Tolerance of cooled animals to acute hypoxia during rewarming

Abstract

Rats cooled to a rectal temperature of 20°C were permitted to rewarm at a simulated altitude of 11,500 m. A greater survival rate was observed in animals so treated than in controls not previously exposed to hypothermia. The loss of hypoxic tolerance was more pronounced within the range of 28°–36°C than in the range of 22°–28°C. The depth of cooling has a notable influence on the tolerance to hypoxia during rewarming when the body temperature of 33°C is reached. Thus far, the most resistant were rats cooled by the closed vessel technique to 18°C and those cooled by immersion to 22°C. The mechanism of this interesting phenomenon is unknown.