Model for Predicting Central Nervous System Oxygen Toxicity from HyperbaricOxygen Exposures in Humans

摘要

Under certain circumstances, Navy divers breathe 100% O2 when working underwater.Serious symptoms of central nervous system (CNS) O2 toxicity can develop from hyperbaric O2 exposure; immersion and exercise are also known to exacerbate toxicity. We developed risk models for quantitative prediction of the probability of developing symptoms using a large set of human data in which occupational exposure conditions were simulated. Exposures were 5 to 265 min at Po2 levels from 20 to 50 feet of sea water (fsw) (1 fsw = 3.06 kPa). Approximately half of the exposures were to a single Po2, while the remainder were more complicated consisting of exposures to multiple levels of hyperbaric 02. In 688 trials, there were 42 exposure-stopping symptoms. We used maximum likelihood to estimate parameters, likelihood ratios to compare model fits, and x2 tests to judge goodness-of-fit of model predictions to observations. The modeling shows that risk has a steep Po2 dependence. A model with autocatalytic features fits the data as well as a simpler model: when Po2 is elevated beyond 34 fsw, risk accumulates rapidly without bound while accumulating toward an asymptote at lower Po2 levels.