Risk of mortality in interrupted exposure to 100 percent O-2: role of air vs. lowered Po2

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Abstract
Four hours per day in air was the shortest interruption of an exposure to 100% O2 at 1 atm (OAP) which produced in mice a significant prolongation of survival time. Risk of mortality was reduced to 1/4 that of continuous exposure and time to death of half the animals was increased from 5 days at 15. An almost identical effect on mortality was observed when the 4-hr. daily period out of OAP was in 100% O2 at a pressure of 200[plus or minus] 5 mm Hg. These results indicate that the presence or absence of N2 in the interrupting atmosphere plays little role in the prolongation of survival time and cast doubt on obstructive atelectasis as a mechanism in O2 toxicity. Water intake was found to be a useful and simple technique for following the course of toxicity. Statistics utilizing the risk of mortality concept proved to be convenient for analyzing truncated time-mortality data.