The article describes a nonpulsatile model of human systemic circulation simulating the effects of posture changes on main indices of blood flow in different vessels and body segments. The model comprises the hemodynamics structural chart, hydrodynamic and hydrostatic circulation models, and a myogenic regulation model The systematic circulation model enables investigation and representation of myogenic regulation of peripheral circulation along different vessels and body segments experimental investigations of which is complicated by inevitable nonlinear distortions. In future an algorithm will be developed to compute values of the main hemodynamic indices for the tilt and standing tests.

Tolerance of +Gz (head-pelvis) centrifugation of pilots was evaluated following simulation of a long flight on single-seat fighter. The experiment involved 5 test-subjects who were exposed to +Gz before and after simulated 8-hr flight with a growth gradient of 0.1 u/s without anti-g suits and muscles relaxed; in addition, limiting tolerance of intricate profile +Gz loads of 2.0 to 9.0 units with a growth gradient of 1.0 u/s of test-subjects in anti-g suits (AGS) with a change-over pressure valve in the peak mode using muscle straining and breathing maneuvers. To counteract the negative effects of extended flight, various seat configurations: with a back inclination at 30 degrees to the +Gz vector and changeable geometry with a back inclination at 55 degrees to the vector. The other counter-measures applied were cool air shower, suit ventilation, physical exercises, lower body massage with AGS, electrostimulation of the back and lumber region, profiling of the supporting and soft parts of the seat, and 30-s exposure to +5 Gz. Hemodynamic and respiration parameters as well as body temperature were measured in the course of 8 hrs of flight and during and shortly after centrifugation. According to the results of the investigation, seat inclination at 55 degrees to the +Gz vector and tested system of countermeasures prevent degradation of tolerance of large (9 u.) loads following 8-hr flight simulation with the use of the modern anti-g gear,

Human respiration parameters were studied in subjects exposed to +Gz (6.0; 7.0, 8.0 and 9.0 g with a 15-s plateau and a g-gradient of 1.0 and 5.0 g/s) with the use of anti-g measures, i.e. a barber chair inclined at 30 or 45 degrees, anti-g suit VKK-15 with a pressure controller, and a positive oxygen pressure. The gas-exchange parameters were found to be indicative of the effectiveness of an anti-g protector. When used together, these protective methods (VKK-15 munitions, an oxygen respirator for positive-pressure breathing, and chair back inclination to 45 degrees) improved g-tolerance significantly.

G-loads tolerance following hypodynamia during extended flights and effectiveness of countermeasures against possible negative impacts were studied. Subjects performed 5-hr simulated flights after which they were centrifuged with a g-gradient of 0.1 u/s in the relaxed state, and with a g-gradient of 1.0 u/s at complex-profiled 2 to 9 units in anti-g suit VKK-15. Tested were three sets of countermeasures (A, B, C) combining the following methods: physical exercises, VKK-15 provided massage of the lower body, 30-s exposure to 5 g, use of the profiled stiff and cushioned seats, electrical stimulation of the back and waist, and an air-cushion. The countermeasures were applied every hour on flight. Hypodynamia during the five-hour fighter flight was shown to have a weak detrimental effect on the pilot's functional state, performance and g-tolerance which were tempered by the proposed combinations of countermeasures.

Studies of the dynamics of human respiratory system parameters during 15-s runs with +Gz loads from 6 to 9 units and rates of rise equal to 1, 2, 3 and 5 units/s showed that increase in the rate of rise produced specific shifts in the breathing cycle structure which characterize the voluntary adaptation of humans to g-loads. Results also make it evident that despite absence of difference in the respiratory reactions during +Gz runs, in the period following exposure the distinct increases in the parameters of external breathing and gas-energy exchange correlated with the rate of g-rise. This allows the conclusion that because of the reasons discussed in the paper the physiological cost of Gz-tolerance grows as the rate of g-rise gets high.

Six test subjects were subjected to NZ and Ny/Nz accelerations in centrifuge cabin having rotation radius of 6.55 m. During rotation, test subjects have determined the position of the subjective visual vertical. The performed studies have demonstrated that during exposure to NZ and Ny/NZ accelerations the image of subjective vertical the direction of which with rise of lateral component approaches the direction of the vector of resultant acceleration. The expressivity of this effect decreases with an increase of the longitudinal component of acceleration. It was suggested that pulling of high lateral accelerations (up to 2-3 units of g) in the flight of advanced highly manoeuvrable aircrafts can hinder in-flight spatial orientation of a pilot due to appearing of the stable illusions of spatial position.

In 8 healthy men exposed within a year to systematic +Gz accelerations with cycles of 2-month work on centrifuge followed by a month rest the functional state of the red blood cells was studied repeatedly and once in 26 fighter pilots. The blood was tested for such indices as hemoglobin, reticulocyte and erythrocyte counts; the functional state of erythrocyte pool was tested using a modified method of acidic erythrograms enabling one to record kinetic parameters of hemolysis: maximum rate of hemolysis and time of its development. Intensity of loads in the cycles of centrifuging was estimated from the Barton index. It is indicated that one of the effects of systematic exposure to +Gz accelerations is an accelerated destruction of the cells with reduced resistivity a function of exposure intensity. The destructive processes induced by accelerations trigger for a short time the mechanism of compensatory activation of the red blood system. Analysis of diagrams of percentage distribution of the parameters of the erythrocyte function after centrifuge runs of various intensity, and in the pilots revealed a significant compensatory activation of the red blood system only in 25% of pilots. The criterion validity of the indices tested for the system of individual control of the adaptive processes strain in the body is discussed.

The paper analyzes the data of expert tilt testing (-80 degrees, 20 min.) of 66 essentially healthy pilots. Hemodynamic reactions were characterized based on the standard concept of functional classes (FC). Good test tolerance was recorded in 86.4% of cases among which 36.4% were referred to FC-I and 50%--to FC-II. Adequate test tolerance (FC-II) was recorded in 10.6%; reduced and poor test tolerance (FC-IV and FC-V)--in 3%. According to ECG and computerized tachooscillography, the adaptive hemodynamic reactions were optimum in pilots of group FC-I as compared with group FC-II and all the more so when compared with FC-III. The last two groups showed some objective symptoms that had not been looked for in the past (a distinct lability of blood pressure, and incomplete hypertensive and hypotensive reactions) that differentiated these groups from FC-I. Results of the analysis made it possible to put forward additional clinical functional criteria to assess tilt tolerance of pilots with different levels of functional tolerance.

The subject of analysis was the data on +3 and +5 Gz tolerance of 130 civilian non-pilot applicants for cosmonauts (men and women, aged 23 to 55) gathered over the past 30 years. Length of the centrifuge arm was 7.25 meters and the total number of primary centrifuge runs was 309. For nearly every second of the applicants (46.7%) acceleration at +5 Gz was an ordeal causing distinct vascular or coronary decompensation. Thus, 29.7% exhibited various combinations of brief visual disturbances, tachycardia, tachypnea, and systolic arterial pressure in the shoulders; in 17%, visual disturbances and/or their precursors were combined with exaggerated cardio-vascular functional parameters, arrhythmia, and serious vegetative disorders. Most of those who had failed to endure the first centrifugation were unable to improve G tolerance during next runs; indeed, they showed negative G-tolerance dynamics. G intolerance grew in significance or was exacerbated by new disorders and their combinations. These results testify against exposure of non-pilot applicants for cosmonauts to +5 G, during the primary medical screening.

Hippocampal place cells can process the environmental inputs and make up a cognitive map in the hippocampus, or strengthen the synaptic connections within an association cortical cell assembly,thus creating a permanent engram for a spatial site. Outputs from the hippocampus are then integrated with other inputs within the nucleus accumbens and finally initiate a goal-directed behavior through the motor circuit.

Subject of the investigation was dynamics of gas-exchange parameters during exposure to lateral and laterolongitudinal g-loads (Gy, Gz, Gz/Gy) in a coach inclined at 300 from the horizontal with a rigid restraint system. Gy values varied between 0.5 and 5.0 units, Gz - between 3.0 and 9.9 units and Gz/Gy - between 2.6/1.8 and 5.0/3.0 units. In all instances, growth gradient of the radial loads was 1.0 u/s, and a period of exposure was up to 30 s. Comparison of the Gz vs. Gy tolerance revealed as a substantial increase of the physiological "cost", so a more visible disbalance of the diffusion/perfusion ratio of the lung. This is consistent with the gas-exchange data according to which lateral g-loads are a stronger stress-factor and more challenging for pilots than the longitudinal g-loads.

Is it possible for a driver to compensate for visual field defects by skill along with eye and head movements? Monocular field defects with a normal second eye are no problem, because a normal binocular visual field is adequate for all areas of traffic. A total bitemporal hemianopia creates a special situation, because the patient loses a three-dimensional space behind a vertical line through the point of fixation. He may have no binocular visual field. In this case the ability to participate in certain traffic situations may be limited with reduced risk profile. A real problem is posed by defects in the binocular visual field, e.g., due to lesions of the suprachiasmal visual pathway or due to ocular diseases causing damage to both eyes (e.g., glaucoma, diabetic retinopathy, etc.). Such defects usually cannot be compensated for, neither by skill nor by eye or head movements. Saccadic eye movement training and other procedures are only of limited help. These procedures may provide some compensation for daily use; a complete restoration of the ability to participate in traffic is not possible. Rare exceptions may be patients with damage to the visual pathway acquired peri- or postnatally or in early childhood when there is still enough plasticity in the visual system to develop mechanisms of compensation by completely changing the system of eye and head movements.

To develop a program of on-line medical monitoring of human subjects during rotation on a short-arm centrifuge (SAC), which is viewed as a promising method of providing artificial gravity, 153 runs were performed with participation of 17 subjects exposed to +Gz at 0.8, 1.2 and 1.6 G up to 40 minutes 3 times a day over a 3-d cycle. It was found that the on-line medical monitoring program for humans exposed to SAC +Gz loads should include recording of the system blood circulation and local circulation in head and leg vessels.

Six subjects were subjected to lateral (+Gy) and longitudinal-lateral (+Gz/+Gy) accelerations in a centrifuge with a rotation radius of 6.55 m. During rotation, test subjects were instructed to indicate the position of subjective visual vertical. Results of this study demonstrated that during exposure to +Gy and +Gz/+Gy accelerations, the direction of the indicated subjective vertical approached the direction of the resultant acceleration vector when the lateral component increased. This observed effect decreases with an increase of the longitudinal component of the acceleration. It was suggested that exposure to (i.e."pulling") high lateral acceleration (up to 2-3 Gy) in highly maneuverable aircraft can hinder spatial orientation of a pilot due to this persistent illusory spatial position as reported above. Our analysis showed that the process of spatial orientation under the conditions of G-load influence becomes more difficult and it is depending on the compromise between visual and vestibular-proprioceptive inputs. On account of this finding, it may be proposed that under conditions of G-load influence, pilots that rely primarily on visual perception may be exposed to higher risk of spatial disorientation.

People routinely learn how to manipulate new tools or make new movements. This learning requires the transformation of sensed movement error into updates of predictive neural control. Here, we demonstrate that the richness of motor training determines not only what we learn but how we learn. Human subjects made reaching movements while holding a robotic arm whose perturbing forces changed directions at the same rate, twice as fast, or four times as fast as the direction of movement, therefore exposing subjects to environments of increasing complexity across movement space. Subjects learned all three environments and learned the low- and medium-complexity environments equally well. We found that subjects lessened their movement-by-movement adaptation and narrowed the spatial extent of generalization to match the environmental complexity. This result demonstrated that people can rapidly reshape the transformation of sense into motor prediction to best learn a new movement task. We then modeled this adaptation using a neural network and found that, to mimic human behavior, the modeled neuronal tuning of movement space needed to narrow and reduce gain with increased environmental complexity. Prominent theories of neural computation have hypothesized that neuronal tuning of space, which determines generalization, should remained fixed during learning so that a combination of neuronal outputs can underlie adaptation simply and flexibly. Here, we challenge those theories with evidence that the neuronal tuning of movement space changed within minutes of training.

Contrary to the general belief that the yellow-blue mechanism has lower spatial resolution than the red-green mechanism, it has been recently claimed that both mechanisms have similar spatial sensitivity (McKeefry et al, 2001 Vision Research 41 245-255). Studying high-spatial-frequency tritanopia (a colour illusion based on spatio-chromatic interactions in human vision), we found strong evidence for the existence of two blue mechanisms-with low and high spatial-frequency resolution. If confirmed, this may resolve the apparent paradox concerning spatial resolution of the yellow-blue mechanism.

CONCLUSION: Saccular and utricular maculae can provide information on the supine static position, considering that both have pronounced curved structures with hair cells having a variety of polarization vectors that enable them to sense an inverted position and thus direct the righting reflex. OBJECTIVE: The vestibular system is essential for the structuring of motor behaviour, senses linear and angular acceleration and has a strong influence on posture and balance at rest, during locomotion and in head body righting reflexes. MATERIAL AND METHODS: Using guinea pigs in the supine position with a symmetrical head and trunk position, the ocular position was analysed to ascertain whether any ocular movement that occurred would adopt a spatial deviation indicative of the subsequent head and body righting. The characteristics of the righting reflex (direction, latency, duration and velocity) were analysed in guinea pigs from position signals obtained from search coils implanted in the eye, head and pelvis. The animals were kept in a supine position for a few seconds or even minutes with the eyes in a stable primary position and the head and body symmetrical and immobile. RESULTS: The righting reflex took place either immediately or after a slow deviation of the eyes. In both cases the righting sequence (eyes, head, body) was stereotyped and consistent. The direction of head and body righting was along the longitudinal axis of the animal and was either clockwise or anticlockwise and the direction of righting was related to the direction of the eye deviation. The ocular deviation and the direction of deviation that initiated and determined the direction of the righting reflex could be explained by possible otolithic activation.

Variations in cardiovascular responses to orthostatic stress were investigated in terms of physiological polymorphism. Variations of physiological measurements are subdivided into individual differences and measurement errors. However, individual differences are often considered to be an error in statistical analysis due to its limitations in experimental design. In order to discuss about the relative contribution of individual difference in cardiovascular responses to postural changes, percent contribution (PC) was estimated using the Taguchi method. Six healthy male adults (age range: 21-27) were subjected to orthostatic stress by inducing a postural inclination of 60 degrees head-up-tilting to the horizontal, and the responses were measured thrice in each subject on different days. The respective changes of heart rate (HR) and stroke volume (SV) in the period from the resting supine to the head-up-tilt position were significantly increased (p < 0.01) and decreased (p < 0.01) without affecting the mean blood pressure (MBP). The PC of individual difference in HR showed a significantly higher ratio of individual difference during the head-up-tilt (71.4-76.2%) compared with supine rest (0.0-50.4%). While the main variations of HR during supine rest were not the individual differences between the subjects, the day-to-day differences within the subject were significant. The PC of individual differences in MBP and SV constantly displayed a significant difference between the subjects. These results suggest that the strategy for maintaining stable cardiovascular regulation may be different even in normal subjects. In the perspective of physiological parameters, PC monitoring may serve as an empirical approach to evaluate physiological polymorphism.