Decompression sickness risk reduced by native intestinal flora in pigs after H2 dives

Decompression sickness (DCS) risk following a simulated dive in H2 was lower in pigs with a native intestinal flora that metabolized H2. Pigs (n = 27; 19.4 +/- 0.2 kg body mass) were placed in a chamber that was pressurized to 22.2-25.5 atm (absolute; 2.2-2.6 MPa) with 84-93% H2 for 3 h. Chamber concentrations of O2, H2, He, N2, and CH4 were monitored by gas chromatography. Release of CH4 from the pigs indicated that intestinal microbes had metabolized H2 After decompressing to 11 atm, the pigs were observed for DCS. Animals with DCS released significantly less (P < 0.05) methane (0.53 +/- 0.37 ppm CH4; n = 5) than those without DCS (1.40 +/- 0.17 ppm CH4; n = 22). The DCS risk reduction was attributed to the loss of roughly 12% of the total volume of H2 that could be stored in the tissues of the pigs. Thus, H2 metabolism by the native intestinal flora of pigs may protect against DCS following a simulated H2 dive.