264 INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



sible that in some localized and perhaps critical areas there is a deficient 

 oxygen supply. This could come about, for example, if blood flow became 

 too slow or stopped completely in local areas. 



CO2 TRANSPORT AND ACID BASE BALANCE 



There are two principle effects of temperature on the carbonic acid- 

 bicarbonate buffer system. A drop in temperature produces 1 ) an increase 

 in the solubility of COo and 2) a decrease in the apparent dissociation 

 constant K'. If a sample of blood is collected and cooled under anaerobic 

 conditions, it will become more alkaline, because the total concentration of 

 CO2 in its various forms cannot change and a greater proportion will 

 exist in the undissociated form. 



If, on the other hand, blood is kept in equilibrium with a constant 

 Pcoo, then the lower the temperature the higher will be the concentrations 

 of both carbonic acid and bicarbonate in the blood. These changes occur 

 in such a relationship to one another that at a constant Pcoo, the pH of 

 true plasma remains almost constant over a wide range of temperatures 

 (15). 



Physiologically, this means that if pulmonary ventilation is so con- 

 trolled as to maintain a constant alveolar Pcoo during cooling, the arterial 

 pH will remain essentially constant unless a metabolic acidosis or al- 

 kalosis occurs. For an excellent discussion of this problem see Brewin 

 et al. (16). 



SUMMARY 



Lowering the body temperature of the anesthetized dog produces a 

 relatively greater reduction in ventilation than in oxygen consumption and 

 CO2 production, with an accompanying hypoxia and respiratory acidosis. 

 At a temperature of about 20°-25°C breathing ceases entirely and as- 

 phyxial death results. If ventilation is continued by artificial means the 

 circulation may continue to be adequate for respiratory gas transjwrt at 

 temperatures down to 15°C or lower, although ventricular fibrillation 

 occurs rather frequently at temperatures below 25°C. Transfer of Oo and 

 COo by diffusion probably remains adequate in both lung and tissues as 

 long as ventilation and circulation are maintained, although there is a 

 possibility that it may fail in localized regions of the body. 



Figui'cs 1 and 2 are based on data obtained in studies supported Ijy funds provided 

 under Contract AF41 (657)-30, with the School of Aviation Medicine, USAF, Randolph 

 Field, Texas. 



REFERENCES 



1. BiGELOW, W. G. ET AL. Oxvgen transport and utilization in dogs at low body 

 temperatures. Am. J. Physiol. 160: 125, 1950. 



