acute mountain sickness
an illness that can affect mountain climbers, hikers, or skiers who have ascended too rapidly above 2,400 m (8,000 ft), especially when coming from sea level. Caused by the effects of reduced atmospheric pressure and oxygen pressure at high altitudes, it affects the nervous system, lungs, muscles, and heart. The faster the ascent and the higher the altitude, the greater is the degree of illness. In two out of every 10,000 cases, swelling occurs around the brain, causing confusion and leading to coma (high-altitude cerebral edema). See also altitude sickness.