Respiratory changes during initial days of acclimatization to increasing altitudes.

The daily changes in respiratory function were monitored in 16 healthy male road inductees at sea level (SL) and at high altitudes (HA) of 3110 m, 3445 m, and 4177 m. Identical studies were also carried out on acclimatized low landers (ALL) staying at 3110 m and at 4177 m for 2 years.Ventilation, tidal volume, and respiratory rate showed significant increases on arrival at HA and remained high during the entire period of observation (p < 0.001). These parameters did not show any appreciable difference between 3110 m and 3445 m. Forced vital capacity (FVC) and forced expiratory volume (L) in 1.0-s (FEC1.0) also did not change on the first day of arrival at HA but decreased significantly (p < 0.001) on the second day at 3110 m. However, both FVC and FEV1.0(L) returned to SL values by day 3 but declined further at 3445 m and at 4177 m. Forced expiratory flow and maximum voluntary ventilation declined on arrival at HA. Peak expiratory flow rate, however, tended to decline during initial days but increased by day 3 and remained elevated during the subsequent residence. Respiratory adaptation to hypoxia in ALL appeared to be different at 3110 m as compared to that at 4177 m. At higher altitude the lung volumes and capacities were markedly decreased, whereas at lower altitudes these parameters were comparable to SL values.We conclude that initial respiratory adjustments in sojourners occur by day 3 at 3110 m and show further decrement at 4177 m with a cyclic variation on day 6, while ALL manifest variability in respiratory adaptation at different altitudes.