The paper represents the ISS-59/60 crew members, main tasks and results of crew training. great attention is paid to the crew activity aboard the Soyuz MS-12 manned transport vehicle (MTV) and ISS. Special attention is paid to extravehicular operations (EVA) performed according to the programs of the RS (Russian Segment) and USOS (US Orbital Segment) of the ISS. The paper also briefly analyzes the implementation of the Russian scientific applied research and experiments program.

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. In all, 115 experiments were performed. Twenty-four hours in HA at 93 kPa and subsequent transition to 37 kPa led up to development of ADS symptoms by one subject in one of 27 experiments (3.7%), and emergence of venous gas bubbles (USI) with the intensity of 2, 70, and 19 points by the Spenser scale in 9 experiments (33.3%). Lower HA pressures (86 kPa, 80 kPa and 73 kPa) did not give rise to ADS though the occurrence of venous GB distinctly tended downward (30.6%, 14.3% and 11.8%) and so did the intensity of their entry into the pulmonary circulation (2, 40, 18 points; 1, 80, 19 points, and 2, 00, 15 points, respectively). Minimal ADS risk was observed in HA at 80 kPa and 73 kPa and did not reach 4% at the confidence level of 95%.

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. None of 24 "ascents" produced clinical signs of ADS. Comparison of the data concerning frequency and time points of detection by ultrasonic Doppler equipment of gas bubbles (GB) in the venous bed during decompression with initial, maximal and mean values of US signal intensity failed to state a significant difference between them. Data of the investigation were confronted with anticipated length of GB dispersion in body tissues.

Extra-vehicular activity (EVA) has a significant role during extended space flights. It demonstrates that humans can survive and perform useful work outside the Orbital Space Stations (OSS) while wearing protective space suits (SS). When the International Space Station 'Alpha' (ISSA) is fully operational, EVA assembly, installation, maintenance and repair operations will become an everyday repetitive work activity in space. It needs new ergonomic evaluation of the work/rest schedule for an increasing of the labor amount per EVA hour. The metabolism assessment is a helpful method to control the productivity of the EVA astronaut and to optimize the work/rest regime. Three following methods were used in Russia to estimate real-time metabolic rates during EVA: 1. Oxygen consumption, computed from the pressure drop in a high pressure bottle per unit time (with actual thermodynamic oxygen properties under high pressure and oxygen leakage taken into account). 2. Carbon dioxide production, computed from CO2 concentration at the contaminant control cartridge and gas flow rate in the life support subsystem closed loop (nominal mode) or gas leakage in the SS open loop (emergency mode). 3. Heat removal, computed from the difference between the temperatures of coolant water or gas and its flow rate in a unit of time (with assumed humidity and wet oxygen state taken into account). Comparison of heat removal values with metabolic rates enables us to determine the thermal balance during an operative medical control of EVA at "Salyut-6", "Salyut-7" and "Mir" OSS. Complex analysis of metabolism, body temperature and heat rate supports a differential diagnosis between emotional and thermal components of stress during EVA. It gives a prognosis of human homeostasis during EVA. Available information has been acquired into an EVA data base which is an effective tool for ergonomical optimization.

Analysis of the extravehicular activity (EVA) sortie experience gained in the former Soviet Union and physiologic hygienic aspect of space suit design and development shows that crewmember productivity is related to the following main factors: space suit microclimate (gas composition, pressure and temperature); limitation of motion activity and perception, imposed by the space suit; good crewmember training in the ground training program; level of crewmember general physical performance capabilities in connection with mission duration and intervals between sorties; individual EVA experience (with accumulation) at which workmanship improves, while metabolism, physical and emotional stress decreases; concrete EVA duration and work rate; EVA bioengineering, including selection of tools, work station, EVA technology and mechanization.

The results of testing a procedure of ultrasonic location of the gas bubbles (GB) in man during space suit operations to simulate an extravehicular activity (EVA) are presented. Doppler echotachocardiograph "Rhythm" operating at ultrasonic frequency of 1.76 mHz was used as a GB detector. The device "Rhythm" integrated with a special flat transducer of 23 mm in diameter and 4 mm in width was positioned on the subject chest above the pulmonary artery projection. During 4-6 hour human operations while wearing pressurized (276-290 mm Hg) space suit, in 7 of 12 tests performed a stable and qualitative signal of the arterial blood flow in the lungs was recorded. In case of an unstable signal, in order that its quality be improved the posture of test subject was changed and the signal was recorded during a short-term expired breath-holding. Cardiac GB formation was noted during 6 tests in 2 subjects. The first GBs appeared at the 30th, 33rd, 70th, 111th, 114th and 180th minute after producing an operating reduced pressure in space suit. The time of GB detection on the average was 89.7 min. The maximum intensity of GB signal was 3-4 scores on Spencer's scale, but altitude decompression sickness symptoms did not develop in the test subjects. The risk of developing the altitude decompression sickness as opposed to the results of control experiments without use of space suit is discussed.

This paper presents the results of 1179 altitude chamber tests of special suits performed by 193 subjects. The probability of altitude decompression disease observed during 29 experiments (2.5%) in 26 test subjects (13.4%) is calculated. The safety of decompression tables is evaluated as applied to the pressure 14-43 kPa after oxygen breathing for 0.25-2 hrs at sea level or for 1-6 hrs at 40 kPa.

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 3.2%. This allowed work of moderate load at the ambient pressure 220 mm Hg after two-hour breathing of oxygen with nitrogen admixture of no more than 5%.

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.

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.