Definition of Altitude, high

Altitude, high: Altitude sickness occurs at high altitude. So what is high altitude?
Altitude is defined on the following scale:

High altitude: 8,000 - 12,000 feet (2,438 - 3,658 meters);
Very high altitude: 12,000 - 18,000 feet (3,658 - 5,487 meters); and
Extremely high altitude: 18,000+ feet (5,500+ meters).
Most people can go up to 8,000 feet (2,438 meters) with minimal effects. If you have been at that altitude before and had no problems, you can probably return to that altitude without problems if (and only if) you are properly acclimatized.
If you have not been to high altitude before, caution is strongly recommended. No specific factors such as age, sex, or physical condition are known to correlate with the susceptibility to altitude sickness. Some people are simply more susceptible than others. There is no telling, so caution is the better part of wisdom.

Definition of Altitude sickness

Altitude sickness: Altitude sickness (or altitude illness) is a disorder caused by being at high altitude. It more 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:

If possible, don't fly or drive to high altitude. Start below 10,000 feet (3,048 meters) and walk up.
If you do fly or drive, do not over-exert yourself or move higher for the first 24 hours.
If you go above 10,000 feet (3,048 meters), only increase your altitude by 1,000 feet (305 meters) per day and for every 3,000 feet (915 meters) of elevation gained, take a rest day.
"Climb High and sleep low." This is the maxim used by climbers. You can climb more than 1,000 feet (305 meters) in a day as long as you come back down and sleep at a lower altitude.
If you begin to show symptoms of moderate altitude illness, don't go higher until symptoms decrease ("Don't go up until symptoms go down").
If symptoms increase, go down, down, down!
Keep in mind that different people will acclimatize at different rates. Make sure all of your party is properly acclimatized before going higher.
Stay properly hydrated. Acclimatization is often accompanied by fluid loss, so you need to drink lots of fluids to remain properly hydrated (at least 3-4 quarts per day). Urine output should be copious and clear.
Take it easy; don't over-exert yourself when you first get up to altitude. Light activity during the day is better than sleeping because respiration decreases during sleep, exacerbating the symptoms.
Avoid tobacco and alcohol and other depressant drugs including, barbiturates, tranquilizers, and sleeping pills. These depressants further decrease the respiratory drive during sleep resulting in a worsening of the symptoms.
Eat a high carbohydrate diet (more than 70% of your calories from carbohydrates) while at altitude.
The acclimatization process is inhibited by dehydration, over-exertion, and alcohol and other depressant drugs.
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.

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:

If possible, don't fly or drive to high altitude. Start below 10,000 feet (3,048 meters) and walk up.
If you do fly or drive, do not over-exert yourself or move higher for the first 24 hours.
If you go above 10,000 feet (3,048 meters), only increase your altitude by 1,000 feet (305 meters) per day and for every 3,000 feet (915 meters) of elevation gained, take a rest day.
"Climb High and sleep low." This is the maxim used by climbers. You can climb more than 1,000 feet (305 meters) in a day as long as you come back down and sleep at a lower altitude.
If you begin to show symptoms of moderate altitude illness, don't go higher until symptoms decrease ("Don't go up until symptoms go down").
If symptoms increase, go down, down, down!
Keep in mind that different people will acclimatize at different rates. Make sure all of your party is properly acclimatized before going higher.
Stay properly hydrated. Acclimatization is often accompanied by fluid loss, so you need to drink lots of fluids to remain properly hydrated (at least 3-4 quarts per day). Urine output should be copious and clear.
Take it easy; don't over-exert yourself when you first get up to altitude. Light activity during the day is better than sleeping because respiration decreases during sleep, exacerbating the symptoms.
Avoid tobacco and alcohol and other depressant drugs including, barbiturates, tranquilizers, and sleeping pills. These depressants further decrease the respiratory drive during sleep resulting in a worsening of the symptoms.
Eat a high carbohydrate diet (more than 70% of your calories from carbohydrates) while at altitude.
The acclimatization process is inhibited by dehydration, over-exertion, and alcohol and other depressant drugs.
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.

Definition of Acute mountain sickness (AMS)

Acute mountain sickness (AMS): Acute mountain sickness (AMS)
is the effect on the body of being in a high altitude environment.
AMS is common at high altitudes, that is above 8,000 feet (2,440
meters). Three-quarters of people have mild symptoms of AMS over
10,000 feet (3,048 meters). The occurrence of AMS depends on the
altitude, the rate of ascent, and individual susceptibility.
Mild AMS: Many people experience mild AMS during the
acclimatization process (the first 1 to 3 days at a given altitude).
Symptoms usually start 12-24 hours after arrival at altitude and
include headache, dizziness, fatigue, shortness of breath, loss of
appetite, nausea, disturbed sleep, and a general feeling of malaise.
These symptoms tend to be worse at night when respiratory drive is
decreased.
Mild AMS does not usually interfere with normal activity and
symptoms generally subside within 2-4 days as the body acclimatizes.
As long as symptoms are mild, and only a nuisance, ascent can
continue at a moderate rate. When hiking, it is essential to
communicate any symptoms of illness immediately to others on your
trip. AMS is considered to be a neurological problem caused by
changes in the central nervous system. It is basically a mild form of
high altitude cerebral edema.
Mild AMS is usually treated with pain medications for headache and
a drug called DIAMOX which allows one 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
going to altitude and continue it for at least 5 days at higher
altitude.
Moderate AMS: Moderate AMS includes severe headache (not
relieved by medication), nausea, vomiting, increasing weakness and
fatigue, shortness of breath, and decreased coordination. Normal
activity is difficult. At this stage, only advanced medications or
descent can reverse the problem. Descending even a few hundred feet
(70-100 meters) may help. Definite improvement is usually seen in
descents of 1,000-2,000 feet (305-610 meters). Twenty-four hours at
the lower altitude usually results in significant improvement. The
person should remain at lower altitude until symptoms have subsided
(up to 3 days). At that point, the person has become acclimatized to
that altitude and can begin ascending again.
The best test for moderate AMS is to have the person "walk a
straight line" heel to toe. Just like a sobriety test, a person with
AMS will be unable to walk a straight line. This is a clear
indication that immediate descent is required. It is important to get
the person to descend before the AMS reaches the point where they
cannot walk on their own.
Severe AMS: Severe AMS presents as an increase in the
severity of the symptoms, including greater shortness of breath at
rest, inability to walk, decreasing mental status, and fluid buildup
in the lungs. Severe AMS requires immediate descent to lower
altitudes: 2,000 - 4,000 feet (610-1,220 meters).
The only cure for AMS is acclimatization or descent. (Based in
part on the Princeton University Outdoor Action "Guide to High
Altitude: Acclimatization and Illnesses" by Rick Curtis).