An illness that can affect mountain climbers, hikers, or skiers who have ascended too rapidly above 8,000 feet (2,400 meters) --especially persons coming from sea level.

Reduced atmospheric pressure and oxygen pressure at high altitude are the causes of this illness. It affects the nervous system,lungs, muscles, and heart. The faster the ascent and the greater the altitude are factors that affect the degree of illness. In mostcases the symptoms are mild, but in severe cases extreme shortness of breath with fluid buildup in the lungs (called pulmonaryedema) develops. Swelling may occur around the brain, causing confusion and leading to coma. The incidence is 2 out of10,000 people.

Education of mountain travelers before ascent is the key to prevention. Basic principles include: gradual ascent, stopping for aday or two of rest for each 2,000 feet (600 meters) above 8,000 feet (2,400 meters); sleeping at a lower altitude when possible;attaining optimal physical conditioning before ascent; and learning how to recognize early symptoms so the party can return tolower altitude before worsening symptoms occur.Mountaineering parties traveling above 9,840 feet (3,000 meters) should carry an oxygen supply sufficient for several days.Acetazolamide (Diamox) may be given as a preventive medication, but therapy must be started before ascent to altitude. Do notconsume alcoholic beverages while taking Diamox.People with underlying cardiac or pulmonary (lung) diseases should avoid high altitudes.