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

Autor: L.D. Homer, S.S. Survanshi, A. L. Harabin
Rok vydání: 1995
Předmět:
Zdroj: Toxicology and Applied Pharmacology. 132:19-26
ISSN: 0041-008X
Popis: Under certain circumstances, Navy divers breathe 100% O 2 when working underwater. Serious symptoms of central nervous system (CNS) O 2 toxicity can develop from hyperbaric O 2 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 P o 2 levels from 20 to 50 feet of sea water (fsw) (1 fsw = 3.06 kPa). Approximately half of the exposures were to a single P o 2 , while the remainder were more complicated consisting of exposures to multiple levels of hyperbaric O 2 . In 688 trials, there were 42 exposure-stopping symptoms. We used maximum likelihood to estimate parameters, likelihood ratios to compare model fits, and χ 2 tests to judge goodness-of-fit of model predictions to observations. The modeling shows that risk has a steep P o 2 dependence. A model with autocatalytic features fits the data as well as a simpler model: when P o 2 is elevated beyond 34 fsw, risk accumulates rapidly without bound while accumulating toward an asymptote at lower P o 2 levels. This autocatalytic feature of risk accumulation implies a testable hypothesis that substantial protection from human CNS O 2 toxicity can be obtained from intermittent exposure (periodic exposure to lower P o 2 ). The models predict that the probability of O 2 toxicity is less than 7% with current Navy limits while breathing 95% O 2 . Probability of symptoms is 2 is maintained at the United States Navy recommended level of 75%.
Databáze: OpenAIRE
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