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A retrospective review of the human centrifuge training database in the Republic of Singapore Air Force was carried out for the period 1995-2006. Six cases of pneumomediastinum were reported in aircrew trainees who underwent ab initio human centrifuge training. Only two of the six cases presented with chest discomfort with or without neck pain, with the rest being incidental findings picked up during routine medical examination. The diagnoses were confirmed by chest radiographs and computed tomography scans of the thorax. This is believed to be attributable to over-zealous or incorrect performance of the anti-G straining maneuver in trainees unaccustomed to a high G environment. Trainees subsequently underwent a structured weights training program and centrifuge training profiles were reviewed and revised to allow graduated G training. All affected trainees recovered uneventfully with conservative management, and were able to return to flying training.

The authors propose the technique of experimental haemorrhagic stroke of a hypertensive type in non-narcotized rats produced by means of gravity overload in the caudocranial vector with the use of a special centrifuge.

Sympathetically mediated tachycardia and vasoconstriction maintain blood pressure during hypergravitational stress, thereby preventing gravitation-induced loss of consciousness. Norepinephrine transporter (NET) inhibition prevents neurally mediated (pre)syncope during gravitational stress imposed by head-up tilt testing. Thus it seems reasonable that NET inhibition could increase tolerance to hypergravitational stress. We performed a double-blind, randomized, placebo-controlled crossover study in 11 healthy men (26 +/- 1 yr, body mass index 24 +/- 1 kg/m2), who ingested the selective NET inhibitor reboxetine (4 mg) or matching placebo 25, 13, and 1 h before testing on separate days. We monitored heart rate, blood pressure, and thoracic impedance in three different body positions (supine, seated, standing) and during a graded centrifuge run (incremental steps of 0.5 g for 3 min each, up to a maximal vertical acceleration load of 3 g). NET inhibition increased supine blood pressure and heart rate. With placebo, blood pressure increased in the seated position and was well maintained during standing. However, with NET inhibition, blood pressure decreased in the seated and standing position. During hypergravitation, blood pressure increased in a graded fashion with placebo. With NET inhibition, the increase in blood pressure during hypergravitation was profoundly diminished. Conversely, the tachycardic responses to sitting, standing, and hypergravitation all were greatly increased with NET inhibition. In contrast to our expectation, short-term NET inhibition did not improve tolerance to hypergravitation. Redistribution of sympathetic activity to the heart or changes in baroreflex responses could explain the excessive tachycardia that we observed.

During early periods of life, modifications of the gravitational environment affect the development of sensory, neuronal and motor systems. The vestibular system exerts significant effects on motor networks that control eye and body posture as well as swimming. The objective of the present study was to study whether altered gravity (AG) affects vestibuloocular and spinal motor systems in a correlated manner. During the French Soyuz taxi flight Andromède to the International Space Station ISS (launch: October 21, 2001; landing: October 31, 2001) Xenopus laevis embryos were exposed for 10 days to microgravity (microg). In addition, a similar experiment with 3g-hypergravity (3g) was performed in the laboratory. At onset of AG, embryos had reached developmental stages 24 to 27. After exposure to AG, each tadpole was tested for its roll-induced vestibuloocular reflex (rVOR) and 3 hours later it was tested for the neuronal activity recorded from the ventral roots (VR) during fictive swimming. During the post-AG recording periods tadpoles had reached developmental stages 45 to 47. It was observed that microgravity affected VR activity during fictive swimming and rVOR. In particular, VR activity changes included a significant decrease of the rostrocaudal delay and a significant increase of episode duration. The rVOR-amplitude was transiently depressed. Hypergravity was less effective on the locomotor pattern; occurring effects on fictive swimming were the opposite of microg effects. As after microgravity, the rVOR was depressed after 3g-exposure. All modifications of the rVOR and VR-activity recovered to normal levels within 4 to 7 days after termination of AG. Significant correlations between the rVOR amplitude and VR activity of respective tadpoles during the recording period have been observed in both tadpoles with or without AG experience. The data are consistent with the assumptions that during this period of life which is characterized by a progressive development of vestibuloocular and vestibulospinal projections (i) microgravity retards the development of VR activity while hypergravity weakly accelerates it; (ii) that microgravity retards the rVOR development while hypergravity caused a sensitization, and that (iii) AG-induced changes of VR activity during fictive swimming have a vestibular origin.

Background: Spaceflight is associated with increased glucocorticoids and catecholamines, both well-known for their immunosuppressive effects. The objective of this study was to develop a model of spaceflight by using a human centrifuge to reproduce launch and landing G forces along with bed rest to simulate microgravity., Hypothesis: Acute changes in G forces are causal factors in neuroendocrine and immune changes., Methods: Ten subjects underwent realistic launch G-force profiles followed by 16 d of 60 head-down tilt bed rest. At the end of the bed rest, subjects were subjected to realistic landing G-force profiles. Stress hormones and changes in leukocyte and lymphocyte subsets were measured in blood and urine samples over the course of the study., Results: Similar to shorter Shuttle missions (i.e., < or = 9 d), plasma cortisol was significantly decreased at simulated landing while urinary epinephrine was significantly increased. Urinary cortisol was significantly increased after simulated launch. The pattern of leukocyte and lymphocyte changes also mirrored the changes found in shorter 9-d spaceflights., Conclusions: These data suggest a role for both catecholamines and glucocorticoids in mediating changes in leukocyte and lymphocyte subsets during simulated microgravity coupled with hypergravity. Our results were also strikingly similar to those from actual Shuttle missions and support our conclusion that we have developed a model of spaceflight.

The influence of long (up to 5 min) flying overloads with moderate values (2-5 U, at the increase and descent rate of 0,6-1,5 U/s) on the functional state and activities of airplane crewmembers was studied during the real flights. It was established that the influence of such overloads causes the unfavorable changes in the functional state and decrease in the effectiveness of crewmembers' (especially of a navigator-operator) actions. It was shown that the use of measure complex (during the flight the crewmembers use anti-overload dress, the pilot informs the navigator-operator about beginning of maneuvering, trainings on statoergometer to improve the crewmembers' static physical endurance) allows increasing the crews' psychophysiologic capacity during the maneuvers accompanied with the effect of complex flying overloads with moderate values.

The release of L-[14C]glutamate via Na+-dependent glutamate transporters functioned in the reverse mode was investigated in cortical synaptosomes under centrifuge-induced hypergravity. The protonophore carbonyl cyanide-p-trifluoromethoxyphenyl-hydrazon (FCCP) induced increase in [Na+]i, depolarized the plasma membrane, dissipated the proton gradient across synaptic vesicles and mitochondrial membrane, caused a fall in both the ATP level and the ATP/ADP ratio. 35 mM KCl-stimulated L-[14C]glutamate release from synaptosomes preliminary treated with 1 microM FCCP considerably increased from 27.0+/-2.2 % to 35.0+/-2.3 % of total accumulated synaptosomal label after centrifuge-induced hypergravity as compared to control animals (P< or =0.05). We found the competitive nontransportable glutamate transporter inhibitor DL-threo-beta-benzyloxyaspartate to inhibit FCCP and high KCL-stimulated release of L-[14C]glutamate. The release would be expected to occur via plasma membrane glutamate transporters. Transportable inhibitor of glutamate transporters-DL-threo-beta-hydroxyaspartate (DL-THA) induced heteroexchange of L-[14C]glutamate from enlarged by FCCP cytosolic pool of the neurotransmitter. DL-THA-evoked release of L-[14C]glutamate was also increased significantly after hypergravity. Combined application of KCl, DL-THA and FCCP unmasked dramatic changes in the activity of the glutamate transporters functioning in the reverse mode after centrifuge-induced G-loading.

Gravity (G)-induced loss of consciousness (G-LOC), which is presumably caused by a reduction of cerebral blood flow resulting in a decreased oxygen supply to the brain, is a major threat to pilots of high-performance fighter aircraft. The application of cerebral near-infrared spectroscopy (NIRS) to monitor gravity-induced cerebral oxygenation debt has generated concern over potential sources of extracranial contamination. The recently developed NIR spatially resolved spectroscopy (SRS-NIRS) has been confirmed to provide frontal cortical tissue hemoglobin saturation [tissue oxygenation index (TOI)]. In this study, we monitored the TOI and the standard NIRS measured chromophore concentration changes of oxygenated hemoglobin and deoxygenated hemoglobin in 141 healthy male pilots during various levels of +G(z) (head-to-foot inertial forces) exposure to identify the differences between subjects who lose consciousness and those who do not during high +G(z) exposure. Subjects were exposed to seven centrifuge profiles, with +G(z) levels from 4 to 8 G(z) and an onset rate from 0.1 to 6.0 G(z)/s. The SRS-NIRS revealed an approximately 15% decrease in the TOI in G-LOC. The present study also demonstrated the TOI to be a useful variable to evaluate the effect of the anti-G protection system. However, there was no significant difference found between conditions with and without G-LOC in subjects with terminated G exposure. Further studies that elucidate the mechanism(s) behind the wide variety of individual differences may be needed for a method of G-LOC prediction to be effectively realized.

We have examined the morphological changes in chondrocytes after exposure to experimental hypergravity. Tibial epiphyseal cartilages of 17-days-old mouse fetuses were exposed to centrifugation at 3G for 16 h mimicking hypergravitational environment (experimental group), or subjected to stationary cultures (control group). Centrifugation did not affect the sizes of epiphyseal cartilage, chondrocyte proliferation, type X collagen-positive hypertrophic zone, and the mRNA expressions of parathyroid hormone-related peptide and fibroblast growth factor receptor III. However, centrifuged chondrocytes showed abnormal morphology and aberrant spatial arrangements, resulting in disrupted chondrocytic columns. Through histochemical assessments, actin filaments were shown to distribute evenly along cell membranes of control proliferative chondrocytes, while chondrocytes subjected to centrifugal force developed a thicker layer of actin filaments. Transmission electron microscopic observations revealed spotty electron-dense materials underlying control chondrocytes' cell membranes, while experimental chondrocytes showed their thick layer. In the intracolumnar regions of the control cartilage, longitudinal electron-dense fibrils were associated with short cytoplasmic processes of normal chondrocytes, indicating assumed cell-tomatrix interactions. These extracellular fibrils were disrupted in the centrifuged samples. Summarizing, altered actin filaments associated with cell membranes, irregular cell shape and disappearance of intracolumnar extracellular fibrils suggest that hypergravity disturbs cell-to-matrix interactions in our cartilage model.

Numerous studies have indicated that dysregulation of the immune system occurs during or after spaceflight. Using 21 day 6 head-down tilt bed rest as a spaceflight analog, this study describes the effects of a daily artificial gravity (AG) countermeasure treatment on immunity, stress, and reactivation of clinically important latent herpes viruses. Blood, saliva, and urine samples were collected from each of the 15 male test subjects (8 treatment, 7 control) periodically throughout the study. The immune assessment consisted of a comprehensive peripheral immunophenotype analysis, intracellular cytokine profiles, and measurement of T cell function. With the exception of mild reactivation of Epstein-Barr (EBV) and Varicella zoster (VZV) viruses, no significant changes in immune function were observed, suggesting that the AG countermeasure and the 21 day head-down tilt bed rest regimen had no adverse effect on immune function.

Background: Pilots of modern fighter aircraft are exposed to substantial physiological and mental stressors. The objective of this study was to investigate how memory performance, in terms of encoding and/or retrieval processes, was affected by sustained +Gz exposure., Method: There were 18 healthy men ranging from experienced fighter pilots to novice riders who participated. A word continuous recognition task (CRT) was employed as a memory test. The task consisted of three consecutive phases: 1) encoding of familiar words at 1 G; 2) encoding and retrieval of words at 70% of the subject's relaxed G-tolerance level, equivalent to +3.7 +/- 0.54 Gz; and 3) encoding and retrieval of words at 1 G. In addition, each subject performed the CRT in a 1-G-only control condition. Physiological and psycho-physiological measures included continuous monitoring of ECG, arterial oxygen saturation, arterial BP at head level, and response time., Results: Data analysis showed that the capability to recognize words encoded at 1 G did not differ between conditions, indicating that the retrieval process was insensitive to increased Gz load. However, the ability to recognize words previously encoded during G exposure was reduced by approximately 10% as compared with control. Since the analysis revealed that the words were perceived, this result suggests that the encoding process was impaired in hypergravity., Conclusion: The results indicate that memory encoding, but not retrieval, was affected negatively when exposed to substantial and sustained +Gz loads.

Harsh environment and extreme factors related to the supposed exploration missions to Mars are considered as well as concomitant human organism reactions. Further investigations are required to get insight into the effects of gravity ranging from microgravity to hypogravity to hypergravity the crew will be exposed to during this voyage. A special emphasis should be placed on the studies of artificial gravity as an alternative to the existing in-flight countermeasures. Other issues to be attended include transitory states of human organism as a response to changes in gravity, effects of ionizing radiation and synergy of the variety of flight factors, and mechanisms of the hypomagnetic effects.

Introduction: Performing specific neck strengthening exercises has been proposed to decrease the incidence of neck injury and pain in high performance combat pilots. However, there is little known about these exercises in comparison to the demands on the neck musculature in flight., Methods: Eight male non-pilots performed specific neck exercises using two different modalities (elastic band and resistance machine) at six different intensities in flexion, extension, and lateral bending. Six Royal Australian Air Force Hawk pilots flew a sortie that included combinations of three +Gz levels and four head positions. Surface electromyography (EMG) from selected neck and shoulder muscles was recorded in both activities., Results: Muscle activation levels recorded during the three elastic band exercises were similar to in-flight EMG collected at +1 Gz (15% MVIC). EMG levels elicited during the 50% resistance machine exercises were between the +3 Gz (9-40% MVIC) and +5 Gz (16-53% MVIC) ranges of muscle activations in most muscles. EMG recorded during 70% and 90% resistance machine exercises were generally higher than in-flight EMG at +5 Gz., Discussion: Elastic band exercises could possibly be useful to pilots who fly low +Gz missions while 50% resistance machine mimicked neck loads experienced by combat pilots flying high +Gz ACM. The 70% and 90% resistance machine intensities are known to optimize maximal strength but should be administered with care because of the unknown spinal loads and diminished muscle force generating capacity after exercise.

Introduction: While the physiologic effects of space travel are documented in healthy individuals, little is known about its impact on medically ill or injured persons. In this study, hemorrhagic shock in primates was used to model a potentially common pathophysiologic condition during exposure to gravitational forces simulating return from Earth orbit. This experiment did not model the effects of cardiovascular deconditioning that normally occur during spaceflight., Methods: Using invasive hemodynamic monitoring, serial cardiovascular and laboratory parameters in baboons (Papio papio) were studied. Subjects were centrifuged at either a low +Gx (3.3 G maximum) or high +Gx (7.8 G maximum) acceleration reentry profile before and after being subjected to either class II (20% volume loss) or class IV (40% volume loss) hemorrhagic shock., Results: Significant alterations in cardiovascular and laboratory parameters occurred during shock and exposure to high and low +Gx acceleration. Shock classification was the primary determinant of change in cardiovascular function. During the experimental protocol, 31 of 32 animals survived (97% survival). After a 1-wk post-protocol observation period, 28 of 32 subjects survived (88% survival)., Conclusions: This preliminary study presents data that suggest that the emergent return of a medically compromised individual without resuscitation may be potentially survivable. However, medical stabilization with volume resuscitation, supplemental oxygen, and noninvasive monitoring would likely optimize clinical outcomes in the event of significant hemorrhagic shock states necessitating emergent deorbit.

Introduction: G protection in the 39 Gripen aircraft is provided by a full coverage anti-G suit, a pressure-breathing system, and anti-G straining maneuvers (AGSM). The purpose was to study (1) the interaction of pressure breathing and AGSM while wearing an anti-G suit; and (2) the G-protective properties of the anti-G suit alone and in combination with the pressure-breathing system., Methods: During rapid onset rate G-time profiles (< or =9 G), 10 subjects were investigated in 5 conditions: (I) sitting relaxed, without any G-protective garment; (II) sitting relaxed and wearing an anti-G suit; (III) sitting relaxed, wearing an anti-G suit, and pressure breathing; IV) wearing an anti-G suit and performing AGSM; and V) wearing an anti-G suit, pressure breathing, and performing AGSM. In supplementary experiments (n=9), the share of the anti-G suit protection afforded by the abdominal bladder was investigated., Results: G tolerance was 3.4 Gz (range: 2.8-4.3) in condition I, > or = 6.5 Gz (4.5-9.0) in II, > or = 8.0 Gz (6.5-9.0) in III, > or = 8.9 Gz (8.5-9.0) in IV and > or = 9.0 Gz (8.5-9.0) in V. In the supplementary experiments, the anti-G suit afforded a 2.8-G protection, a third of which was contributed by the abdominal bladder. In the relaxed state, pressure applied to the airways was transmitted undistorted to the intrathoracic space. During AGSM, intrathoracic pressure rose to 10-14 kPa, regardless of whether AGSM was performed with or without pressure breathing., Discussion and Conclusions: The anti-G suit and the pressure breathing system provide G protection of > or = 4.6 G, of which the anti-G suit contributes about 3.0 G. The C-protective properties of the anti-G suit and those of pressure breathing appears to be additive, whereas the G protection afforded by pressure breathing does not add to that provided by AGSM.

It has been found that sustained centrifugation on Earth may evoke sickness symptoms that are similar to those of the Space Adaptation Syndrome (SAS). As in SAS, incidence of this 'Sickness Induced by Centrifugation' (SIC) is about 50% and the symptoms are particularly evoked by head movements. By systematically varying the G-load and duration of centrifugation, the current study investigated the characteristics of the gravitational stimulus that is required for SIC to occur. Subjects were exposed to centrifugation at 2 and 3Gx, for a duration of 45 and 90 minutes. A standardized head movement protocol was used to evoke SIC after centrifugation. The results show that in six out of 12 subjects (50%) no serious symptoms were elicited. In the remaining subjects, the effects of the 3G runs exceeded those of the 2G runs, and within each G-level symptom intensity was higher for the 90 min than for the 45 min exposure. An exponential fit on this data showed that the time constant of adaptation to the gravitational stimulus was about 60 minutes. This suggests that short duration exposures (i.e. <60 min) are not likely to induce serious SIC.

Objectives: Visual disturbances are commonly accepted criteria for acceleration tolerance assessment. Researchers during centrifuge experiments use them as a safe criterion for cessation of acceleration exposure. Visual disturbances analysis is a non-invasive method of assessing retinal blood flow. Limitation of visual stimuli perception is a measure of physiological state of the experiment participants before hemodynamic changes, which reach a critical level manifested by G-induced loss of consciousness. Detection of these disturbances play an important role during the acceleration tolerance assessment. In this study, an attempt was made to answer the question on how many mistakes or incorrect reactions had to be identified to classify the ability of the pilot to fly on military jets., Materials and Methods: A new computer-aided research apparatus of our own design was used to assess visual disturbances, being a criterion of +Gz tolerance. In the center of monitor screen, a line of 3 light points was projected. During the centrifuge test, green lateral lights randomly changed their shapes from circles to squares while central light, being a point of vision fixation, remained unchanged. To assess its efficacy, 14 volunteers participated in the tests with various stimuli exposure. The authors aimed at selecting parameters of stimuli and exposure so that the division of reactions presented in the table would correspond with the score scale appropriate for our goals., Results: Preliminary tests showed that appropriately selected light intensity of the exposed stimuli enables the use of test results to assess the number of erroneous reactions, and consequently the level of pilots' concentration during centrifuge tests., Conclusions: It has been found that the chosen luminance range of the projected light points is correct as it allows to evaluate the reactions, which should be considered erroneous. Additionally, prolongation of the correct reaction time to the mean value of about 400 ms facilitates better differentiation of results. Proper results evaluation, depending on the number of errors, lack of reactions or prolonged reactions made the assessment easier with computer-aided methods.

We investigated, during the first postnatal week, a voltage-gated sodium current (INa) transiently expressed in neonatal utricular hair cells in rats raised in hypergravity. Its electrophysiological properties did not differ significantly from those recorded from rats raised in normal gravity, but a delay was observed in their developmental expression. In normal gravity conditions, INa expression is maximal at postnatal days 1-2, conferring on the hair cells the ability to fire action potentials, and is down-regulated during the first postnatal week, whereas in hypergravity conditions, the down-regulation is delayed by 4 days. This is the first demonstration showing that development under enhanced gravity affects the transient excitability phase that characterizes neonate utricular hair cells, by delaying a critical period of vestibular development.

Introduction: Prevalence of G-induced loss of consciousness (G-LOC) in the United Kingdom Royal Air Force (RAF) was found to be 19.3% in 1987. With the introduction of the Typhoon, a fourth generation aircraft, the prevalence of G-LOC has been re-assessed to determine the effectiveness of current G tolerance training., Method: A survey was sent to 4018 RAF aircrew, irrespective of their current role. Information was requested on G-LOC, role and aircraft type, experience, and attitudes toward G-LOC prevention., Results: Responses were received from 2259 (56.2%) individuals, 882 (39%) of whom were current fast jet aircrew. At least one episode of G-LOC was reported by 20.1% of all respondents. In front line aircraft, prevalence of G-LOC among the 882 fast jet aircrew who responded was 6%. In the whole group, G-LOC was reported most commonly in aircrew under training (70.9%), and was most prevalent in training aircraft (77.4% of G-LOC events). At the time of the G-LOC, 64% of aircrew had less than 100 h total flying time. G-LOC was reported most frequently between +5 to +5.9 Gz, and "push-pull" maneuvers were associated with 31.3% of G-LOC events. Pulling G was not considered a problem by 50.6% of respondents, although over 80% recognized the value of flying currency, use of an anti-G suit, and physical fitness, and 55.6% felt that centrifuge training would be valuable., Discussion: The prevalence of G-LOC in the RAF has changed little since 1987, and there remains considerable scope for aircrew education, particularly with the introduction of the Typhoon.

Female astronauts have been reported to have a higher incidence of post-flight orthostatic intolerance (POI) compared with that of their male counterparts. POI may result from increased permeability of the endothelial cell (EC) layer in the vasculature. The goal of this study has been to determine whether estradiol (E(2)) and dihydrotesterone (DHT) alter human umbilical vein ECs (HUVECs) responses to short term (10 min) hypergravity (1-3 g) mimicking the g force experienced by astronauts during liftoff. E(2) and DHT rapidly (within 5 min) activated MAPK (mitogen-activated protein kinase) in HUVEC at 1 g in a receptor-dependent manner. Liftoff inhibited MAPK phosphorylation, and rapid E(2) and DHT activation of MAPK was blocked. Liftoff simulation or brief (5-90 min) treatment with E(2) or DHT at 1 g had no effect on the expression of the EC tight-junction protein occludin. However, 24-h pre-treatment of HUVECs with E(2) and DHT prior to liftoff simulation significantly increased occludin expression, and hypergravity exposure did not alter this increase. These data provide evidence for a possible protective effect of E(2) and DHT on EC function as indicated by increased occludin; this may help maintain the integrity of EC tight junction and could thus retard or reduce the incidence of POI.

Cytologic and morphometric investigations of the hypothesis, thyroid, thyroid and pancreas of rats after 19-d centrifugation at 2G revealed suppression of somatotropic hormone production by hypophyseal somatotrophs and insulin by pancreatic beta-cells, and intensification of thyrotrophic hormone production by hypophyseal thyreotrophs, thyroxin by thyreoid parenchyma and glucagon by pancreatic alpha-cells. These change in hormone production are viewed as an endocrine mechanism of the divergence of plastic processes and energy metabolism in animals subjected to chronic exposure to hypergravity.

The aim of this study was to determine the changes in the pancreas structure after acute and chronic exposure of organism to gravitational overloads (GO). The experiments were conducted in 36 outbred albino male rats, 12 rats formed the control group. GO effect was modeled using the centrifuge; the value of the overload thus created amounted to 4,0-6,0 gravitational units. Pancreas structure was studied using histological, electron microscopic and morphometric methods. It was found that after acute exposure to GO, mainly the reactive changes were demonstrated all the pancreatic structures studied: acinocytes, endocrinocytes, blood vessels and nervous apparatus. Chronic exposure to GO resulted in both reactive modifications, similar to those described after an acute exposure, and various compensatory-adaptive and destructive changes.

Introduction: The present study aimed to investigate the effect of intensive cycle training with short-arm centrifuge-induced hypergravity during bed rest on muscle size and function., Methods: This study involved 10 healthy men who were divided into 2 groups: a countermeasure group, BR-CM (n = 5); and a control group, BR-Cont (n = 5). The BR-CM subjects partook in intensive cycle training (to 90% of maximum HR) with short-arm centrifuge-induced artificial gravity on alternate days during 20-d bed rest. Muscle volume of the thigh and maximum voluntary contraction (MVC) during isometric knee extensions was measured before and after bed rest. Muscle functional magnetic resonance imaging (mfMRI) and electromyogram (EMG) of the quadriceps femoris were obtained during submaximal knee extension exercises at a load of 30% MVC., Results: The volume of the total thigh muscles was maintained in the BR-CM group (-1%), whereas it was not in the BR-Cont group (-9%, p < 0.05). MVC decreased in the BR-CM (7%) and BR-Cont groups (23%). EMG activity in the BR-CM group after bed rest was significantly lower than that of before; however, no significant change was found in the BR-Cont group. There were no significant changes in the resting and exercised mfMRI signals in either the BR-CM or BR-Cont groups., Conclusion: These results suggest that intensive cycle training with hypergravity maintained the size of human skeletal muscles during bed rest.

Analysis of +Gx tolerance of 15 members of short-term ISS missions and 9 members of long-term ISS missions aboard the Soyuz vehicles showed good tolerance during insertion and satisfactory during descent provided the use of in-flight countermeasures and anti-g suit Kentaur inside the vehicle. Objective data about the tolerance of off-nominal +Gx (6.26 and 8.1 G) pointed to a more pronounced sinus tachycardia and tachypnea in a ballistic descent following long-duration weightlessness as compared with nominal. Physiological deviations were transient, functional by character. Cardiac arrhythmia was largely observed during return to Earth. Two cosmonauts were found to develop prognostically unfavorable ECG indications during off-nominal descent. Main factors in these deviations could be age (above 45) and existence of some individual specifics of cardiac rhythm regulation. These results emphasize the necessity of more careful screening of candidates older than 45 years, as weightlessness may impact their general condition and tolerance of g-loads during return to Earth.

In this study the effects of hypergravity were analyzed on cerebellar Purkinje cells during early development in rats. The cerebellum is a key structure in the control and the adaptation of posture and anti-gravity activities. This holds particularly when external conditions are modified. Three groups of rats were conceived, born and reared in hypergravity (2g). At postnatal day 5 (P5), P10 or P15, they were exposed to normal gravity and at P40, the cerebella were investigated on the expression of calbindin-D28k and inositol-3-phosphate (IP3) in Purkinje cells. Control animals were bred in the same conditions but at 1g. Immunoreactivity of Purkinje cells was studied in lobules III and IX of the vermis. Lobule IX of the vermis is one of the targets of primary otolithic vestibular projections, and lobule III served as a control, being much less related with vestibular inputs. The results show that hypergravity induces a decrease in calbindin and IP3 labeling in 20% of Purkinje cells of lobule IX without any change in lobule III. Animals transferred from 2g to 1g at P5 or P10 showed the most pronounced effects and much less at P15. This study demonstrates that early development of the cerebellum is highly sensitive to changes in gravity. Ages until P10 are critical for the development of vestibulo-cerebellar connections, and in particularly the calcium signaling in Purkinje cells.

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,

Background: Motion sickness is a common aeromedical problem that may occur in pilots exposed to increased gravitoinertial load in the head-to-foot direction (+Gz). Since motion sickness may affect autonomic nervous functions including cardiovascular control, it was hypothesized that it might interfere with cardiovascular responses to high +Gz, thereby decreasing G tolerance., Methods: G tolerance and cardiovascular responses to increased G load were studied in nine subjects in a centrifuge environment under two conditions. In the motion sickness condition, the subject was exposed to a motion sickness provocation (MSP) comprising repeated rapid changes in G load in combination with a regimen of head movements. In the control condition the subject was exposed to similar cumulative G-time stress, but without the MSP. Mean arterial pressure (MAP) was measured. An index of peripheral vascular resistance was achieved by measuring the difference in skin temperature between the forearm and fingertip (deltaT(forearm-fingertip))., Results: MSP decreased gradual-onset rate G tolerance from 5.1 +/- 1.0 G (mean +/- SD) to 4.6 +/- 0.9 G. There was no change in gradual-onset rate G tolerance in the control condition. Rapid-onset rate G tolerance was lower in the motion sickness (2.9 +/- 0.5 G) than in the control (3.4 +/- 0.3 G) condition. MSP reduced MAP by 11 mmHg and deltaT(forearm-fingertip) by 4.2 +/- 4.1 degrees C. In the control condition MAP and deltaT(forearm-fingertip) were unaffected., Conclusions: Motion sickness may reduce the arterial pressure response to the extent that the capacity of an individual to withstand increased G loads in the head-to-foot direction is significantly diminished.

Introduction: Only one previous study has assessed almost loss of consciousness (A-LOC) in operational fighter pilots, reporting an incidence rate of 14%. Research also indicates that 8-13% of pilots have experienced G-induced loss of consciousness (G-LOC). A-LOC can be as insidious as G-LOC due to the associated altered state of awareness and relative incapacitation time, making it a significant risk factor in the high +Gz environment. Royal Australian Air Force (RAAF) pilots currently fly the F/A-18 and Hawk 127, producing +Gz accelerations up to +7.5 Gz, which places these pilots at risk of both A-LOC and G-LOC., Methods: A survey was administered to 100 active RAAF fighter pilots requesting information on G-induced visual and cognitive disturbances, A-LOC symptoms, and G-LOC. Details regarding type of aircraft, flying maneuvers performed and mission outcome were also sought., Results: There were 65 RAAF fighter pilots who completed the survey (age 20-53 yr, height 168-193 cm, weight 64-110 kg, jet hours 30-5700 h). Of these pilots, 98% indicated they had experienced at least one visual or cognitive disturbance in the high G environment: gray-out 98%; black-out 29%; and A-LOC symptoms 52%, including abnormal sensation in limbs, disorientation, and confusion. There were 9% who indicated they had experienced G-LOC (50% were the pilot flying the aircraft)., Discussion: These findings indicate that RAAF fighter pilots are experiencing a similar rate of visual disturbances and G-LOC when compared with other air forces. However, RAAF pilots reported a much higher incidence of A-LOC compared with the only other study of operational fighter pilots.

Intermittent hypergravity was evaluated as a method to prevent the unfavorable nervous effects of microgravity. It was shown that intermittent exposure to hypergravity (2 G, 1 h. a day) of rats during 24-d tail-suspension put a barrier to changes in the ultrastructure of the brain somatosensory cortex associated with a reduction in the afferent input to the somatosensory cortex from the hind limbs.

Proximal lower limb amputations (trans-femoral) usually leave amputees with significant functional disturbances. This article contains information regarding three pilots with trans-femoral amputations that returned swiftly to continue their aeronautical careers despite their disabilities. Adaptations are needed in the limb prostheses to enable the amputees to access the minimally spaced cockpit.

Introduction: Flight-induced neck pain at high Gz loads or during sustained rotary-wing missions may be caused by limitations in neck muscle function. A better understanding of the contributing factors of excessive external load and internal neck-stabilizing mechanisms would improve the ability to prevent and treat such pain. The aim of this single-blinded cross-sectional study was to evaluate neck neuromuscular function in fighter and helicopter pilots who suffered from frequent neck pain., Methods: Subjects with pain were 16 fighter pilots (FP-P) and 15 helicopter pilots (HP-P) with frequent neck pain episodes who were compared with pain-free controls (FP-C and HP-C). In all groups, neck extensor and flexor muscles were studied by measuring 1) the strength of maximum voluntary contraction (MVC), and 2) fatigue due to a submaximal isometric contraction. The decline (slope) of the electromyogram (EMG) median frequency power spectra was used as an index of fatigue, while initial median frequency (fi) was taken from the intercept of the regression line., Results: Two-way analysis of variance (ANOVA) revealed interaction effects for extensor MVC. Post hoc testing showed that FP-P had significantly lower extensor MVC (p = 0.03) than FP-C, while there was no such difference for the HP-P vs. HP-C or between the two control groups. There were no significant effects for MVC-balance (flexors/extensors); nor were there any fi or extensor EMG-slope effects. However, there were interaction effects for flexor EMG-slopes: HP-P showed lower slopes than did HP-C (p = 0.02)., Conclusions: To protect and stabilize the head and neck in high Gz environments, higher neck muscle strength is needed; less muscle strength in FP-P may cause further pain and perhaps reduced mission effectiveness. Less localized steep slopes for HP-P might reflect impaired muscle functioning. Specific preventive and clinical attention may be warranted for different types of pilot.

Introduction: This study determined the trends of reported G-induced loss of consciousness (G-LOC) mishaps from 1980--1999, and determined potential risk factors in pilot characteristics; specifically, 30/60/ 90-h and sortie history, total flight hours, total hours in the aircraft, age, height, weight, and BMI., Methods: Using aircraft malfunction mishaps to reflect a cross-section of USAF pilots, potential risk factors were determined using a case-control method; cases were all G-LOC mishaps and controls were aircraft malfunction mishaps. The data consisted of 2002 mishap pilots in the history of the F-16, F-15, F-15E, and A-10 from 1980-1999., Results: During this time, G-LOCs represented only 2.5% of all mishaps. The mean engagement number for G-LOC mishaps was three at an average of 8 Gs. A poor anti-G straining maneuver was cited in 72% of the mishaps, fatigue and G-suit malfunction in 19%, low G-tolerance at 14%, and 37% were student pilots. Within pilot characteristics, only two factors were found to be statistically significant: the time in the aircraft and pilot age. In the F-16, there was a 3.5 times greater chance of experiencing a G-LOC mishap if the pilot had less than 600 h in the aircraft [3.5 (1.7-7.2, 95%CI)], and a 9.5 times greater chance in the F-15 [9.5 (2.2-41.9, 95%CI)]. There was a 4.5 times greater chance of experiencing a G-LOC mishap if under the age of 30 in the F-16 [4.5 (2.3-8.5, 95% CI)] and a 3 times greater chance in the F-15 [2.8 (1.2-6.8, 95% CI)]., Discussion: Though it is difficult to predict who will experience G-LOC, emphasis on prevention must be concentrated in training and in pilots new to the aircraft.

Introduction: Nausea and motion sickness are important operational concerns for aviators and astronauts. Understanding the underlying mechanisms associated with motion sickness may lead to new treatments. The goal of this work was to determine if changes in cerebral blood flow precede the development of nausea in subjects susceptible to motion sickness., Methods: Cerebral flow velocity in the middle cerebral artery (transcranial Doppler), BP, and end-tidal CO2 were measured while subjects were rotated on a centrifuge (250 degrees x s(-1)). Following 5 min of rotation, subjects were translated 51.5 cm off-center, creating a +1 Gx centripetal acceleration in the nasal-occipital plane., Results: There were 10 subjects who completed the protocol without symptoms while 5 developed nausea (4 while off-center and 1 while rotating on-center). Prior to nausea, subjects had significant increases in BP (+13 +/- 3 mmHg, p < 0.05) and cerebrovascular resistance (+46 +/- 17%, p < 0.05) and decreases in cerebral flow velocity both in the second (-13 +/- 4%) and last minute (-22 +/- 5%) before symptoms (p < 0.05). In comparison, subjects resistant to motion sickness demonstrated no change in BP or cerebrovascular resistance in the last minute of off-center rotation and only a 7 +/- 2% decrease in cerebral flow velocity. All subjects had significant hypocapnia (-3.8 +/- 0.4 mmHg, p < 0.05); however, this hypocapnia could not fully explain the cerebral hypoperfusion associated with the development of nausea., Conclusions: These data indicate that reductions in cerebral blood flow precede the development of nausea. Further work is necessary to determine what role cerebral hypoperfusion plays in motion sickness and whether cerebral hypoperfusion can be used to predict the development of nausea in susceptible individuals.

Objective: To study the protective effects of low gravity preconditioning against learning and memory function impairment induced by high gravity exposure in rats., Method: Twenty-four male SD rats were randomized equally into control group, high gravity exposure group (+10 Gz/3 min) and low gravity preconditioning group (LGP group, preconditioned by a daily exposure to +4 Gz/3 min for 3 days before +10 Gz/3 min exposure). Both the learning and memory abilities of the rats in the 3 groups were examined after +10 Gz/3 min exposure., Results: In open field test, the rats exposed to +10 Gz/3 min, in comparison with the control rats, exhibited significantly declined total square-crossing and rearing (SCR) on days 0 and 2 (P<0.05), with also significantly prolonged stay in the central square at 0 d(P<0.01). In the low gravity preconditioned rats, SCR declined and length of stay in the central square increased significantly on day 0 (P<0.01). Compared with the rats in +10 Gz/3 min group, the rats in the LGP group showed decreased length of stay in the central square on day 2, and such changes was statistically significant on day 6 (P<0.05), but there was no difference in SCR at all time points. In Y-maze test, the number of times of right reaction (RR) decreased and the reaction time (RT) increased significantly in +10 Gz/3min group compared with those of the control group (P<0.01), whereas no significant differences were found between the control group and LGP group. Compared with +10 Gz/3 min group, the RR was increased (P<0.01) and RT shortened significantly (P<0.01) in LGP group. In the step-through test, the latent time (LT) increased (P<0.05) on day 0 but was then shortened significantly on day 6 in + 10 Gz/3min group (P<0.01), and no difference was found between LGP group and the control group. LT on day 6 increased significantly (P<0.01) in LGP group as compared with the +10 Gz/3 min group., Conclusion: High gravity exposure-induced rat learning and memory impairment can be markedly improved by lower gravity preconditioning.

Introduction: Electroencephalographic (EEG) correlates of Gz-induced loss of consciousness (G-LOC) were examined to better understand the mechanisms of G-LOC., Methods: There were 10 subjects (4 women) who provided 35 G-LOC episodes during which 13 channels of EEG and eye activity were recorded. Subjects simultaneously performed tracking and mathematical tasks prior to and following G-LOC. The performance data and cerebral regional oxygen saturation (rSO2), as measured using near infrared spectroscopy, were correlated with the EEG changes., Results: Across all subjects, seven EEG events were identified and measured. The two most significant were found over widespread scalp sites. They were a 1-2 Hz waveform just prior to G-LOC and a very large, approximately 1 Hz waveform just prior to regaining consciousness. These were associated with a drop of rSO2 levels to approximately 90% of the pre-G-LOC baseline levels. rSO2 levels returned to pre-G-LOC levels within approximately 15 s following G-LOC while EEG and performance measures took approximately 60 s., Discussion: There were two unique EEG waveforms found, one preceding unconsciousness and the other preceding the return to consciousness during G-LOC episodes. Further, the supply of oxygen to the brain was rapidly restored, within approximately 15 s, while the EEG and performance data showed that approximately 60 s were required for the brain to regain functional integrity. The delay in performance and EEG recovery following G-LOC demonstrates that the recovery of brain activity to support cognitive function requires more than just the restoration of normal oxygen levels.

Aerobatics is an aerial sport which has many physiological constraints, principally cardiovascular, with a risk if not adapted of sudden mid-air incapacity which could jeopardise aviation safety, and thus justifies the selection and surveillance of pilots. The aeronautical constraints during flight are multiple, related to the environment traversed, how the aircraft functions and its movements. Those which cause accelerations (+G in particular) pose the problem of haemodynamic tolerance because they can induce loss of consciousness due to cerebral hypoxia. Tolerance of acceleration varies among individuals; it can be improved with training, certain protective manoeuvres, and is reduced by hypoxia, certain medications, dehydration and heat. Moreover, in aerobatics certain tricks require manoeuvres which reduce this tolerance to +G accelerations. This is the "push-pull" effect (&#95;G acceleration immediately followed by +G acceleration). This leads to a risk of sudden loss of consciousness with a load factor much lower than that which the pilot knows he is capable of tolerating. Besides the haemodynamic effects, the existence of an actual acceleration cardiomyopathy has been suggested but has not been proven in man. Finally, while changes in cardiac rhythm during accelerations are usual and relate to changes in vaso-sympathetic balance, ventricular and supra-ventricular rhythm disturbances are rare and are related to the intensity and duration of the acceleration.

Background: This study was performed to test the feasibility of an experimental approach for assessing voice changes during exposure to increased +Gz acceleration. Such changes are probably due to mechanical alterations of the structures involved in voice production. This may be relevant to automatic speech analysis for flight control. Because voice control by means of auditory feedback may compensate for acceleration effects, the investigations included conditions with masked auditory feedback., Method: Four male subjects read standard speech test material while seated in a human centrifuge both during sustained +3 Gz acceleration and in a reference condition. Both test runs were repeated with masking of the auditory feedback by a white noise presented via headphones. Microphone and acceleration signals were recorded on a PC-based dynamic signal acquisition board. Long-time average spectra (LTAS), fundamental frequency (F0), and the frequency of the first, second, and third formant (F1, F2, F3) of the vowels /a/, /o/, and /i/ were extracted from the microphone signal for the different conditions., Results: LTAS clearly differed between the masking conditions, but not between reference and +3 Gz conditions. F0 clearly rose with auditory masking and showed a small increase under +3 Gz acceleration. Several effects of +3 Gz acceleration on formant frequencies were found, all of rather small magnitude. Increased acceleration lowered F2 for the vowel /i/. A decrease of F3 was observed for vowels /i/ and /o/., Conclusion: This pilot study has shown the feasibility of an experimental approach to assessing voice changes during exposure to increased +Gz acceleration. Exposure to +3 Gz showed small effects on FO and several formant frequencies. A definitive forthcoming study should assess the significance of these effects by investigating a greater number of subjects during exposure to acceleration higher than +3 Gz.

Despite advances in G-protection, F-16 student pilots continue to demonstrate G-performance inadequacies. The G-Risk Indicator Management (GRIM) Program was introduced at Luke Air Force Base in 2000 to facilitate early detection of G-related problems and to aid in the establishment of tailored ground training programs designed to enhance a student's performance under G. Assessment of anthropomorphic data, previous G-performance, anaerobic fitness, and centrifuge qualification scores comprise the initial assessment in the GRIM Program. Observations from these assessments are used to qualitatively determine the level of risk for the student. In the absence of any historical controls, no conclusions could be drawn with regards to the overall efficiency of the GRIM program. Significant differences were found between groups for anaerobic test scores, centrifuge scores, and gradebook comments. The results from this non-experimental study suggest the need for future studies to better determine the validity of G-risk indicators.

Most astronauts experience spatial disorientation after exposure to weightlessness, indicating that constant gravity is utilized as a stable external reference during spatial cognition. We attempted to elucidate the role of constant gravity in spatial learning using a radial arm maze test on rats housed in a hypergravity environment (HG) produced by a centrifuge device. Male Wistar rats were kept in 2G linear acceleration for 2 weeks before the spatial learning task, which lasted for 10 days. The control rats were placed close to the centrifuge device but not exposed to hypergravity. Spatial learning was evaluated by the accuracy and the re-entry rate, which were the rate of correct arm entries and the rate of entries into the arms that they had already visited, respectively. Locomotor activity was measured by number of entries per minute. The number of baits the animal took per minute was also measured. The results showed that accuracy was significantly inferior and the re-entry rate was significantly higher in the HG rats than in the controls, suggesting that animals use a constant gravity as a stable external reference in spatial learning. However, these differences disappeared at 5 days later, indicating that the HG rats learned the spatial task more rapidly than the controls. Locomotor activity was higher in the HG rats and there was no difference in number of baits per minute between the HG and control animals. In conclusion, if one sensory cue necessary for spatial cognition is disturbed by gravity change, animals can subsidize with other sensory cues such as proprioceptive and motor efference copy signals through increased locomotor activities.

Gravity represents a stable reference for the nervous system. When the individual is increasing in size and weight, gravity may influence several aspects of the sensory and motor developments. To clarify this role, we studied age-dependent modifications of several exteroceptive and proprioceptive reflexes in five groups of rats conceived, born and reared in hypergravity (2 g). Rats were transferred to normal gravity (1 g) at P5 (post-natal day 5), P10, P15, P21, and P27. Aspects of neural development and adaptation to 1 g were assessed until P40. Hypergravity induced a delay in growth and a retardation in the development of contact-righting, air-righting, and negative geotaxis. However, we found an advance in eye opening by about 2-3 days in HG-P5 and HG-P10 rats and an increase in grip-time. No differences were found in tail and grasp reflexes. Our results show that hypergravity leads to a retarded development of motor aspects which are mainly dependent upon the vestibular system.

To simulate the effects of prolonged standing in the workplace on the leg muscles, we subjected mice to centrifugation for 6 wk. The absolute wet weight of leg muscles and internal organs of mice were measured after exposure to 3G by centrifugation for 6 wk and at 2 wk after removal of centrifugation. The weight of the soleus muscle (antigravity muscle) significantly increased after 6-wk exposure to centrifugation, but it decreased to its control weight 2 wk after removal of centrifugation. In contrast, the wet weights of the anterior tibial muscle, liver, and kidneys of mice centrifuged for 6 wk were significantly lower than those of the control mice; they had returned to control levels 2 wk after removal of centrifugation. It was therefore suggested that prolonged standing enlarged the leg muscles but its effect did not last for a long period of time after stopping prolonged standing. Western blot analysis of proteins extracted from the soleus muscle showed that vinculin and alpha-actinin in the centrifuged mice increased slightly, but there were no differences in the heat shock protein 70 (HSP70) and desmin levels between the centrifuged mice and control mice. No difference in HSP 70 suggested that muscle damage did not exist after 6 wk centrifugation.

Introduction: Spaceflight is associated with a shift of interstitial fluid toward the skin of the head and a fluid loss that can decrease superficial tissue thickness (TT). To collect the physiological data needed to develop techniques for monitoring the hydration status of astronauts during spaceflight, we investigated the changes in TT induced by a 12-h nil-by-mouth period and a 30-min period of +2 Gz hypergravity measured at forehead and tibia., Methods: There were 16 male volunteers who were twice subjected to 30 min of +2 Gz acceleration in a human centrifuge, once following an oral fluid load of 250 ml x h(-1) (procedure A), and once following a nil-by-mouth period of 12 h (procedure B). The TT at the forehead (TT-f) and tibia (TT-t) was measured before (t0), after 10 min (t10), and after 30 min (t30) of hypergravity using a miniature 10 MHz A-mode ultrasound device. The bodyweight, hematocrit (HCT), and plasma viscosity (PVS) were measured at tO and t0., Results: The nil-by-mouth period induced a significant weight loss and increase in HCT and PVS. A significant increase was noted in TT-t, but not in TT-f (p < 0.05). Following both procedures, exposure to hypergravity produced declines in TT-f at t10 and t30 compared with baseline (p < 0.05), whereas TT-t was not influenced., Conclusions: Changes in interstitial fluid load of superficial tissues can be tracked by A-mode ultrasonography. Fluid loss-induced changes are best detected at the tibia, hypergravity-induced changes at the forehead.

Introduction: Most arrhythmias during centrifuge training are physiological responses to high +Gz stress. However, potentially dangerous arrhythmias occasionally occur during centrifuge training. We reviewed all arrhythmias recorded during the Japan Air Self-Defense Force (JASDF) centrifuge training from April 2001 to March 2003, and developed a criterion for suspending G-training based on observed arrhythmias., Method: There were 195 male fighter pilots who received high-G centrifuge training monitored with electrocardiographs (ECGs). We evaluated types and occurrences of all arrhythmias during high-G training over a 24-mo period., Results: Sinus arrhythmia (48.7%), single premature atrial contraction (32.3%), and single (58.5%) or paired (9.7%) premature ventricular contraction were commonly occurring arrhythmias during high-G training. We considered these arrhythmias as variant physiological responses to high-G training (category 1). In addition, we observed ventricular tachycardia (2.6%), paroxysmal supraventricular tachycardia (1.5%), and paroxysmal atrial fibrillation (0.5%). Further investigation of these trainees revealed a significant proportion with cardiac anomalies. As a result, the JASDF currently categorizes these arrhythmias as indicators to suspend G-training and initiate cardiac workup (category 3). Other arrhythmias, such as non-sustained ventricular tachycardia (VT) or Morbitz type I atrioventricular (AV) block, were considered borderline anomalies; whether training was allowed to continue depended on the decision of the physicians monitoring the training (category 2)., Conclusion: Routine ECG monitoring during centrifuge training is recommended to catch the pathology underlying dangerous arrhythmias for flight safety. Our proposed criterion for stopping the centrifuge is intended to differentiate between serious arrhythmias and arrhythmias of physiologic response.

When normal subjects are exposed to hypergravity [5 times normal gravity (5 G)] there is an impaired arterial oxygenation that is less severe in the prone compared with supine posture. We hypothesized that under these conditions the heterogeneities of ventilation and/or perfusion distributions would be less prominent when subjects were prone compared with supine. Expirograms from a combined rebreathing-single breath washout maneuver (Rohdin M, Sundblad P, and Linnarsson D. J Appl Physiol 96: 1470-1477, 2004) were analyzed for vital capacity (VC), phase III slope, and phase IV amplitude, to analyze heterogeneities in ventilation (Ar) and perfusion [CO(2)-to-Ar ratio (CO(2)/Ar)] distribution, respectively. During hypergravity, VC decreased more in the supine than in the prone position (ANOVA, P = 0.02). Phase III slope was more positive for Ar (P = 0.003) and more negative for CO(2)/Ar (P = 0.007) in the supine compared with prone posture at 5 G, in agreement with the notion of a more severe hypergravity-induced ventilation-perfusion mismatch in supine posture. Phase IV amplitude became lower in the supine than in the prone posture for both Ar (P = 0.02) and CO(2)/Ar (P = 0.004) during hypergravity as a result of the more reduced VC in the supine posture. We speculate that results of VC and phase IV amplitude are due to the differences in heart-lung interaction and diaphragm position between postures: a stable position of the heart and diaphragm in prone hypergravity, in contrast to supine in which the weight of the heart and a cephalad shift of the diaphragm compress lung tissue.

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.

The purpose of this study was to test a variety of microgravity countermeasures and anti-G suit (AGS) in long-term bed-rest and to approve them during 169-days space flight.

During gestation and early postnatal development, the animal's size and weight rapidly increase. Within that period, gravity affects sensory and motor development. We studied age-dependent modifications of several types of motor reflexes in 5 groups of rats conceived, born and reared in hypergravity (HG; 2 g). These rats were transferred to normal gravity (NG; 1 g) at various postnatal days, and their behavioral reflexes were compared with a control group which was constantly kept under NG. HG induced a retarded development of vestibular dependent reflexes. Other types of motor behavior were not delayed.

Pilots' physiological measurement in conditions of alternating plus and minus Gz (gravitational acceleration) has been done during real flights. The comparison of physiological responses during flights at the safe altitude of 7000 ft and low level flights at the altitude of 900 ft over ground bears on the evaluation of changes of the continuous blood pressure and the heart rate. High level of pilots' plus-minus Gz tolerance is essential requirement to cope with low level flights in agile aircraft. It was proved that the sinusoidal profile during real flights is possible to use for pilots' tolerance to plus and minus Gz load evaluation. A system for the physiological signal acquisition in a cockpit of combat aircraft was developed for this purpose.