DOES THE TIME-COURSE OF BUBBLE EVOLUTION EXPLAIN DECOMPRESSION-SICKNESS RISK

A probabilistic model of decompression sickness (DCS) risk based on li near-exponential (LE) kinetics has given the best fit of the human air and nitrox DCS database. To test the hypothesis that its success may be due to the formation of a gas phase during decompression, we develo ped a physiologically based bubble evolution model using a numerical s olution of a partial differential equation system. Because of the comp utational intensity of this method, it could not be used to fully expl ore our hypothesis. Consequently, we compared the solution with that o f a computationally simpler approximation that was previously publishe d by Van Liew and found the two approaches gave similar results. Using the simpler model, assuming bubble densities of 1 and 1,000 bubbles/c m(3), we found a tissue time constant of at least 80 min (equivalent t o perfusion of 1/80 ml . g(-1) . min(-1)) was required to achieve a de lay in bubble dissolution comparable to the prolonged risk of DCS pred icted by the LE model. We suggest that the persistence of single bubbl es in a uniformly perfused homogeneous tissue alone is unlikely to exp lain persistent DCS risk.