Effects of inert gases on tolerance of rats to hypoxia.

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Abstract
Male rats were exposed to 20.9, 8.3, 6.6, and 4.9% O2 in He, N2, A, or SF6 for 4 hr. in a small chamber. Each hypoxic mixture induced an early hyperp-nea followed by normal or subnormal breathing.rate. In 4.9% 62, slow, deep breathing was found earliest and most frequently in rats in SF6 followed by A, N2, and He. A decline in body temperature of 2.1[degree]-8.8[degree]C occurred during exposure to hypoxia; the greatest drop occurring in He. At 8.3 and 20.9% O2 the mean body temperature was highest in A, suggesting that A has a physiological effect. All rats survived 4 hr. in 8.3% O2 irrespective of the inert gas used. More rats survived 4 hr. in He-4.9% O2 than in any of the other gases, and the mean arterial O2 saturation of the rats in He was 17% higher than in N24.9% O2. Only 1 rat in A-4.9% O2 survived 4 hr.; none survived 4 hr. in SF6-4.9% O2.