Effect of real and simulated weightlessness on the characteristics of the static otolith reflex

To determine the role of the support-proprioceptive factor in functioning of the vestibular system, in particular, the role of static torsional otolith-cervical-ocular reflex (OCOR), the latter was studied in 16 subjects after a seven-day “dry” horizontal immersion and in 14 cosmonauts after a prolonged exposure to weightlessness (for 126–195 days). OCOR was studied by the videooculography method during alternately tilting the head towards the right or left shoulder by an angle of 30° in the frontal plane before the flight and before immersion, as well as on days 1, 3, and 7 after the completion of the immersion experiment and on days 1 (2), 4 (5), and 8 (9) after the spaceflight. For the first time it was demonstrated that elimination of the support and minimizing the proprioceptive afferentation may lead to the absence or inversion of the static torsional OCOR, as well as to a positional nystagmus against the background of the inverted reflex. Comparison of OCOR in cosmonauts after prolonged exposure to weightlessness and in the subjects examined after immersion revealed similarity in this reaction. However, changes in OCOR after immersion were encountered only in 60% of the subjects, whereas after the spaceflight, in 90% of the cosmonauts examined. The post-flight changes in OCOR were more pronounced and long-lasting.     

The effects of support-proprioceptive deprivation on visual-manual tracking and vestibular function

In order to determine the effects of support and proprioceptive afferentation on the characteristics of visual-manual tracking (VMT), we used a model of weightlessness—horizontal dry immersion. Altogether 30 subjects who stayed in the immersion bath from 5 to 7 days were examined to evaluate the accuracy of the VMT in tasks to pursue the jerky (saccadically) and smooth (linear, pendular and circular) movement of a point visual stimulus. Examinations were performed before, during and after immersion using electrooculography (to record eye movements) and a joystick (to record hand movements) with a biological visual feedback—one of the two visible stimuli on the screen matched the current angle of the joystick handle. Computerized visual stimulation programs were presented to subjects using virtual-reality glasses. We analyzed the time, amplitude and velocity characteristics of the visual and manual tracking (VT and MT respectively), including the efficiency ratio (eVT and eMT) and the gain (gVT and gMT) as the respective ratios of the amplitudes and velocities of the eyes/hand movements to the stimulus movement. eVT was significantly reduced in comparison to the baseline all the time, while the subject lay in the immersion bath and until R+4 day after immersion. eMT decreased significantly only on I-1 and I-3 days of immersion. gVT significantly differed from the baseline only on I-3 and I-6 days of immersion and R+1 day after immersion. We found no significant changes in gMT. Evaluations of the vestibular function (VF) were performed before and after immersion using videooculography. We analyzed the static torsional otolith-cervical-ocular reflex (OCOR), the dynamical vestibular-cervical-ocular reactions (VCOR), spontaneous eye movements (SpEM), and the accuracy of the perception of the subjective visual vertical (SVV). After immersion, 47% of all subjects had a significant reduction of OCOR with a simultaneous significant increase of VCOR on 37% of subjects, as well as significant changes in the accuracy of the perception of the SVV, which correlated with changes in OCOR. We found a correlation between characteristics of the VT and MT and between the characteristics of the VF and VT, but we found no correlation between VF and MT. We discovered that removal of the support and minimization of the proprioceptive afferentation has a greater impact upon the accuracy of the VT than the accuracy of the MT.     

Vestibular function and space motion sickness

The vestibular system plays an important role in intersensory interactions and gravitation is a natural stimulus for its receptors. Weightlessness alters the input signals of the otoliths and their effect on the pattern and dynamics of changes in the vestibular function (VF), which is accompanied by development of space adaptation syndrome (SAS) and space motion sickness (SMS). These changes occur both during the spaceflight (SF) and after returning to Earth, but the mechanisms of their development are still poorly understood and require special studies. In total, 47 Russian cosmonauts (crewmembers of long-term International Space Station (ISS) missions) have participated in the studies into VF before and after SF and nine of them, in onboard studies during SF (129–215 days) as a part of the Virtual space experiment (stage 1). Electro- and video-oculography are used to record spontaneous eye movements (SpEM), static vestibular–ocular responses during head tilts to the right or left shoulder (static otolith–cervical–ocular reflex, OCOR), and dynamic vestibular-ocular response during the head rotation around the longitudinal axis of the body. The examination is accompanied by personal and questionnaire survey on subjective responses and complaints of cosmonauts about SAS and SMS. Significant changes in SpEM (drifts of eyes, spontaneous and gaze-evoked nystagmus, and arbitrary saccades) and a decrease in OCOR (statistically significant decrease in the amplitude of ocular counter-rolling in response to head tilts up to its absence or inversion, an atypical OCOR) are observed during SF. An atypical OCOR is observed at the beginning of adaptation to weightlessness in seven of the nine cosmonauts (the first one to two weeks of SF) and repeatedly throughout the flight in all cosmonauts regardless of whether it is their first flight or not. Atypical vestibular responses after SF, similar to the responses during SF, are observed in several cosmonauts by day 9 after flight. It has been shown that atypical OCOR variants are more frequently observed in the subjects lacking any previous space experience, as well as a more pronounced decrease in this response with a concurrent increase in the response of the semicircular canals. It is also demonstrated that repeated SFs lead to a considerable shortening in the after-flight readaptation to terrestrial conditions and a considerable decrease in the degree of vestibular disorders. In the initial period of SF, the changes in VF are correlated with the complaints and manifestations of SAS and SMS; however, the complaints and the corresponding symptoms are unobservable during the further flight despite significant changes in the VF state. The patterns of the VF disorders associated with the impact of weightlessness and observed during and after SF are very similar, allowing these disorders to be regarded as SAS and SMS of different severities (intensities).     

Visual-manual tracking and vestibular function during a seven-day dry immersion

A seven-day dry immersion experiment provided the opportunity to study the effects of decreased proprioceptive tactile and support afferentations on the vestibular function and visual-manual tracking. Before and after immersion, six subjects participated in a video oculographic evaluation of the static torsion otolith-cervicoocular reflex (OCOR) in response to head tilt by 30° in the frontal plane and dynamic vestibular-cervicoocular reactions to head longitudinal rotations at 0.125 Hz. In addition, the hand-eye motor coordination of tracking a jerky (sinusoidal) or smooth (linear) movement of point targets along the horizontal or vertical lines was evaluated on the basis of the data of electrooculography and records of manipulations with the joystick during immersion. A computerized test was performed in virtual glasses displaying images of visual stimuli and hand motor acts. The computed parameters included the reaction’s latent time, amplitude, speed and time of eye and hand movements, and gains of optooculomotor reactions and manual tracking as a ratio of eye/hand to visual stimulus speed. Testing was carried out before the experiment, after 3 h of immersion, on days 3 and 6 of staying in the bath, in the initial hours after immersion and on the third day of recovery. It was shown that removal of support and minimization of proprioceptive afferentation had a profound effect on the ocular tracking rather than pursuing the visual stimulus by hand. The accuracy of manual tracking was better in comparison with the eye tracking in all subjects. This was the first observation of changes in the peripheral vestibular system in two out of six subjects, i.e., inversion of the static torsion OCOP and positional nystagmus against a background of converted reflex, which did not change the parameters of the visual-manual tracking.     

Effect of optokinetic stimulation on visual–manual tracking under the conditions of support-proprioceptive deprivation

The effects of additional dynamic visual stimuli (retinal optokinetic stimulation (ROKS)) on the visual–manual tracking (VMT) indicators in the absence of support afferentation and with a reduced level of proprioceptive afferentation were determined using a model of horizontal “dry” immersion. The accuracy of the VMT of jerky and smooth (linear, pendular, and circular) movements represented by visual dot stimuli was evaluated in all 18 participants aged 19–31 before, during and after their exposure to a five- to seven-day immersion bath. The eye movements were recorded by electrooculography, while the hand movements were recorded by a joystick with a biological visual feedback (the current angle of the joystick handle was imaged on the screen). Computerized visual stimulation tests were presented, through virtual reality glasses, to subjects in the absence and against the background ROKS. We analyzed the temporal and the amplitude- and velocity-related visual and manual tracking (VT and MT) characteristics, including the efficiency (e) and gain (g) coefficients as the ratios between the amplitudes and velocities of eye/hand movements and the amplitude of stimulus movements. The efficiency and gain coefficients of both VT and MT without ROKS were significantly decreased against the baseline during the entire period including three days of immersion and 3 post-immersion days. The most pronounced worsening was observed in the VT parameters. Whereas the VT and MT parameters remained unchanged against the threshold ROKS before the immersion, they were improved during and after the immersion (the improvement was significant on the fifth to seventh day of immersion and on the thirdthird post-immersion day, compared to the test indicators on the clean screen). The most pronounced impact of ROKS was observed in the VT parameters. The vestibular function (VF) was evaluated by videooculography before and after immersion. We analyzed the static torsional otolith-cervicalocular reflex (OCOR), dynamic vestibular-cervical-ocular reactions (VCOR), vestibular reactivity (VR), and spontaneous eye movements (SpEM). A significant decrease in OCOR (gOCOR was 0.1, compared to the background gOCOR value of 0.25) was detected alongside a simultaneous significant increase in the VCOR/VR parameters in 28% of subjects on day R + 1 after immersion. Correlational has been found between the parameters of VT and MT, as well as between those of VF and VT, but no correlation has been found between the VF and MT characteristics. The results have shown that the removal of support afferentation and the minimization of proprioceptive afferentation more affected the accuracy of VT rather than that of MT. The correlational links between the studied parameters against the background of ROKS were not only preserved, but also intensified. The obtained results confirm the development of sensory deprivation (and afferent deficit) under the exposure to an immersion bath and indicate the approach to correcting the sensory deprivation through additional ROKS.     

Effects of long-term space flights on organization of horizontal gaze fixation reaction

Results of Russian-Austrian space experiment "Monimir" which was a part of international space program "Austromir" are presented in this paper. Characteristics of horizontal gaze fixation reaction (hGFR) to visual targets were analyzed. Seven crewmembers of "Mir" space station expeditions took part in the experiment. Experiments were carried out 4 times before space flight, 5 times in flight and 3-4 times after landing. There were revealed significant alterations in characteristics of gaze fixation reaction during flight and after its accomplishing, namely: an increase of the time of gaze fixation to the target, changes of eye and head movements' velocity and increase of the gain of vestibular-ocular reflex, that pointed out to the disturbances of the control mechanisms of vestibular-ocular reflex in weightlessness caused by changes of vestibular input's activity. There was discovered also the difference in the strategies of adaptation to microgravity conditions among the cosmonauts of flight and non-flight occupation: in the first group exposure to weightlessness was accompanied by gaze hypermetry and inhibition of head movements; in the second one--on the contrary--by increase of head movement velocity and decrease of saccades' velocity.     

Visual–manual tracking after long spaceflights

This study presents the results of the pre- and postflight clinical and physiological examination (CPE) and scientific experiment “Sensory Adaptation-2” at the Gagarin Research and Test Cosmonaut Training Center, which involved 14 Russian cosmonauts, crewmembers of long-term international spaceflights ISS-28/29 to ISS 36/37, who were in microgravity from 159 to 195 days. The cosmonauts were aged 35–50 years. The studies were conducted twice before the spaceflight (the background), as well as on days R+1(2), R+4(5), and R+8(9) after landing. In the study of visual–manual tracking (VMT), eye movements were recorded by the electrooculography method (EOG), and hand movements were recorded by a joystick (the screen represented the current tilt angle of a joystick handle). The examinations were conducted using stimulation computer programs, were presented to an examined subject on the screen of the Sensomotor hardware–software complex. The examinations took place in the dialog mode and included the EOG calibration; VMT within ±10° on the screen with blank background (the smooth linear and sinusoidal movement of a point target with a frequency of 0.16 Hz in the vertical and horizontal directions). The study estimated the time, amplitude, and velocity characteristics of visual and manual tracking (VT and MT), including the effectiveness (ec) and gain (gc) coefficients as the ratios of the amplitude and velocity of eye/hand movements to the amplitude and velocity of the visual stimulus. The study of the vestibular function (VF) was performed before and after the spaceflight using videooculography. The static torsion otolith–cervical–ocular reflex (OCOR), dynamic vestibular–cervical–ocular reactions (VCOR), vestibular reactivity, and spontaneous eye movements were assessed. The study of VF in the first postflight days has shown a sharp decrease (up to its complete absence) of static vestibular excitability accompanied by the increased dynamic reactivity of the vestibular system. The study of VTM in the first postflight days has shown a significant decrease in the ec and gc of VT as well as correlations between the parameters of VT and MT and between the parameters of VF and VT and has not found a correlation between the parameters of VF and MT. The conditions of the spaceflight have been revealed to affect the accuracy of VT more strongly than the accuracy of MT. A complete return of the characteristics of VMT and VF to the baseline was observed on R+8(9) days after the spaceflight.     

Down training of the elderly soleus H reflex with the use of a spinally induced balance perturbation.

The purpose of this study was to determine the ability of the elderly central nervous system to modulate spinal reflex output to functionally decrease a spinally induced balance perturbation. In this case, the soleus H reflex was used as the source of perturbation. Therefore, decreasing (down training) of the soleus H reflex was necessary to counteract this perturbation and to better maintain postural control. In addition to assessing the effect of this perturbation on the H reflex, static postural stability was measured to evaluate possible functional effects. Ten healthy young subjects (age: 27.0 +/- 4.6 yr) and 10 healthy elderly subjects (age: 71.4 +/- 5.1 yr) participated in this study. Subjects underwent balance perturbation on 2 consecutive days. On day 1 of perturbation, significant down training of the soleus H reflex was demonstrated in both young (-20.4%) and elderly (-18.7%) subjects. On day 2 of perturbation, significant down training of the soleus H reflex was again demonstrated in both young (-24.6%) and elderly (-21.0%) subjects. Analysis of static stability after the 2 days of balance perturbation revealed a significant 10.1% decrease in the area of sway in elderly subjects. In conclusion, this study demonstrated that healthy, elderly subjects compared with young subjects were equally capable of down training the soleus H reflex in response to a balance perturbation. Furthermore, the improvement in static stability through balance training may provide further evidence that balance can be retrained and rehabilitated in subjects with decreased reflex function.     

Lung volume changes in response to altered breathing gas pressure during upright immersion

Since elastic and flow-resistive respiratory work are volume dependent, changes in lung volume during immersion affect respiratory effort. This investigation examined changes in lung volume with air delivery pressure modifications during upright immersion. Static pressure-volume relaxation relationships and lung volumes were obtained from ten immersed subjects breathing air at four delivery pressures: mouth pressure, lung centroid pressure (PLC), and 0.98 kPa above and below PLC. The PLC is the static lung pressure which returns the respiratory relaxation volume (VR) to normal and was previously determined to be +1.33 kPa relative to pressure at the sternal notch. Lung volume changes observed when breathing air at mouth pressure were reversed when air was supplied at PLC. The expiratory reserve volume (ERV) and VR were reduced by 58% and 87%, respectively, during uncompensated immersion. These differences indicated an active defence of ERV and implied that additional static respiratory work was required to overcome transrespiratory pressure gradients.     

Prediction of alterations in cardiac functions (ECG data) in the course of the permanent monitoring of cosmonauts starting from selection until return to earth after short space flights

Analysis of alterations in the cardiac activity on the basis of electrocardiographic (ECG) findings in 29 cosmonauts of flight and ground professions aged from 29 to 61 years after 34 short (8–30 days) space flights (SFs) between 1982 and 2006 has been carried out. The ECG data at the stage of clinical selection, clinical-physiological examination (CPE) before a SF, at the stage of the launch of a spacecraft (SC) into orbit and its landing on Earth and at the stage of postflight CPE have been analyzed. The analysis of cardiac activity parameters on the basis of ECG data at different stages of observations has led to the identification of three groups of cosmonauts. There were no significant changes or negative tendencies in the alteration of ECG data in the first group (55.2% of the total number of cosmonauts) during the observation period from selection to the end of the SF. The changes that later became more pronounced during the landing on Earth and were retained during postflight CPE have been found in the second group of cosmonauts (in 34.5% cases) at the time of selection and preflight CPE. Considerable disturbances in cardiac activity that are dangerous for human health have been found in ECGs in the third group (10.3%) during the descent from orbit. The data from the study are the first step in the investigation of possible medical risks for the development and improvement of requirements for the medical selection of crews and the admission of subjects with partial health insufficiency on SFs.     

Some changes of the heart bioelectric activity at the cosmonauts under the influence of LBNP in the long duration flights

There was selected the group of the cosmonauts, who carry out long duration flights on the orbital complex "Mir", in which the tolerance of LBNP test was evaluated as poor (by hemodynamic indices--heart rate, arterial pressure, rheoencephalographic indices). The in-depth analysis of the electrocardiogram (in DS leads) indices was carry oiled on possible disturbances of conductivity and dynamics of temporary or amplitude characteristics. Furthermore is carry oiled the comparative estimation of these indices with the results of ECG analysis at the cosmonauts, who tolerance test good. Studies showed that the most informative ECG indices are the R, T-amplitudes and QT-interval. Under the influence of LBNP, especially during rarefactions on 45 and 50 mm Hg was noted reduction in the R, T-amplitude and the relative extension of QT-interval. The directivity of changes in these indices are identical for the cosmonauts with good and poor tolerance of the test; however in flight manifestation of the changes is more significant for the cosmonauts with poor tolerance of LBNP test. Thus, in the formation of orthostatic stability together with the hemodynamic influences take part the bioelectric processes, which are formed in the myocardium.     

Influence of long-term spaceflight on neuromechanical properties of muscles in humans.

Reflex and elastic properties of the triceps surae (TS) were measured on 12 male cosmonauts 28-40 days before a 3- to 6-mo spaceflight, 2 or 3 days after return (R+2/+3) and a few days later (R+5/+6). H reflexes to electrical stimulations and T reflexes to tendon taps gave the reflex excitability at rest. Under voluntary contractions, reflex excitability was assessed by the stretch reflex, elicited by sinusoidal length perturbations. Stiffness measurements concerned the musculoarticular system in passive conditions and the musculotendinous complex in active conditions. Results indicated 1) no changes (P > 0.05) in H reflexes, whatever the day of test, and 2) increase in T reflexes (P < 0.05) by 57%, despite a decrease (P < 0.05) in musculoarticular stiffness (11%) on R+2/+3. T reflexes decreased (P < 0.05) between R+2/+3 and R+5/+6 (-21%); 3) increase in stretch reflexes (P < 0.05) on R+2/+3 by 31%, whereas it decreased (P < 0.05) between R+2/+3 and R+5/+6 (-29%). Musculotendinous stiffness was increased (P < 0.05) whatever the day of test (25%). Links between changes in reflex and stiffness were also studied by considering individual data. At R+2/+3, correlated changes between T reflexes and musculoarticular stiffness suggested that, besides central adaptive phenomena, musculoarticular structures took part in the reflex adaptation. This mechanical contribution was confirmed when data collected at R+2/+3 and R+5/+6 were used because correlations between changes in stretch reflexes and musculotendinous stiffness were improved. In conclusion, the present study shows that peripheral influences take part in reflex changes in gravitational unloaded muscles, but can only be revealed when central influences are reduced.     

Regulation of wrist stiffness by the stretch reflex

In restoring the angular position after a displacement, the role of the muscle stretch reflex was investigated by comparing the restored angular torques and angular positions in the wrist under ischaemic and non-ischaemic conditions in normal human subjects. The wrist compliance (COM), defined as the dynamic relation between the angular position and the angular torque of the joint, was calculated to quantify the changes in the restoration of a displacement after abolishing the stretch reflex by ischaemia. The elasticity from the COM-function was found to be single most important factor controlled by the stretch reflex. The elasticity that equals the static stiffness of the system increased by more than 100%, from 0.21 Nm degree-1 with abolished reflex to 0.45 Nm degree-1 with intact reflex. Our results have shown that the stretch reflex assists in the rapid return of the limb to its original position after a mechanical displacement. When the reflex was blocked by ischaemia, the perturbation displaced the limb further away from the initial position.     

Effects of long-term space flights on the organization of the horizontal gaze fixation reaction

The results of the Russian-Austrian space experiment Monimir, which was a part of the international space program Austromir, are presented. The characteristics of the horizontal gaze fixation reaction (hGFR) to the visual targets were studied during long-term space flights. Seven crewmembers of the space station Mir participated in our experiment. The subjects were tested four times before the flight, five times during the flight, and three to four times after landing. During the flight and after accomplishing, the characteristics of gaze fixation reaction changed regularly: the reaction time and coefficient of the gain of vestibular-ocular reflex increased; the velocities of eye-head movements increased and decreased. These changes were indicative of a disturbed control of the vestibular-ocular reflex under microgravity conditions because of variability of the vestibular input activity. The cosmonauts that had flight and non-flight professional specializations differed in strategies of their adaptation to the microgravity conditions. In the former, exposure to microgravity was accompanied by gaze hypermetry and inhibition of head movements; conversely, in the latter, the velocity of head movements increased, whereas that of saccades decreased.     

Behavioural and functional vestibular disorders after space flight: 2. Fish,amphibians and birds

The review presents data on functional changes in fish, amphibians and birds associated with otolith organ activity after exposure to weightlessness during spaceflight. These data are of importance both for solving some fundamental problems of vestibulology and for practice. In the latter case, lower vertebrates are considered as a convenient and, most importantly, adequate model to unravel the mechanisms of vestibular disorders in humans. Analysis of the experimental results shows that weightlessness exerts no substantial effect on the formation and functional state of the otolith system in embryos of fish, amphibians and birds developing during spaceflight. Moreover, they even promote faster embryonic development of fish and amphibians as shown for mammalian fetuses. The experiments show that both in lower and higher vertebrates weightlessness brings about similar functional and behavioral changes. For example, in fish hatchlings and amphibian tadpoles (without lordosis) the vestibulo-ocular reflex was more pronounced immediately after orbital spaceflight than in control. An analogous alteration in the otolith reflex was observed in most cosmonauts after short-time space missions. In adult terrestrial vertebrates, as well as in humans, immediately after landing there was found a drop in the level of activity and deterioration of the equilibrium function and motor coordination. Another interesting finding was an unusual looping behavior when fish and tadpoles swam in loops post landing. Presumably, unusual motor activity of animals, as well as illusions arising in cosmonauts and astronauts during the transition from 1 to 0 g, have the same background being associated with changes in the stimulation pattern of the otolith organs. Considering the similarity of vestibular responses, the use of animal models seems very promising as allowing different invasive techniques.     

Variation of the State of Lower Limb Veins in Cosmonauts during Long-term Missions

This paper reports changes in the main parameters of lower limb veins in 35 cosmonauts in the course of six-month space missions. Major reduction in the leg volume was shown in all cosmonauts, as well as a significant increase in venous capacitance and compliance. The rate of lower leg vein filling exhibited different trends; it was decreased in the majority of cosmonauts (n = 26, 74%) and increased in the rest (n = 9, 26%). Increases in venous capacitance, compliance, and filling rates may impact orthostatic stability (OS). These changes are among the pathophysiological mechanisms of the OS loss in spaceflight.     

Osteoclast-activating system in cosmonauts after long-term international space station missions

The results of studying the system of the osteoprotegerin/receptor activator of nuclear factor kappa-B ligand (OPG/RANKL) in 22 Russian cosmonauts after long-term (124–199 days) International Space Station missions are presented. It was found that early readaptation period is associated with changes in the serum concentrations of OPG and RANKL and the production rate of OPG and RANKL in phytohemagglutinin (PHA)-stimulated and non-stimulated mononuclear cells of peripheral blood in vitro. The extent of these changes varied in different subjects. Our data suggest that the OPG/RANKL cytokine system takes part in the processes of bone remodeling in cosmonauts after long-term missions.     

Calcium metabolism characteristics in microgravity]

The results of research of calcium exchange parameters at cosmonauts taken part in long space flights (SF) onboard of orbital stations "SALUT" and "MIR" within 1978-1998 were generalized. The analysis of data received during observation of 44 cosmonauts (18 of them have taken part in long SF twice) was done. The observation was carried out before and after SF by duration 30-438 days. The content of a total calcium in blood serum was increased basically by the increase of its ionized fraction after flights of moderate (3-6 months) and large duration (6-14 months) along with the significant increase of PTH and decrease of calcitonin levels. The content of osteocalcin after SF was increased. Three cosmonauts participated in research of calcium kinetics using stable isotopes before, in time and after a 115-day SF. Reduction of intestinal absorption, excretion through a gastrointestinal tract, and increase of calcium excretion with urine were marked in time of SF. In early postflight period a level of intestinal absorption, on the average, was much lower than in SF, and the calcium removal through intestine was increased. Both renal and intestinal excretion of calcium were not normalized in 3.5-4.5 months after end of SF. Increase of resorbtive processes in bone tissues which induced negative bone balance during flight was observed in all test subjects, proceeding from estimations of speed of the basic calcium flows made on the basis of mathematical modeling. The conclusion about decrease in speed of bone tissue remodeling and strengthening of its resorption proves to be true by data of research of biochemical and endocrine markers.     

Cytogenetic studies of blood lymphocytes of cosmonauts after long-ter, space flights

An analysis was performed of unstable chromosomal aberrations in peripheral blood of 36 cosmonauts after long-term space missions on "Mir" orbital station. 25 cosmonauts were examined before their flights to score spontaneous yields of cytogenetical damage. In all cases the doses absorbed by crews during space flights did not exceed permissible levels of irradiation, adopted for cosmonauts. The frequencies of chromosomal-type aberrations after space missions were found to increase significantly compared to the pre-flight levels. The yields of dicentrics and centric rings on the average were as high as 0.12 +/- 0.02 and 0.47 +/- 0.06% before and after the 1st flight, 0.18 +/- 0.05 and 0.71 +/- 0.11% before and after the 2nd flight respectively. During the inter-flight periods, usually lasted 1.5-2 years, the yields of chromosome damage lowered, but did not reach their spontaneous values. After each next flight the yields of chromosome aberrations increased again. The cytogenetical damage detected in cosmonauts' peripheral blood lymphocytes after chronic action of low doses of space radiation points out a possible increase in risks of stochastic effects in distant future for crews after long-term space missions.     

Metabolic features of cosmonauts after ballistic descent from the Earth orbit

The features of metabolic reactions in five cosmonauts after long-term flights on the International Space Station (ISS) and landing along a ballistic trajectory and in the cosmonauts returning to Earth in the mode of automatic controlled descent were studied. Venous blood samples were collected, and 50 biochemical parameter values that reflect the functional state of organs and tissues and characterize the main metabolic pathways were determined. On the first day of the recovery period after ballistic descent, the activity of the myocardial, liver, and gastrointestinal enzymes in the blood serum of cosmonauts was increased 1.3- to 2.1-fold; a number of the parameter values exceeded the upper normal limit. The level of C-reactive protein increased fivefold as compared with the preflight values. Marked signs of glycolysis, glycogenolysis and lipolysis activation as well as disorders of acid–base balance were observed. Changes in the biochemical parameter values in cosmonauts after landing along a ballistic trajectory differed significantly from those revealed in the same cosmonauts after long-term missions followed by automatic controlled descent to Earth. Negative metabolic changes tendency after landing along a ballistic trajectory remained for at least 14 days of the recovery period. It was concluded that changes in the metabolic reactions of cosmonauts after long-term missions to the ISS depend on the flights final stage conditions. After landing on Soyuz spaceships in the ballistic descent mode, the cosmonauts had adverse prognosis changes in the biochemical values characterizing the state of the cardiovascular system and marked shifts in the activity of the liver and gastrointestinal constellation enzymes. The dynamics of carbohydrate, lipid, and protein metabolism as well as acid–base balance indicates a significant tension of all body systems and exhaustion of its functional reserves.