[Justifying hyperbaric oxygenation use for medical correction in individuals working in extreme conditions].

Experimental studies were conducted to justify possibility of hyperbaric oxygenation to correct functional state in individuals working in extreme conditions. Studies were aimed to determine stress resistance in apparently healthy individuals, to choose hyperbaric oxygenation method and mode.

[Prevention of altitude decompression sickness during simulation of egress from the cabin of space vehicle with hypobaric artificial atmosphere]. / Profilaktika vysotnoi dekompressionnoi bolezni pri imitatsii vykhodov iz kabiny kosmicheskogo korablia s gipobaricheskoi iskusstvennoi gazovoi atmosferoi.

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%.

[The assessment of the risk of altitude decompression sickness during simulation of repeated (with 12 hour interval) exits into open space]. / Otsenka riska vysotnoi dekompressionnoi bolezni pri imitatsii povtornykh (s 12-chasovym intervalom) vykhodov v otkrytyi kosmos]

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.

[Effect of a nitrogen admixture in the inhaled oxygen on the effectiveness of 2-hour desaturation before decompression from 760 to 220 mm Hg]. / Vliianie primesi azota vo vdykhaemom kislorode na éffektivnost' dvukhchasovoi desaturatsii pered dekompressiei ot 760 k 220 mm rt. st.

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%.

[Probability of altitude decompression sickness following a drop in pressure from 840 to 308 mm Hg]. / Veroiatnost' vysotnoi dekompressionnoi bolezni posle perepada davlenii ot 840 do 308 mm rt. st.

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.