Fiziologiâ čeloveka

During space flight, the changes in the functions of the upper limbs can affect the quality of operator activity. At the same time, there are very few data on this topic, because most of the research is focused on the structure and functions of the lower extremities. The aim was to study the characteristics of the grip force control during the decrease of the support and proprioceptive sensory signals in the conditions of the ground-based model of the effects of space flight – dry immersion (DI). The duration of DI exposure was 21 days. 10 male volunteers performed tests using a hand dynamometer for maximal voluntary contraction, the maintenance of the reference force, the reproduction of this force from memory, and the grip force gradation test. The subjects performed this series of tests before exposure to DI, then on days 1, 3, 5, 10, 15, and 20 of DI, and days 1 and 3 of the recovery period. The results show that DI exposure led to an increase in proprioceptive sensitivity in the tasks without visual feedback when with open eyes from day 5 of DI the subjects were more mistaken in the reproduction of the reference force using the dominant hand. The sensory processing/modulation disorder under DI factors may cause this phenomenon.

Head-down bed rest (HDBR) is one of the best known models of the effects of weightlessness. The responses of the cardiovascular system to thoracocranial blood redistribution continue to be studied in relation to changes in the volumes of the heart chambers and the structure of the heart muscle. The assessment of myocardial stretch, individual response of the heart muscle to HDBR and stratification of the risk of developing heart failure according to the dynamics of a cardiomarker, independent of the influence of such factors as gender, age, body weight, glomerular filtration rate, anemia and hypovolemia, is relevant. The aim of the work was to investigate the influence of factors of 21-day HDBR on the level of the ST2 myocardial stretch biomarker. The effect of 21-day HDBR on the level of ST2 cardiomyocyte stretch marker was studied for the first time. The level of ST2 significantly decreased by the end of HDBR. The data obtained are of practical importance in relation to the problems of medical selection of cosmonauts and test volunteers. Background levels, variability of indicators during HDBR and the recovery period indicate the absence of risks for the development of heart failure and cardiofibrosis in this sample of subjects in this study.

Studies in conditions of head-down tilt bed rest are widely used experiments which imitate redistribution of body fluids similar to the redistribution of fluid media in microgravity. To study the mechanism of development of spaceflight-associated neuro-ocular syndrome (SANS) in head-down tilt bed rest studies scientists have evaluated, among other things, participants’ visual system parameters. The main symptom of SANS is an edema of an optic disc and a retina. To date, the results describing the influence of head-down tilt bed rest on the visual system are ambiguous, which determines the relevance of further research. The aim of the study is to analyze retinal morphometry in the optic disc area and macular area in participants before and after 21-day head-down tilt bed rest. The study was performed using an optical coherence tomography with angiography function (Optovue RTVue XR Avanti System) before and after 21-days of head-down tilt bed rest. In 4 participants (8 eyes) (men, mean age ± standard deviation: 29.3 ± 3.9 years) the macular zone and optic disc area were evaluated according to standard scanning modes. To analyze the values obtained, we used mean tendency scores, mean comparison criteria, and graphical analysis. The results of the retinal thickness in the optic disc zone were consistent with those of other researchers, indicating a possible increase in retinal thickness, but our results did not reach the level of statistical significance. A statistically significant thickening of the retina in the macular zone was shown for the first time, but the increase is significantly less in amplitude than the thickening of the nerve fiber layer in the optic disc zone. Analysis of vascular density under head-down tilt bed rest conditions was performed for the first time both for the optic disc zone and the macula zone, but additional studies are required to obtain steady conclusions. For the first time, an increase in retinal thickness in the macula zone in participants of head-down tilt bed rest experiments was shown; for the optic disc zone, data consistent with the results of other researchers were obtained. For the first time, angiographic data were obtained for the macula and optic disk areas, but the obtained differences in vascular density did not reach the level of statistical significance.

The effects of long-term anti-orthostatic hypokinesia (bed rest – BR, a model of gravitational unloading) on the dynamics of orthostasis-induced changes in the content of total (THb), deoxygenated (HHb), and oxygenated (OHb) hemoglobin in the calf at the level of the gastrocnemius muscle medial head were studied using the near-infrared spectroscopy. In seven young men, 2−4 days before and on the 19th day of BR, a passive head-up tilt test was performed (15 min in the supine position, then 15 min at 65°). After BR, there was an increase in heart rate and a decrease in stroke volume in the supine position, as well as more pronounced changes in these parameters during orthostasis. Blood pressure in the supine position and orthostasis did not change after BR. THb content increased gradually during orthostasis and reached a plateau by the end of the test; after BR, an increase in the half-rise time and a two-fold increase in the plateau level were observed. Tissue HHb content by the end of the tilt test also increased after BR. The dynamics of OHb before BR was more complicated: this indicator grew, reached a maximum during a minute, and then gradually decreased to half of the maximum by the end of the test. After BR, the dynamics of OHb changed drastically: the signal increased gradually and reached a level that was twice the peak value of OHb content before BR. The results allow us to conclude that exposure to BR weakens the compensatory constriction of calf vessels during tilt test; consequently, it is followed by higher blood filling of calf vascular bed, which, in turn, leads to smaller SV during orthostasis.

8 male volunteers aged 26 to 44 years were examined, who were in the “Arfa” hypomagnetic environment simulation facility for 4 hours at a normal magnetic field level (background session), and twice within 24 hours: one session during hypomagnetic environment simulation. environment with an attenuation coefficient of 500, and one − in the conditions of the terrestrial magnetic field (placebo). Venous blood was collected at the end of each session. The values of 48 biochemical parameters reflecting the state of organs and tissues, as well as the main links of metabolism, were determined in plasma and serum. Psychological testing of the testers was carried out using the questionnaires “Assessment of acute physical fatigue” by R. Kinsman and P. Weiser adapted by A.B. Leonova and “Assessment of acute mental fatigue” by A.B. Leonova and N.N. Savicheva. The level of physical condition of the participants of the experiment was assessed according to the method of D.N. Davidenko. As a result of the first biochemical screening examination and psychological testing of volunteers who were in a simulated space-level hypomagnetic environment, it was established that the effect is stressful, accompanied by the activation of glycolysis, lipolytic processes, affects the acid-base balance of the body, the state of the vascular endothelium, leads to to changes in the hepato-biliary system. At the same time, the index of physical fatigue among the volunteers increases, and the level of physical condition significantly decreases. Subjectively, pronounced changes in the biochemical parameters of stressful orientation are not felt.

The review presents literature sources confirming the key aspects of the theory of allostasis and its relationship with the theory of homeostasis, as well as some neurophysiological aspects of allostatic systems, include autonomic regulation, which determine the relationship between the brain and the cardiovascular system. One of the aspects of allostatic regulation is heart rate variability, which reflects the state of the body’s plastic constants and their changes under space flight conditions.