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:
Preventive medications for altitudes illness are two drugs: one called DIAMOX (acetazolamide) and the other called dexamethasone (a steroid).
DIAMOX (acetazolamide) allows a person to breathe faster and so metabolize more oxygen, thereby minimizing the symptoms caused by poor oxygenation. This is especially helpful at night when respiratory drive is decreased. Since it takes a while for DIAMOX to have an effect, it is advisable to start taking it 24 hours before you go to altitude and continue for at least 5 days at higher altitude.
Dexamethasone (a steroid) is likewise a prescription drug. It decreases brain and other swelling reversing the effects of acute mountain sickness (AMS). Like DIAMOX, it should be used with caution and only on the advice of a physician because of possible serious side effects. It may be combined with DIAMOX. No other medications have been proven valuable for preventing AMS. (Based in part on the Princeton University Outdoor Action "Guide to High Altitude: Acclimatization and Illnesses" by Rick Curtis).
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.
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