Webster's New World Medical Dictionary

altitude, acclimatization to
See 
acclimatiza-
tion to altitude.
altitude illness
See 
altitude sickness.
15
altitude illness
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altitude sickness
Sickness caused by being at a
high altitude, usually above
2,400 meters
(approximately 8,000 feet). The cause of altitude
sickness is a matter of oxygen physiology. At sea
level the concentration of oxygen is about 21 per-
cent, and the barometric pressure averages 760 mm
Hg. As altitude increases, the concentration remains
the same, but the number of oxygen molecules per
breath is reduced. At 5,400 meters (approximately
12,000 feet) above sea level, the barometric pres-
sure is only 483 mm Hg, so there are roughly 40
percent fewer oxygen molecules per breath. In
order to oxygenate the body effectively, the breath-
ing rate must increase. This extra ventilation
increases the oxygen content in the blood—but not
to sea level concentrations. Because the amount of
oxygen required for activity is the same at high alti-
tude as at sea level, 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 buildup in the lungs and the
brain. Prevention measures for altitude sickness
include avoiding or retreating from high-altitude
areas, gradual acclimatization, and medication. The
acclimatization process is inhibited by dehydration,
overexertion, and intake of alcohol and depressant
drugs. Preventive medications include acetazo-
lamide (brand name: Diamox) and dexamethasone
(a steroid). See also 
acclimatization to altitude;
acute mountain sickness.