MUSCULAR EXERCISE AT GREAT ALTITUDES.

Abstract

Oxygen intake, ventilation and heart rate were measured in six subjects performing ergometer exercise at various altitudes from sea level to 7,440 m (24,400 ft) (Bar. 300 mm Hg) during a Himalayan expedition lasting 8 months. Oxygen intake for a given work rate was constant and independent of altitude, up to the maximum work rate that could be maintained for 5 min. Maximum oxygen intake declined with increase of altitude, reaching 1.46 liters/min at 7,440 m (24,400 ft) in the best subject. Ventilation (STPD) for a given work rate was independent of altitude in light and moderate exercise but increased at each altitude as maximum oxygen intake was approached. Ventilation values of 140–200 liters (BTPS)/min were observed at altitudes above 4,650 m (15,300 ft). Heart rates at altitude were higher at low and moderate work intensities, but the same as or lower than the corresponding sea-level value for the same work load, as maximum oxygen intake was approached. Breathing oxygen at sea-level pressure at 5,800 m (19,000 ft) reduced ventilation and heart rate for a given work rate, restored work capacity almost to sea-level values and increased maximum heart rate. With the aid of data on blood, lung diffusion, and cardiac output from companion studies, the oxygen transport system was analyzed in three subjects, including a high-altitude Sherpa; and evidence is put forward that lung diffusion, cardiac output, and the high oxygen cost of extreme ventilation all contributed to the limitation of exercise at 5,800 m (19,000 ft). respiration, work and altitude; ventilation, work and altitude; heart rate, work and altitude; O2 transport system at high altitudes; altitude acclimatization Submitted on July 29, 1963