Model for Predicting Central Nervous System Toxicity from Hyperbaric OxygenExposure in Man: Effects of Immersion, Exercise, and Old and New Data

摘要

We analyzed symptoms of central nervous system (CNS) oxygen toxicity from 1726controlled human hyperbaric O2 exposures at PO2 (Partial pressure of O2) levels ranging from 0.3 to 2.9 atmospheres (atm) using risk models and maximum likelihood analysis, and tested specific hypotheses with likelihood ratios. The data were sorted into dry and immersed, no-exercise, and exercise conditions; new studies were separated from those before 1972. The analysis showed that CNS toxicity, in contrast to pulmonary, increases non-linearly with O2 level (power on O2 > 2) and time: the longer an exposure has been, the riskier additional exposure becomes (power on time > 1.2). Immersion and exercise each significantly increased the risk of toxicity at any PO2 and time combination. Older studies of immersed, exercised subjects predicted significantly more risk than new studies conducted under comparable conditions and could not be combined for parameter estimation. Reasons for this incompatibility are discussed. Parameters obtained from only the new data predict that current U.S. Navy depth/time limits for O2 diving should keep the incidence of O2 toxicity below 1%, provided recommended purging procedures are followed.