Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “GRAVITY”

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 325 records · Page 18Linked to original sources
PubMed1998

Gravity cavernosometry and assessment of complete smooth muscle relaxation: helpful in the differential diagnosis of cavernous leakage?

OBJECTIVE: To establish whether the relationship between cavernosal pressures and gravitational pressures of infused liquid during gravity cavernosometry is linear when complete smooth muscle relaxation is achieved and whether the determination of this relationship could be helpful in the differential diagnosis between organic and functional cavernous leakage. METHODS: Gravity cavernosometry was performed in 50 impotent patients. The cavernosal pressure was measured at at least four different gravitational pressures of the infused liquid. RESULTS: A linear relationship was obtained in all patients with normal maximal cavernosal pressure at gravity cavernosometry. A flat or nonlinear relationship was found in those with abnormal maximal pressure, whatever the cause of cavernous leakage. CONCLUSIONS: A linear relationship between cavernosal and gravitational pressures characterizes complete smooth muscle relaxation during gravity cavernosometry. However, the usefulness of the determination of this relationship is not yet established.

Adult↗
PubMed2003

Antagonism between apoptotic (Bax/Bcl-2) and anti-apoptotic (IAP) signals in human osteoblastic cells under vector-averaged gravity condition.

A functional disorder associated with weightlessness is well documented in osteoblasts. The apototic features of this disorder are poorly understood. Harmful stress induces apoptosis in cells via mitochondria and/or Fas. The Bax triggers cytochrome c release from mitochondria, which can be blocked by the Bcl-2. Released cytochrome c then activates the initiator caspase, caspase-9, which can be blocked by the anti-apototic (IAP) family of molecules. The effector caspase, caspase-3, finally exerts DNA fragmentation. We conducted this study to examine the apoptotic effects of vector-averaged gravity on normal human osteoblastic cells. Cell culture flasks were incubated on the clinostat, which generated vector-averaged gravity condition (simulated microgravity) for 12, 24, 48, and 96 hours. Upon termination of clinostat cultures, the cell number and cell viability were assessed. DNA fragmentation was analyzed on the agarose-gel electrophoresis. The mRNA levels for Bax, Bcl-2, XIAP, and caspase-3 genes were analyzed by semi-quantitative RT-PCR. Twenty-four hours after starting clinostat rotation, the ratios of Bax/Bcl-2 mRNA levels (indicator of apoptosis) were significantly increased to 136% of the 1G static controls. However, the XIAP mRNA levels (anti-apoptotic molecule) were increased concomitantly to 138% of the 1G static controls. Thus, cell proliferation or cell viability was not affected by vector-averaged gravity. DNA fragmentation was not observed in clinostat group as well as in control group. Finally, the caspase-3 mRNA levels were not affected by vector-averaged gravity. Simulated microgravity might modulate some apoptotic signals upstream the mitochondrial pathway.

Adult↗
PubMed2004

Effects of Gravity on ZBLAN Glass Crystallization.

The effects of gravity on the crystallization of ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF glasses have been studied using the NASA KC-135 and a sounding rocket. Fibers and cylinders of ZBLAN glass were heated to the crystallization temperature in unit and reduced gravity. When processed in unit gravity the glass crystallized, but when processed in reduced gravity, crystallization was suppressed. A possible explanation involving shear thinning is presented to explain these results.

Crystallization↗
PubMed2006

Effect of gravity on the dynamics of nonequilibrium fluctuations in a free-diffusion experiment.

Diffusion is commonly believed to be a homogeneous process at the mesoscopic scale, being driven only by the random walk of fluid molecules. On the contrary, very large amplitude, long wavelength fluctuations always accompany diffusive processes. In the presence of gravity, fluctuations in a fluid containing a stabilizing gradient are affected by two different processes: diffusion, which relaxes them, and the buoyancy force, which quenches them. These phenomena affect both the overall amplitude of fluctuations and their time dependence. For the case of free diffusion, the time-correlation function of the concentration fluctuations is predicted to exhibit an exponential decay with correlation time depending on the wave vector q. For large wave vector fluctuations, diffusion dominates, and the correlation time is predicted to be 1 / (Dq2). For small wave vector fluctuations, gravitational forces have time to play a significant role, and the correlation time is predicted to be proportional to q2. The effects of gravity and diffusion are comparable for a critical wave vector q(c) determined by fluid properties and gravity. We have utilized a quantitative dynamic shadowgraph technique to obtain the temporal correlation function of a mixture of LUDOX(R) TMA and water undergoing free diffusion. This technique allows one to simultaneously measure correlation functions achieving good statistics for a number of different wave vectors in a single measurement. Wave vectors as small as 70 cm(-1) have been investigated, which is very difficult to achieve with ordinary dynamic light-scattering techniques. We present results on the transition from the diffusive decay of fluctuations to the regime in which gravity is dominant.

Journal Article↗
PubMed2004

Bioconvective pattern formation of Tetrahymena under altered gravity.

Bioconvection is a result of the negative gravitactic behavior of microorganisms. When the top-heavy density gradient generated by gravitaxis grows sufficiently large, an overturning convection occurs leading to a formation of characteristic patterns, which involve highly concentrated aggregation of cells into extended two-dimensional structures. Although gravity is a crucial factor, few experiments have been done with reference to gravity as an experimental variable. In order to gain an insight into the hydrodynamic as well as biological dependence of the convective motion on gravity, we investigated changes in bioconvective patterns of Tetrahymena under altered gravity acceleration generated by a long-arm centrifuge. Bioconvective patterns recorded of three different cell strains (T. pyriformis, T. thermophila and its behavioral mutant, TNR) were analyzed quantitatively using space-time plot and Fourier analysis. For example, under subcritical conditions, when T. pyriformis (1.0 x 10(6) cells ml(-1)) was placed in a 2 mm-deep chamber, no spatial pattern was observed at 1 g. When the suspension was centrifuged, however, patterns began to appear as acceleration increased over a critical value (1.5 g), and then remained steady. The formation was reversible, i.e. the patterns disappeared again as acceleration decreased. Under supracritical conditions, i.e. when a suspension of the same density was placed in a 4 mm-deep chamber, a steady state pattern was formed at 1 g. The pattern spacing in the steady state was observed to decrease stepwise in response to step increases in acceleration. Fourier analysis demonstrated that for TNR the mean wave number changed almost simultaneously with step changes in acceleration, whereas the responses were less sharp in the wild-type strains. This may suggest that the locomotor phenotype of the cell, such as its avoiding response ability, has a crucial role in bioconvective pattern formation. These findings are discussed in relation to former theoretical studies.

Animals↗
PubMed2005

Effect of an increase in gravity on the power output and the rebound of the body in human running.

The effect of an increase in gravity on the mechanics of running has been studied by using a force platform fixed to the floor of an aircraft undergoing flight profiles, resulting in a simulated gravity of 1.3 g. The power spent to maintain the motion of the centre of mass of the body is approximately 1.3 times greater than on Earth, due to a similar increase of both the power spent against gravity and to sustain the forward speed changes. This indicates that the average vertical displacement per unit distance and the average direction of the push are unchanged. The increase in power is mainly due to an increase in step frequency rather than to an increase in the work done at each step. The increase in step frequency in turn is mainly due to a decreased duration of the effective aerial phase (when the vertical force is less than body weight), rather than an increase in the stiffness of the bouncing system. The maximal speed where step frequency can match the resonant frequency of the bouncing system is increased by approximately 5 km h(-1) at 1.3 g. These results suggest a similar running mechanics at higher gravity, maintained at the expense of greater energy expenditure.

Adult↗
PubMed2000

Laboratory outreach: student assessment of flow cytometer fluidics in zero gravity.

Due to the the clinical utility of the flow cytometer, the National Aeronautics and Space Administration (NASA) is interested in the design of a space flight-compatible cytometer for use on long-duration space missions. Because fluid behavior is altered dramatically during space flight, it was deemed necessary to validate the principles of hydrodynamic focusing and laminar flow (cytometer fluidics) in a true microgravity environment. An experiment to validate these properties was conducted by 12 students from Sweetwater High School (Sweetwater, TX) participating in the NASA Reduced Gravity Student Flight Opportunity, Class of 2000. This program allows high school students to gain scientific experience by conducting an experiment on the NASA KC-135 zero gravity laboratory aircraft. The KC-135 creates actual zero-gravity conditions in 30-second intervals by flying a highly inclined parabolic flight path. The experiment was designed by their mentor in the program, the Johnson Space Center's flow cytometrist Brian Crucian, PhD, MT(ASCP). The students performed the experiment, with the mentor, onboard the NASA zero-gravity research aircraft in April 2000.

Aircraft↗
PubMed2000

Culture in vector-averaged gravity under clinostat rotation results in apoptosis of osteoblastic ROS 17/2.8 cells.

Space flight experiments and studies carried out in altered gravity environments have revealed that exposure to altered gravity conditions results in (mal)adaptation of cellular function. In the present study, we used a clinostat to generate a vector-averaged gravity environment. We then evaluated the responses of osteoblast-like ROS 17/2.8 cells subsequent to rotation at 50 revolutions per minute (rpm) for 6-24 h. We found that the cells started to detach from the substrate between 12 h and 24 h of rotation in clinostat but not in stationary cultures or after horizontal rotation (the latter serving as a motion control for turbulence, shear forces, and vibrations). At 24 h, 35% of clinorotated cells had detached and the cells underwent apoptotic death as evidenced by DNA fragmentation analysis, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) staining, and flow cytometry with Annexin V staining. The apoptotic death was associated with perinuclear distribution of cell-surface integrin beta1 and disorganization of actin cytoskeleton. These results suggest that vector-averaged gravity causes apoptosis of osteoblasts by altering the organization of the cytoskeleton. We hypothesize that apoptotic death of osteoblasts might play an important role in the pathogenesis of osteoporotic bone loss as observed in actual space flights.

Actins↗
PubMed1990

[A study on the relation between stomatognathic system and the systemic condition, concerning the influence of experimental occlusal interference on upright posture, particularly on gravity fluctuation and the antigravity muscles].

The purpose of this study is to reveal the relation between stomatognathic system and the systemic condition. In the present study, experimental occlusal interference was given to the first molar on main mastication side of 6 healthy subjects and the influence on the upright posture was evaluated through simultaneous measurements of changes in activity of antigravity muscles via electromyography, other than the measurement of loci of the gravity fluctuation for stabilograph before and after the interference was provided. The following results were obtained, 1. Loci of gravity fluctuation 1) All parameters tended increase 24 hours after the interference was provided. 2) The decreasing trend was noted 24 hours after the interference was removed. 3) At one week after the interference was removed all analysis items tended to restore to the normal range. 2. Activity of antigravity muscles In some of the subjects, the muscular activity showed the same trend as the changes of analysis items of gravity fluctuation. 3. The above results suggest that the evaluation of the loci of the gravity fluctuation may be helpful to assess the therapeutic effect of malocclusion.

Electromyography↗
PubMedDate not supplied

Closed-loop, estimator-based model of human posture following reduced gravity exposure.

A computational and experimental method is employed to provide an understanding of a critical human space flight problem, posture control following reduced gravity exposure. In the case of an emergency egress, astronauts' postural stability could be life saving. It is hypothesized that muscular gains are lowered during reduced gravity exposure, causing a feeling of heavy legs, or a perceived feeling of muscular weakness, upon return to Earth's 1 g environment. We developed an estimator-based model that is verified by replicating spatial and temporal characteristics of human posture and incorporates an inverted pendulum plant in series with a Hill-type muscle model, two feedback pathways, a central nervous system estimator, and variable gains. Results obtained by lowering the variable muscle gain in the model support the hypothesis. Experimentally, subjects were exposed to partial gravity (3/8 g) simulation on a suspension apparatus, then performed exercises postulated to expedite recovery and alleviate the heavy legs phenomenon. Results show that the rms position of the center of pressure increases significantly after reduced gravity exposure. Closed-loop system behavior is revealed, and posture is divided into a short-term period that exhibits higher stochastic activity and persistent trends and a long-term period that shows relatively low stochastic activity and antipersistent trends.

Adult↗
PubMed2000

Performance of a water suction system using hydrophilic fibrous cloth under low gravity and microgravity in parabolic flight.

For suction of water from a water supply vessel including both water and air under microgravity and g-jitter conditions, a water suction system using hydrophilic fibrous cloth was developed and its performance was evaluated at 0.01-0.02 g-realized for 20 s by parabolic flight in an aircraft. Vessels used for the experiment were glass flasks and had a suction port for suction filtration. A piece of hydrophilic fibrous cloth was arranged along the inner surface of the vessels and the end was fixed to the suction port of the vessels. In vessel without hydrophilic cloths and containing 220 mL of water, the water did not move more than 5 mm along the inner surface and did not reach the suction port under low gravity. When hydrophilic cloths were used, on the other hand, water gathered onto the cloth surface, moved up along the cloth and reached the suction port under low gravity. The amount of water sucked from vessels varied with the amount of water in the vessel and the sectional area of hydrophilic cloths. When the vessels including both water and air were flown during parabolic flight (10(-4) g), water in the vessel moved along the cloth and a water film was formed on the cloth. These results indicated that it is possible to suck water using the fibrous cloth suction system under low gravity and microgravity conditions. Under low gravity conditions, it was difficult to suck water only. However, it is not necessary to separate water from air when the system is used for supplying water to plant root medium consisting of both liquid and gas phases.

Acceleration↗
PubMed2000

[Response of siphoneal alga (Vaucheria sessilis) to the gravity factor].

Growth and development of siphonal alga Vaucheria sessilis under changed gravity and the role of cytoskeletal structures in gravitational response were studied. Hypergravity (3 g) and "hypogravity" were generated by slow clinostating at 7-8 rev/min and rapid clinostating at 35, 70, 135 rev/min, respectively. The experiments in microgravity were flown aboard biosatellite Bion-11. As was shown, V. sessilis responded to changed gravity by inhibition of rate of growth and increasing the number of nuclei in the strand as a result of activation of mitotic processes. Modulation of the course of the gravitational response with anticytoskeletal agents points to involvement of the cytoskeleton. The cortical circuit of actin microfilaments and the cytoplasm stream directed by this structure appear to be the most sensitive to changes in gravity. Gravity-sensitive V. sessilis is another promising object of research in the field of gravitational biology.

Eukaryota↗
PubMed2001

[Altered behaviour and expression of Fos in rats born in hypergravity and their re-adaptation to the normal gravity].

Changes in behaviour relevant to the vestibular system were studied in Long-Evans rats which were fertilized, born and housed in 2 acceleration of gravity for 4 months and thereafter exposed to 1 acceleration of gravity, and expression of Fos protein in the brain stem was examined. Data from the hypergravity rats were compared respectively with those from the rotation group and the labyrinthectomized group. Static and locomotion modes of the hypergravity rats were changed, tension of extensor was enhanced and the abilities in locomotion equalization and orientation in swimming and air-righting response were reduced. The adaptation process varied with different behaviours. The time for recovery of the ability of orientating in swimming was the longest, taking more than 1 month. The Fos protein expression provides a useful tool for mapping brain functional activities after sensory stimulation, showing a low basal level in normal and labyrinthectomized groups. The hypergravity rats, on the other hand, exhibited more Fos-positive cells in the superior colliculus, inferior colliculus, periaqueductal gray, raphe dorsal nucleus and solitary nucleus. In contrast, the inferior olivary nuclei, locus coeruleus and vestibular nuclei were not strongly labeled. These spatial patterns of Fos expression suggest that a decrease in gravity-inertial force may activate a neural pathway different from the vestibulo-olivar pathways activated by an increase in gravity-inertial force.

Adaptation, Physiological↗
PubMed1996

First use of cognitive algorithms in investigations under compensated gravity.

In the present paper the use of cognitive algorithms for solving a wide spectrum of problems which often arise in investigations under compensated gravity is suggested. Applying such algorithms in the preparation and performance of experiments provides a substantial assistance to the experimentator as the behaviour of complex processes can be described and predicted correctly even when unexpected perturbations occur. Furthermore, an essential advantage of cognitive computing consists in the fact that the description and optimisation of the processes considered are possible also in such cases in which the corresponding basic equations are not known or not treatable practically. For convenience, the basic ideas of cognitive algorithms are discussed here. Due to their special relevance for investigations under compensated gravity algorithms based on fuzzy logic (FL) and artificial neuronal networks (ANN) are elucidated more in detail. In order to illustrate some advantages of cognitive computing exemplary results for the flow field induced by coaxial rotating disks are given. This represents the first attempt to use the benefits provided by cognitive algorithms in investigations under compensated gravity. The flow field between rotating disks plays an important role not only in experiments under compensated gravity but also in a wide range of terrestrial applications. A comparison of the results found by solving the Navier-Stokes equations and those from the prediction performed by ANN adequately trained shows an excellent agreement. However, the calculation times needed by the ANN are significantly smaller than that of the direct numerical simulation. Therefore, the real time prediction of the results from a running experiment seems to be possible.

Algorithms↗
PubMed1997

Is central optokinetic nystagmus gravity-dependent?

Up-down asymmetry of vertical optokinetic nystagmus (OKN) has been attributed to a potential effect of gravity. This suggestion has been supported by some investigations in microgravity where a reverse of up-down asymmetry (downward OKN greater than upward OKN) was found. In joint Bulgarian-Russian space experiment "Labyrinth", the part "Optokinez" was devoted to central OKN and its gravity dependence. We aimed at answering questions: 1) Was central optokinetic nystagmus gravity dependent, in particular vertical OKN? If it was: 2) What happened with up-down asymmetry in adaptation period to weightlessness and re-adaptation period to gravity. Furthermore, in our recent study (3) on upright standing humans we found a consistent downward prevalence in central vertical OKN. Thus, a new question arises: What determines the direction of up-down OKN asymmetry?

Eye Movements↗
PubMed1998

Alterations in rat horizontal vestibulo-ocular reflex phase as a function of orientation in gravity.

The effect of changes in static and dynamic gravity signals on the phase accuracy of the horizontal vestibulo-ocular reflex (HVOR) was studied in rats using chronically implanted scleral search coils to monitor eye movements. Rats were sinusoidally rotated using a range of different frequencies (0.035-2 Hz) in a plane which always activated the horizontal semicircular canals but in one of three different orientations with regard to gravity which differentially activated the otolith organs: 1) upright-normal static gravity signal, no dynamic otolith activation; 2) inverted-inverted static gravity signal, no dynamic otolith activation; 3) on-side-dynamic activation of the otolith organs. In the upright orientation, the HVOR shows a phase advance at 0.2 Hz and below but not at 0.5 Hz and above. Phase accuracy of the HVOR was further degraded in the inverted orientation with rats showing large phase leads at 0.2 Hz and below. In contrast, accuracy of the HVOR was significantly improved at 0.2 Hz and below in the on-side orientation with phase accurate eye movements down to the lowest frequency tested. The results further support the idea that otolith organs play an important role in VOR generation by supplementing the semicircular canals' response to angular head movements.

Animals↗
PubMed2002

Gravity of aortic arch calcification as evaluated in adult Greek patients.

BACKGROUND: The aim of the present study was to evaluate the gravity of aortic arch calcification in adult Greek patients. METHODS: A total of 1027 patients (498 men, 529 women) were included. Aortic arch calcification was assessed by means of posteroanterior chest X-rays. These were studied by two radiologists blinded to the patients' medical records. Calcification was graded as follows: grade 0 (no visible calcification), grade 1 (small spots of calcification or single thin calcification of the aortic knob), grade 2 (one or more areas of thick calcification), grade 3 (circular calcification of the aortic knob). All patients were clinically and electrocardiographically examined for coronary artery disease. The other parameters included in the analysis were age, sex, smoking, body-mass index, hypertension, dyslipidemia, diabetes mellitus and history of stroke. RESULTS: Calcification gravity was grade 0 in 421 patients (41%), grade 1 in 308 patients (30%), grade 2 in 216 patients (21%) and grade 3 in 82 patients (8%). In simple regression analysis the gravity of aortic arch calcification was positively correlated with age (p=0.01), diabetes mellitus (p=0.014), hypertension (p=0.022), dyslipidemia (p=0.038) and coronary artery disease (p=0.041). In multiple regression analysis it was associated with age (p=0.019), diabetes mellitus (p=0.02) and hypertension (p=0.03). CONCLUSIONS: Gravity of aortic arch calcification in adult Greek patients may easily be assessed on routine chest X-rays and is positively correlated with coronary artery disease, as well as important cardiovascular risk factors (age, diabetes mellitus, hypertension and dyslipidemia).

Adult↗
PubMed1976

Hormones and the growth of plants in response to gravity.

Plants are remarkable amongst living things in that all their parts (leaves, stems, roots and flowers) can orientate their position in response to gravity. Roots normally grow downwards towards the stimulus, shoots upwards away from the stimulus, while leaves and special kinds of stems like underground rhizomes or aerial runners have adaptations to grow horizontally, approximately at right angles to the gravitational field. This directional positioning of the organ in relation to gravity is achieved by a regulation of the growth of enlarging cells below the meristems or within the organ. Mature tissues in which further cell growth is precluded are therefore unable to reorientate if their position in the field is changed. Under conditions of zero gravity, roots and shoots continue to grow in opposite directions and the orientation of laterals with respect to the apex is essentially normal. This demonstrates the inherent polarity of plant cells and the internal correlative growth regulation that each organ exerts upon its neighbours. The perception of gravity, involving statoliths, membranes and "wound" ethylene, is discussed, together with the mechanisms by which the subsequent growth responses can be mediated by changes in endogenous hormones. Evidence for how such hormonal changes can lead to modifications of the rate, extent and reorientation of cell growth is reviewed for several geotropically responding systems.

Abscisic Acid↗