A model for predicting central nervous system oxygen toxicity from hyperbaric oxygen exposures in humans

Area of Science:

• Hyperbaric Physiology
• Toxicology
• Risk Modeling

Background:

• Navy divers may breathe 100% oxygen underwater, increasing central nervous system (CNS) oxygen toxicity risk.
• Immersion and exercise are known factors that exacerbate CNS oxygen toxicity.
• Quantitative prediction models are needed to assess toxicity risk under simulated occupational exposure conditions.

Purpose of the Study:

• To develop and validate risk models for predicting the probability of CNS oxygen toxicity symptoms in divers.
• To analyze the relationship between oxygen partial pressure (PO2) and toxicity risk.
• To evaluate the potential protective effect of intermittent oxygen exposure.

Main Methods:

• Simulated occupational exposure data from 688 trials involving divers breathing hyperbaric oxygen.
• Exposure durations ranged from 5 to 265 minutes at PO2 levels of 20 to 50 feet of seawater (fsw).
• Maximum likelihood estimation, likelihood ratio tests, and chi-squared tests were used for model development and validation.

Main Results:

• Risk of CNS oxygen toxicity shows a steep dependence on PO2.
• A model with autocatalytic features indicated risk accumulates rapidly above 34 fsw and asymptotically at lower PO2 levels.
• Current Navy limits (95% O2) predict <7% probability of toxicity; 75% O2 predicts <1% probability.

Conclusions:

• The developed models provide quantitative predictions of CNS oxygen toxicity risk for Navy divers.
• The autocatalytic nature of risk accumulation suggests intermittent oxygen exposure could mitigate toxicity.
• Maintaining inspired oxygen fraction (FIO2) at 75% significantly reduces predicted toxicity risk.