Effects of hyperoxic gas mixtures on energy metabolism during prolonged work

These experiments were designed to study selected respiratory and metabolic responses to exercise in hyperoxia. Four subjects were examined during 30-min bicycle ergometer rides at both 40% and 80% of their aerobic maximum. The VO2 was significantly increased at both work levels breathing 60% O2 versus 21% O2, while VCO2 showed no significant change during the 40% exercise tests but was significantly decreased during the 80% intensity rides. The average increase in the volume of O2 taken up during 30 min of hyperoxic exercise, compared with normoxia, was 3.3 liters at the 40% exercise level and 5.6 liters at the 80% level. Neither the magnitude of the O2 nor the CO2 storage calculated for the exercise bouts could explain these increases. Steady-state criteria for the gas stores were established by the stable values of PETCO2, VO2, VCO2, and VI from minute 6 through 30 at both work levels. R values decreased during the hyperoxic tests suggesting the possibility of a shift toward increased fatty acid metabolism.