Increasing activity of H-2-metabolizing microbes lowers decompression sickness risk in pigs during H-2 dives

The risk of decompression sickness (DCS) was modulated by varying the bioch emical activity used to eliminate some of the hydrogen (H-2) stored in the tissues of pigs (19.4 +/- 0.2 kg) during hyperbaric exposures to H-2. Treat ed pigs (n = 16) received intestinal injections of Methanobrevibacter smith ii, a microbe that metabolizes H-2 to water and CH4. Surgical controls (n = 10) received intestinal injections of saline, and an additional control gr oup (n = 10) was untreated. Pigs were placed in a chamber and compressed to 24 atm abs (20.6-22.9 atm H-2). After 3 h, the pigs were decompressed and observed for symptoms of DCS for 1 h. Pigs with M. smithii had a significan tly lower (P < 0.05) incidence of DCS (44%; 7/16) than all controls (80%; 1 6/20). The DCS risk decreased with increasing activity of microbes injected (logistic regression, P < 0.05). Thus the supplemental tissue washout of t he diluent gas by microbial metabolism was inversely correlated with DCS ri sk in a dose-dependent manner in this pig model.