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.