Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Hypergravity”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,063 records · Page 59Linked to original sources
PubMed2003

+Gz protection of a new bladder anti-G system.

OBJECTIVE: A new bladder anti-G system was developed to get better +Gz protection. The purpose of this study was to assess the +Gz protection afforded by it on the centrifuge. METHOD: Six male subjects using the new bladder anti-G system were exposed to 10-15 s ladder-shaped +Gz profiles without anti-G straining maneuver (AGSM), then exposed to + 5-9 Gz simulated aerial combat maneuver (SACM) with leg straining. RESULT: The +Gz protection and the +Gz-time tolerance were obtained. The anti-G effectiveness of the advanced bladder system was 5.33 +/- 0.26 G. All subjects passed the +5-9 Gz SACM, but the effort and fatigue were lower. CONCLUSION: The +Gz protection afforded by this system is high. The suggested scheme of the new bladder anti-G system is feasible.

Adolescent↗
PubMed2003

Characteristics of human body dynamic responses to landing impact in supine position.

OBJECTIVE: To study the characteristics of human body dynamic responses to landing impact. METHOD: Five healthy young men were exposed to 4-10 G for 50-80 ms half-sine acceleration pulse at 20 degrees supine angle and 10 G for 50 ms impact at 30 degrees to 60 degrees supine angles. The acceleration curves on the dropping platform of the impact tower, the seat, the human head, shoulder, chest and ilium, as well as ECG of the subjects were recorded. RESULT: The peaks of acceleration at the subject head, shoulder, chest, and ilium along chest-back direction rose with the increase of the impact level. The overshoots of acceleration at the subject head along head-ilium direction and chest-back direction were 93% and 102% respectively for 10 G at 20 degrees supine angle. With increase of supine angle, acceleration response at the subject along chest-back direction decreased. Acceleration response at the subject head along head-ilium direction was minimum at 40 degrees supine angle. CONCLUSION: Transfer function of the human body to landing impact demonstrated that human body had a series of resonance frequencies which were 25 Hz, 34 Hz, 39 Hz, 43 Hz, 50 Hz, 64 Hz, and 70 Hz respectively.

Acceleration↗
PubMed2003

[Effects of +Gz exposure time on memory and behavior in rats].

OBJECTIVE: To explore the effect of +Gz exposure time on memory and behavior in rats. METHOD: Twenty-four male SD rats were randomly divided into control group (A), +10 Gz/3 min group (B) and +10 Gz/5 min group (C). Rats in group A and B were exposed to +10 Gz for 3 min or 5 min respectively. Changes of memory and behavior in rats were observed after +Gz exposure. RESULT: As compared with control, percentage of right reflex decreased significantly and reaction time lengthened significantly immediately, 1 d, 2 d, 4 d and 6 d after +10 Gz/5 min exposure (P<0.01); reaction time lengthened significantly immediately and 2 d after +10 Gz/3 min exposure (P< 0.01). As compared with +10 Gz/3 min, percentage of right reflex decreased significantly and reaction time lengthened significantly at 1 d, 2 d, 4 d and 6 d after +10 Gz/5 min exposure (P<0.01). As compared with control and +10 Gz/3 min, time stayed in center grille lengthened significantly immediately after +10 Gz/5 min exposure (P<0.01); balancing function decreased significantly immediately and 2 d after +10 Gz/5 min exposure (P< 0.01). CONCLUSION: It is suggested that +10 Gz/ 3 min exposure may induce a provisional disturbance in memory function and a change in behavior in rats, and +10 Gz/5 min exposure may induce a sustained disturbance in memory function and an obvious change in behavior in rats.

Acceleration↗
PubMed2003

[Effects of nutritional intervention on brain functions and its related biochemical indexes in mice exposed to high +Gy].

OBJECTIVE: To study the effects of nutritional intervention on changes of monoamines in rats brain, certain amino acids in rats serum and maze behaviors caused by high +Gy exposure. METHOD: The mice were arranged into control group (Group A), +Gy group (Group B) and +Gy nutritional intervention group (group C). Group A was not exposed to +Gy. Both Group B and group C were exposed to +10 Gy for 8 min. Three hours before +Gy exposure distilled water was given to mice in group B by gavage. The day before exposure pyridoxal fortified water was given and 3 h before exposure mixed amino acids solution were given by gavage to group C. Maze test scores were recorded for all groups. After the maze test was completed, blood was collected through the eyes for serum amino acids and brain tissue was collected by decollation for monoamines and gamma-glutamyl transferase (GGT) activity determinations. RESULT: After +Gy exposure maze test scores and brain NE concentrations decreased and abnormal behaviors were found. While other monoamine transmitters increased significantly. In group C maze behaviors improved and biochemical changes induced by +Gy exposure alleviated. CONCLUSION: High +Gy exposure can induce changes of neural transmitters coming from nutritional metabolites in central nervous system. As a result, brain functions are affected. Nutritional intervention can alleviate this negative effect to some extent.

Amino Acids↗
PubMed2003

Muscle activity in pilots with and without pressure breathing during acceleration.

BACKGROUND: Fighter pilots are frequently exposed to high acceleration (+Gz) forces during sorties. To counter these forces the pilots wear anti-G ensembles, use positive pressure breathing for G protection (PBG), and perform anti-G straining maneuvers (AGSMs). The purpose of this study was to analyze the muscle activity during sustained high G when no positive pressure breathing was used (control) compared with that during the use of PBG. METHOD: Seven Swedish Air Force fighter pilots volunteered to be exposed to gradual and rapid onset runs to +9 Gz with and without PBG in a human centrifuge. Surface electromyography was recorded from the intercostals, rectus abdominis, vastus lateralis, biceps femoris, and gastrocnemius lateralis. Measured variables included mean muscle activity, relative time with high muscle activity levels, and individual activation preferences. RESULTS: G duration tolerance was significantly longer (p = 0.028) when PBG was used (57 s) compared with control (32 s) during rapid onset runs. The vastus lateralis and the gastrocnemius lateralis generated activity > 50% of a reference contraction for a longer relative time during control (5.8% and 33.6%, respectively) than during PBG (0.3% and 12.7%, respectively). Cumulative muscle activity during acceleration was compared between trials and indicated that some pilots preferred contracting their leg muscles and others their abdominal muscles. CONCLUSION: G duration tolerance time increased when PBG was used during rapid onset sustained exposures. Less relative time with high muscle activity was seen during the use of PBG in two groups of leg muscles. The pilots seemed to have individual muscle activation sequence preferences while performing the AGSMs.

Acceleration↗
PubMed2003

Production of isometric forces during sustained acceleration.

BACKGROUND: The operation of high-performance aircraft requires pilots to apply finely graded forces on controls. Since they are often exposed to high levels of acceleration in flight, we investigated to what extent this ability is degraded in such an environment. METHODS: Twelve healthy non-pilot volunteers were seated in the gondola of a centrifuge and their performance was tested at normal gravity (1 G) and while exposed to sustained forces of 1.5 G and 3 G oriented from head to foot (+Gz). Using an isometric joystick, they attempted to produce force vectors with specific lengths and directions commanded in random order by a visual display. RESULTS: Acceleration had substantial effects on the magnitude of produced force. Compared with 1 G, maximum produced force was about 2 N higher at 1.5 G and about 10 N higher at 3 G. The size of this effect was constant across the different magnitudes, but varied with the direction of the prescribed force. CONCLUSIONS: Acceleration degrades control of force production. This finding may indicate that the motor system misinterprets the unusual gravitoinertial environment and/or that proprioceptive feedback is degraded due to increased muscle tone. The production of excessive isometric force could affect the safe operation of high-performance aircraft.

Acceleration↗
PubMed2003

Effects of dietary supplementation of certain nutrients on maze performance and biochemical indices in mice after exposure to high +Gz.

OBJECTIVE: To explore the possible effects of nutritional supplements on brain function as reflected by Water Maze test performance in mice after +Gz exposure. METHOD: Mice were arranged into control group (group A), +Gz group without nutritional supplementation (group B) and +Gz plus nutritional supplementation group (group C). Each group contains 12 mice. Mice in group A were not exposed to +Gz while mice in both group B and group C were exposed to 8 min + 10 Gz. Distilled water was gavaged to group B mice 3 h before +Gz exposure. On the day before +Gz exposure pyridoxol fortified water was given and 3 h before exposure mixed amino acids solution were gavaged to group C mice. Water Maze test was done and scores were recorded in all groups. After the Water Maze test was completed, blood was collected through the eyes for serum amino acid determinations and brain tissue was collected by decollation for monoamine determination and gamma-glutamyl transferase (GGT) activity evaluation. RESULT: After +Gz exposure, longer completion time and more mistakes were observed in Water Maze test in group B as compared with group A and a trend of improvement in group C was noticed. The ratio of brain 5-HT to dopamine (DA) was significantly reduced in group C as compared with group B. Gamma glutamyl transferase (GGT) activity in brain tissue in group C and group B increased significantly. CONCLUSION: High sustained +Gz exposure significantly reduces Water Maze test performance in mice (longer completion time and more mistakes). It seems that there is a trend of improvement in Water Maze performance in mice in dietary nutritional supplementation group, which might be due to significant reduction in ratio of brain 5-HT to DA in mice with nutritional supplementation.

Amino Acids↗
PubMed2003

Effect of 30-min +3 Gz centrifugation on vestibular and autonomic cardiovascular function.

INTRODUCTION: Repeated exposure to increased +Gz enhances human baroreflex responsiveness and improves tolerance to cardiovascular stress. However, it is not known whether such enhancements might also result from a single, more prolonged exposure to increased +Gz. Our study was designed to investigate whether baroreflex function and orthostatic tolerance are acutely improved by a single prolonged exposure to +3 Gz, and moreover, whether changes in autonomic cardiovascular function resulting from exposure to increased +Gz are correlated with changes in otolith function. METHODS: We exposed 15 healthy human subjects to +3 Gz centrifugation for up to 30 min or until symptoms of incipient G-induced loss of consciousness (G-LOC) ensued. Tests of autonomic cardiovascular function both before and after centrifugation included: 1) power spectral determinations of beat-to-beat R-R intervals and arterial pressures; 2) carotid-cardiac baroreflex tests; 3) Valsalva tests; and 4) 30-min head-up tilt tests. Otolith function was assessed during centrifugation by the linear vestibulo-ocular reflex and both before and after centrifugation by measurements of ocular counter-rolling and dynamic posturography. RESULTS: Of the 15 subjects who underwent prolonged +3 Gz, 4 were intolerant to 30 min of head-up tilt before centrifugation but became tolerant to such tilt after centrifugation. The Valsalva-related baroreflex as well as a measure of the carotid-cardiac baroreflex were also enhanced after centrifugation. No significant vestibular-autonomic relationships were detected beyond a vestibular-cerebrovascular interaction reported earlier in a subset of seven participants. CONCLUSIONS: A single prolonged exposure to +3 Gz centrifugation acutely improves baroreflex function and orthostatic tolerance.

Adult↗
PubMed2003

Chiari-I malformation in two fighter pilots.

This report describes two cases of Chiari Malformation Type I (Chiari-I) in fighter pilots of the Turkish Air Force. Chiari-I is a congenital malformation characterized by herniation of cerebellar tonsils through the foramen magnum. Patients have symptoms and signs related to dysfunction of the brainstem, spinal cord, and cerebellum. They generally are symptomatic in the earlier years of life. However, asymptomatic cases can eventually become symptomatic in later years. Symptoms can be provoked by increasing intracranial pressure (Valsalva or straining). We report on two pilots with Chiari-I malformation who had no symptoms or signs in their daily activities. Furthermore, these pilots had successfully completed physiological training, including centrifuge training, without any symptoms. However, they suffered from headache, neck spasms, and/or disequilibrium under +Gz during flight training sorties. The clinical presentation, diagnosis, treatment, possibility of acquired cases, and aeromedical disposition of Chiari malformations are discussed.

Adult↗
PubMed2003

[Effect of push-pull maneuver on distribution of DNA and NO content in rats' brain tissue].

OBJECTIVE: To study the effect of push-pull maneuver on cerebral apoptosis and NO content of rats. METHOD: Ninety male Wistar rats were randomly divided into the control group, +Gz exposure group and the push-pull maneuver group. The rats were killed after 30 min exposure, 3 h, 12 h, 24 h or 48 h exposure, and the brain tissues were taken. The variation of NO content measured was using chemical colormetry. Then flow cytometric method was adopted to examine the distribution diagram of cortex and hippocampus-cell DNA for determination of percentage of A0 peak, which could express apoptosis degree. RESULT: NO content in +Gz exposure group and push-pull group are significantly different from that of control at 30 min, 3 h and 12 h. And the difference between +Gz group and push-pull group are also significant, but not at 24 h and 48 h. Comparing with the control group, the apoptosis amount of cortex and hippocampus-cell of +Gz exposure group and push-pull maneuver group increased obviously at 3 h, 12 h and 24 h, reached its peak at 24 h, and had no remarkable difference at 48 h. The comparison of the apoptosis amount of cortex cell and hippocampus cell between push-pull maneuver group and +Gz exposure group, difference at 3 h and 24 h and remarkably different at 12 h. CONCLUSION: High +Gz and push-pull maneuver may increase the percentage of cerebral apoptosis amount and NO content. Comparing with the +Gz exposure group, the push-pull maneuver group will cause more increase in apoptosis amount and NO content, but this damage is reversible.

Aerospace Medicine↗
PubMed2003

[Structural and functional organisation of the spleen lymphoid tissue after exposure to hypergravitation].

Using the stereologic methods and quantitative analysis of the cells of lymphoid series in the splenic white pulp of Wistar rats, the changes were studied after continuous 5-day-long exposure to hypergravitation of 2 G. The injurious effect of hypergravitation was manifested in the reduction of the dimensions of periarterial lymphoid sheaths (PALS) and of lymphoid nodules, marginal zone dilatation and the disappearance of lymphoid nodules with germinal centers. Changes in the cell population of the white pulp are indicative of the suppression of blast-transformation and cell reproductive activity (as demonstrated by the disappearance of blast cells and the mitotic cells) and the reduction of lymphocytopoiesis in the organ lymphoid tissue. The proportion of immature plasma cells is increased. The changes demonstrated are more pronounced in PALS than in lymphoid nodules. The significant cellular reorganization of the marginal zones is the reflection of compensatory processes, which develop in response to the injurious effect of hypergravitation on the lymphoid tissue of the spleen.

Animals↗
PubMed2003

[Growth, reproductive function, and tolerance to load tests in rats under repetitive adverse conditions].

Wistar rats were subjected to a 3.5-day water deprivation once a month in the period of 1 to 10 months of age. The rats' adaptive abilities proved sufficient for compensation of adverse effects, the rats preserved their normal motor activity, emotionality, and orienting behaviour in the intervals between the effects. In the reproductive period, the males manifested a normal sexual behaviour and fertilizing capacity of their spermatozoids. In the end of the experiment, the experimental animals did not differ from the control animals.

Adaptation, Physiological↗
PubMed2003

Feeling free, feeling 0-g!

Following the great success of the Student Parabolic Flight Campaigns that it organised in 1994 and 1995, ESA decided to make them an annual event for students from the Agency's Member States. An initiative of ESA's Education Office, the campaigns give talented students a unique opportunity to experience weightlessness whilst performing their own scientific experiments, and hopefully encourage them to consider pursuing a career in space. The fifth Student Parabolic Flight Campaign (SPFC) took place from Bordeaux-Merignac Airport in southwest France in the first weeks of September 2002, with more than 120 students participating. Their thirty-two experiments had been selected in a Europe-wide competition and covered a wide variety of disciplines. The great enthusiasm shown by the students and the wide coverage that the campaign received in the media demonstrated the growing interest in space education and the promotional value of the campaign.

Adolescent↗
PubMed2003

Acceleration-induced near-loss of consciousness: the "A-LOC" syndrome.

BACKGROUND: There is an insidious phenomenon that can occur when aircrew are exposed to +Gz stress even at levels that are insufficient to cause +Gz-induced loss of consciousness (G-LOC). Under these circumstances aircrew exhibit an altered state of awareness that was termed Almost Loss of Consciousness (A-LOC) by the U.S. Navy in the late 1980's. A-LOC is a syndrome that includes a wide variety of cognitive, physical, emotional, and physiological symptoms. While A-LOC has been observed in centrifuge studies and reported in flight for over 15 yr, a definitive description of the syndrome does not exist. METHODS: Nine subjects were exposed to short +6, 8, and 10 Gz pulses of increasing duration until they experienced G-LOC. Instrumentation included two channels of ECG and near infrared spectroscopy (NIRS) to measure relative cerebral tissue oxygenation (rSo2). Subjects indicated +Gz-induced visual symptoms (light loss, LL) by pressing a switch when LL began and releasing it when total vision was restored. Short-term memory loss was assessed using a simple math task. Data analysis included a description and the time course of the physical, physiological, cognitive, and emotional responses. RESULTS: There were 66 episodes of A-LOC that were identified out of a total of 161 +Gz pulse exposures. Many incidents of sensory abnormalities, amnesia, confusion, euphoria, difficulty in forming words, and reduced auditory acuity were documented. Often these responses occurred in multiple subjects and at different +Gz levels. One of the most common symptoms was a disconnection between cognition and the ability to act on it. There was a significant reduction in rSo2 over baseline, greater overshoot in rSo2 (increase in oxygenation above baseline after the +Gz exposure), faster fall in rSo2 during +Gz stress, and prolonged recovery time associated with A-LOC as compared with +Gz exposures without symptoms. CONCLUSION: Evaluation of the range of symptoms associated with A-LOC can lead to a program to increase pilots' awareness of the phenomenon and further our understanding of the relationship between the outward symptoms and the underlying physiological changes.

Adult↗
PubMed2003

Contrast sensitivity after +Gz acceleration.

BACKGROUND: This study was designed to determine the extent and duration of contrast sensitivity (CS) loss after high sustained +Gz acceleration in a centrifuge. METHODS: The subjects were 12 healthy male flight surgeons between 20 and 22 (mean = 21.1) yr of age. The human centrifuge at the Aviation Physiology Research Laboratory in Tainan, Taiwan, was used to expose the subjects to an acceleration profile. Each subject experienced three centrifuge runs made up of one gradual onset and two rapid onset profiles. Contrast sensitivity (CS) was measured before, and at 5 min, 10 min, and 20 min for the right eye; and 7 min, 12 min, and 22 min for the left eye after the acceleration. Both eyes were measured with the right eye being tested first. RESULTS: There was a generalized depression of CS at 5-12 min for both eyes. The depression was more severe at low and medium frequencies (1.5, 3.0, 6.0 cycles per degree, cpd) than at a high spatial frequency (18.0 cpd). There was a significant decrease in CS of the right eye at 1.5 cpd (p < 0.05 between control and 5 min), and on the left eye at 3.0 cpd (p < 0.05 between control and 7 min, p < 0.05 between control and 12 min) and 6.0 cpd (p < 0.05 between control and 12 min). The CS loss was more obvious at 5-12 min for both eyes, and there was only partial recovery at 22 min after the acceleration. CONCLUSIONS: These results demonstrated that +Gz acceleration is associated with CS loss. The recovery time was greater than expected. Factors other than ocular blood flow may be involved in the prolonged CS loss.

Adult↗