132 



PHYSIOLOGY OF INDUCED HYPOTHERMIA 



Z 



UJ 



U 



a. 



UJ 

 Q. 



Fig. 2. — Lethal oxygen tension in normal and thyroid-fed rats at different ambient tempera- 

 tures. White blocks show metabolic rate (per cent of normal BMR). Black bars show lethal 

 oxygen tension (per cent of the value found in rats at 30° C). A and a are normal rats; B and 

 b are thyroid-fed rats. Values averaged from 5 experiments. 



creased by a reduction of oxygen tension less significant in terms of vital functions. 

 Hypothermia induced under these conditions reaches the protective temperature 

 levels and helps the animal to survive further lowering of oxygen tension. 



The severity of anoxia and the question of the "oxygen debt." It is im- 

 portant to stress the fact that it is the complementary heat production which is 

 decreased Ijy the lowered oxygen tension under the sealed container conditions 

 described above. Hypothermia reaches deep levels long before the production of 

 heat has fallen below the level of the BMR. The oxygen tension which is not suffi- 

 cient to insure the complementary production of heat (i.e., the maintenance of the 

 normal body temperature) is more than sufficient to maintain the vital oxidative 

 processes. The fall of the metal)olic rate below the level of the BMR takes place 

 only when deep hypothermia is present, so that such a great depression of oxygen 

 consumption is not the result of oxygen lack alone but of the lowered tissue temper- 

 ature as well. 



Although the oxygen uptake recorded on recovery can be signilicanlly liigher in 



