Influence of hyperoxia on pulmonary O2 uptake kinetics following the onset of exercise in humans

The purpose of this study was to examine the influence of hyperoxic gas (50% O2 in N2) inspiration on pulmonary oxygen uptake (V˙O2) kinetics during step transitions to moderate, severe and supra-maximal intensity cycle exercise. Seven healthy male subjects completed repeat transitions to moderate (90% of the gas exchange threshold, GET), severe (70% of the difference between the GET and V˙O2 peak) and supra-maximal (105% V˙O2 peak) intensity work rates while breathing either normoxic (N) or hyperoxic (H) gas before and during exercise. Hyperoxia had no significant effect on the Phase II V˙O2 time constant during moderate (N: 28 ± 3 s versus H: 31 ± 7 s), severe (N: 32 ± 9 s versus H: 33 ± 6 s) or supra-maximal (N: 37 ± 9 s versus H: 37 ± 9 s) exercise. Hyperoxia resulted in a 45% reduction in the amplitude of the V˙O2 slow component during severe exercise (N: 0.60 ± 0.21 L min−1 versus H: 0.33 ± 0.17 L min−1; P < 0.05) and a 15% extension of time to exhaustion during supra-maximal exercise (N: 173 ± 28 s versus H: 198 ± 41 s; P < 0.05). These results indicate that the Phase II V˙O2 kinetics are not normally constrained by (diffusional) O2 transport limitations during moderate, severe or supra-maximal intensity exercise in young healthy subjects performing upright cycle exercise.