EFFECTS OF CHANGES IN ARTERIAL pGO, ON CEREBRAL 

 BLOOD FLOW AND METABOLISM DURING HYPOTHERMIA 



JEROME KLEINERMAN 



As Dr. IMcOueen has noted, there is evidence'' - that the cerehral hlood ilow and 

 cerehral oxygen consumption decrease proportionately with temperature at least 

 to the levels studied, i.e., 25° C. The problem that is not yet clear is whether at 

 these hypothermic levels the decreased metabolic activity constitutes or contriluites 

 to hypoxia of the cerebral tissues. 



The reactivity of the cerebral vasculature to alternations in arterial pC( )•_. is well 

 known. It seemed logical, then, to see if this mechanism of reaction is functioning 

 at hypothermic levels. If blood flow would be increased by raising the ApCO^ in 

 hypothermia, then a natural method for increasing flow to the cerebral tissues 

 exists and more oxygen would be presented to the brain and could be extracted if 

 hypoxia really existed. 



The nitrous oxide method of Kety and Schmidt, slightly modified for hypo- 

 thermic animals was used. Dogs were used in the majority of these studies ; how- 

 ever, confirmatory results were obtained in five monkeys. The ApCO^ was varied 

 by inhaling various mixtures of CQo (2% and S^/c). 



In figure 1 the arterial pCO^ is plotted on the abscissa and the cerebral blood 

 flow on the ordinate. It is obvious that even at hypothermic levels the cerebral 

 flow increases with increasing ApC( )2 values. 



8 



7 



60 



Li. 



50 

 CD 



O 40 



0= N CO2 



• = 5% COe 

 X=2% CO2 



30 • 



20 



X. • 



10 ^ 



o 



? 

 



10 20 30 40 50 60 70 80 90 100 

 A pC Oe 



Fig. 1. — Effects of ApCO., on cerebral blood flow in hypothermia. 



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