Oxygen pulse in guinea pigs in hyperbaric helium and hydrogen

Kayar, Susan R., and Erich C. Parker. Oxygen pulse inguinea pigs in hyperbaric helium and hydrogen. J. Appl. Physiol. 82(3): 988-997, 1997.We analyzedO₂ pulse, the total volume of O₂ consumed per heart beat, inguinea pigs at pressures from 10 to 60 atmospheres. Animals were placedin a hyperbaric chamber and breathed 2%O₂ in either helium (heliox) orhydrogen (hydrox). Oxygen consumption rate(O₂) was measured by gaschromatographic analysis. Core temperature and heart rate were measuredby using surgically implanted radiotelemeters. TheO₂ was modulated over afourfold range by varying chamber temperature from 25 to 36°C. There was a direct correlation betweenO₂ and heartrate, which was significantly different for animals in heliox vs.hydrox (P = 0.003). By usingmultivariate regression analysis, we identified variables that weresignificant to O₂ pulse: bodysurface area, chamber temperature, core temperature, and pressure.After normalizing for all nonpressure variables, the residualO₂ pulse was found to decreasesignificantly (P = 0.02) with pressurefor animals in heliox but did not decrease significantly(P = 0.38) with pressure for animalsin hydrox over the range of pressures studied. This amounted to aroughly 25% lower O₂ pulse fornormothermic animals in 60 atmospheres heliox vs. hydrox. These resultssuggest that reduction of cardiovascular efficiency in a hyperbaricenvironment can be mitigated by the choice of breathing gas.