Recovery from pulmonary oxygen toxicity: a new (ESOT) model.

Arieli has previously demonstrated that the exposure metric K could be used to predict pulmonary oxygen toxicity (POT) based on changes in Vital Capacity (VC). Our previous findings indicate that the Equivalent Surface Oxygen Time (ESOT) allows the estimation of POT without loss of accuracy compared to K. In this work, we have further investigated POT recovery. The K metric assumes that the recovery of POT is to be controlled by exposure to pO₂. This results in a counterintuitively slow estimated recovery after exposure to low pO₂. Similarly, K overestimates POT during intermittent hyperoxic exposures. We used results from previous studies to train the parameters of a new ESOT recovery model. The predicted recovery of ESOT (ESOT_rec) after initial hyperoxic exposure (ESOT_I) of duration t_exp (h) and recovery time t (h) can be calculated as ESOT_rec=ESOT_I · e^-f with f=0.439 · t · 0.906^t_exp. For intermittent exposures, the function ESOT(n)=(n · a · ln(b · n+1)+c) · t_exp · pO₂^2.285 will approximate POT (ESOT(n)) after n sessions of pO₂ (atm) for time t_exp (min) in each cycle. Parameters a, b, and c are specific for each cycling pattern. These ESOT functions will better predict the development of POT during intermittent hyperoxic exposures as well as recovery after a broader range of continuous hyperoxic exposures than K. We recommend limiting hyperoxic exposures in surface-oriented diving to ESOT=660, 500, and 450 for a maximum of one, five, and seven consecutive days, respectively. A minimum of 48 hours of recovery should follow. These limits can probably be relaxed for intermittent exposures.