Heart Rate During Muscular Work in Man Exposed to Prolonged Hypoxia

Abstract

Heart rate was recorded on four subjects performing muscular work at sea level, during a 4-week sojourn at 14,250 feet altitude, during reacclimatization to sea level conditions and during acute exposure in an altitude chamber. The heart rate of two of these subjects after acclimatization seemed to approach a relatively low ceiling at high work rates. This probably limited their cardiac output and oxygen transport. It was observed that an increase in oxygen supply (Pio₂) during heavy work in these subjects, however, promptly increased the heart rate well above this ceiling (in one case from 138 to more than 160 beats/min. within 15 seconds.) This response was observed only in acclimatized subjects. After reacclimatization to sea level, when acute hypoxia in the altitude chamber was removed by switching to oxygen during work, heart rate invariably decreased. Submitted on January 27, 1958