MEDICINE AND ALTITUDE
By Dr. Clare O'Leary and Pat Falvey.

THE EFFECT OF HIGH ALTITUDE ON THE HUMAN BODY

At an altitude above 10,000 feet, most humans will experience symptoms, the type and severity of which will vary from individual to individual. These symptoms develop as a result of a relative lack of oxygen in the atmosphere; the pressure of oxygen at the top of Mount Everest is only 1/3 that at sea level. If a human was exposed to this altitude suddenly, he/she would lose consciousness immediately. Climbers survive at this altitude because they gain height very slowly. This gives the body time to gradually adapt to the effects of the reduced oxygen. This process is termed acclimatisation.

These changes associated with acclimatisation occur over a period of days to weeks. Some individuals respond more slowly and less effectively than others; this is unpredictable, but can be guided by previous experience.

If individuals fail to acclimatise or do not allow themselves adequate
time to acclimatise properly, a range of illnesses can occur; the mildest form being acute mountain sickness, and the more severe forms being high altitude pulmonary oedema (fluid in the lungs) and high altitude cerebral oedema (swelling of the brain). These are explained in more detail below. As a guide to the rate of acclimatisation, it is generally recommended that above 3,000m, each night's camp should be about 300m above the previous one. Every 2-3 days a rest day should be added; the team remains based at the same site for two nights.

On rest days, trips to higher altitude and back appear to stimulate acclimatisation; this is generally practiced by climbers, although there
is some evidence that exercise is a risk factor for acute mountain sickness (AMS).

The other major health effects at altitude are a result of the harsh weather conditions, which bring the risk of hypothermia and frostbite.