Pulmonary oxygen toxicity in saturation dives with PO2 close to the lower end of the toxic range - A quantitative approach.

Pulmonary oxygen toxicity (POT) has been extensively described at partial pressures of oxygen (PO2) ≥ 1 bar, but much less so at lower PO2. We proposed the POT index [K = t2 × (PO2)4.57] as a means of evaluating the severity of POT, expressed either as reduced lung function or the incidence of POT in a group of divers. In the exponential recovery process (e - [- 0.42 + 0.384 × (PO2)ex] × tr), the time constant increases linearly from 0.0024 to 0.54 h-1 for a PO2 of 1.1 to 2.5 bar. A linear relationship was demonstrated between the incidence of POT and the POT index, given by the equation: POT incidence % = 1.85 + 0.171 × K. In saturation diving, PO2 is kept close to the lower end of the toxic limits for POT, which is approximately 0.5 bar. We suggested that at this low range of PO2, the two processes of cumulative toxicity and recovery operate simultaneously. For one example of saturation diving, we show that a recovery time constant of 0.0135 h-1 yields the measured incidence of POT. We therefore propose the formula K = t2 × PO24.57 × e-0.0135 × t for calculation of the POT index in further analyses of POT in saturation diving.