136 



PHYSIOLOGY OF INDUCED HYPOTHERMIA 



COOLING PROCEDURE 



REWARMING PROCEDURE 



T-Vz" 



WATER ~ _ 



ZZ BATH — _ 



( + 40°) - 



3'/,' 



Fig. 4. — Illustration of the cooling and rewarming stages and procedures. 



oxygen. Diiiferent heating devices were tested but the use of diathermy shown in 

 the fihn proved to be the most successful (fig. 5). Maximal rate of recovery in rats 

 (80-100 per cent of long-term survivors) was achieved by the use of microwave 

 diathermy whose penetration properties allow localization to a small area (And jus 

 and Lovelock, 1955). For monkeys, however, a more conventional diathermy was 

 used (30 Mc.) because of the need for deeper penetration. Our greatest difficulty 

 with monkeys was the danger of superficial burns. Blocks of ice placed between 

 the diathermy electrodes and the body surface diminished that danger. 



THE PHYSIOLOGY OF INDUCED HYPOTHERMIA 



The physiology of hypothermia varies markedly with the technique, especially 

 if pharmacological agents are used. For example, at a body temperature around 

 30° C, the metabolic rate can range from readings higher than normal BMR to 

 values many times lower, depending solely on the use of anesthetics. 



Also, the physiological features of hypothermia at one level change appreciably 

 with time. For example, at a certain level of hypothermia the metabolic rate can be 

 significantly higher than the BMR during the first hours and significantly lower 

 for many hours afterward. The blood sugar level can change from hyperglycemic to 

 hypoglycemic values. 



The hypothermic states. It is well known that the fall of body tempcratm-e 

 does not influence all physiological ftinctions in the same manner. The general clas- 

 sification of hypothermia stages which we are using is based on experiments with 

 unanesthetized animals (fig. 6). 



