Exercise-induced cerebral deoxygenation among untrained trekkers at moderate altitudes

The pathophysiology of altitude-related disorders in untrained trekkers has not been clarified. In the present study, the effects of workload on cardi ovascular parameters and regional cerebral oxygenation were studied in untr ained trekkers at altitudes of 2 700 m and 3 700 m above sea level. We stud ied 6 males and 4 females at each altitude, and their average ages were 31. 3 +/- 7.1 y at 2 700 m and 31.2 +/- 6.8 y at 3 700 m, respectively. The res ting values of heart rate and mean blood pressure were not significantly di fferent at 2 700 m and 3 700 m than at sea level. However, increases in the se values after exercise were more prominent at high altitudes (heart rate increase = 51.6% at 2 700 m and 70.4% at 3700 m; mean blood pressure increa se: 19.0% at 2 700 m and 17.2% at 3 700 m). In addition, post-exercise bloo d lactate concentration was significantly higher at 3 700 m than at sea lev el or at 2 700 m (i.e., 7.6 mM at 3 700 m, 3.8 mM at 2 700 m, and 4.17 mM a t 0 m, respectively). Exercise induced an acute reduction in the arterial o xygen saturation value (SpO(2)) at 2 700 m and 3 700 m (i.e., 11.2% reducti on at 2 700 m and 9.4% at 3 700 m), whereas no changes were observed at sea levee. The resting values of regional oxygen saturation (rSO(2))-measured by a near infra-red spectrophotometer at sea level, 2700 m, and 3700 m-were nearly identical. Exercise at sea level did not reduce this value. In cont rast, we observed a decrease in rSO(2) after subjects exercised at 2 700 m and 3 700 m (i.e., 26.9% at 2 700 m and 48.1% at 3 700 m, respectively). Th e rSO(2) measured 2 min and 3 min after exercise at 3 700 m was significant ly higher than the preexercise value. From these observations, we concluded that alterations in cardiovascular parameters were apparent only after an exercise load occurred at approximately 3 000 m altitude. Acute reduction i n cerebral regional oxygen saturation might be a primary cause of headache and acute mountain sickness among unacclimatized trekkers.