4 pH U W W P J H <eca>dtwg ta P. A«mo, 1065. PQ2 own Hg © 300 | T 230 §_- 200 p - 150 > 100 90 • 80 • 70 • 60 30 • 40 30 23 £ - 2 0 • 10 9 • a 7 • 6 • 5 3 2.5 2X3 PQ_ mm Hg corraciad © •98.8 O2SATO/0 A T 3 7 ' C A N D pH 7.40 5 0 - E g 40- 33 - 30 2 3 - 20- 15 - 1 0 - ^ 9 8 90 80 •70 •60 50 £ - 4 0 30 20 • 15 •10 •6.5 To r e a d t h e c o r r e c t e d PC>2 ( s c a l e D) o r SaO ( s c a l e E) t h e m e a s u r e d t e m p e r a t u r e o r pH ' i s f o u n d on s c a l e A o r B and a s t r a i g h t l i n e i s drawn t o t h e me a s u r e d P0 on s c a l e C , 51 APPENDIX C SUBJECT PHYSIOLOGIC DATA SUBJECT AGE (yrs) HEIGHT (cms) WEIGHT (kg) V02MAX (ml/kg/min) TREADMILL VELOCITY (m/sec) HVR (l/%ASa02) 1 21 192.0 80.7 61.8 11.5 0.43 2 30 178.0 71.8 63.8 13.0 0.43 3 18 180.2 70.1 62,6 11.5 0.78 4 23 185.6 81.2 61.5 11.75 1.12 5 22 179.5 69.5 64.9 12.25 1.05 6 25 179.0 67.7 61.1 12.25 1.03 7 23 182.6 79.7 64.8 11.75 0.22 8 18 180.2 70.1 62.6 11.5 0.22 9 26 185.0 81.0 67.3 . 12.5 1.22 .10 24 169.0 61.4 66.8 12.5 0.87 11 28 179.5 74.3 61.7 11.75 0.43 12 27 184.8 73.6 61.8 11.75 0.26 52 APPENDIX D PULMONARY FUNCTION TESTS SUBJECT FVC PRED. (1) FVC MEASURED (1) % FEV 1 (1) % FVC PEAK FLOW (1/min) 1 6.34 6.05 95.4 4.94 86.1 442 2 5.17 5.13 99.2 3.79 73.8 333 3 5.89 6.47 109.8 5.74 88.7 655 4 5.91 5.72 96.8 4.16 72.7 391 5 5.51 6.07 110.2 3.47 57.1 487 6 5.38 4.53 84.2 3.71 81.9 482 7 5.64 5.12 90.8 3.65 71.2 316 8 5.64 4.84 85.8 3.83 79.1 401 9 5.41 6.18 114.2 4.39 71.0 532 10 4.76 4.29 90.1 3.37 78.6 473 11 5.26 5.37 1.02 4.31 80.2 492 12 5.71 5.30 92.8 4.56 86.0 500 53 APPENDIX E HYPOXIC VFJCT1ATORY RESPONSE DATA 2 A and R for the line VE = A(Sa02) + Vo SUBJECT 10 11 12 TEST ONE A R2 0.41 0.80 0.42 0.72 0.78 0.70 1.25 0. 1.05 0.70 1.10 0.89 0.15 0.29 0.22 0.63 1.98 0.87 0.87 0.77 0.43 0.77 0.18 0.49 TEST TwO A R2 0.45 0.82 0.44 0.72 0.99 0.91 0.% 0.93 0.08 0.25 0.07 0.12 1.22 0.70 0.14 0.45 -O.01 0.01 TEST THREE A R2 0.28 0.40 0.21 0.81 0.26 0.82 HVR USED 0.43 0.43 0.78 1.12 1.05 1.03 0.22 0.22 1.22 0.87 0.43 0.26 COMMENTS mean of 1,2. mean of 1,2. mean of 1,2. mean of 1,2. mean of 1,3. poor 002 control in 2. mean of 1,3. two best fit t i n g lines. 1 not used poor C02 control 1 used as best f i t subject hyperventilated- at start of 1,2. VE i s observed ventilation, A = AVE/ l%ASa02, Vo i s calculated ventilation when Sa02 = 0 54 APPENDIX F SUBJECT DATA SUBJECT 1 TIME (min) R 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00 2:15 2:30 2:45 3:00 3:15 3:30 3:45 4:00 4:15 4:30 4:45 5:00 pH 7.434 7.442 7.848 7.463 7.463 7.436 7.417 7.404 7.391 7.380 7.371 7.365 7.355 7.345 7.337 7.341 7.320 7.310 7.300 7.285 7.285 PC02 (torr) 36.5 35.3 37.7 37.7 36.0 36.1 39.3 34.1 36.1 35.4 36.9 34.6 37.2 36.7 36.4 32.9 32.6 37.3 30.3 31.7 30.5 P02 (torr) 91 106 100 92 93 93 98 92 93 87 89 87 85 86 87 86 88 81 85 80 84 Sa02 (%) 97.4 98.3 98.2 97.6 97.7 97.5 97.7 97.3 97.2 96.5 96.7 96.4 96.0 96.0 96.0 96.1 96.1 94.8 95.4 94.4 95.0 V02(l/min) 1.33 2.78 3.95 4.52 4.20 4.58 4.32 4.65 4.28 4.62 4.64 4.42 4.82 4.77 4.62 4.87 4.78 4.78 4.70 4.86 VE(l/mixi BTR 58.0 88.0 107.5 130.3 131.5 146.4 142.5 157.1 146.8 161.3 162.7 156.3 167.4 169.0 167.9 164.1 169.1 169.1 166.9 170.9 SUBJECT 2 TIME (min) R 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00 2:15 2:30 2:45 3:00 3:15 3:30 3:45 4:00 4:15 4:30 4:45 5:00 pH 7.442 7.465 7.451 7.431 7.408 7.380 7.353 7.353 7.337 7.319 7.279 7.260 7.242 7.230 7.213 7.201 7.183 7.165 7.146 7.137 7.122 PC02 (torr) 36.5 34.1 38.7 35.8 39.4 40.4 40.6 40.9 40.0 36.4 39.4 39.9 40.0 38.5 39.3 38.6 38.5 38.4 38.4 38.5 38.1 P02 (torr) 113 131 113 97 97 97 94 97 99 95 98 94 92 94 90 91 88 87 87 87 85 Sa02 (%) 98.6 99.2 98.6 97.8 97.6 97.4 97.0 97.2 97.3 Q8 f\ 96.6 96.0 95.5 95.7 94.9 rv. n Cll. 1 93.7 no n no / V02(l/min) 1.44 1.84 3.42 3.67 3.81 3.88 3.95 3.94 3.96 3.% 4.10 4.11 4.17 4.10 4.Z5 4.23 4.18 4.14 4.21 3.90 VE(l/miri BTR 5) 57.6 67.4 88.9 99.4 107.1 117.4 125.9 129.9 129.5 130.0 135.7 136.2 139.7 135.9 139.0 144.5 141.3 138.4 138.2 124.7 SUBJECT 3 TIME (iron) R 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00 2:15 2:30 2:45 3:00 3:15 3:30 3:45 4:00 4:15 4:30 4:45 5:00 pH 7.440 7.444 7.458 7.453 7.449 7.429 7.423 7.405 7.400 7.388 7.382 7.375 7.367 7.368 7.351 7.353 7.351 7.346 7.334 7.331 7.328 RD2 (torr) 34.2 36.6 37.1 38.4 37.8 37.8 34.2 40.2 36.4 36.2 34.0 35.9 33.0 34.3 34.6 32.9 32.3 32.6 35.6 35.1 32.2 P02 (torr) 119 117 103 106 102 104 99 109 102 109 105 104 108 102 101 103 102 95 96 91 96 Sa02 (%) 98.8 98.8 98.3 98.4 98.2 98.2 97.9 98.3 97.9 98.2 98.0 97.9 98.1 97.8 97.6 97.7 97.6 97.1 97.0 96.5 97.0 V02(l/ndn) 1.48 2.39 3.47 3.70 3.86 3.59 3.78 3.81 3.88 3.69 3.85 4.02 3.86 4.00 4.12 4.03 3.95 4.28 4.09 4.15 VE(l/min BTR 5) 52.3 71.8 90.8 96.9 112.6 118.6 128.2 133.2 134.5 130.0 132.4 133.2 129.4 132.4 136.6 136.6 130.6 144.4 134.3 134.0 SUBJECT 4 TIME (min) R 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00 2:15 2:30 2:45 3:00 3:15 3:30 3:45 4:00 4:15 4:30 4:45 5:00 pH 7.440 7.442 7.442 7.431 7.417 7.3% 7.384 7.368 7.335 7.338 7.322 7.311 7.295 7.282 7.272 7.266 7.256 7.244 7.230 7.221 7.207 KD2 (torr) 38.4 38.1 39.2 37.0 37.9 40.2 37.4 37.9 38.1 38.0 40.9 39.6 37.3 36.8 39.4 38.7 37.3 36.3 37.2 37.4 35.7 P02 (torr) 100 107 88 83 83 86 86 86 93 89 83 84 84 83 84 86 86 85 84 82 85 Sa02 (%) 98.0 98.4 97.1 96.5 96.4 96.5 96.4 96.3 96.8 96.3 95.3 95.2 95.1 94.7 94.8 95.0 94.9 94.5 94.1 93.0 94.0 V02(nti/min) 1.08 2.20 4.42 4.50 4.64 4.45 4.69 4.41 4.35 4.64 4.35 4.69 4.46 4.83 4.59 4.73 4.66 4.67 4.77 4.56 VE(l/niiii BTR 5) 39.3 57.2 89.4 96.2 107.8 112.4 124.6 124.8 117.8 123.1 121.1 129.7 121.7 136.8 133.9 140.7 150.5 132.8 140.3 140.4 SUBJECT 5 TIME (nrLn) R 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00 2:15 2:30 2:45 3:00 3:15 3:30 3:45 4:00 4:15 4:30 4:45 5:00 pH 7.437 7.404 7.439 7.430 7.404 7.376 7.366 7.347 7.330 7.320 7.313 7.295 7.282 7.275 7.255 7.250 7.234 7.223 7.205 7.194 7.179 KD2 (torr) 40.3 40.2 39.1 38.8 40.4 42.9 41.2 39.0 41.5 39.6 38.7 38.3 37.3 39.5 38.3 35.4 38.7 36.9 36.4 36.1 37.7 P02 (torr) 105 107 105 96 92 93 95 92 89 88 87 86 86 83 82 82 80 80 81 81 79 Sa02 (%) 98.2 98.2 98.2 97.6 97.2 97.0 97.1 96.7 96.1 96.0 95.8 95.5 95.2 94.6 94.1 94.0 93.4 93,1 93.1 92.9 91.7 V02(l/min) 0.60 1.38 2.44 3.64 3.93 3.93 4.02 3.89 4.22 4.01 4.07 4.24 4.10 4.24 4.33 4.35 4.19 4.46 4.19 4.36 vEQ/min BTR 5). 22.8 55.2 76.3 96.3 107.4 114.1 123.6 124.1 134.7 129.5 134.6 139.8 131.6 137.9 139.0 140.2 137.8 145.7 139.6 144.7 SUBJECT 6 TIME (min) R 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00 2:15 2:30 2:45 3:00 3:15 3:30 3:45 4:00 4:15 4:30 4:45 5:00 pH 7.400 7.424 7.413 7.390 7.371 7.348 7.332 7.315 7.300 7.266 7.238 7.235 7.213 7.194 7.178 7.160 7.149 7.132 - - PC02 (torr) 39.2 34.9 38.0 40.8 41.5 40,6 39.6 39.4 40.1 41.3 42.5 40.0 41.4 39.5 41.8 39.2 38.6 40.6 - - - P02 (torr) 106 122 101 94 95 95 92 93 90 87 84 88 83 83 81 84 81 81 - - - Sa02 (%) 98.1 98.8 97.9 97.2 97.1 97.0 96.6 96.5 96.0 95.1 94.3 94.8 93.5 93.3 92.5 92.9 92.1 91.4 - - - V02(l/min) 1.69 2.04 3.12 3.86 3.48 3.93 3.89 3.77 4.00 3.62 4.11 3.94 4.08 3.94 4.15 4.25 3.59 - - - VE(l/nun BTR 5) 59.6 76.0 86.5 103.7 106.1 121.3 125.5 122.8 128.6 120.6 131.7 130.5 133.3 127.2 130.1 137.5 120.0 - - - SUBJECT 7 TIME (min) R 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00 2:15 2:30 2:45 3:00 3:15 3:30 3:45 4:00 4:15 4:30 4:45 5:00 pH 7.451 7.439 7.463 7.432 7.416 7.384 7.365 7.358 7.348 7.341 7.328 7.314 7.304 7.299 7.285 7.265 7.264 7.249 7.236 7.299 7.215 PC02 (torr) 33.4 38.6 37.3 38.4 39.4 41.5 36.7 41.1 38.3 .41.2 41.2 39.7 36.6 39.5 41.5 38.5 39.9 40.3 41.3 40.9 41.1 P02 (torr) 100 112 107 96 86 86 85 84 89 84 87 80 78 79 85 86 77 76 75 79 75 Sa02 (%) 91.8 98.5 98.5 97.7 96.7 96.4 96.2 95.8 96.3 95.6 95.9 94.7 94.1 94.2 95.0 95.1 93.1 92.6 92.1 93.1 91.5 V02(l/mLn) 2.84 3.14 4.41 4.98 4.79 4.88 5.00 5.20 4.90 5.07 5.22 5.07 4.96 5.19 4.95 5.23 5.10 5.15 5.15 4.96 VE(l/min BTR 92.6 103.3 111.8 128.5 127.8 129.3 132.3 143.9 137.5 143.0 148.1 143.6 143.0 150.0 142.6 150.1 146.4 150.7 150.3 145.1 SUBJECT 8 TIME (min) R 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00 2:15 2:30 2:45 3:00 3:15 3:30 3:45 4:00 4:15 4:30 4:45 5:00 pH 7.460 7.431 7.424 7.411 7.397 7.377 7.362 7.350 7.322 7.318 7.300 7.289 7.277 7.263 7.247 7.236 7.218 7.215 7.203 7.196 7.182 P002 (torr) 32.9 38.8 39.7 40.3 39.8 35.7 38.3 38.2 37.3 36.4 38.6 37.8 39.6 36.3 37.8 36.6 37.6 34.2 35.5 35.0 36.0 P02 (torr) 109 78 77 82 79 80 • 83 82 79 82 79 76 78 78 73 73 73 74 74 75 74 Sa02 (%) 98.6 95.8 95.5 96.1 95.5 95.5 95.8 95.4 94.8 95.1 94.2 93.5 93.8 93.4 91.9 91.6 91.1 91.4 91.2 91.2 90.8 V02(l/min) 1.78 3.11 3.72 3.82 3.79 3.92 3.83 3.82 3.92 4.05 3.92 4.09 3.94 3.89 4.22 4.23 4.22 4.11 4.07 3.98 VE(l/nrin BTR 5) 47.3 69.6 85.3 98.9 107.7 118.7 123.7 124.2 127.7 134.6 133.0. 136.6 138.2 133.7 137.6 141.4 144.2 140.8 145.8 137.2 SUBJECT 9 TTME (min) R 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00 2:15 2:30 2:45 3:00 3:15 3:30 3:45 4:00 4:15 4:30 4:45 5:00 PH 7.431 7.473 7.472 7.469 7.437 7.422 7.392 7.384 7.368 7.355 7.335 7.327 7.312 7.298 7.284 7.277 7.259 7.248 7.233 7.219 7.208 F002 (torr) 38.3 31.4 34.4 35.4 36.2 36.0 36.6 36.6 36.6 36.4 36.7 36.8 36.7 36.6 35.9 36.9 36.9 34.7 36.1 35.9 35.6 P02 (torr) 107 123 122 103 91 91 84 87 83 82 78 78 77 76 73 72 72 73 70 70 71 Sa02 (%) 98.3 99.9 99.0 98.3 97.4 97.3 96.3 96.5 95.9 95.6 94.7 94.4 94.1 93.7 92.7 92.3 91.7 91.9 90.6 90.2 90.1 V02(l/min) 1.09 2.30 4.15 4.94 4.74 4.67 5.10 5.07 5.13 5.18 5.24 5.43 4.32 5.44 5.52 5.37 5,45 5.58 5.43 5.59 VE(l/miii BDR 5) 45.1 87.1 130.6 157.1 166.9 167.2 181.5 185.6 183.2 183.1 185.6 188.1 181.9 184.8 187.0 179.3 182.5 184.8 179.2 184.7 SUBJECT 10 TTME (min) R 0:15 0:30 0:45 1:00 1:15 1:30 • 1:45 2:00 2:15 2:30 2:45 3:00 3:15 3:30 3:45 4:00 4:15 4:30 4:45 5:00 pH 7.434 7.475 7.478 7.430 7.417 7.405 7.373 7.360 7.331 7.313 7.286 7.280 7.273 7.254 7.236 7.226 7.209 7.198 7.187 7.190 7.161 P002 (torr) 27.4 30.3 32.7 31.4 35.2 35.2 36.8 35.8 36.2 35.8 33.6 37.4 34.1 33.8 35.4 34.5 35.5 34.6 35.4 33.0 35.7 P02 (torr) 125 117 103 91 89 91 89 87 86 86 83 81 84 84 78 81 77 77 76 75 75 Sa02 (%) 99.0 98.9 98.4 97.4 97.1 97.2 96.7 96.3 95.9 95.7 94.9 94.5 94.8 94.7 93.1 93.6 92.1 92.0 91.5 91.4 90.6 V02(l/nrin) 1.61 2.11 3.57 3.88 3.65 3.85 3.87 4.13 4.07 4.17 4.30 4.21 4.15 4.36 4.13 4.35 4.40 4.35 4.40 4.14 VE(l/min BTR 5) 66.8 90.2 114.5 128.0 129.8 134.4 139.2 148.3 145.9 151.2 155.7 151.5 148.2 154.5 147.4 151.2 156.2 151.2 152.5 141.4 SUBJECT 11 TIME (min) R 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00 2:15 2:30 2:45 3:00 3:15 3:30 3:45 4:00 4:15 4:30 4:45 5:00 pH 7.443 7.470 7.480 7.455 7.439 7.436 7.395 7.379 7.357 7.340 7.331 7.317 7.298 7.285 7.268 7.260 7.244 7.242 7.123 7.213 7.207 PG02 (torr) 44.1 40.3 43.4 36.3 35.8 38.7 39.2 39.2 42.6 41.3 39.8 40.8 41.2 41.3 42.3 41.0 40.8 40.4 40.6 38.9 41.8 P02 (torr) 101 126 106 98 88 83 89 77 75 74 73 73 70 70 69 70 70 71 69 68 66 Sa02 (%) 98.0 99.1 98.4 98.0 97.1 96.6 96.9 95.0 94.3 93.8 93.4 93.2 92.0 91.6 90.9 91.0 90.5 91.0 89.7 89.1 88.1 VD2(l/nrin) 2.07 2.65 4.09 4.22 3.98 4.19 4.45 4.42 4.43 4.62 4.41 4.52 4.65 4.58 4.75 4.67 4.64 4.68 4.60 4.80 VE(l/min BTR 89.5 105.7 143.9 143.9 136.6 141.6 150.9 151.2 152.6 156.4 151.0 151.9 151.7 150.9 155.2 154.2 152.2 153.6 153.1 159.4 SUBJECT 12 TIME (min) R 0:15 0:30 0:45 1:00 1:15 1:30 1:45 2:00 2:15 2:30 2:45 3:00 3:15 .3:30 3:45 4:00 4:15 4:30 4:45 5:00 pH 7.440 7.424 7.436 7.406 7.394 7.375 7.365 7.342 7.336 7.336 7.327 7.314 7.307 7.289 7.281 7.272 7.261 7.260 7.241 7.231 7.228 FO02 (torr) 34.4 32.0 36.5 37.4 37.9 35.7 39.3 40.0 38.4 37.7 36.5 37.5 37.7 37.2 37.8 37.0 37.2 36.1 36.1 35.4 35.7 P02 (torr) 113 98 94 75 76 76 76 76 75 74 75 71 71 71 67 69 68 68 70 68 71 Sa02 (%) 98.6 97.9 97.6 95.0 95.0 94.9 94.7 94.2 94.0 93.8 94.0 93.7 92.5 92.0 90.7 91.3 90.6 90.7 90.7 90.0 90.9 V02(l/rtrLn) 1.31 2.08 4.61 3.93 4.13 4.13 4.37 4.38 4.44 4.07 4.38 4.30 4.26 4.44 4.45 4.63 4.22 4.58 4.56 4.62 VE(l/ndn BTR 5) 62.3 70.0 103.8 102.7 109.5 108.7 116.0 125.8 138.9 131.0 133.6 129.7 125.9 129.5 128.9 136.0 129.6 136.2 140.3 145.4 APPENDIX G EQUIPMENT AND SUPPLIES: E q u i p m e n t : 1. C a r d i a c m o n i t o r 2. Beckman M e t a b o l i c Measurement c a r t 3. H e w l e t t - P a c k a r d d a t a a q u i s i t i o n s y s t e m 4. s p i r o m e t e r 5 . C02 s e n s o r 6. 02 s e n s o r 7. b r e a t h i n g bag and c i r c u i t 8. n i t r o g e n gas and two way R u d o l p h v a l v e 9. c a r b o n d i o x i d e gas 10. b l o o d gas a n a l y z e r 11. t r e a d m i l l 12. c l o c k 1 3 . pneumo t a c h 14. e a r o x i m e t e r S u p p l i e s : 1. A r t e r i a l c a n n u l a s 20 2. p l a s t i c s y r i n g e s 100 3. # 22 gauge n e e d l e s 100 4. # 18 gauge n e e d l e s 20 5. 20 cc s y r i n g e s 20 6. 5 cc s y r i n g e s 20 7. #20 b u t t e r f l y i . v 20 8. h e p a r i n l o c k s 20 9. O P - s i t e 20 10. c o m p r e s s i o n t a p e 1 r o l l 11. h e p a r i n 1000 u/ml 10ml 5 b o t t l e s 12. n o r m a l s a l i n e 500 ml 16 bags 13. bandages 14. a l c o h o l swabs 15. 2x2 gauze P e r s o n n e l : Day one: 1- p u l m o n a r y f u n c t i o n t e s t s 2- t r e a d m i l l r u n and Beckman Day two: E x e r c i s e t e s t 1 - t i m e r 1 - l a b o r a t o r y a s s i s t a n t 1 - s a m p l e r Day t h r e e : 1 - r e c o r d e r 1-gas m i x t u r e 61 APPENDIX H EXERCISE VENTILATION STUDY The p u r p o s e of t h i s s t u d y i s t o r e l a t e t h e changes i n a r t e r i a l o xygen c o n c e n t r a t i o n and b r e a t h i n g d u r i n g heavy p h y s i c a l work. The s u b j e c t s a r e r e c r u i t e d on a v o l u n t e e r b a s i s and a r e n o r m a l h e a l t h y males who a r e h i g h l y t r a i n e d . On the f i r s t t e s t i n g s e s s i o n you w i l l have measures o f your l u n g f u n c t i o n s and maximum v o l u n t a r y v e n t i l a t i o n . T h i s e n t a i l s b r e a t h i n g t h r o u g h a m o u t h p i e c e so t h a t your volume o f e x p i r a t i o n and f l o w r a t e can be measured. These p r o c e d u r e s a r e not a s s o c i a t e d w i t h any s i g n i f i c a n t r i s k . F o l l o w i n g t h e s e d e t e r m i n a t i o n s you w i l l be a s k e d t o b r e a t h e t h r o u g h a n o t h e r a p p a r a t u s . D u r i n g t h i s measure t h e c o n c e n t r a t i o n o f oxygen i n t h e i n s p i r e d gas w i l l be g r a d u a l l y be d e c r e a s e d and t h e change i n your b r e a t h i n g i n r e s p o n s e t o t h i s w i l l be measured. T h i s p r o c e d u r e w i l l be done under m e d i c a l s u p e r v i s i o n and your h e a r t w i l l be m o n i t o r e d t h r o u g h o u t . E x t r e m e l y r a r e l y i r r e g u l a r i t i e s i n h e a r t r h ythm have been r e p o r t e d w i t h t h i s p r o c e d u r e . O t h e r c o m p l i c a t i o n s have not been r e p o r t e d . On t h e n e x t t e s t i n g s e s s i o n , you w i l l have your maximal oxygen u p t a k e a c c o r d i n g t o e s t a b l i s h e d s t u d y p r o t o c o l on a t r e a d m i l l . The work l o a d on t h e t r e a d m i l l w i l l be i n c r e a s e d , i n s t a g e s u n t i l you a r e u n a b l e t o c o n t i n u e , w h i l e t h e gas c o n c e n t r a t i o n s a r e d e t e r m i n e d i n your e x p i r e d gas as you b r e a t h e t h r o u g h a m o u t h p i e c e . The r i s k s of t h i s p r o c e d u r e a r e m i n i m a l ; some minor d i s c o m f o r t i n t h e jaw m u s c l e s and some i n c r e a s e d a w a r e n e s s o f yo u r b r e a t h i n g may be n o t i c e d . Once y o u r m a x i m a l oxygen u p t a k e i s d e t e r m i n e d , y o u w i l l be b r o u g h t back on a n o t h e r day and w i l l p e r f o r m a f i v e m i n u t e r u n a t 100% of your V02 max. D u r i n g t h i s r u n you w i l l a g a i n b r e a t h e t h r o u g h t h e mouth p i e c e so t h a t your r a t e of v e n t i l a t i o n can be measured. A l s o a t t h i s t i m e you w i l l have an i n d w e l l i n g c a n u l a i n you r r a d i a l a r t e r y . T h i s p r o c e d u r e i n v o l v e s some minor d i s c o m f o r t s i m i l a r t o t h a t of h a v i n g a c o n v e n t i o n a l b l o o d sample t a k e n . The r i s k s of t h i s p r o c e d u r e w i l l be m i n i m i z e d by u s i n g t r a i n e d p h y s i c i a n w i t h s p e c i a l e x p e r t i s e i n t h i s p r o c e d u r e . These r i s k s i n c l u d e a s m a l l chance o f i n f e c t i o n or i n c r e a s e d b l e e d i n g a t t h e s i t e o f t h e p u n c t u r e . In e x t r e m e l y r a r e i n s t a n c e s an a n e u r i s m o r d i l a t i o n a t t h e s i t e of t h e c a t h e t e r i n s e r t i o n c o u l d o c c u r . Spasm of t h e a r t e r y c a u s i n g i m p a i r e d b l o o d s u p p l y t o t h e hand c o u l d a l s o o c c u r r a r e l y and you. w i l l be c h e c k e d t o i n s u r e a d e q u a t e a l t e r n a t e b l o o d s u p p l y p r i o r t o i n s e r t i o n of t h e c a n n u l a . The b e n e f i t s of the s t u d y i n c l u d e t h e o p p o r t u n i t y t o p a r t i c i p a t e i n p h y s i o l o g i c r e s e a r c h , and the o p p o r t u n i t y t o have a V02 max d e t e r m i n a t i o n . I F YOU HAVE ANY QUESTIONS ABOUT THE STUDY PROCEDURES WE WILL BE HAPPY TO ANSWER THEM NOW OR AT ANY TIME. I have r e a d and u n d e r s t a n d t h e above and a g r e e t o p a r t i c i p a t e i n t h e s t u d y . I u n d e r s t a n d t h a t I have t h e r i g h t t o w i t h d r a w a t any t i m e , w i t h o u t q u e s t i o n . DATE : " SIGNATURE: WITNESS: 62

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