On the likelihood of decompression sickness during H-2 biochemical decompression in pigs

A probabilistic model was used to predict decompression sickness (DCS) outc ome in pigs during exposures to hyperbaric H-2 to quantify the effects of H -2 biochemical decompression, a process in which metabolism Of H-2 by intes tinal microbes facilitates decompression. The data set included 109 exposur es to 22-26 atm, ca. 88% H-2, 9% He, 2% O-2, 1% N-2, for 0.5-24 h. Single e xponential kinetics described the tissue partial pressures (Ptis) of H-2 an d He at time t: Ptis = integral (Pamb - Ptis).tau (-1) dt, where Pamb is am bient pressure and tau is a time constant. The probability of DCS [P(DCS)] was predicted from the risk function: P(DCS) = 1 - e(-r), where r = integra l (Ptis(H2) + Ptis(He) - Thr - Pamb).Pamb(-1) dt, and Thr is a threshold pa rameter. Inclusion of a parameter (A) to estimate the effect of H-2 metabol ism on P(DCS): Ptis., = integral (Pamb - A - Ptis(H2)).tau (-1) dt, signifi cantly improved the prediction of P(DCS). Thus lower P(DCS) was predicted b y microbial H-2 metabolism during H-2 biochemical decompression.