height, influence on an organism

From Big Medical Encyclopedia

HEIGHT, influence on an organism — distance down from sea level to any point of the land surface or in the atmosphere. The term «height» is used willows to practice of mountain ascensions, aircraft, air and space medicine for the characteristic of degree of rarefaction of the atmosphere in mountains, cabins of aircraft and in pressures chamber. With V.'s increase natural change of processes and the phenomena (so-called high-rise zonality) caused by change (decrease) up of density, the atmospheric pressure, temperature, vlago-and dust content, increase of intensity of solar radiation and space radiation is observed. The main manifestation of V. is depression of the atmosphere, decrease in barometric pressure and the oxygen content.

The first scientific explanation of negative effect of the factors connected with height, confirmed experimentally belongs to the fr. physiologist Beru (P. Bert, 1878) and to the Russian scientist I. M. Sechenov (1879). By them it was shown that negative influence of V. on an organism is generally caused by a lack of oxygen of inhaled air, partial pressure to-rogo in process of rise decreases by V. in proportion to decrease in the general barometric pressure (see the Atmosphere). The lack of oxygen of inhaled air leads to reduction of oxygenation of blood in lungs, and, therefore, to deterioration in supply with oxygen of bodies and body tissues, i.e. to a condition of a hypoxemic hypoxia (see. Hypobaropathy ).

Rises in pressures chamber, mountain ascensions can increase resistance of an organism to a hypoxia on V., but it is possible to prevent harmful effects of V. only improvement of supply of an organism with oxygen with the help oxygen and respiratory equipment (see). However this method is effective only to V. of 10 — 12 km. At further increase in V. giving even does not protect pure oxygen from a hypoxia because of low barometric pressure. Therefore at the heights more than 12 km it is necessary to apply special high-rise equipment (see) or space suits (see).

Degree of manifestation of adaptive reactions, functional disturbances or pathological changes in an organism generally depends on height of rise and time of influence. At the same time individual resistance to a hypoxia, speed of rise and other factors have a certain value. In the course of activity of people V. Hron can be exposed hron, and to acute influence of factors, V.'s influence takes place at long stay in mountains. In these conditions there is an adaptation and acclimatization of an organism to V.'s influence that leads to certain reorganizations in functioning of the main systems of an organism and to increase in portability of V. (see. Adaptation to height ). Acute influence of V. is usually observed in practice of aviation flights (depressurization of a cabin of the airplane at the height more than 5000 m at failure of the oxygen and respiratory equipment) and at mountain ascensions.

Depending on reaction of a human body to a lack of oxygen B. it is conditionally possible to divide into several zones (certain reactions are characteristic of each zone).

Indifferent zone — to 1500 — 2000 m over at river of m. At stay in this zone of noticeable changes in functioning of the main systems of an organism and in subjective feelings it is not observed. Working capacity remains completely for all time spent for Century.

Zone of full compensation — from 2000 to 4000 m above sea-level. Working capacity remains during rather long time (several hours) due to increase in lung ventilation, minute volume of blood and redistribution of a blood-groove. Physical. the work demanding significant increase in oxygen consumption is carried out with difficulties.

Zone of incomplete compensation — from 4000 to 5500 m over at river of m. Deterioration in health with decrease in working capacity is observed. Emergence of euphoria and inadequate behavior is possible. Long stay on such V. is followed by emergence of heavy feeling in the head, headaches, drowsiness, difficulty of focusing, the general decrease in working capacity. Small physical. work becomes difficult.

Critical range — from 5500 to 8000 m above sea-level. Working capacity is sharply reduced. Performance physical. works are almost excluded. The progressing deterioration in the general state is noted. The high probability of emergence high-rise is characteristic of this zone faint (see), time of its emergence generally depends on individual stability to hypoxias (see). At the height more than 7000 m preservation of consciousness at the person perhaps within a short period of time, a cut it is accepted to call reserve.

Intolerable zone — it is higher than 8000 m above sea-level. It is characterized by very short reserve time (of 2 — 3 min. to 10 — 20 sec. depending on V.) then there comes the deep syncope and if not to take a measure to the termination of influence of V., death is possible.

The main forms of decompressive frustration

V.'s Impact on an organism is not limited only to a lack of oxygen though this factor and is dominating. At rise on V. owing to reduction of the barometric pressure (decompression) in an organism there can be functional, and in nek-ry cases also irreversible changes, to-rye received the general name of decompressive frustration. Distinguish three main forms of decompressive frustration: high-rise meteorism, high-rise pains and high-rise fabric emphysema.

High-rise meteorism it is more often shown in the form of abdominal distention and pains. Its reason — expansion of the gases which are in a stand-at-ease in went. - kish. path. The extending gas at the complicated exit stretches a stomach and intestines that can cause pain. The gases which increased in volume push aside a diaphragm up that leads to reduction of depth of a breath and nek-rum to difficulty of blood circulation. In some cases abdominal pains can become the reason of deterioration in the general state (weakness, cold sweat, nausea appears). The passage of flatus from intestines and from a stomach takes off unpleasant effects and improves health. Prevention of a high-rise meteorism consists in a special diet, at Krom products with high gas-forming ability (peas, vegetables, black bread) are excluded.

High-rise pains arise owing to transition of gases, and first of all nitrogen, contained in fluid and semi-fluid mediums of an organism in the dissolved state, in gaseous state with vesiculation (see. Compressed-air disease ). High-rise pains can arise on V. more than 7000 m. The probability of their emergence increases with V.'s increase and the time spent for it, and also during the performance physical. works. The clinical picture is various and in many respects depends on localization, the sizes and evolution of the formed bubble. Can take place of feeling of pain in any large joint (humeral, knee, elbow), retrosternal pains, and also a skin itch, cough, paresis are more rare. Extremely rare, but very dangerous form are the frustration coming owing to focal defeat of c. N of page. After descent to V. less than 7000 m of pain usually disappear. However the possibility of emergence of the secondary, remote frustration arising in several hours after descent since Century is not excluded.

Fast changing of barometric pressure, especially during descent with V., can cause pain on average an ear and paranasal sinuses. It is promoted by the nek-ry anatomic features and a condition of a mucous membrane of a nasopharynx complicating equalization of pressure in a drum cavity and adnexal bosoms with surrounding pressure. At sharp pressure differences an opportunity is not excluded barotraumas (see).

An effective remedy of prevention of high-rise pains is release of an organism from the dissolved nitrogen (desaturation) before rise on V. that is reached by inhalation of pure oxygen. The accumulated experience demonstrates that 30 — 60-minute inhalation of oxygen before rise on V. in overwhelming number of cases prevents development of severe forms of decompressive frustration.

High-rise fabric emphysema can appear only on V. where barometric pressure is lower than elasticity of water vapors in body tissues (V. more than 19 000 m). In this case in body tissues there can occur process of steam formation (boiling). Externally high-rise fabric emphysema is expressed in emergence and bystry increase in hypodermic swellings. On site swellings the unpleasant tension of skin and slight pain is felt. During descent to V. lower than 19 000 m owing to condensation of water vapors of swelling quickly disappear. High-rise fabric emphysema can develop also at stay in high-rise equipment — on opened (not compensated by counter-pressure) body parts.

A security measure from an adverse effect of harmful factors of V. are hermetic cabins, to-rye in total with the oxygen and respiratory equipment and high-rise equipment ensure safety and necessary conditions for flights practically on any V. (see. Flights ). In aircraft with hermetic cabins the possibility of emergence of high-rise decompressive frustration is practically excluded, and in nek-ry cases also need for additional oxygen food disappears (by passenger airplanes).

Bibliography: Armstrong G. An air medicine, the lane with English, M., 1954; Ivanov D. I. and Hromushkin A. I. Life support systems of the person at high-rise and space flights, M., 1968, bibliogr.; Isakov P. K. and d river. Theory and practice of air and space medicine, M., 1971, bibliogr.; Lavnikov A. A. Bases of an air medicine. M, 19 75, bibliogr.; Fundamentals of bioastronautics and medicine, under the editorship of O. G. Gazenko and M. Calvin, t. 1 — 3, M., 19 75, bibliogr.

L. G. Golovkin.