Altitude is defined on the following scale:
High: 8,000 - 12,000 feet (2,438 - 3,658 meters)
Very High: 12,000 - 18,000 feet (3,658 - 5,487 meters)
Extremely High: 18,000+ feet (5,500+ meters)
There are no specific factors such as age, sex, or physical condition that correlate with susceptibility to altitude sickness.
What Causes Altitude Illnesses?
The concentration of oxygen at sea level 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 properly oxygenate the body, your breathing rate (even at rest) must increase. This extra ventilation increases the oxygen content in the blood, but not to sea level conditions. Since the amount of oxygen required for activity is the same, the body must adjust to having less oxygen. In addition, for reasons not entirely understood, high altitude and lower air pressure causes fluid to leak from the capillaries which can cause fluid build-up in both the lungs and the brain. Continuing to higher altitude without proper acclimatization can lead to potentially serious, even life-threatening illnesses.
Many climbers take Diamox in an attempt to decrease the physical effects of high altitude.
Acute Mountain Sickness (AMS)
AMS is common at high altitude. At elevations over 10,000 feet (3,048 meters), 75% of people will have mild symptoms. The occurrence of AMS is dependent upon the elevation, the rate of ascent, and individual susceptibility. The symptoms of mild AMS are headache, dizziness, fatigue, shortness of breath, loss of appetite, nausea, disturbed sleep, and a general feeling of malaise.
I like to describe it as a feeling of being drunk and hungover at the same time.
Moderate AMS
Moderate AMS includes severe headache that is not relieved with medication, nausea, and vomiting, increasing weakness and fatigue, shortness of breath, and decreased coordination (ataxia). Normal activity is difficult at best. A good test for moderate AMS is to have the person "walk a straight line" heel to toe. A person with ataxia will be unable to walk the straight line. This is a clear indication that immediate descent is required. It is important to get the person to descend before the ataxia reaches a point where they cannot walk on their own at which point a litter evacuation would be required.
Severe AMS
Symptoms of Severe AMS include shortness of breath at rest, inability to walk, decreasing mental status, and fluid build-up in the lungs. Severe AMS requires immediate descent to lower altitudes (2,000 - 4,000 feet).
There are two other forms of altitude illness, High Altitude Pulmonary Edema (HAPE), and High Altitude Cerebral Edema (HACE). When these occur, it is usually with people going too high too fast or going very high and staying there. The lack of oxygen results in leakage of fluid through the capillary walls into either the lungs or the brain.
Diamox
Diamox is a trade name for the prescription drug Acetazolamide, a carbonic anhydrase inhibitor. Its principal
medical use is in the treatment of glaucoma, but it has been used successfully by mountaineers to
counter moderate altitude AMS. It works in this context by increasing the excretion of bicarbonate through the kidneys,
and so increasing the acidity of the blood, which helps it to carry more oxygen.
Acetazolamide belongs to the sulfonamide group. Caution is
therefore needed with people who are sensitive to these medications. Side effects which are known and occur most often are: tingling
in finger tops, hands and lips; different sense of taste, ringing in
the ears; increase in urination.
Diamox intake: in most cases, 125mg every 12 hours is enough
(1/2 of the standard 250mg pill). For nighttime periodical
breathing treatment: 125mg taken one hour prior to sleep.
High Altitude Pulmonary Edema (HAPE)
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