Effect of hyperoxia and hypoxia on oxygen uptake and leg blood flow during human submaximal exercise

We hypothesized that O2 delivery to exercising legs, at the onset of submaximal kicking exercise, would be maintained near control levels during hyperoxia and would be reduced during hypoxia. Alveolar oxygen uptake (VO2alv), leg oxygen uptake (VO2mus) and leg blood flow (LBF) responses were determined in normoxic (FiO2=0.21), hypoxic (FiO2=0.14) and hyperoxk (FiO2=0.70) gas breathing conditions. Eight healthy subjects performed transitions in leg kicking exercise from rest to 50W. LBF was measured continuously with Doppler methods, VO2alv was measured breath-by-breath at the mouth and VO2mus was determined from LBF and radial artery and femoral vein blood samples. VO2alv, VO2mus and LBF were not affected by altered gas breathing at rest or at any of the exercise time points. At rest there were no differences in O2 delivery to the legs in either hyperoxia or hypoxia, compared to normoxia. O2 delivery to the exercising legs was decreased at all exercise time points after 40s of exercise in hypoxia. The finding of similar VO2mus responses at the onset of exercise for all gas conditions demonstrates that physiological adaptations in blood flow and O2 extraction took place during this submaximal exercise to counter significant alterations in arterial O2 content.