[Prevention of altitude decompression sickness during simulation of egress from the cabin of space vehicle with hypobaric artificial atmosphere].

Based on the proposed semiempiric nomograms, the study was aimed at selection and investigation of normoxic N2-O2 hypobaric atmosphere (HA) at 93-73 kPa, and evaluation of effectiveness of the gas mixture against the altitude decompression sickness (ADS) during 6-hr simulation of extravehicular activities at 37 kPa without prebreathing. Subjects were 22 healthy males from 20 to 50 yr. old.

[The assessment of the risk of altitude decompression sickness during simulation of repeated (with 12 hour interval) exits into open space].

Purpose of the investigation was to assess contribution of repeated (with a 12-hr interval) decompression to the risk of altitude decompression sickness (ADS) by simulation of 6-hr extravehicular activities (EVA) of space crewmembers in altitude chamber. The protocol included "ascents" of 6 essentially healthy male subjects at the age of 24 to 51 to the altitude of 7,600 m (37 kPa) following 30-min prebreathing (elimination of nitrogen from the body by breathing pure oxygen through a mask at the ambient pressure of 73 kPa = 2,600 m). Each subject participated in 2 experimental exposures: first initial and then repeated decompression.

[Quantification of combined effect of physical-chemical factors by the parameters of human external breathing].

Quantitative evaluation of the combined effect of physical-chemical factors, i.e. hypodynamia, ionizing radiation at small doses, noise, vibration, and altered gas composition of the atmosphere was accomplished during 3- and 15-day experiments with exposure of 11 volunteers (factually 16 subjects) to specified environment in hyperbaric chamber by the parameters of external breathing.

[Hypobaric atmosphere and decompression safety of outer space explorations on the first days of flight].

54 subjects aged 21-47 participated in 8 series of experiments (298 altitude investigations) aimed at selecting decompression-safe protocols for transition from hypobaric normoxic environment to reduced pressure. Experimental data is discussed and some protocols for safe transition to reduced pressure are recommended. The experiments allowed to display in diagram form the ratio of permissible magnitudes of residual pressure (the working pressure in the extravehicular suit) to the duration of a preliminary exposure in normoxic hypobaric conditions.

[Changes in the maximum permissible supersaturation coefficient in altitude decompression].

This paper presents experimental data obtained during 383 altitude chambers tests in which 70 subjects participated. The purpose of the tests was to verify experimentally the safety of altitude decompression regimens that simulated transition from the orbital station atmosphere at a normal barometric pressure to the space suit oxygen atmosphere at a lowered pressure. The results help better understand correlations between the maximal allowable super-saturation coefficient and total postdecompression pressure.

[Comparative study of decompression-induced formation of gas bubbles using ultrasonic equipment and the development of altitude-decompression disorders].

442 altitude experiments on 40 volunteers were performed. Gas bubbles in venous blood were detected using an ultrasonic Doppler system functioning in a continuous mode at a frequency of 5 MHz. The threshold of bubble formation was identified in 31 test subjects and that of emergency of altitude-decompression disorders, in 28 test subjects.

[Sensitivity of the respiratory regulatory apparatus to CO2 under simulated space flight conditions].

Using the rebreathing method, CO2 sensitivity of the respiration regulation system was investigated during a year-long enclosure study and head-down tilt tests of varying duration (up to 120 days). During the exposures CO2 and H+ were built up in the body. In the course of the enclosure study CO2 sensitivity was reduced.

[Analysis of clinical symptoms of cases of human decompression disease in altitude chamber studies].

Over 2400 altitude chamber ascents in which 130 volunteers participated were performed using different decompression tables. The cases of decompression disease were classified in terms of its types and severity. It is stressed that the experiments involved in decompression studies have to be extremely careful because the disease may have various and sudden manifestations.

[Relation between the probability of development of altitude-decompression disorders and the duration of pre-exposure to a hypobaric atmosphere].

Healthy volunteers, aged 21-47 years, were kept in an altitude chamber. Before decompression to a residual pressure of 293.3 GPa the test subjects were consecutively exposed to 1120 GPa for 2 hrs and then to 733.

[Effect of a nitrogen admixture in the inhaled oxygen on the effectiveness of 2-hour desaturation before decompression from 760 to 220 mm Hg].

The ground-based experimental study of denitrogenation by oxygen breathing showed that two-hour denitrogenation was inadequate if the breathing gas contained about 10% nitrogen or if the process included 3-10 min of air breathing. The reduction of the nitrogen content in the breathing gas to 0.4-5% eliminated severe forms of the decompression disease and decreased significantly the incidence of its mild forms to 3.

[Probability of altitude decompression sickness following a drop in pressure from 840 to 308 mm Hg].

The decompression from the hyperbaric air atmosphere with the pressure 840+/-5 mm Hg and subsequent 40 min exposure to the hypobaric atmosphere 308+/-1 mm Hg containing 40 to 95% O2 cause a decompression disease in 5-40% cases. The probability of the disease depends on the duration of nitrogen saturation at an increased pressure, physical fitness and individual susceptibility to decompression sickness.