Effect of different ascent profiles on performance at 4,200 m elevation.

Two groups of sea level residents were studied at the summit of Mauna Kea (4,200 m elevation) following ascent by vehicle. "Commuters" spent 6 h at the summit, while "shiftworkers" lived on the mountain for 5 d. Although PaO2 levels were lower in commuters, they experienced fewer altitude sickness symptoms than shiftworkers on the first day at 4,200 m. After 5 d, shiftworkers reported fewer symptoms and performed better at tests of numerate memory and psychomotor ability than commuters. At high altitude, pulse rates were increased in both groups, but only shiftworkers exhibited an elevation in systemic blood pressure. Arterial-alveolar oxygen tension gradients were not increased at 4,200 m. Despite frequent and rapid ascents and descents, with minimal provision for acclimatization, high altitude pulmonary and cerebral oedema were uncommon.