HYPOBAROPATHY

From Big Medical Encyclopedia

HYPOBAROPATHY — the disease resulting from considerable and bystry decrease in partial pressure of oxygen (pO 2 ) in a surrounding gaseous fluid.

In 1918 Mr. Schneider (E. S. of Schneider) suggested to combine the morbid conditions arising at people in flight at rises on height in the uniform nosological form called by it a hypobaropathy. Armstrong (G. Armstrong, 1957), H. H. Sirotinin (1957), D. I. Ivanov (1960), etc. included all morbid conditions in the concept «hypobaropathy», to-rye arise at people at mountain ascensions, high-rise flights or rises in a pressure chamber, i.e. in all cases when disease state arises owing to stay in conditions of a gaseous fluid with the lowered pO 2 . This point of view is divided not by all. It is offered to differentiate V. from mountain disease (see), the clinical picture differing in an originality. Century. proceeds sharply; serious morbid condition, including a loss of consciousness, develops extremely quickly and almost directly after rise on big height (during the time measured for minutes or even in tens of seconds). Victims lose the critical relation to a surrounding situation and do not show any complaints to deterioration in health. The last would define special danger of V.

The mountain disease develops rather slowly. Its symptoms are shown, as a rule, in several hours (sometimes days) after rise. Victims show numerous complaints (a headache, dizziness, abdominal pains, nausea, short wind, weakness, etc.).

Nek-ry researchers [Opitz (E. Оpiz, 1941), M. P. Brestkin, P. M. Graminitsky (1968), etc.] apply the term «acute hypoxemic hypoxia», edges arises in a gaseous fluid with much the lowered pO 2 and in many cases completely within several minutes disappears at recovery of normal pO 2 .

An etiology and a pathogeny

by Works of B of ER and (P. Bert, 1878) and I. M. Sechenova (1879) it was for the first time established that an origin of V. acute air hunger is. Bør noted that at V.'s development. at animals disturbances of activity of c have the leading value. and. page, its high sensitivity to an anoxemia. Development of air hunger can be caused by decrease in barometric pressure with inevitable at the same time falling of pO 2 in air or decrease in the oxygen content in air or in an artificial gaseous fluid hermetically the closed rooms. The first situation can arise during high-rise flights in aircraft with cabins opened ooze or after the disturbance of tightness of cabins closed ooze; the second — owing to failure of the systems regenerating air in hermetic cabins and rooms.

A pathogeny

In V.'s pathogeny. are closely bound the adaptive reactions directed to a pas improvement of transport of oxygen to cells and the pathological reactions caused by deficit of oxygen. These reactions can be presented in the following sequence. Deficit of oxygen in the environment leads to decrease in partial pressure in an alveolar air and an arterial blood. Decrease in partial pressure in an arterial blood leads to irritation of chemoceptors of reflexogenic vascular zones (sinocarotid and aortal). Strengthening of an impulsation (afferentation) from chemoceptors is the beginning of many reflex adaptive reactions defining increase in minute volume of breath, minute volume of blood, stimulation of pituitary and adrenal system and nadbulbarny formations of a brain, including also bark. Development of a hyperventilation leads to emergence of a hypocapny. It would play a part in V.'s pathogeny., since can be the cause of disturbances of regulation of blood circulation and breath (see. Hypocapny ). At major deficit of oxygen in an arterial blood against the background of adaptive reactions there are changes of activity ts.n.s., to-rye are shown in the form of touch and motive disturbances. At the same time first of all the most sensitive to influence of a lack of oxygen suffer in blood of structure: photoreceptor cells of an eye, bark of big hemispheres, hippocampus, cerebellum, etc.

Studying of uslovnoreflektorny activity and overseeing by behavior of animals in experimental conditions allowed to assume that at V.'s development. there are phase changes of excitability of c. N of page: during an initial stage dominance of processes of excitement is noted, and at the expressed manifestation of symptoms of V. processes of braking prevail.

Essential value for disclosure of a pathogeny of V. had elektrofiziol. researches. At animals on EEG and at registration of bioelectric activity of separate cellular structures of c. and. page in development of V. it was established that the functional condition of neurons of bark of big cerebral hemispheres changes as a result both humoral, and reflex influence of a lack of oxygen on them of blood. Stimulation of chemoceptors of a sinocarotid and aortal zone the lowered partial pressure of oxygen causes excitement of a mesh formation of a trunk of a brain with the subsequent activating influence it on overlying structures of hemispheres. In this initial phase of a hypoxia, as a rule, on EEG activation of high-frequency fluctuations was noted. Its emergence on time almost matched development of a hyperventilation. Denervation of sinocarotid area eliminates these reactions that testifies to their reflex origin. Strengthening of excitement in bark of big hemispheres in an initial stage of development of a hypoxia is demonstrated also by results of animal experiments, in process to-rykh biopotentials of separate nervous cells were registered. So, at registration of biopotentials of gigantopiramidalny neurocytes of bark of big cerebral hemispheres increase in pulse activity was noted: frequency of impulses increased, their emergence became more rhythmical. In experiences on neyronalno the isolated strip of bark of big hemispheres the stimulating influence of a hypoxia on neurons of bark of big hemispheres was also noted. It was shown in reduction of the threshold of electric irritation and in strengthening of digit activity. During manifestation of the expressed disturbances of activity of a brain owing to considerable decrease in pO 2 in blood and fabrics on EEG waves of high amplitude 0 and A dominate. During development of an agonal state amplitude and frequency of A-waves decreases and bioelectric activity gradually disappears. At assignment of biocurrents from neyronalno the isolated strip of bark of big hemispheres decrease in digit activity and increase in a threshold of electric irritation is noted. In certain cases bioelectric activity of separate gigantopiramidalny neurocytes was completely oppressed and not recovered after switching to breath by the air rich with oxygen, despite visible general recovery of EEG. These changes on EEG indicate the direct damaging action of a hypoxia on neurons. The mechanism of this phenomenon at V.'s development. it is caused by the fact that at progressive decrease r 02 blood continuously increase number of the nervous cells testing acute oxygen insufficiency. In the beginning oxygen insufficiency is tested by cells, the most remote from capillaries. During the falling of pO 2 in the environment to a critical level (42 mm of mercury.) consumption by cells of oxygen decreases and metabolism is broken.

At a hypoxia all types of a metabolism suffer, however the most essential value has disturbance of carbohydrate metabolism, a cut causes decrease in resynthesis adenosine triphosphoric to - you are (ATP) and excess accumulation in cells of intermediate products: the recovered nicotinamide adenine dinucleotide, milk and pyroracemic acids. These changes lead to disturbance of an intracellular homeostasis — to reduction of pH and loss of selective permeability of a cell membrane, as defines the beginning of development patol, changes. The sequence of emergence of such changes (according to E. F. Kotovsky and L.L. Shimkevich, 1971) it is presented in the form: change of permeability of a cellular membrane → disturbance of ionic balance → swelling of mitochondrions → stimulation of glycolysis → reduction of maintenance of a glycogen → suppression of synthesis and strengthening of an albuminolysis strengthening of synthesis of lipids → destruction of mitochondrions, ergastoplazma, intracellular mesh device → fatty decomposition of cytoplasm. This process comes to the end with destruction of membranes of lysosomes and an exit of hydrolases that leads to an autolysis and full disintegration of a cell. These changes of chemism and ultrastructure of a cell would define development characteristic of V. patomorfol. pictures, including and emergence of various depth of disturbances of structure of cells of c. N of page, vacuolation of protoplasm, spraying of chromatophilous substance or full tigroliz, pycnosis of kernels, wrinkling of cells, their necrobiosis and lysis. Similar patomorfol. changes are described by many authors at the people who died from V. Development patomorfol. changes at V. demands certain time. If V. led to death of an animal in 2 — 5 min., disturbances of structure of cells were not found in them, and small hemorrhages in a brain and heart were noted. Various sensitivity of cells to a hypoxia is caused by features of their structure and level of a metabolism. The arisen cells are especially sensitive to a hypoxia evolutionarily most late. Bystry emergence (is explained by it at development of a hypoxia) disturbances of structure of cells of c. N of page and especially — neurons of bark of big hemispheres. In the analysis of a pathogeny of acute V., arising at big heights, it must be kept in mind a possibility of development of decompressive frustration (see. Decompressive disease ).

For the first time V. it was described in 19 century by the aeronauts flying in balloons.

In the analysis of the records made by them in flights at the heights of 6000 — 7000 m disturbances of handwriting were noted: increase in the sizes of letters, a gap between them, were noted grammatical mistakes, including perseveration of separate syllables, words and the whole phrases. These records were the first documents indicating emergence of deep disturbances of c. and. page at V.'s development.

As showed researches, weight and V.'s outcome. depend on size and the speed of decrease in pO 2 in inhaled air. I. M. Sechenov established dependence of changes of pO 2 in an alveolar air of pAO 2 from changes of size of barometric pressure. This dependence can be approximately defined from the following equation: pAO 2 = (In — pH 2 O) • With — pACO 2 , where In — the size of barometric pressure; pH2O — the partial pressure of water vapors at body temperature 37 ° (this size is constant and equal to 47 mm of mercury.); With — percent of the oxygen content in gas mixture; pACO 2 — partial pressure of carbon dioxide in an alveolar air (it depends on the level of ventilation of the lungs and can vary in the range from 45 to 20 mm of mercury.).

Short-term decrease in pACO 2 to 20 mm of mercury., according to I. M. Sechenov, poses a serious threat for life. Further A. Krog established that such danger arises already at RASO 2 , equal 30 mm of mercury.

Development and manifestation of symptoms of V. is defined by degree and speed of increase of deficit of oxygen. Animals (dogs, cats, etc.) at the heights of 6000 — 7000 m can be within many hours and even several days. At the heights of 10 000 — 12 000 m deep disturbances of activity of c. and. pages are shown the first minute after rise. At the heights of 15 000 m and more V. proceeds extremely sharply as in the first seconds there is a deoxygenation of blood — transition of oxygen from blood in alveoluses since tension of oxygen in blood is higher, than in alveoluses. Due to the deoxygenation of an organism breath holding does not increase duration of stay at such height. For these reasons reproduction of forms B., arising at the height more than 10 000 m in the conditions of standard barometric atmosphere pressure at breath by gas mixtures, extremely oxygen-deficient or even almost deprived of it, it cannot be carried out fully. At breath by pure nitrogen V.'s signs. appear in 25 — 30 sec., and a loss of consciousness — in 40 — 50 sec.

According to E. A. Kovalenko and Chernyakov (1972) data, at the heights of 20 000 m death of dogs occurs in 1 — 2 min. Acute form B. Beck (N. investigated Beck, 1970) in experiences on a chimpanzee. After bystry depression of air in a pressure chamber to several millimeters hg animals already in 12 sec. lost an active pose and ceased to react to a surrounding situation adequately. The clonic, and then tonic spasms following loss of a pose, and bystry (in 40 — 50 sec.) emergence of a terminal state would confirm extremely heavy current of V. After descent from height of animals it was possible to save only in cases when they in the conditions close to vacuum,


would be no more than 3 — 3,5 min. == the Clinical picture == Systematic long-term studying of V., arising at people in a rise time in a pressure chamber, at breath by gas mixtures, oxygen-deficient, and at breath in the closed volume, gave the chance to allocate two main forms B. — kollaptoidny and unconscious. The Kollaptoidny form most often meets at rather moderate deficit of oxygen at the height of 5000 — 6000 m or at breath by the gas mixtures containing 9 — 12% of oxygen. The unconscious form results from major deficit of oxygen at the heights of 7000 — 10 000 m or at breath by the gas mixtures containing less than 8% of oxygen. Both forms B., especially the second, proceed sharply and quickly lead to development of serious morbid conditions. It would be possible to allocate still the third form B., edges on a clinical current it is close to mountain disease (see). It arises at people at hours-long stay at the heights of 4000 — 6000 m and proceeds much easier, than kollaptoidny and unconscious forms.

During the studying of dynamics of development of V. four stages were conditionally allocated: the first — hidden when visible signs are absent; the second — compensated when adaptive reactions to a lack of oxygen are expressed (in these stages the general state and working capacity remain at rather satisfactory level); the third — dekompensirovanny when V.'s symptoms clearly would be shown., the general state worsens and working capacity is lost; the fourth — there are serious, life-threatening morbid conditions. Sequence of development of stages of V. is defined by degree of a hypoxia and individual resistance to a lack of oxygen.

That circumstance that in the eclipse period of development of V. is important. after rise even on small heights (1500 — 3000 m) people against the background of good health have changes in c. N of page, to-rye can exert negative impact on working capacity, especially on difficult elements of professional activity, napr, piloting of the airplane at landing approach. So, at the heights of 1500 — 2000 m changes of sight, decrease in light sensitivity of the eye adapted to darkness, and also disturbances of space perception were noted. Therefore at night flights it is recommended to use breathing oxygen since height of 2000 m. At the height of 4000 — 5000 m at many people before manifestation of any external signs of V. disturbances of intellectual working capacity were noted. On an ECG during this period of development of V. are noted: sinus tachycardia, flattening of a tooth of T in all assignments, reduction of size of teeth of R2, R3 and teeth of R in the left chest assignments, in 2% of cases developing of ventricular premature ventricular contraction; nek-ry persons have a shift of intervals is S — T below the isoelectric line (to 1 mm).

The Kollaptoidny form of a hypobaropathy arises at almost healthy people in 5 — 30 min. after rise (in a pressure chamber) on height of 5000 m in 3% of cases. At persons with functional insufficiency of regulation of cardiovascular system it arises, by data A. P. Apollonova and D. I. Ivanov, in 25% of cases. After rise on height of 6000 — 7000 m this form B. arises at almost healthy people in 10 — 15% of cases. At the heights of 8000 m and more kollaptoidny form B. meets seldom. At this form B. the health worsens: there is the general weakness, feeling of heat in all body or only in the head, sight changes (before eyes a gray or black veil); slightly more rare the lack of air, a sonitus, nausea and dizziness is felt. Outward and behavior of inspected changes: there is a pallor of integuments of the person, perspiration amplifies (on a forehead large drops of sweat), features are pointed just as it happens at the person tired heavy physical. work; eyes seem deeply sunk down, their expression becomes suffering. V. which is often raised at the beginning of development. a physical activity and euphoria are replaced by the general block; the pose becomes held down, the look is long fixed on separate objects. Relation to a surrounding situation indifferent. Consciousness remains a long time kept, however all instructions and teams of the doctor are perceived slowly and often carried out as if reluctantly. If not to provide the victim with normal oxygen food (descent from height, supply of oxygen), its state can sharply worsen — there will come the loss of consciousness. Urezheniye of heart rate or a lowering of arterial pressure would be one of the first signs of emergence of a kollaptoidny form B. Degree and speed of manifestation of these reactions would define features of a clinical current of V. At falloff of cerebral circulation there is vazo-vagal syncope (see). It is the reason or the accruing bradycardia, or considerable decrease in peripheric resistance that also leads to falling of arterial pressure. If at development of a collapse parasympathetic reactions prevail, then sinus tachycardia is replaced by bradycardia; at the same time migration of the center of the leading excitement from a sinus node in underlying departments of the carrying-out system of heart is often noted; at the same time nek-ry persons have also ventricular premature ventricular contraction.

In the mechanism of development of a collapse in nek-ry people an essential role is played by a hypocapny. These can explain lack of therapeutic effect at such persons after switching to breath with oxygen. Clear therapeutic effect of oxygen is shown only after elimination of a hyperventilation during recovery of pACO 2 .

At the persons steady against a hypoxia, in several hours of stay at the heights of 4000 — 6000 m V.'s development would be noted., the clinical picture a cut is close to an acute form of a mountain disease. The diseased has a headache, an acrimony, sharply decreases intellectual and physical. working capacity — even insignificant muscular work causes short wind and tachycardia. At the same time complaints to the general weakness, nausea, an abdominal pain, the dispeptic phenomena are frequent.

The unconscious form often comes without the expressed harbingers. The diseased does not feel unpleasant feelings, moreover, it loses the adequate relation to a surrounding situation and to the state: does not notice errors during the performance psikhofiziol. tests and at the solution of elementary arithmetic tasks, disturbances of handwriting and appreciable grammatical errors. The loss of consciousness comes suddenly. In nek-ry cases it is preceded by attacks of clonic spasms, as a rule, in the working muscles. Sharpness of a current of V. determines extent of decrease in saturation of blood by oxygen. At the height of 15 500 m and V. is higher. proceeds sverkhostro — the loss of consciousness comes without any harbingers in 12 — 15 sec. after rise. No changes of outward and behavior to a loss of consciousness are noted.

At the heights of 7000 — 7500 m V.'s current. depends on individual stability — time of possible stay at this height fluctuates from 2 — 3 to 20 — 30 min. and more. The behavior during nek-ry time happens inadequate — high spirits and the noncritical relation to a surrounding situation are sometimes noted. Shortly before a loss of consciousness the person becomes inexpressive, a look stiffened (empty), nek-ry persons have a twitching of muscles of a brush then clonic spasms extend to all hand and can become generalized. There comes the loss of consciousness, at a cut within several seconds the diseased keeps an active pose. Changes of an ECG, breath, blood pressure in development of this form B. demonstrate that deep disturbances of c. N of page, including a loss of consciousness, arise against the background of development of the expressed compensatory and adaptive reactions of breath and blood circulation. Important diagnostic indicator of development of V. and its weights are changes of EEG. During manifestation of disturbances of handwriting and intellectual frustration on EEG 0 waves of the increased amplitude appear (at first in frontal assignments). In process of increase of weight of V. the number and amplitude 0-and A-waves gradually increase, they dominate on EEG during emergence of spasms and disturbance of consciousness. A loss of consciousness at this form B. carry to homeostatic faints since it the anoxemia — considerable decrease in oxygenation of blood is the reason. At this form B. cerebral circulation a nek-swarm time after a loss of consciousness remains on rather high level therefore recovery of normal supply of an organism with oxygen (descent from height, breath by oxygen) brings to bystry, during 10 — 20 sec., to recovery of consciousness and disappearance of all symptoms of V.

Treatment

sick V.'s Switching. on breath by oxygen or mix of oxygen the content of 3 — 5% of carbon dioxide gas is the only reliable method of treatment of this disease. In mild cases oxygen therapy leads to a bystry and complete recovery of health. It must be kept in mind that sometimes giving oxygen leads to the short-term, but quickly taking place deterioration in the general state, i.e. to development of a so-called paradoxical effect of oxygen. The reflex mechanism is the cornerstone of this phenomenon, the starting moment to-rogo is change of character of the impulsation from vascular reflexogenic zones arriving to vasculomotor and to respiratory centers. At severe forms of V., when the diseased a long time is unconscious, or in cases when the loss of consciousness arises repeatedly and is followed by attacks of spasms and vomiting (such cases are described at V.'s development. in flights), in addition to oxygen therapy, drug treatment is necessary. For prevention and elimination of post-hypoxemic wet brain it is recommended to use the drugs having dehydrational effect: Mannitolum, dextran, glucose [Basbi (D. E. Busby, 1968)].

The forecast

In hard cases completely of V. is not possible to recover a normality of health often also. leads to emergence hron, diseases of c. N of page (post-hypoxemic encephalopathy, post-hypoxemic visual disturbances, mentalities and memories).

Prevention

the Most effective remedy of prevention of V. use of the oxygen equipment supporting normal intake of oxygen in an organism is. For increase in stability of kV. it is reasonable to train in the conditions of a pressure chamber — regular rises on gradually increasing heights from 3000 to 5000 m, and also in the conditions of highlands.

See also Adaptation to height , Height , Hypoxia .


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V. B. Malkin.

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