• 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]).
    But most people can go up to 8,000 feet (2,438 meters) with minimal effect.

• What are the symptoms of Altitude Sickness or AMS
    The symptoms of Mild AMS are headache, dizziness, fatigue, shortness of breath, loss of appetite, nausea, disturbed sleep, and a general feeling of malaise. Symptoms usually start 12-24 hours after arrival at altitude and begin to decrease in severity about the third day. 

• What causes atitude Sickness or AMS happen (by Rick Curtis, Director, updated 07071999)
    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 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, 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 altitudes without proper acclimatization can lead to potentially serious, even life-threatening illnesses.

• Prevention of Altitude Illnesses
    Basically, there are two categories to prevent it, proper acclimatization and preventive medications.
1, proper acclimatization
   -Do exercises to keep you good healthy condition before coming to Tibet.
   -Avoid catching a cold
   -Make sure you did not have any serious problem with heart and lungs.
   -Less activities for the first several days in Tibet, walk slowly, drink more water.
   -Ascend to higher altitude gradually.
2. preventive medications
   -Hong Jin Tian, a kind of traditional Tibetan medicine, comes from Plant, you can easily buy the aqua distilled from the Hong Jin Tian plant.
   -Diamox (Acetazolamide), it allows you to breathe faster so that you 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 five days at higher altitude. The recommendation of the Himalayan Rescue Association Medical Clinic is 125 mg. twice a day (morning and night). (The standard dose was 250 mg., but their research showed no difference for most people with the lower dose, although some individuals may need 250 mg.) Since Diamox is a sulfonamide drug, people who are allergic to sulfa drugs should not take Diamox. Diamox has also been known to cause severe allergic reactions to people with no previous history of Diamox or sulfa allergies.
   -Dexamethasone (a steroid) is a prescription drug that decreases brain and other swelling reversing the effects of AMS. Dosage is typically 4 mg twice a day for a few days starting with the ascent. This prevents most symptoms of altitude illness. 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.