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The study of literature and aviation incidents during the depressurization of the aircraft cabin in the altitude higher than 12 km. Shows that their serious outcomes are often connected with wrong evaluation of the emergency situation by pilots, making incorrect decision and carrying out inadequate actions. In order to improve psychophysiologic training for stratosphere flights and to increase their safety the authors suggest approbated methods of periodic altitude chamber flights of flying personnel to the altitude of 13.5 km., imitating the stress situation during the depressurization of the cabin and enabling to form adequate algorithm of pilots' behaviour in these conditions.

The article has analyzed the main development and improvement stages of medical support of high-altitude flight safety. Test results of a full-scale model of the on-board active flight-safety system [symbol: see text]-2 have been given. There have been formulated prospective trends of further studies of the complex system development of crew-life support, widespread use of computer-aided technologies, as well as practical introduction of rehabilitating hypoxy-based trainings in order to increase in the pilot organism functional reserves.

In simulating acute hypoxic hypoxia with the participation of male volunteers, the authors investigated the antihypoxic and antioxidative activity of metabolic drugs (jakton, amtizole succinate, nootropil, probucol, and a mixture which consists of jakton, amtizole succinate, and probucol). The pharmaceuticals were shown to have heterodirectional effects on lipid peroxidative processes. Drugs having a pronounced antioxidative activity (such as probucol and the mixture) promotes oxygen utilization during hypoxia and posthypoxic reoxygenation chiefly by the oxygenase pathway. This rearrangement of oxygen utilization processes caused an increase in human high-altitude resistance. The use of the above drugs is a promising trend in the development of an adaptative response to hypoxia in persons engaged in hazardous jobs.

During a simulated long-term mission with participation of male volunteers biochemical effects of various conditions of oxygen supply including breathing the cabin air at 2.4 km, pure oxygen, and intermittent hypoxia/hyperoxia, i.e. breathing the cabin air for 50 min and pure O2 for 10 min every hour in flight were studied. This assessment of respiration conditions by biochemical criteria allowed to recognize the combination of short hyperoxia and cabin air as the optimum to be taken into accounted in attacking the problem of oxygen supply of aviators in extended flights.

Under simulation of acute hypoxic hypoxia with participating the volunteers (men) there has been studied the predictor significance of the biochemical indices characterising an intensity of lipoperoxidation process, hormonal status and level of fermentemia. It is indicated that the following indices, namely, LDH, a [symbol: see text]-DPDH, MPD, secondary products of POL, SOD, insulin, cAMP and cAMP/cGMP have the prognostic validity. The revealed combination of the reliable relations was approximated by the equations of one-factor regression. As this takes place, the analysis of the presented dependencies between tolerance for hypoxia and biochemical indices allowed one to recognize the most probable mechanisms of resistance to the effect of this factor. The performed discrimination analysis for 6 biochemical variables (cAMP, LDH, SOD, MPO, MDA, TC) made it possible to create discriminant equations and to formulate the decisive rules to class the individuals into the ranks with different tolerance to the oxygen deficiency. The high informative capacity of the mentioned approach is recommended by the authors for a more wide use when developed the expert system to evaluate the human functional state as applied to the effect of extreme environmental factors and activity.

The paper outlines the basic landmarks of the activity of the workers of the RF State Research Test Institute of Aviation and Space Medicine who have solved the problems of altitude flight safety provision, designed various sets of oxygen and altitude equipment. The main results of the investigations made by the Altitude Department of the Institute are summed up and some promising directions of its workers' activities are shown.

The authors studied efficiency of life supply by means of Oxygenation Equipment Complex (OEC) for pilots subjected to depressurization of the cabin in emergency on altitudes under 20 km. OEC provides breathing under the excessive oxygen pressure and light-weight ammunition. Efficiency of the complex was evaluated through polling the examinees, the time of the discomfort occurrence, changes of the cardiorespiratory and visual parameters, functional tests and quality of the piloting. The studies proved OEC to be effective means for saving the life and the performance maintaining when the depressurization of the cabin on altitudes under 20 km. The authors estimated "reserve time" for the pilot's performance maintaining within the altitudes of 14-16-18-20 km and revealed the factors delimiting efficiency of OEC in the studied conditions.

A new method of altitude chamber climbs of flight personnel (for familiarization and training) has been worked out. The aim of this method is to form among aircrew members the skills to recognize hypoxia in flight and to train them in taking practical measures to remove it. This method appeared to be informative: hypoxia awareness was registered after 3-9 minutes of staying at an altitude of 5000-6000 m in 93% of tested persons. The time necessary to carry out such a familiarization climb in an altitude chamber in comparison with a high-altitude test is 2.5-3 times shorter. This method is safe for pilot's health, practicable in the conditions of any military air unit and flying school, and can also be used for the examination of flying personnel health and functional status of their organism.

The article studies the possibility of man to self-diagnose the development of hypoxia and take decisive actions on its elimination with the help of flight living facilities. Four variants of hypoxia were modeled at hyperbaric chamber and flight simulator. The differences between these four variants were the following: strength, increase velocity and duration of hypoxia, the level of "notification" about the oxygen conditions for tested persons. The authors make a conclusion that man is capable of discovering hypoxia both at rest and active operating state, that gives the possibility to take an adequate decision on coming out from critical situation caused by hypoxia.

In four experimental runs (30 test subjects in 407 tests), the beneficial effect of hyperbaric oxygenation (HBO) on flight tolerance was demonstrated. HBO sessions (7-8 sessions of an hour in duration during 10-12 days at pO2 = 2 atm) helped subjects with poor altitude tolerance to increase the altitude ceiling by 1 km and reserve time at altitudes of 6-7 km by 3-4 min, the effect being persistent for 2-3 months. Statokinetic tolerance of subjects with medium motion sickness susceptibility grew by 2-2.5 times after the above HBO sessions. As compared to regular rest, the HBO treatment shortened two-fold the period of recovery of the health state and work capacity of operators, which went down during flight, and increased 15-20% the time of repeated work prior to failure in a stressful environment.

As a result of 64 experiments carried out on 24 test subjects, it has been shown that extreme overwarming due to moderate and heavy thermal loads can be prevented with the aid of heat release through sweat evaporation from the surface of the body under the action of a rarefied atmosphere (termed vacuum sweat evaporation). The test subjects wearing altitude suits remained in a thermal altitude chamber at 40 and 55 degrees C for 8 to 3 hours at rest and doing light work at altitudes of 7 to 25 km without marked signs of overwarming. The entire heat release occurred only through vacuum sweat evaporation from the surface of the body that was under the altitude suit during a gradual decrease of the chamber pressure to 20 mm Hg (equivalent to an altitude of 25 km). The findings give support to the hypothesis that heart release via vacuum sweat evaporation from the surface of the body can be used as a method of controlling thermal homeostasis during high altitude and space flights.

It has been shown experimentally that the development of altitude decompression disease at 250 and 180 mm Hg can be prevented by preliminary desaturation in the nitrogen-oxygen hypobaric atmosphere (60% N2 and 40% O2 at 550 mm Hg). This has been demonstrated in 38 experiments on 21 test subjects. The use of this atmosphere in space cabin prevents the development of decompression disease upon a decrease of the cabin pressure to 250 mm Hg and upon extravehicular activity in a space suit with 180--200 mm Hg.

By the method of Astrup-Zigaard-Andersen the acid-base balance in the blood of men and dogs exposed to hypercapnic atmospheres with a normal, increased and decreased oxygen content was investigated in 164 experiments. Variations in the acid-base equilibrium were compared with changes of physiological functions. The relationship between the acid-base balance and the carbon dioxide concentration as well as the oxygen concentration in the breathing air was established. The toxic effects of sharp hypercapnia and hyperoxia were shown to cumulate. The positive effect of moderate hypercapnia on the tolerance to normobaric hypoxia in long-term experiments was noted.

This paper presents pooled data about the factors determining health status and work capacity of aircrew using positive pressure breathing systems at altitudes over 12,000 m. It is indicated that the system compensating positive pressure is primarily responsible for the protective and ergonomic characteristics of altitude equipment.

In order to study the chronic form of decompression disease, clinical and physiological examinations of 38 test subjects were carried out. They participated in 133 chamber experiments and were exposed to an altitude of 11,000--12,000 m for 2--3 to 20--24 hours after desaturation of different duration. Besides, histological and histochemical examinations of organs and tissues of 3 dogs were performed. During 70, 110 and 140 days the dogs were exposed 20, 33 and 35 times to an altitude of 12,000 m for 2--2.5 hours without preliminary desaturation. No persistent pathological changes were found in the animal or human body.

In 54 pressure chamber experiments 12 healthy male test subjects took part. Their pneumotachograms and other physiological parameters at a positive pressure breathing of 30 mm Hg at sea level and of 125--130 mm Hg at an altitude of 25,000 m at rest and while exercising were recorded. High altitude facilities and pneumotachograph were modified to meet the experimental requirements. The changes in pneumotachographic readings depended on the excess intrapulmonary pressure, its variations with respect to the respiratory stages, efficiency of the external counterpressure on the body, as well as motor activity of the test subjects. The pneumotachographic procedure allows qualitative and quantitative evaluations of external respiration upon excess intrapulmonary pressure, and study of the mechanism of these changes supported by other physiological methods.

Six 3-day experiments were carried out in an altitude chamber in which 6 test subjects took part. The experiments simulated repeated extra-vehicular activities--intensive work at an altitude of 10,000 m in a helmet or at an altitude of 40,000 m on a space suit pressurized at 200 mm Hg. It was demonstrated that altitude decompression could be prevented by desaturation--prolonged exposure to the hypobaric atmosphere (430 mm Hg) and 100% O2 or a 40% O2 and 60% N2 mixture. During the 3-day experiment the test subjects made seven 3--4 hour excursions, showing no symptoms of decompression disease.

Forty altitude chamber experiments were carried out in which 18 test subjects participated. The purpose of the experiments was to prevent decompression sickness in a pilot using an altitude compensatory suit and oxygen mask. It was demonstrated that oxygen breathing on the ground and at an altitude of 8 km for 20 and 50-60 min eliminated severe symptoms and lowered the frequency of occurrence of mild symptoms of decompression sickness during the subsequent 10-20 and 60-120 min exposures to altitudes of 40,000 and 11,000 m respectively. An increase in the absolute pressure to 240-290 mm Hg in the altitude garment prevented decompression sickness of altitudes of 11,000-15,000 m and eliminated it if it occurred at lower barometric pressure.

A large number (550) pressure chamber experiments in which 200 suited subjects simulated an egress from the spacecraft (decompression from 760 to 20--10 mm Hg) showed a relationship between decompression sickness frequency and severity, space suit absolute pressure (160--310 mm Hg), time of the exposure (1--10 hours) and desaturation (15--60 min), and exercise load (150--400 Cal/hr). Without desaturation there were no decompression sickness symptoms at a suit pressure of 270--310 mm Hg. An egress into space in a suit at a pressure of 160--230 mm Hg after 15--60 min desaturation induced bends of different severity. Less frequent cases of decompression sickness in our experiments as compared with the literature data (obtained on unsuited subjects) can be attributed to the peculiar kinematics of movements and excessive pressure in the suit.