1304

Specialia

Effects of skin-cooling on hemodynamic, ventilatory, and arterial blood gas variables in cattle Variables

Ts(~ Tr(~ HR (min-1) Q (nfl/inin/kg) SV (ml/kg) Pp~ (ram Hg) TPVR (ram Hg/ml/min/kg) Pao(mlnHg) TSVR (ram Hg[ml/min/kg) f (min) VE (ml/min/kg, BTPS) VT(ml/kg, BTPS) PaO~ (mmHg) PaCO~ (nun Hg) pHa

Skin-cooling Before

After

38.6 • 39.8 =k0.0 96 i 3 133 =k 7 1.39 :t- 0.06 30 -l- 2 0.24 :~ 0.02 104 4- 3 0.80 -~ 0.06 85 • 7 400 ~ 30 5.0 4- 0.3 68 ~- i 36 :t: 1 7.46 :t- 0.01

32.9 :t: 0.5 b 39.7 q- 0.1 92 ~- 2b 129 =[: 4 b 1.34 2~ 0.05 32 + 2 0.26 i 0.02 b 112 :t: 4 b 0.92 + 0.05 b 40 =c 4 b 220 4- 10 b 6.5 • 0.8 66 i 1 37 • 1 7.46 -4- 0.01

Ts, skin temperature; Tr, rectal temperature; TPVR, total pulmonary vascular resistance; TSVR, total systemic vascular resistance. ~Mean values ~ SEM are shown for 12 animals (except n = 10 for Pao and TSVR). bBefore and after values differ significantly, p < 0.05 (determined by a paired t-test).

EXPERIENTIA 31]11

m o d e r a t e l a b o r a t o r y t e m p e r a t u r e s a r t e r i a l blood g a s e s reflect a l v e o l a r v e n t i l a t i o n a s d e t e r m i n e d b y n o n - t h e r m o r e g u l a t o r y m e c h a n i s m s . I f v a r i a t i o n s in e n v i r o n m e n t a l t e m p e r a t u r e f r o m 15 t o 25~ a f f e c t e d a l v e o l a r v e n t i l a tion, t h e n m u c h b l o o d g a s d a t a collected f r o m n o r m o x i c a n d h y p o x i c c a t t l e m i g h t be s u b j e c t to r e i n t e r p r e t a tion4,6-% T h e t h e r m o r e g u l a t o r y - i n d u c e d d i s a s s o c i a t i o n between minute and alveolar ventilation might account for t h e l a c k of c o r r e l a t i o n b e t w e e n c h a n g e s in m i n u t e v e n t i l a t i o n a n d a r t e r i a l b l o o d g a s e s o b s e r v e d in c a t t l e exp o s e d t o s i m u l a t e d h i g h a l t i t u d e ~ a n d t o c a r o t i d b o d y excision 1~ I t is o b v i o u s t h a t a t t e n t i o n m u s t be p a i d t o a m b i e n t t e m p e r a t u r e w h e n m i n u t e v e n t i l a t i o n is u s e d as a v a r i a b l e in s t u d i e s of v e n t i l a t o r y c o n t r o l in c a t t l e . M i n u t e v e n t i l a t i o n w o u l d p r o b a b l y be m o r e closely r e l a t e d t o a l v e o l a r v e n t i l a t i o n if c a t t l e w e r e s t u d i e d a t a n a m b i e n t t e m p e r a t u r e s o m e w h a t lower t h a n 25 ~

Summary. Cooling t h e s k i n of c a t t l e a t a n a m b i e n t t e m p e r a t u r e of 25~ d e c r e a s e d c a r d i a c o u t p u t a n d increased s y s t e m i c and p u l m o n a r y vascular resistances. Minu t e v e n t i l a t i o n w a s r e d u c e d b y a b o u t 5 0 % . T h e r e w a s no c h a n g e in a l v e o l a r v e n t i l a t i o n as m e a s u r e d b y a r t e r i a l blood gases. T h e s e r e s u l t s i n d i c a t e t h a t t h e r m o r e g u l a t o r y v e n t i l a t i o n h a s s i g n i f i c a n t c a r d i o p u l m o n a r y e f f e c t s in cattle at normal laboratory temperatures.

I. F. MCMURTRY 11, J. T. REEVES, D. H. WILL a n d R. F. GROVER

Results and Discussion. T h e c a r d i o p u l m o n a r Y effects of s k i n - c o o l i n g are s h o w n in t h e Table. I n t h e cooled area, s k i n t e m p e r a t u r e w a s lowered b y n e a r l y 6 ~ T h e d e c r e a s e in s k i n t e m p e r a t u r e p r o b a b l y e v o k e d a p e r i p h e r a l v a s o constriction t h a t elevated systemic arterial pressure d e s p i t e a r e d u c t i o n in c a r d i a c o u t p u t . T h e e l e v a t e d s y s t e m i c p r e s s u r e m i g h t h a v e c a u s e d t h e fall in h e a r t r a t e v i a i n c r e a s e d b a r o r e c e p t o r a c t i v i t y . T h e i n c r e a s e in t o t a l p u l m o n a r y r e s i s t a n c e c o u l d h a v e b e e n r e l a t e d to p u l m o n a r y v a s o c o n s t r i c t i o n or t o a n i n c r e a s e d left a t r i a l p r e s sure. If t h i s p u l m o n a r y e f f e c t of s k i n - c o o l i n g is e x a g g e r a t e d in a cold e n v i r o n m e n t , it m i g h t a c c o u n t for t h e h i g h e r i n c i d e n c e of h y p o x i c p u l m o n a r y h y p e r t e n s i o n a n d b r i s k e t d i s e a s e in c a t t l e d u r i n g cold w e a t h e r a t h i g h a l t i t u d e s 1. A f t e r t h e s k i n w a s cooled, r e s p i r a t o r y r a t e a n d m i n u t e v o l u m e were r e d u c e d b y a b o u t 5 0 % . A r t e r i a l blood g a s e s were not altered. These results suggest t h a t a l t h o u g h c a t t l e h y p e r v e n t i l a t e a t a n a m b i e n t t e m p e r a t u r e of 25 ~ the increased ventilation represents p a n t i n g and alveolar g a s e x c h a n g e is n o t a f f e c t e d . E n v i r o n m e n t a l t e m p e r a t u r e m u s t a p p a r e n t l y a p p r o a c h 40 ~ before t h e r m o r e g u l a t o r y ventilation influences alveolar ventilation and arterial b l o o d g a s e s ~. T h u s , it c a n be i n f e r r e d t h a t in c a t t l e a t

Cardiovascular Puhnonary Research Laboratory, University of Colorado Medical Center, 4200 East Ninth Avenue, Denver (Colorado 80220, USA), and Department o/ Physiology and Biophysics, Colorado State University Fort Collins (Colorado 80521, USA), 15 April 1975.

6 R. F. GROVER,J. T. REEVES, D. H. WILL and S. G. BLONT, JR. J. appl. Physiol. 18, 567 (1963). 7 D. H. WILL, C. S. CARD, G. D. VANDLANDINGHAMand A. F. ALEXANDER, Physiologist IO, 347 (1967). 8 D. H. WILL, J. L. HICKS, C. S. CARD, J. T. REEVES and A. F. ALEXANDER,J. appl. Physiol. 38, 495 (1975). 9 D. H. WILL, J. L. HICKS, C. S. CARD and A. F. ALEXANDER,J. appl. Physiol. 38, 491 (1975). 10 G. E. BISGARDand J. H. K, VOaEL,J. appl. Physiol. 31,431 (1971). 11 Acknowledgments. We thank LINDA PANEPINTO, BEA KAPLAN and I~ARY MUNROEfor technical assistance and DIANN SMITH for typing the manuscript. This work was supported by NIH grant No. HL 14985 and by a grant to Dr. WILL from the Colorado Heart Association.

S e a s o n a l V a r i a t i o n s of C a r d i a c O u t p u t in R a t s D a t a o n t h e c a r d i a c o u t p u t of r a t s g i v e n in t h e l i t e r a t u r e r a n g e b e t w e e n 142 m l / k g / m i n 1 a n d 457 m l / k g / m i n ~. T h i s great variability was a t t r i b u t e d to different techniques, or t o d i f f e r e n c e s ill t h e age, s t r a i n a n d s e x of t h e a n i m a l s a. I n o u r l a b o r a t o r y d e t e r m i n a t i o n of c a r d i a c o u t p u t were p e r f o r m e d in r a t s of t h e s o m e s t r a i n a n d s e x a n d n e a r l y t h e s a m e age o v e r 4 y e a r s ; i n s p i t e of t h e c o n s t a n t exp e r i m e n t a l c o n d i t i o n s , v a l u e s v a r i e d g r e a t l y . T r y i n g to f i n d a n e x p l a n a t i o n for t h i s p h e n o m e n o n , we h a v e det e c t e d s e a s o n a l v a r i a t i o n s in t h e c a r d i a c o u t p u t of r a t s .

Materials and methods. W e u s e d m a l e W i s t a r r a t s (conv e n t i o n a l a n i m a l s ; d e a l e r P. B / i u m l e r , W o l f r a t s h a u s e n ) w e i g h i n g 320 to 400 g w h i c h were h o u s e d a t 23 ~ a n d fed with Altromin pellets and t a p water ad libitum. The 1 j. KAPITOLA,F. KOLBEL,M. SCH1JLLEROV~,and O. SCHREIBEROV~, Physiologia bohemos. 22, 137 (1973). Y. C. LIN, C. A. DAWSONand S. M. HORVATH,Comp. Biochem. Physiol. 33, 90t (1970). a M. ViZEK and I. ALBRECHT, Physiologia bohemos. 22, 573 (1973}.

15. 11. 1975

1305

Specialia

a n i m a l s were a n e s t h e t i z e d w i t h 1.2 g/kg u r e t h a n e i.p. T h e r e c t a l t e m p e r a t u r e of t h e a n e s t h e t i z e d a n i m a l s was k e p t a t 36.5 4- 0.5~ w i t h t h e aid of a h e a t e d o p e r a t i o n table, a r e c t a l t h e r m o c o u p l e a n d a n Y S I t e l e t h e r m o m e t e r m o d e l 73 (Yellow Springs I n s t r u m e n t Co., Yellow Springs, Ohio). A r t e r i a l b l o o d p r e s s u r e was r e c o r d e d f r o m t h e left carotid artery with a Statham pressure transducer on a ' H e l c o s c r i p t o r ' (Hellige, F r e i b u r g ) a n d h e a r t r a t e t a k e n f r o m t h e p u l s a t o r y c h a n g e s of b l o o d pressure. W e d e t e r mined cardiac output by the thermo-dilution method and c a l c u l a t e d p e r i p h e r a l r e s i s t a n c e as d e s c r i b e d p r e v i o u s l y 4. B e g i n n i n g in N o v e m b e r 1971, h o w e v e r , a n e l e c t r o n i c c a l c u l a t o r ~ (Herzzeitvolumen-Messger~Lt H Z V B N 6560, A u g u s t F i s c h e r KG., G 6 t t i n g e n ) was used. T h e c o m p a r i son of t h e 2 m e t h o d s for d e t e r m i n a t i o n of c a r d i a c o u t p u t r e v e a l e d n o differences in t h e results. A f t e r t h e p r e p a r a t i o n of t h e a n i m a l s a n d t h e c a l i b r a t i o n of t h e a p p a r a t u s , a n a d a p t a t i o n t i m e of a b o u t 30 rain was n e c e s s a r y to r e a c h a s t e a d y state. T h e r e a f t e r all p a r a m e t e r s were m e a s u r e d 3 t i m e s a t i n t e r v a l s of 5 to 10 min. T h e v a l u e s g i v e n in t h i s p a p e r are m e a n s b a s e d on t h e l a s t of t h e s e 3 d e t e r m i n a t i o n s . P h a r m a c o l o g i c a l t r e a t m e n t s were p e r f o r m e d o n l y a f t e r d e t e r m i n a t i o n of t h e basic values. Res*dts and discussio,z. All values of c a r d i a c o u t p u t m e a s u r e d d u r i n g t h e s a m e m o n t h were c o m p i l e d a n d t h e m e a n s of t h e s e values are g i v e n in F i g u r e 1. E v i d e n t l y , t h e r e are large differences in t h e s e v a l u e s of cardiac o u t p u t . T h e e x t r e m e s were 245 m l / k g / m i n m e a s u r e d in J u n e 1970 or 244 m l / k g / m i n in M a r c h 1972, o n t h e one h a n d , a n d 415 m l / k g / m i n in N o v e m b e r 1970, o n t h e o t h e r h a n d . T h u s , c a r d i a c o u t p u t of r a t s differed b y a b o u t 70%. C o n s i d e r i n g t h e t r a c e of t h e cardiac o u t p u t , seasonal v a r i a t i o n s are e v i d e n t . T h e low v a l u e s were f o u n d in spring a n d s u m m e r , t h e h i g h ones in a u t u m n a n d winter. A f u r t h e r d e t e r m i n a t i o n of c a r d i a c o u t p u t (not s h o w n in F i g u r e 1) was p e r f o r m e d in O c t o b e r 1973. Again a h i g h v a l u e was f o u n d (373 m l / k g / m i n ) w h i c h is c o m p a r a b l e w i t h t h a t m e a s u r e d in O c t o b e r 1970. F r o m M a y 1970 to April 11971, c a r d i o v a s c u l a r experim e n t s were p e r f o r m e d m o s t f r e q u e n t l y . Values of c a r d i a c o u t p u t , h e a r t rate, s t r o k e v o l u m e , blood pressure, a n d p e r i p h e r a l resistance, r e g i s t e r e d in t h i s period, are compiled in F i g u r e 2. As c a n be seen, c h a n g e s of c a r d i a c o u t p u t were a c c o m p a n i e d b y c o i n c i d e n t c h a n g e s of h e a r t r a t e a n d s t r o k e volume. H o w e v e r , t h e s t r o k e v o l u m e was m u c h m o r e i m p l i c a t e d in t h e seasonal c h a n g e s of cardiac

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4 0 . STRUBELT, (~. BACK, l~. UIIL and G. ZETLER, N a u u y n - S c h n l i e d e b e r g ' s Arch. l~harmak. 271, 346 (1971). 5 H. SLAMA a n d J. PIIPER, Z. l