title: Work performance breathing normoxic nitrogen or helium gas mixtures.
abstract: Twelve subjects completed a progressive treadmill test to maximal aerobic capacity while breathing air or a 79% helium--21% oxygen gas mixture (HeO2). Metabolic and thermoregulatory responses to work while breathing the two mixtures were compared at rest, 30-40%, 60-70%, and 85-90% of maximal performance, and at maximal effort. Ventilation, ventilatory equivalent, and respiratory rates were increased and oxygen uptakes decreased by breathing HeO2 when the level of work exceeded 85-90% of maximum. Heat loss through the respiratory tract was greater breathing HeO2. The reduction in maximal oxygen uptake is probably due to a reduction in the oxygen cost of breathing a less dense gas. It was not related to a lower body temperature and probably not to O2 transport or circulatory limitation. HeO2 breathing had no effect on maximal mechanical work capacity.
mesh_terms: D000328:Adult; D001833:Body Temperature Regulation; D005260:Female; D006371:Helium; D006801:Humans; D008168:Lung / Q000502:physiology; D008297:Male; D008451:Maximal Voluntary Ventilation; D009584:Nitrogen; D010101:Oxygen Consumption; D005082:Physical Exertion; D012119:Respiration; D014797:Vital Capacity
chemical_list: D006371:Helium; D009584:Nitrogen