Extension of Oxygen Tolerance in Man. Predictive Studies 6.

In order to determine rates of recovery from different degrees of oxygen poisoning, oxygen exposure periods of 20, 60, or 120 min were systematically alternated with a constant normoxic interval whose duration was also varied systematically in different exposures. Durations of normoxic intervals were selected to provide the same hyperoxic: normoxic ratios for each of the three oxygen exposure periods. This was done to determine whether the toxic events accumulated over a relatively long oxygen exposure (120 min) reversed on return to normoxia at the same rate as those that accumulated during shorter oxygen exposures (60 or 20 min). Intact animal responses to the selected patterns of intermittent exposure were determined at oxygen pressures of 1.5, 2. 0, and 4.0 ATA. This range of oxygen pressures allowed comparison of results obtained at 1.5 and 2.0 ATA, where effects of pulmonary oxygen toxicity were not influenced by concurrent convulsions, with comparable data obtained at 4.0 ATA, where there were prominent interactions between pulmonary and central nervous system effects of oxygen toxicity.