April 1999 |
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When Alexander the Great took his army from India to Tibet in the 4th century B.C., he described the Himalayan region as "the mountain of the great headache". The most important change of environment that all human beings are exposed to in high mountain areas is the drop in atmospheric pressure. At the top of Everest, pressure is only 320 hPa, while at sea level it is 1013 hPa (one hectoPascal = one millibar). It should be pointed out, however, that it is not the breakdown of the gases that make up the air (oxygen, 21%, nitrogen, 78%, rare gases, 1%) that is reduced (because in fact, this remains the same at any altitude), but the partial pressure of each component. This is why the quantity of oxygen that our lungs can absorb falls significantly the higher we go above sea level (nearly 70% less at the top of Everest). To simplify things, it can be said that at 8 000 m, for example, the gases in the air "penetrate" to the inside of the lungs with less force. It is this lack of fuel to the body that gives mountaineers problems with getting their muscles and brain to function properly. Other elements also play a role in variations in pressure. As the atmosphere is thicker at the equator than it is at the poles, the air pressure there is therefore higher. This explains why at the top of Everest (whose latitude is close to the equator), it is higher than had always been supposed. This theory had long been the subject of fierce debate until Messner and Habeler succeeded in climbing the giant without oxygen in 1978. The season, variations in zones of high and low pressure, as well as sudden changes of temperature, are all other factors that are of great importance in the phenomenon of pressure variations. The greatest danger on an expedition, apart from an accident, is acute altitude sickness, usually caused by inadequate acclimatisation to high altitudes. This clinical symptoms of altitude sickness include the following: headaches (96% of cases), insomnia (70%), anorexia (38%), nausea (35%). They may also be associated with breathing difficulties, a dry cough and, sometimes, dizziness or very localised swellings. In 99% of cases, these symptoms can be overcome spontaneously by taking aspirin. Failing this, the best treatment is to go back down a few hundred metres. In 1% of cases, the symptoms may become worse. Two accidents may then occur: pulmonary oedema (a choking feeling, noisy breathing, blue lips, frothy spittle) and cerebral oedema (fatigue, vomiting, dizziness, strange behaviour and possible coma). Both of these cases are an extreme emergency, it is vital to go back down immediately and medical treatment is essential. When these problems occur, there are three golden rules: do not go up too high, do not climb too quickly (no more than 400 m a day on average over 3,500 m), go up sufficiently high to become acclimatised, and do not stay up too high for too long.
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