Increasing activity of H2-metabolizing microbes lowers decompression sickness risk in pigs during H2dives

The risk of decompression sickness (DCS) was modulated by varying the biochemical activity used to eliminate some of the hydrogen (H2) stored in the tissues of pigs (19.4 ± 0.2 kg) during hyperbaric exposures to H2. Treated pigs ( n = 16) received intestinal injections of Methanobrevibacter smithii, a microbe that metabolizes H2to water and CH4. Surgical controls ( n = 10) received intestinal injections of saline, and an additional control group ( n = 10) was untreated. Pigs were placed in a chamber and compressed to 24 atm abs (20.6–22.9 atm H2). After 3 h, the pigs were decompressed and observed for symptoms of DCS for 1 h. Pigs with M. smithii had a significantly lower ( P < 0.05) incidence of DCS (44%; 7/16) than all controls (80%; 16/20). The DCS risk decreased with increasing activity of microbes injected (logistic regression, P < 0.05). Thus the supplemental tissue washout of the diluent gas by microbial metabolism was inversely correlated with DCS risk in a dose-dependent manner in this pig model.