Hypoxia

According to the degree of influence of climatic and geographical factors on humans, the existing classification subdivides (conditionally) mountain levels into:

- low mountains - up to 1000 m. Here a person does not experience (compared to areas located at sea level) the negative impact of a lack of oxygen, even during hard work;

- middle mountains - ranging from 1000 to 3000 m. Here, under conditions of rest and moderate activity, no significant changes occur in the body of a healthy person, since the body easily compensates for the lack of oxygen;

—high mountains—over 3000 m. What is characteristic of these altitudes is that even under conditions of rest, a complex of changes caused by oxygen deficiency is detected in the body of a healthy person. If at medium altitudes the human body is affected by the entire complex of climatic and geographical factors, then at high altitudes the lack of oxygen in the tissues of the body—the so-called hypoxia—becomes decisive.

The highlands, in turn, can also be conditionally divided (Fig. 1) into the following zones (according to E. Gippenreiter):

a) Zone of complete acclimatization—up to 5200–5300 m. In this zone, thanks to the mobilization of all adaptive reactions, the body successfully copes with oxygen deficiency and the manifestation of other negative factors of the influence of altitude. Therefore, it is still possible to locate long-term posts, stations, etc. here; that is, live and work constantly.

b) Zone of incomplete acclimatization—up to 6000 m. Here, despite the activation of all compensatory and adaptive reactions, the human body can no longer fully counteract the influence of altitude. With a long (several months) stay in this zone, fatigue develops, the person weakens, loses weight, atrophy of muscle tissue is observed, activity sharply decreases, and so-called high-altitude deterioration develops—a progressive deterioration in the general condition of a person during prolonged stay at high altitudes.

c) Adaptation zone—up to 7000 m. The body’s adaptation to altitude here is short-lived and temporary. Already with a relatively short (about two to three weeks) stay at such altitudes, the adaptation reactions become exhausted. In this regard, clear signs of hypoxia appear in the body.

d) Partial adaptation zone—up to 8000 m. When staying in this zone for 6-7 days, the body cannot provide the necessary amount of oxygen even to the most important organs and systems. Therefore, their activity is partially disrupted. Thus, the reduced performance of systems and organs responsible for replenishing energy costs does not ensure restoration of strength, and human activity largely occurs at the expense of reserves. At such altitudes, severe dehydration of the body occurs, which also worsens its general condition.

e) Limit (lethal) zone—over 8000 m. Gradually losing resistance to the effects of altitude, a person can stay at these altitudes at the expense of internal reserves only for an extremely limited time, about 2-3 days.

The given values ​​of the altitudinal boundaries of the zones have, of course, average values. Individual tolerance, as well as a number of factors outlined below, can change the indicated values ​​for each climber by 500-1000 m.

The body's adaptation to altitude depends on age, gender, physical and mental state, degree of training, degree and duration of oxygen starvation, intensity of muscle effort, and the presence of high-altitude experience. The individual resistance of the body to oxygen starvation also plays an important role. Previous illnesses, poor nutrition, insufficient rest, and lack of acclimatization significantly reduce the body’s resistance to mountain sickness—a special condition of the body that occurs when inhaling rarefied air. The speed of climb is of great importance. These conditions explain the fact that some people feel some signs of mountain sickness already at relatively low altitudes—2100-2400 m, others are resistant to them up to 4200-4500 m, but when climbing to altitudes of 5800-6000 m, signs of mountain sickness, expressed to varying degrees, appear in almost all people.

The development of altitude sickness is also influenced by some climatic and geographical factors: increased solar radiation, low air humidity, prolonged low temperatures and their sharp difference between night and day, strong winds, and the degree of electrification of the atmosphere. Since these factors depend, in turn, on the latitude of the area, distance from water areas and similar reasons, the same height in different mountainous regions of the country has a different effect on the same person. For example, in the Caucasus, signs of mountain sickness can appear already at altitudes of 3000-3500 m, in Altai, Fan Mountains and Pamir-Alai - 3700-4000 m, Tien Shan - 3800-4200 m and Pamir - 4500-5000 m.