The effects of breathing a helium-oxygen gas mixture on maximal pulmonary ventilation and maximal oxygen consumption during exercise in acute moderate hypobaric hypoxia

Abstract

To test the hypothesis that maximal exercise pulmonary ventilation ( V˙Emax ) is a limiting factor affecting maximal oxygen uptake ( V˙O2max ) in moderate hypobaric hypoxia (H), we examined the effect of breathing a helium–oxygen gas mixture (He–O2; 20.9% O2), which would reduce air density and would be expected to increase V˙Emax . Fourteen healthy young male subjects performed incremental treadmill running tests to exhaustion in normobaric normoxia (N; sea level) and in H (atmospheric pressure equivalent to 2,500 m above sea level). These exercise tests were carried out under three conditions [H with He–O2, H with normal air and N] in random order. V˙O2max and arterial oxy-hemoglobin saturation (SaO2) were, respectively, 15.2, 7.5 and 4.0% higher (all p < 0.05) with He–O2 than with normal air ( V˙Emax , 171.9 ± 16.1 vs. 150.1 ± 16.9 L/min; V˙O2max , 52.50 ± 9.13 vs. 48.72 ± 5.35 mL/kg/min; arterial oxyhemoglobin saturation (SaO2), 79 ± 3 vs. 76 ± 3%). There was a linear relationship between the increment in V˙Emax and the increment in V˙O2max in H (r = 0.77; p < 0.05). When subjects were divided into two groups based on their V˙O2max , both groups showed increased V˙Emax and SaO2 in H with He–O2, but V˙O2max was increased only in the high V˙O2max group. These findings suggest that in acute moderate hypobaric hypoxia, air-flow resistance can be a limiting factor affecting V˙Emax ; consequently, V˙O2max is limited in part by V˙Emax , especially in subjects with high V˙O2max .