[EFFECT OF VOLUNTARY BREATH-HOLDING AND COGNITIVE LOADS ON REGIONAL CEREBRAL BLOOD FLOW AND BIOELECTRIC ACTIVITY OF THE BRAIN].

Cerebral blood flow and bioelectric activity were studied in 10 normal volunteers in order to assess cerebrovascular reactivity during different types of functional testing. The transcranial Doppler was used to measure linear blood velocity (LBV) in the middle cerebral artery (MCA) during maximal voluntary breath-holding (apnea), controlled verbal association test and tactile memory test. Simultaneous electroencephalography (EEG) registered the bioelectric activity of the brain cortex. Both investigations were performed continuously in the course of each test. Breath-holding induced a smooth symmetric increase of CMA blood velocity; LBV rose to maximum values in the majority of the volunteered subjects. Two subjects with small focal changes in the brain's white matter displayed an asymmetric blood flow reaction to apnea. Gain in LBV was materially less during the cognitive tests; the verbal test decreased LBV in one half of the subjects and increased LBV in the other. The tactile memory test increased LBV which was particularly high in the left CMA of all subjects. LBV dynamics during the cognitive tests was essentially different from what was observed in apnea. Blood flow variations in the course of equally the verbal and tactile tests had a regular undulatory character. Concurrent LBV and EEG monitoring made it possible to compare and contrast dynamics of the cerebral blood velocity and bioelectric activity directly during testing and thus to reveal peculiar reactions of the cerebral blood flow to cognitive and physiological testing.

[Scatological investigations during 105-day isolation].

Dynamics of the gastrointestinal functioning was reconstructed by analysis of the scatological data from volunteered subjects before, on days 16, 35, 45, 60, 90 and after completion of 105-day isolation experiment. The analysis showed that scatological investigations performed in the conditions imitating life in an exploration vehicle environment are instrumental in detecting deviations in the GI function indicative of pancreas excretory and hepar biliary excretion and synthetic hypofunction that can be responsible for intestinal dysfunction. Normalization of scatological parameters following the experiment witnesses to functional genesis of the changes observed during the exploration mission simulation.

[The influence of extended exposure in artificial hypercapnic environments on the function of external respiration and gas exchange]. / Vliianie dlitel'nogo nakhozhdenia v iskusstvennykh giperkapnicheskikh sredakh na funktsiiu vneshnego dykhaniia i gazoobmen.

Effects of artificial hypercapnic atmosphere were studied in a series of ten 40-d experiments with participation of 42 volunteers aged from 20 to 61 years. Partial pressure of carbon dioxide was maintained at 27 +/- 2 mm Hg (3.4-3.8% CO2); partial pressure of oxygen was in the range of 122-136 mm Hg. Barometric pressure, air temperature and humidity had normal values. Results of the experiments were subjected to the variation analysis. Continuous breathing the gas mixture with specified PCO2 increased CO2 sensitivity of the breathing center in all age-groups both at rest and during exercise. The ventilatory reaction of subjects aged 41-61 grew to a less degree as compared to the subjects below 40. Medical selection of members for space crew to go to a distant voyage should take into consideration the parameters of oxygen demand and the volume of pulmonary ventilation per a time unit.

[Sensitivity of the respiratory center to carbon dioxide during prolonged exposure of humans to gas environment with unchanging level of hypercapnia]. / Chuvstvitel'nost' dykhatel'nogo tsentra k uglekislomu gazu pri dlitel'nom nakhozhdenii cheloveka v gazovoi srede s neizmeniaiushchimsia urovnem giperkapnii.

Effects of moderate CO2 concentrations (2.2-3.2%) on external respiration were studied in a series of extended (30-d) continuous tests with volunteered human subjects. In one test, PCO2 in the gas mixture was maintained at 15-19 mm Hg (2.0-2.5%), in the other, at 20-23 mm Hg (2.7-3.0%). Partial pressure of oxygen was controlled at 144-152 mm Hg (19-20%) with the barometric pressure, temperature and humidity at the norm. As compared with the onset, at the end of the first test parameters of the external respiration were changed neither at rest nor during exercises. At the end of the second test, the minute pulmonary ventilation showed a steady rise in synch with the duration of exposure growing in 2.5 times at rest and in 1.7-2 times during physical exercises suggesting an increase in the respiratory center sensitivity to the CO2 level under study. Hence, breathing CO2 at 2.7-3.0% for many days did not sensitize the respiratory center of the human subjects.

[Composition of exhaled air, gas and energy metabolism and bio- chemical indicators of the blood and urine in humans after long- term exposure to hypercapnia and hypoxia]. / Sostav vydykhaemogo vozdukha, gazoénergoobmen i biokhimicheskie pokazateli krovi i mochi u cheloveka pri dlite'nom nakhozhdenii ego v usloviiakh giperkapnii i gipoksii.

Four volunteers were enclosed for 40 days in a hypercapnic environment. Their average age was 41-59 years, body weight, 66-90 kg, and height 173-182 cm. During the study the ambient temperature was 19-23 degrees C, relative humidity, 50 +/- 20%; pO2, 19-19.5%; and pCO2, 1.3%. On test days 21-22 and 38-39 pCO2 was increased to 4% and pO2 was decreased to 17%. The time, within which pCO2 was increased to 4% on test days 38-39 when compared to test days 21-22, grew 1.5-fold and amounted to 40 hours. The subjects had three meals a day, consuming canned foodstuffs, the caloric value of which was 2982 kcal/day. In the study the following parameters were measured: malonic dialdehyde in venous blood; catalase, lactate, pyruvate, urea, acid-base content, gases in capillary blood; total nitrogen, ammonia, urea, creatinine and uric acid in 24-hour urine samples. Nitrogen balance and protein nutrition index were calculated. Results were processed using Student's t-test. During exposure lipid peroxidation increased and catalase decreased; malonic dialdehyde in blood increased, being correlated with lower hydrocarbons in exhaled air; gas and energy turnover during hypercapnic intervals enhanced. The above changes in the exhaled air composition, gas and energy turnover, biochemical blood and urine parameters remained within adaptation norm. By the second week of the recovery period the above parameters, except for nitrogen metabolism which remained slightly inhibited, returned to the normal.

[Dynamics of acid-base equilibrium of the blood in humans a long-term exposure to an atmosphere containing acetic acid vapors]. / Dinamika kislotno-shchelochnogo sostoianiia krovi cheloveka pri dlitel'nom nakhozhdenii v atmosfere, soderzhashchei pary.

Two experimental series, each of 20 days in duration, were carried out using 8 healthy test subjects, aged 25 to 44 years. The purpose of the experiments was to identify the effect of two different concentrations of acetic acid vapors in an enclosed environment on blood acid-base equilibrium and gases. In both experimental series ambient temperature was increased to 33 degrees C during the last three days of exposure in order to better evaluate the acetic acid vapor effect. The most significant changes in acid-base equilibrium were detected when the vapor concentration amounted to 25 mg/m3.