title: Effects of varying concentrations of N2/O2 and He/O2 on exercise tolerance in man.
abstract: Hyperoxic gas mixtures improve exercise tolerance in humans. It is not clear whether this improvement is due to 1) a decreased anaerobiosis in the working cell, 2) a decreased cost of breathing resulting from the relative hypoventilation in hyperoxia, 3) the reduction of a possible metabolic depressant-N2, or a combination of these. This study made use of He/O2 breathing mixtures to gather data relative to #2 and #3, primarily. Ten subjects ran to exhaustion on a treadmill breathing one of four mixtures-20 O2/80 N2, 20 O2/80 He, 80 O2/20 N2, 80 O2/20 He. Running time to exhaustion, minute ventilation, respiratory frequency, tidal volume, and heart rate were measured. Performance increased significantly on hyperoxic mixtures (P < .001) and He/O2 mixtures (P < .001). Although the peak ventilatory volumes were higher on He/O2 mixtures, the ventilatory mass moved was significantly less (P < .001) on those mixtures conceivably resulting in a decreased cost of breathing. These data did not reject any of the hypotheses but offered the greatest support for hypothesis #2.
mesh_terms: D000328:Adult; D006371:Helium / Q000494:pharmacology*; D006801:Humans; D008297:Male; D009584:Nitrogen / Q000494:pharmacology*; D010100:Oxygen / Q000494:pharmacology*; D010101:Oxygen Consumption; D010807:Physical Endurance / Q000187:drug effects*; D012119:Respiration / Q000187:drug effects
chemical_list: D006371:Helium; D009584:Nitrogen; D010100:Oxygen