SUPERCOOLING AND FREEZING— ANDJUS, LOVELOCK axd SMITH 143 



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DISCUSSION 



Dr. F. John Lcivis: My colleague, Dr. Niazi, has been able to cool several warm 

 blooded animals to the levels reached by Dr. Andjus in rats. We lower the body 

 temperature of mice, dogs, and monkeys to about 0° C. We have cooled rats to as 

 low as minus 4° C. with survival, but unlike Dr. Smith's hamsters which are super- 

 cooled, we have never produced ice in them. The technique is different from that em- 

 ployed by Andjus and Smith but many of the physiological changes are probably 

 the same. It has pleased us to learn that it is easier to cool monkeys to these low 

 temperature levels than it has been to cool either rats or dogs. It is about as easy to 

 cool mice as it is monkeys. 



The technique involves the use of artificial respiration throughout. In the mice, 

 rats, and monkeys 5 per cent carbon dioxide in oxygen is given during cooling until 

 cardiac standstill occurs. Standstill seems to be important in surviving the very 

 lowest levels of hypothermia. In the dogs, it has been necessary to use a different 

 technique in order to get a fairly high percentage of standstill ; for the dogs the 

 carbon dioxide is discontinued and oxygen is given at temperatures below 20° C. 



The movie shows the incubation of the monkey after anesthetic induction with 

 pentothal. We have used larger doses of pentothal than are usually used for lesser 

 degrees of cooling. The electrocardiograph leads are attached and the monkey is 

 cooled in blankets containing coils. 



This shows the function of the artificial respirator. The respiratory rate was 

 about 10 to 12 per minute. As the temperature went down, the cardiac rate slowed. 

 The electrocardiograph shows the changes that Dr. Hegnauer demonstrated so well 

 earlier. 



You can see now that the rate is much slower. An hour and forty minutes after 

 cooling the heart stopped at about 14° C. When the heart doesn't beat for five 

 minutes we discontinue the respiration. In this case the animal's heart was in stand- 

 still with the respiration stopped for 56 minutes. 



In rewarming we use hot water and warm only the chest to begin with. If vou 

 warm the entire body you are apt to get neurological damage. The lowest tempera- 

 ture reached in this animal was 9.5° C. Monkeys have been cooled to 4 or 5° C. We 

 have done only five but four of them survived. After this animal was rewarmed. the 

 heartbeat returned to al)Out 180 per minute, the normal rate. The animal, ten minutes 

 after his temperature had returned to 36° C, still looked a little groggy. 



Dr. John W. Severinghaiis: What was the oxygen tension in the jar when the 

 animals were removed ? 



Dr. R. K. Andjus: The CO.. concentration was 16 per cent, and that of Oo was 

 low, about 3 per cent. 



Dr. IV. Parkins: How long did it take to freeze these animals? Did you keep 

 them frozen for more than an hour? 



