Reduction of maximum heart rate in acute, severe hypoxia

By determining a ceiling for heart rate increase in a given exercise with increment of simulated altitude up to 7,000 m, a reduction of maximum heart rate (HR max) in acute hypoxia was experimentally ascertained. Such a reduction was similarly observed immediately after a high-altitude expedition. In addition, the reduction rate against altitude was close to that shown previously in chronic hypoxia, indicating that the reduction of HR max might be independent of altitude acclimatization.