Changes in exercise heart rate in lowlanders after prolonged stay at high altitude (4000 m)

Studies were conducted on cardiac frequency during submaximal and maximal work on 26 sea-level residents prior to transfer to and during stay at high altitude for 1, 10, and 20 months. Maximal O2 uptake and performance in a 1.6 km run were observed. Results indicated a significant drop in Vo2 after arrival at altitude followed by recovery with further stay. The mean maximum heart rate decreased to 182.8 beats/min after 1 month at high altitude from a seal-level mean value of 188.4 beats/min. It increased to 199.2 beats/min and decreased to 185.6 beats/min after 10 and 20 months, respectively. Heart rate, during submaximal work requiring 1.0 and 1.5 102/min, indicated the highest rate after 1 month at altitude and decreased with prolonged stay, but remained higher than the sea-level value. These changes were compared with the high-altitude native residents.