Effects of hyperoxic gas mixtures on exercise tolerance in man.

This study was undertaken to determine the effects of O2-enriched gases on performance. Nine trained subjects ran to exhaustion on the treadmill on five different occasions breathing one of a range of hyperoxic gas mixtures--20%, 40%, 60%, 80%, or 100% O2. Each subject worked at a workload determined to be 110% of that necessary to elicit his maximum O2 uptake. The exercise bouts were scheduled one week apart to minimize the effects of training and fatigue. The subjects were given no cues as to the mixtures being breathed or to their running times. The parameters measured included running time, minute ventilation, and heart rate. The results indicate that the maximum performance time increases significantly as the O2 fraction of the gas is increased. Contrary to other published literature, 100% O2 increases performance significantly over 60% O2. Ventilation at any point in time is decreased when breathing hyperoxic mixtures. This decrease appears to be more a function of breathing frequency than of tidal volume. Terminal heart rates are not significantly different regardless of the O2 fraction of the inspired gas.