PROBABILISTIC MODELS OF THE ROLE OF OXYGEN IN HUMAN DECOMPRESSION-SICKNESS

Probabilistic models of human decompression sickness (DCS) have been s uccessful in describing DCS risk observed across a wide variety of N-2 -O-2 dives but have failed to account for the observed DCS incidence i n dives with high For, during decompression. Our most successful previ ous model, calibrated with 3,322 N-2-O-2 dives, predicts only 40% of t he observed incidence in dives with 100% O-2 breathing during decompre ssion. We added 1,013 O-2 decompression dives to the calibration data. Fitting the prior model to this expanded data set resulted in only a modest improvement in DCS prediction of O-2 data. Therefore, two O-2-s pecific modifications were proposed: Po-2-based alteration of inert ga s kinetics (model 1) and Po-2 contribution to total inert gas (model 2 ). Both modifications statistically significantly improved the fit, an d each predicts 90% of the observed DCS incidence in Oa dives. The suc cess of models 1 and 2 in improving prediction of DCS occurrence sugge sts that elevated Po, levels contribute to DCS risk, although less tha n the equivalent amount of Nz. Both models allow rational optimization of O-2 use in accelerating decompression procedures.