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 901 records · Page 50Linked to original sources
PubMed1991

Space adaptation syndrome: multiple etiological factors and individual differences.

Space motion sickness is a significant operational concern in the American and Soviet space programs. Nearly 70% of all astronauts and cosmonauts are affected to some degree during their first several days of flight. It is now beginning to appear that space motion sickness like terrestrial motion sickness is the consequence of multiple etiological factors. As we come to understand basic mechanisms of spatial orientation and sensory-motor adaptation we can begin to predict etiological factors in different motion environments. Individuals vary greatly in the extent to which they are susceptible to these different factors. However, individuals seem to be relatively self-consistent in terms of their rates of adaptation to provocative stimulation and their retention of adaptation. Attempts to relate susceptibility to motion sickness during the microgravity phases of parabolic flight maneuvers to vestibular function under 1G and 0G test conditions are described.

Adaptation, Physiological↗
PubMed1989

Simulation of Space-Adaptation Syndrome on Earth.

The three Spacelab D-1 Scientist Astronauts were exposed to a 1.5 h centrifuge run in the supine position, resulting in a linear 3 g acceleration. They used their space experience to evaluate their readaptation to normal gravity and compared their observations with 'Space Adaptation Syndrome'. After the centrifuge runs, the vestibular visual system appeared to be modified in a very specific and reproducible manner. Readaptation to the normal 1 g environment took at least 6 h. During this period there was a striking similarity to the astronauts' experience during adaptation to weightlessness in space. Vestibular tests were subsequently performed, which confirmed these subjective findings.

Adaptation, Physiological↗
PubMed1998

[A study on EEG-Encephalofluctuographic characteristics in alpha frequency band in pilots].

The frequency-fluctuation characteristics in alpha frequency band were studied by EEG-Encephalofluctuographic Technology (EEG-ET) in 261 pilots. The electrical activity was recorded from 12 scalp monopolar leads of the international 10-20 system using linked ear lobes as reference. The components of the competitive frequency-fluctuation structure in alpha frequency band was analysed. The results showed that the predominant frequency component of the competitive structure was 9 Hz in the 261 normal healthy pilots. The second was 10 Hz. And the third was 7 Hz. The other competitive frequency components were inhibited. The relative entropy value (percentage) of the competivity structure was calculated for each EEG derivation of each pilot. We also analysed the spectra of the EEG-Encephalofluctuograph. We found that there was a dominant power peak at 21.39mHz in 57 pilots who complained in-flight blackout sometimes during acceleration.

Acceleration↗
PubMed1998

Effect of +Gz on plasma levels of calcitonin gene related peptide, endothelin and renal function in pilots.

The effect of positive acceleration on plasma levels of calcitonin gene related peptide (CGRP), and endothelin as well as renal function in pilots were observed in this study. 20 pilots were exposed to +2.5 Gz 10 s and +3.0 Gz 10 s with an interval of 5 min without anti-G suits. Samples of plasma and serum were taken 2Omin before and after exposure. Plasma levels of CGRP and endothelin after the exposure were significantly increased (P<0.01), but alkaline phosphatase(AKP), blood levels of beta 2-microglobulin(beta 2-MG), Ca2+ in serum showed no significant change (P>0.05) as compared with those before exposure. There was a correlation between CGRP and endothlin (r=0.772, P<0.01). It is concluded that positive acceleration(+2.5, +3.0Gz) could increase plasma levels of CGRP and endothlin but did not affect renal function.

Acceleration↗
PubMed1992

Gravity effects on cellulose assembly.

The effect of microgravity on cellulose synthesis using the model system of Acetobacter xylinum was the subject of recent investigations using The National Aeronautics and Space Administration's Reduced Gravity Laboratory, a modified KC-135 aircraft designed to produce 20 sec of microgravity during the top of a parabolic dive. Approximately 40 parabolas were executed per mission, and a period of 2 x g was integral to the pullout phase of each parabola. Cellulose biosynthesis was initiated on agar surfaces, liquid growth medium, and buffered glucose during parabolic flight and terminated with 2.0% sodium azide or 50.0% ethanol. While careful ground and in-flight controls indicated normal, compact ribbons of microbial cellulose, data from five different flights consistently showed that during progression into the parabola regime, the cellulose ribbons became splayed. This observation suggests that some element of the parabola (the 20 sec microgravity phase, the 20 sec 2 x g phase, or a combination of both) was responsible for this effect. Presumably the cellulose I alpha crystalline polymorph normally is produced under strain, and the microgravity/hypergravity combination may relieve this stress to produce splayed ribbons. An in-flight video microscopy analysis of bacterial motions during a parabolic series demonstrated that the bacteria continue to synthesize cellulose during all phases of the parabolic series. Thus, the splaying may be a reflection of a more subtle alteration such as reduction of intermicrofibrillar hydrogen bonding. Long-term microgravity exposures during spaceflight will be necessary to fully understand the cellulose alterations from the short-term microgravity experiments.

Acetobacter↗
PubMed1991

Parabolic flight as a tool to measure ocular counterrotation in a reduced force environment.

Five unmedicated subjects were flown in parabolic flight. The aircraft, a Caravelle, performed single parabolae every 2 to four minutes. This resulted in alternating phases of normal, hyper-, hypo- and again hyper-gravity. Subjects sat yoga fashion upright facing towards the aircraft cockpit. Head and/or trunk were deflected 30 degrees from the upright, stimulating otolith and/or neck receptors. During each pullup, low-g phase and pullout of the parabolae a picture of the left eye was recorded on video tape. On the ground ocular roll (OCR) was determined from these video recordings. OCR ranged from 0.9 to 6.9 degrees in l-g and from 1 to 7.2 degrees under high-g, depending on head and trunk position. Neck receptor contribution was found to induce OCR of 0.2 degree to 2.1 degrees in two subjects.

Adult↗
PubMed1991

Subjective luminous line perception under changing g-load and body-positions in parabolic flight.

Five healthy subjects were subjected to parabolic flight with laterally tilted head, trunk, or body position. A vertical luminous line was viewed by the subjects in a head-fixed goggle device. During normal, hyper- and hypogravity phases subjective luminous line orientation was measured. The data imply that stimulation of the neck position receptors markedly influences the perception of the subjective vertical as well as mechanisms of convergence of otolithic signals and visual information within the brain.

Adult↗
PubMed1997

Sympathetic nerve response to microgravity induced by parabolic flight.

The aim of this study was to clarify how muscle sympathetic nerve activity (MSNA) in humans, which plays an important role in blood pressure control against gravity, is altered under microgravity conditions. Subjects were seated in a jet aircraft with their legs extended. MSNA was recorded microneurographically from the tibial nerve of the sitting subjects with simultaneous monitoring of electrocardiogram, blood pressure, respiration, and intrathoracic blood volume during parabolic flights. In the Air Force training area, the aircraft made parabolas up to 10 times. At the entry to microgravity, intrathoracic blood volume increased, systemic blood pressure was elevated, and MSNA was suppressed. However, this MSNA suppression lasted only 10-15 sec, and then followed by an enhancement to the end of the parabolas. We conclude that MSNA is suppressed at the onset of microgravity during parabolic flight in response to loading of the cardiopulmonary volume receptor due to a cephalad body fluid shift. However, this MSNA suppression is transient during such dynamic gravitational changes as those induced by parabolic flight, probably modulated by arterial baroreceptors.

Adult↗
PubMed1997

Increased chronic acceleration exposure enhances work capacity.

Adult male chickens adapted to 1.75 or 2.5 G from long term centrifugation, were maximally exercised on an animal treadmill at 1 g (Earth's gravity) and compared with the exercise capacities of control chickens raised at 1 g. The increased-G birds had statistically significantly greater exercise capacities than the controls during the first 3 weeks of the study after the initial exercise exposure. Thereafter however for the following two months of the study, there was no difference in either group's exercise capacities. This early increased work capacity was attributed to the increased-G birds improved ability to maximize their muscular strength with neurological adaptation. The increased-G birds lost body mass at a 31% greater rate during exercise than the controls although this difference was not statistically significant. This increased body mass loss was considered to have resulted from increased use of glycogen during exercise.

Acceleration↗
PubMed1997

Cerebral blood flow velocity and cranial fluid volume decrease during +Gz acceleration.

Cerebral blood flow (CBF) velocity and cranial fluid volume, which is defined as the total volume of intra- and extracranial fluid, were measured using transcranial Doppler ultrasonography and rheoencephalography, respectively, in humans during graded increase of +Gz acceleration (onset rate: 0.1 G/s) without straining maneuvers. Gz acceleration was terminated when subjects' vision decreased to an angle of less than or equal to 60 degrees, which was defined as the physiological end point. In five subjects, mean CBF velocity decreased 48% from a baseline value of 59.4 +/- 11.2 cm/s to 31.0 +/- 5.6 cm/s (p<0.01) with initial loss of peripheral vision at 5.7 +/- 0.9 Gz. On the other hand, systolic CBF velocity did not change significantly during increasing +Gz acceleration. Cranial impedance, which is proportional to loss of cranial fluid volume, increased by 2.0 +/- 0.8% above the baseline value at the physiological end point (p<0.05). Both the decrease of CBF velocity and the increase of cranial impedance correlated significantly with Gz. These results suggest that +Gz acceleration without straining maneuvers decreases CBF velocity to half normal and probably causes a caudal fluid shift from both intra- and extracranial tissues.

Acceleration↗
PubMed1998

Effects of hyperdynamic fields on input-output relationships and long-term potentiation in the rat hippocampus.

The effects of a 2G force environment on synaptic plasticity were examined in the rat hippocampus. Field potentials from neurons in the CA1 pyramidal cell layer were evoked by stimulation of the afferent Schaffer collateral/commissural fibers in an in vitro slice preparation. Input-output (I-O) relationships of the circuit were determined before and after tetanizing stimuli given to induce long term potentiation (LTP), a form of neural plasticity. I-O curves from animals exposed to 2G via centrifugation for either 2 or 14 days were not different from those obtained in control (1G) animals. Similarly, induction of LTP was equivalent in all groups, showing increases in maximum amplitude, slope and midpoint response of the fitted Boltzmann functions compared to un-tetanized controls. Comparison of slices from dorsal and ventral hippocampus showed the location of the slice had no effect of LTP expression. We conclude that, in contrast to other reports of functional changes in the central nervous system under altered force environments, cellular mechanisms of synaptic plasticity, which may underlie learning and memory, are preserved in the hippocampus.

Action Potentials↗
PubMed1998

Chronic 2G exposure affects c-Fos reactivity to a light pulse within the rat suprachiasmatic nucleus.

This study examined the effect of the hyperdynamic environment on the function of the retinohypothalamic tract. Rats were exposed to either 2 days or 21 days of 2G via centrifugation. During the last hour of 2G exposure, one series of rats was exposed to a 1 hour phase-shifting light pulse while the second series of rats did not receive a light pulse. In addition a groups of 1G controls was exposed to the same 1 hour lighting paradigm. All animals were processed for c-Fos within the SCN. The 1G controls showed the normal response to light in which significantly greater numbers of c-Fos positive neurons were found in the SCN of the light pulsed rats relative to that of the nonlight pulsed rats. However, rats exposed to 2 days of 2G did not show the same response to light. Light pulsed rats and nonlight pulsed rats exhibited few c-Fos positive neurons within the SCN. A recovery in the effect of light to induce c-Fos reactivity within SCN neurons occurred in the rats exposed to 21 days of 2G. These results suggest that exposure to 2G can temporarily suppress the responsiveness of the SCN to the phase-shifting effects of light mediated by the retinohypothalamic tract.

Adaptation, Physiological↗
PubMed1993

The behavioral reactions of a snake and a turtle to abrupt decreases in gravity.

We report here on the behavioral reaction of two reptiles to abrupt decreases in gravity. One striped rat snake, Elaphe quadrivirgata, and three striped-neck pond turtles, Mauremys japonica, were exposed to microgravity on parabolic flight, during the filming of a documentary for the NHK television station in Japan. The video films revealed that the snake reflexively responded to the shift from hyper- to hypogravity by taking up a defensive posture--on the first parabola, the snake struck at itself. The turtles actively extended their limbs and hyper-extended their neck in microgravity, a posture which is identical to the displayed during their contact "righting reflex", when placed upside-down in normal gravity. The aggressive display of the snake was unexpected, although the righting response of the turtles was consistent with that shown by other vertebrates, including fish and mammals, exposed to microgravity. An implication of these observations is that the afferent signal for the righting reflex of vertebrates in normal gravity must be the unloading of ventral receptors in the sensory system, rather than the loading of dorsal receptors. These are the first behavioral records for any reptiles exposed to hypogravity.

Aggression↗