Pathophysiology of motor functions in prolonged manned space flights.

The influence of weightlessness on different parts of the motor system have been studied in crew members of 140 and 175 days space flights. It has been shown that weightlessness affects all parts of the motor system including (i) the leg and trunk muscles, in which severe atonia, a decrease of strength and an increase of electromyographic cost of contraction have been observed, (ii) the proprioceptive elements and the spinal reflex mechanisms in which decreased thresholds accompanied by decreases of maximal amplitude of reflexes and disturbances in cross reflex mechanisms have been found. and (iii) the central mechanisms that control characteristics of postural and locomotor activities. The intensities and durations of disturbances of different parts of the motor system did not correlate to each other, but did correlate with prophylactic activity during space flight. The data suggest a different nature of disturbances caused by weightlessness in different parts of the motor system.     

Certain approaches to the development of on-board automated training system

Perspectives of long-term space programs make it necessary to develop autonomous computer expert system for crew-members physical state control. The purpose of the work--to develop a set of objective formalizable physiological indices of working capacity suitable for reliable algorithmization of physical state control. Investigations were performed in on-earth microgravity simulation (3- and 7-day dry immersion, 6 subjects; 4-month antiorthostatic hypokinesy, 10 subjects) with volunteers' participation as well with 34 members of MIR-station expeditions during flights. Model exercise investigations were made also with 20 young male volunteers to evaluate the validity of different physical state indices. A set of indices was found which, being simple enough for measuring, performs to get satisfactory adequate evaluations of current organism physical state in long-term real or simulated microgravity. It was proved that some ergometric indices along with heart rate derivatives could reflect real working ability even better than traditional characteristics of organism energy systems state.     

Adaptation of neuromuscular activation patterns during treadmill walking after long-duration space flight

The precise neuromuscular control needed for optimal locomotion, particularly around heel strike and toe off, is known to he compromised after short duration (8- to 15-day) space flight. We hypothesized here that longer exposure to weightlessness would result in maladaptive neuromuscular activation during postflight treadmill walking. We also hypothesized that space flight would affect the ability of the sensory-motor control system to generate adaptive neuromuscular activation patterns in response to changes in visual target distance during postflight treadmill walking. Seven crewmembers, who completed 3- to 6-month missions, walked on a motorized treadmill while visually fixating on a target placed 30 cm (NEAR) or 2 m (FAR) from the subject's eyes. Electronic foot switch data and surface electromyography were collected from selected muscles of the right lower limb. Results indicate that the phasic features of neuromuscular activation were moderately affected and the relative amplitude of activity in the tibialis anterior and rectus femoris around toe off changed after space flight. Changes also were evident after space flight in how these muscles adapted to the shift in visual target distance.     

Effects of long-duration space flight on target acquisition

The purpose of the study was to explore the effects of long-duration space flight on the acquisition of specific visual targets in the horizontal plane. Seven cosmonauts (4 high performance pilots and 3 non-pilots) who had flown between 186–198 days on Mir served as subjects. Baseline testing was performed 4 times prior to launch and 4 times following landing at different intervals totrack recovery. During testing the subjects were required to acquire targets that were randomly presented with both a head and eye movement using a time optimal strategy. Prior to flight two unique head movement strategies, related primarily to piloting experience, were used for target acquisition. Non-pilots employed a Type-I strategy consisting of high velocity head movements with large peak amplitudes, while high performance pilots used primarily low velocity, small amplitude head movements (Type-II) to acquire the targets (p<0.02). For both strategies peak head velocities increased as the angular distance to the target increased (p<0.01) resulting in greater discrimination between strategies for the 60° targets. While preflight eye velocity between strategies did not reach statistical significance, postflight testing revealed a decrease in eye velocity for Type-I compared with their preflight performance (p<0.02) for the 60° targets. Postflight, the Type-I group showed a decrease in head velocity (p<0.20) while the Type-II group compensated by increasing head velocity (p<0.02). Variability for both of the head and eye parameters tended to increase postflight for both types of strategies.     

Some approaches to medical support for Martian expedition

Medical support in a Martian expedition will be within the scope of crew responsibilities and maximally autonomous. Requirements to the system of diagnostics in this mission include considerable use of means and methods of visualization of the main physiological parameters, telemedicine, broad usage of biochemical analyses (including "dry" chemistry), computerized collection, measurement, analysis and storage of medical information. The countermeasure system will be based on objective methods of crew fitness and working ability evaluation, individual selection of training regimens, and intensive use of computer controlled training. Implementation of the above principles implies modernization and refinement of the countermeasures currently used by space crews of long-term missions (LTM), and increases of the assortment of active and passive training devices, among them a short-arm centrifuge. The system of medical care with the functions of prevention, clinical diagnostics and timely treatment will be autonomous, too. The general requirements to medical care during the future mission are the following: availability of conditions and means for autonomous urgent and special medical aid and treatment of the most possible states and diseases, "a hospital", and assignment to the crew of one or two doctors. To ensure independence of medical support and medical care in an expedition to Mars an automated expert system needs to be designed and constructed to control the medical situation as a whole.     

Efficacy of periodic centrifugation of primates during 4-week head-down tilt.

Creation of artificial force of gravity (AFG) to counteract the negative consequences of microgravity in manned space missions of extended duration is one of the high-priority problems of space biology and medicine. However, there are a number of especial effects of AFG (namely, structural changes in muscles and bones, and some other system) which need implantation of electrodes and sensors and are possible only with animals. That is why it is of particular interest to make studies with monkeys whose reactions to changed gravity bear much resemblance with human. The purpose of the investigation was development of a protocol of periodic gravity loads as a counter-measure against the hypokinetic syndrome in Macaca mulatta. Two series of experiments were performed. In the series, animals were split into two groups of 6 species each who were motor restrained with the head end tilted downward at 5 degrees (HDT) for 28 days. Monkeys of group-2 were periodically subjected to centrifugation (HDT+G). During the first series of experiments rotation was conducted in the +Gz direction at g-loads from 1.2 to 1.6 units for 30-40 minutes 4-5 times a week. In the second series, g-load was equal to 1.2 units and the animals were rotated 30 min. 2-3 time a week. The criterion of Y-training protocol efficacy was a test +Gz run at 3 units for 30 s. during which functioning of the cardiovascular systems and its controls was evaluated. The test run was performed prior to and after HDT. Following HDT the animals of group HDT+G were more resistant to the test than their counterparts who had not been trained on the centrifuge. Data of the investigation imply that following HDT and HDT+G alike reduced the amount of total bodily fluids (by approximately 5%), the intracellular component (approximately 4%), and plasma volume (by 6-7%). Yet, there are radical differences between the groups in the levels of reduction in extracellular fluids (by 11% and 6.5%, respectively, P<0.05) and the interstitial component (by 11.5% and 6.5, respectively, P<0.05). Prophylactic centrifugation during HDT was also positive to the muscular blood flow in lower extremities.     

The use of in-flight foot pressure as a countermeasure to neuromuscular degradation

The purpose of this study was to determine whether applying foot pressure to unrestrained subjects during space flight could enhance the neuromuscular activation associated with rapid arm movements. Four men performed unilateral arm raises while wearing--or not wearing--specially designed boots during a 81- or 115-day space flight. Arm acceleration and surface EMG were obtained from selected lower limb and trunk muscles. Pearson r coefficients were used to evaluate similarity in phasic patterns between the two in-flight conditions. In-flight data also were magnitude normalized to the mean voltage value of the muscle activation waveforms obtained during the no-foot-pressure condition to facilitate comparison of activation amplitude between the two in-flight conditions. Foot pressure enhanced neuromuscular activation and somewhat modified the phasic features of the neuromuscular activation during the arm raises.     

Mechanisms of spinal motoneurons survival in rats under simulated hypogravity on earth

It was previously shown that different cell types in vivo and in vitro may die via apoptosis under weightlessness conditions in space as well as in simulated hypogravity on the Earth. We assessed survivability of spinal motoneurons of rats after 35-day antiorthostatic hind limb suspension. Following weight bearing, unloading the total protein content in lumbar spinal cord is dropped by 21%. The electrophysiological studies of m. gastrocnemius revealed an elevated motoneurons’ reflex excitability and conduction disturbances in the sciatic nerve axons. The number of myelinated fibers in the ventral root of experimental animals was insignificantly increased by 35-day of antiorthostatic hind limb suspension, although the retrograde axonal transport was significantly decreased during the first week of simulated hypogravity. The results of the immunohistochemical assay with antibodies against proapoptotic protein caspase 9 and cytotoxicity marker neuron specific nitric oxide synthase (nNOS) and the TUNEL staining did not reveal any signs of apoptosis in motoneurons of suspended and control animals. To examine the possible adaptation mechanisms activated in motoneurons in response to simulated hypogravity we investigated immunoexpression of Hsp25 and Hsp70 in lumbar spinal cord of the rats after 35-day antiorthostatic hind limb suspension. Comparative analysis of the immunohistochemical reaction with anti-Hsp25 antibodies revealed differential staining of motoneurons in intact and experimental animals. The density of immunoprecipitate with anti-Hsp25 antibodies was substantially higher in motoneurons of the 35-day suspended than control rats and the more intensive precipitate in this reaction was observed in motoneuron neuritis. Quantitative analysis of Hsp25 expression demonstrated an increase in the Hsp25 level by 95% in experimental rats compared to the control. The immunoexpression of Hsp70 found no qualitative and quantitative differences in control and experimental lumbar spinal cords. Taken together our results show that (1) rat motoneurons survived after 35-day antiorthostatic hind limb suspension and the changes in neurons had a mostly functional character, and (2) the increased immunoexpression of Hsp25 can be considered as the anti-apoptotic factor.     

Decrease of contractile properties and transversal stiffness of single fibers in human soleus after 7-day “dry” immersion

The simulation model of “dry” immersion was used to evaluate the effects of plantar mechanical stimulation (PMS) and high frequency electromyostimulation (EMS) on the mechanical properties of human soleus fibers under the conditions of gravitational unloading. We examined contractile properties of single fibers by means of tensometry, transversal stiffness of sarcolemma and different areas of the contractile apparatus by means of atomic force microscopy. It was shown that there is a reduction of transversal stiffness in single muscle fibers under hypogravitational conditions. Application of different countermeasures could compensate this effect. Meanwhile pneumostimulation and electro stimulation act in quite different way. Therefore, pneumostimulation seems to be more effective. The data obtained can be considered as the evidence of the fact that such countermeasures as PMS and electromyostimulation influence on muscle fibers in quite different ways and PMS efficiency is likely to be higher. On the basis of our experimental data on transverse stiffness of mechanotransductional nodes and the contractile apparatus, we can assume that support stimulation allows prevention of destructive processes in muscle fibers. Electrostimulation seems to stimulate contractile activity only without suppression of impairment of the fiber mechanical properties.