INFLUENCE OF MODERATE ALTITUDE RESIDENCE (2200 METERS) ON THE ACUTE MOUNTAIN SICKNESS AND EXERCISE RESPONSE DURING EARLY HYPOBARIC HYPOXIA (4270 METERS).

摘要

The primary objectives of this study were to examine the influence of life-long moderate altitude residence on (1) the development of acute mountain sickness (AMS) and (2) the response to maximum exercise, during early hypobaric hypoxia. Seven low altitude natives (LANs, 740 Torr) and nine moderate altitude natives (MANs, 587 Torr) were studied at their residence location and again one to four weeks later in a hypobaric chamber at a simulated altitude of 4270 meters (447 Torr). AMS symptom responses and resting physiological data were obtained at six specific time points during the first 48 hours of testing. Following this carefully controlled adaptation period, six LANs and eight MANs performed an incremented workload test on a bicycle ergometer to voluntary exhaustion. Symptoms of AMS were less pronounced (p < 0.05) in MANs at 447 Torr, compared to LANs. Fewer and less severe clinical manifestations of AMS, and the physiological response profile, demonstrated by MANs suggests better adaptation to the hypoxic stress associated with early exposure to 447 Torr. Exercise tests revealed significantly greater differences (p < 0.05) in percent change of several maximum exercise variables, going from residence altitude to 447 Torr, LANs. The decrement in maximum aerobic power (VO(,2)(' )max) was 15% in MANs compared to 34% in LANs. In general, the changes in maximum exercise variables were twice as large as in LANs. Significant negative correlations (p < 0.05), between combined AMS symptoms and the percent change in several maximum exercise variables, indicates that fewer AMS symptoms may be related to a smaller decrement in the maximum exercise response at 447 Torr. The serum cortisol and aldosterone response to maximum exercise was also examined. Cortisol responses were similar in LANs and MANs at both testing locations. Changes in post-exercise aldosterone concentrations were less pronounced (p < 0.01) in MANs at 447 Torr. Correlations between the percent change in these hormonal responses, going from residence altitude to 447 Torr, and the percent change in various maximum exercise variables may further help to explain group differences in exercise performance at 447 Torr.