Definition of Altitude illness
Altitude illness: Altitude illness (or altitude sickness) is a disorder caused by being at high altitude. It commonly occurs above 8,000 feet (2,440 meters).
The cause of altitude illness is a matter of oxygen physiology. At sea level the concentration of oxygen is about 21% and the barometric pressure averages 760 mmHg. As altitude increases, the concentration remains the same but the number of oxygen molecules per breath is reduced. At 12,000 feet (3,658 meters) the barometric pressure is only 483 mmHg, so there are roughly 40% fewer oxygen molecules per breath.
In order to oxygenate the body effectively, your breathing rate (even while at rest) has to increase. This extra ventilation increases the oxygen content in the blood, but not to sea level concentrations. Since the amount of oxygen required for activity is the same, the body must adjust to having less oxygen.
In addition, high altitude and lower air pressure cause fluid to leak from the capillaries which can cause fluid build-up in both the lungs and the brain. Continuing to higher altitudes without proper acclimatization can lead to potentially serious, even life-threatening illnesses.
The prevention of altitude illnesses falls into two categories, proper acclimatization and preventive medications. A few basic guidelines for proper acclimatization are:
The acclimatization process is inhibited by dehydration, over-exertion, and alcohol and other depressant drugs.
There are preventive medications for altitude illness. These medications should be used with caution, and only on the advice of a physician because of possible serious side effects.
This entry does not deal with acute mountain sickness (AMS) or, in any detail, with acclimatization. For information on these topics, please see the respective entries to Acute mountain sickness (AMS) and to Acclimatization.
Last Editorial Review: 10/30/2013
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