Operation Everest II: Maximal Oxygen Uptake at Extreme Altitude.

摘要

Chronic exposure to high altitude reduces maximal O2 uptake (VO2 max). At extreme altitudes approaching the summit of Mt. Everest (inspiratory PO2(PIO2) = 43 Torr), mean VO2 max have been determined to be 15.3 ml/kg-1/ub two subjects who breathed 14% O2 at 6,300 m on Mt. Everest (West et al., J. Appl. Physiol.54:1188-1194, 1983). To provide a more complete description of performance near the limits of human tolerance to chronic hypoxia, we measured VO2 amx in volunteers in an altitude chamber before, during, and after a 40-day decompression to a barometric pressure (PB) of 240 Torr (PIO2 = 43 Torr). In five of eight subjects studied at sea level and PB of 464, 347, 289, and 240 Torr, VO2 max was reduced from 4.13 to 1.17 1/min (49.1-15.3 ml/kg-1/min-1) in agreement with the prior study. Although the range decreased, the rang order among the subjects was preserved. Arterial O2 saturation at maximum effort decreased (46% by ear oximetry), but minute ventilation, respiratory frequency, and tidal volume did not. Sustained hyperventilation was crucial to exercise performance during chronic, severe hypoxemia. VO2 max was lower after altitude exposure compared with initial sea level values, indicating that exposure had not improved sea level exercise capacity. Keywords: Hypoxia; Exercise; Arterial oxygen saturation; Tidal volume; Breathing frequency; Heart rate; Reprints. (KT)