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To plan for any future rescue of personnel in a disabled and pressurized submarine, the US Navy needs a method for predicting risk of decompression sickness under possible scenarios for crew recovery. Such scenarios include direct ascent from compressed air exposures with risks too high for ethical human experiments. Animal data, however, with their extensive range of exposure pressures and incidence of decompression sickness, could improve prediction of high-risk human exposures. Hill equation dose-response models were fit, by using maximum likelihood, to 898 air-saturation, direct-ascent dives from humans, pigs, and rats, both individually and combined. Combining the species allowed estimation of one, more precise Hill equation exponent (steepness parameter), thus increasing the precision associated with human risk predictions. These predictions agreed more closely with the observed data at 2 ATA, compared with a current, more general, US Navy model, although the confidence limits of both models overlapped those of the data. However, the greatest benefit of adding animal data was observed after removal of the highest risk human exposures, requiring the models to extrapolate.

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No abstract

This project developed and evaluated a new mathematical decompression model with asymmetrical gas kinetics. The intended application was to support U.S. Navy diving operations involving surface decompression with oxygen (02) following air diving (Sur-D 02). Before this effort, the most sophisticated model for predicting human risk of decompression sickness (DCS) following exposure to elevated 02 mixtures was one developed in 1998 and based on only a small amount of Sur-D 02 data. The present effort added more than 4,000 dives, particularly dives with high 02 and/or Sur-D 02, to the data for calibration of the new model. About half of the added dives were experimental exposures involving rats, in the hope that higher-risk animal dives would improve prediction accuracy for higher-risk human dives. It was also thought that sharing parameters between the species, particularly those parameters defining the effect of 02 on decompression risk, might enhance model performance. However, we were unable to demonstrate an advantage of the rat-human model over the human-only or the 1998 models. We used all three models to evaluate three possible alternative Sur-D 02 procedures, each alternative having more flexibility than those currently in use but varying in amounts of DCS risk. The Navy can now evaluate changes in Sur-D 02 procedures by using all three models. When new procedures are considered for Fleet use, this approach may enhance decision making without requiring a manned dive trial. CONTENTS