Survival of rats and mice without oxygen in deep hypothermia

¹ Department of Physiology, University of Rochester, Rochester, New York

Adult rats and mice that were cooled quickly below 11°C core temperature usually ceased to breathe. Suspension of breathing and heartbeats was tolerated at 2°C for 1 hour, whether artificial breathing was given or not and whether air or nitrogen filled the lungs. At heart temperatures of 10°C, where heart beat was maintained, rats survived artificial ventilation with nitrogen for 0.4 hour; ventilation with air for 2 hours. Anaerobic survival at 10°C was not demonstrably shortened by inhibitors of glycolysis (fluoride, iodoacetate). Reanimation of 90% of rats and mice under optimal conditions was accomplished by artificial warming, accompanied by artificial ventilation with air under intermittent positive pressure. Each process that becomes suspended at its biological zero apparently has a limited time within which rewarming may restore it. The limitation of times less than 1.5 hours was imposed mostly by anoxia. Properties of animals that were injured by anoxia or by hypothermia seemed to vary, since animals might die even after breathing was restored.

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