Effect of humidity on hyperoxic toxicity.

Time to onset of hyperbaric oxygen-induced convulsions was measured in mice and rats exposed to hyperbaric oxygen (515-585 kPa) under conditions of low humidity (dry gas, < 10% relative humidity) or in a humidified environment (60% relative humidity). At all pressures tested, the duration of convulsive activity was markedly increased (P < 0.001), because of the earlier onset of severe generalized convulsions, in the groups of rodents exposed to the higher humidity. Pulmonary oxygen poisoning was determined by increases in lung wet and dry weights. Such pulmonary damage was also significantly (P < 0.001) increased in the humidified groups. Hyperoxic toxicity was also measured in rats and mice exposed to approximately 100% oxygen (normobaric hyperoxia) under conditions of 30 or 62% relative humidity. In contrast to the results obtained with hyperbaric oxygen exposure, there was slightly less toxicity in the rodents maintained at 62% compared with 30% humidity in normobaric hyperoxia.