12 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



thermia has been assumed to occur by some investigators, NoelP" reported that the 

 EEG changes; observed were not typical of anoxia but were similar to eserine poison- 

 ing. He suggested that the breakdown of acetylcholine might be delayed at low tem- 

 peratures. It should be noted that Dill and Forbes^" found no evidence of arterial 

 unsaturation since the oxygen dissociation curve shifted sufficiently to the left to 

 maintain a normal arterial saturation. 



This shift in the oxygen dissociation curve to the left with lowered blood tem- 

 peratures is not as disastrous an event as many investigators have believed. Con- 

 comitant with this tendency, accumulation of CO2 has been demonstrated to result 

 in a respiratory acidosis. This state of acidosis results in a shift of the oxygen dis- 

 sociation curve to the right. In consequence of these opposing shifts of the oxygen 

 dissociation curve, the resultant curve may be relatively normal in shape. Over- 

 ventilation, as practiced by some investigators, lowers the blood CO2 levels, leaving 

 the temperature effect on the oxygen dissociation curve in command, so that some 

 interference with oxygen exchange may result. 



The ventilation equivalent was reported by Dill and Forbes^^ to be increased. The 

 respiratory volume of most of their patients was large in comparison with the 

 volume of oxygen removed. Normal persons at rest remove from 3 to 5 per cent 

 of oxygen from inspired air and this proportion is not altered greatly during mod- 

 erate activity. This observation has not been confirmed in the hypothermic dog- but 

 the discrepancy may lie in the marked shivering and high oxygen consumption in the 

 patients of Dill and Forbes (fig. 3). It should be emphasized that the respiratory 

 center responds normally to CO2 at low body temperatures."^ 



Finney et alr^ found a marked fall in the R.Q. with reduction in the body tem- 

 perature. The R.Q. was observed to fall as low as 0.32 provided that shivering had 

 been suppressed. Even during shivering the R.Q. could fall below 0.70. Similar 

 results have been found by the present authors and Gray ct ol. (communicated 

 today) observed a low R.Q. in isolated cooled livers. 



The reduction in oxygen consumption of the total organism with lowered body 

 temperatures is apparently shared by all organs. This has l)een observed for the 

 brain, kidney and liver. -°' '^° Whether any of these or other tissues have a dispropor- 

 tionately greater or smaller change in oxygen utilization cannot be evaluated on the 

 basis of presently available data. 



The patterns of heat exchange have not been completely analyzed during the 

 development or maintenance of the hypothermic state. Heat losses are enormous 

 at the beginning of cooling despite the increase in metabolism.^' -> ^^ Analyses of 

 the pattern of heat losses during a steady state of lowered body temperature are 

 in progress but definitive conclusions are not as yet available (figs. 4, 5, and 6). 



Lyman and Chatfield^^ have reviewed the changes which occur in protein and fat 

 metabolism during hibernation but these variables have not been followed in the 

 hypothermic non-hibernator. Finney, Dworkin and Cassidy-^ found that hypothermia 

 resulted in a diminished respiratory quotient in non-shivering dogs and an increased 

 quotient when the animals were shivering". They thought that this represented a 

 change in the character of the animal's metabolism. However, in the light of present 

 knowledge of carbon dioxide retention and elimination in hypothermia and shiver- 

 ing, this conclusion is not completely justified. 



