SEARCH · PubMed Health

Results for “GRAVITY”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 739 records · Page 41Linked to original sources

PubMed1988

Effects of two gravity inversion methods on heart rate, systolic brachial pressure, and ophthalmic artery pressure.

The purpose of this study was to investigate the effects of two static gravity inversion methods with either ankle or thigh suspension on heart rate (HR), systolic brachial pressure (SBP), and ophthalmic artery pressure (OAP). Twenty healthy subjects were assigned randomly to one of two treatment groups of 10 subjects each. Each group completed a 25-minute protocol with two 5-minute inversion periods. The research attempted to control for treatment anxiety and for the effects of ocular plethysmography (the procedure used to measure OAP). A 2 X 2 multivariate analysis of variance for repeated measures was used to analyze the differences of cardiovascular change between the two inversion methods. The hypothesis that the subjects' HRs, SBPs, and OAPs would not differ between ankle and thigh suspension methods for five minutes of inversion was not rejected. Leg position did not affect the HR or arterial responses during full static inversion. Gravity inversion produced no significant changes in HR and SBP between 2.5 and 5 minutes of inversion. Arterial pressures measured at 5 minutes of static inversion did not differ from arterial pressures measured between 2.5 and 5 minutes, but because of increases in OAP during inversion, ocular safeguards are recommended for subjects during inversion.

Adult↗

PubMed1994

Evaluation of the gravity-correction feature of a Kin-Com isokinetic dynamometer.

BACKGROUND AND PURPOSE: Torques reflecting muscle performance must be corrected for the effects of gravity if error-free ratio-scaled data are to be obtained. Ratio-scaled data are necessary, for example, to report muscle performance characteristics in terms of ratios or percentages or in the form of ratios with another muscle (eg, ratio of hamstring to quadriceps femoris muscle peak torque). The purpose of this study was to determine the error associated with the gravity-correction procedure of the Kin-Com dynamometer when a weight or limb segment is weighed at different lever arm positions. METHODS: A known weight was suspended from the lever arm of the Kin-Com dynamometer. The rotational component of gravitational forces on the weight was measured at 11 different angular positions. We compared the force measurement obtained from the Kin-Com with the predicted rotational component at each angular position. The gravitational forces on a subject's limb segment (leg) were then measured at 12 different angular positions in each of two trunk positions (sitting and supine). We compared the force measurement obtained from the Kin-Com with the predicted rotational component for each position. Forces measured for the two trunk positions with the lever arm horizontal were compared. Forces measured with the knee extended were compared with forces measured with the lever arm horizontal. RESULTS: The dynamometer accurately recorded the rotational component of gravitational forces for the weight suspended from the lever arm. There was a progressively greater discrepancy between measured forces and predicted forces for the leg as the lever arm was moved from horizontal to 50 degrees below the horizontal. The force recorded with the Kin-Com was greater when the subject's knee was in full extension than when the lever arm was horizontal, which placed the subject's knee in a flexed position. A small difference was noted between the measured forces with the lever arm horizontal when the subject was sitting compared with when the subject was positioned supine. CONCLUSION AND DISCUSSION: When weighing a leg with this dynamometer, we recommend that the lever arm be as close to the horizontal position as possible. Positions of proximal joints should be chosen that do not put two joint muscles in stretched positions.

Adult↗

PubMed1999

Growth factor-induced signal transduction in adherent mammalian cells is sensitive to gravity.

Epidermal growth factor (EGF) activates a well-characterized signal transduction cascade in a wide variety of cells. This activation leads to increased cell proliferation in most cell types. Among the early effects evoked by EGF are receptor clustering, cell rounding, and early gene expression. The influence of gravity on EGF-induced EGF receptor clustering and gene expression as well as on actin polymerization and cell rounding have been investigated in adherent A431 epithelial cells with the use of sounding rockets to create microgravity conditions. EGF-induced c-fos and c-jun expression decreased in microgravity. This was caused by alteration of the EGF receptor and protein kinase C-mediated signal transduction pathways. In contrast, neither the binding of EGF to the receptor nor the receptor clustering were changed under microgravity conditions. Because cell morphology was also modulated under microgravity conditions, and the growth factor-induced signal transduction cascades have been demonstrated to be linked to the actin microfilament system, it is tempting to suggest that the actin microfilament system constitutes the gravity-sensitive cell component.

Actins↗

PubMed2003

Loss of T cell precursors after spaceflight and exposure to vector-averaged gravity.

Using fetal thymus organ culture (FTOC), we examined the effects of spaceflight and vector-averaged gravity on T cell development. Under both conditions, the development of T cells was significantly attenuated. Exposure to spaceflight for 16 days resulted in a loss of precursors for CD4+, CD8+, and CD4+CD8+ T cells in a rat/mouse xenogeneic co-culture. A significant decrease in the same precursor cells, as well as a decrease in CD4-CD8- T cell precursors, was also observed in a murine C57BL/6 FTOC after rotation in a clinostat to produce a vector-averaged microgravity-like environment. The block in T cell development appeared to occur between the pre-T cell and CD4+CD8+ T cell stage. These data indicate that gravity plays a decisive role in the development of T cells.

Animals↗

PubMed1999

Gravity affects the preferred vertical and horizontal in visual perception of orientation.

The aim of this study was to evaluate the influence of gravity on the representation and storage of visual orientation information. On earth, measurements of response time and variability for a task of aligning remembered visual stimuli showed a distinct preference for horizontally and vertically oriented stimuli when the body and gravitational axes were aligned. This preference was markedly decreased or disappeared when the body axis was tilted with respect to gravity but was maintained for tests performed in microgravity. We conclude that subjects acquire and store visual orientation in a multi-modal reference frame that combines proprioceptive and gravitational information when both are available.

Adult↗

PubMed2003

Gravity influences the development of inputs from the brain to lumbar motoneurons in the rat.

We investigated the influence of gravity on the maturation of electrical properties of lumbar motoneurons and the development of their inputs from ventral descending pathways, which are important for the control of posture and locomotion. Using electrophysiological approaches in the in vitro brain stem-spinal cord preparation of neonatal rats born and reared in hypergravity field we demonstrate that: (1) the postnatal development of descending inputs to lumbar enlargement was reduced in animals submitted to hypergravity; (2) similar developmental pattern of basic electrical properties observed between motoneurons of hypergravity and control animals could not account for the changes in descending inputs. We concluded that gravity was critical to shape development of the supraspinal afferents in the lumbar spinal cord throughout the postnatal period.

Animals↗

PubMed2001

Diagnosing deltoid injury in ankle fractures: the gravity stress view.

In the lateral malleolar ankle fracture without talar shift there is much uncertainty regarding the diagnosis of deltoid ligament injury severe enough to require surgical treatment. The current study evaluated the mechanical integrity of the ankle using a novel gravity-stress mortise radiographic view, which is practical for clinical use. Eight cadaveric lower extremities were tested under the following conditions: (1) intact ankle, (2) distal fibular oblique osteotomy, (3) plated fibula after osteotomy, (4) transection of the superficial deltoid with fibula osteotomized or plated, and (5) all possible combinations of deep deltoid transection with superficial deltoid transected or repaired and fibula osteotomized or plated. For each condition, a mortise radiograph was taken of the specimen while it was mounted horizontally, lateral side down. Fibular osteotomy with or without transection of the superficial deltoid did not alter the mortise radiograph appearance of the ankles. With combined deep and superficial deltoid transection and fibular osteotomy, the talus always (eight of eight specimens) showed a lateral shift of 2 mm or greater and a valgus tilt of 15 degrees or more. The gravity stress view of the ankle was found to reproducibly document destabilizing deltoid ligament damage.

Ankle Injuries↗

PubMed2002

Effect of gravity on localization of chondrocytes implanted in cartilage defects.

The transplantation of autologous chondrocytes under a periosteal flap has been used to treat focal cartilage defects. Results have been promising but occasionally involve complications ranging from graft hypertrophy to detachment. The objective of this study was to determine if gravitational forces affect the uniformity of cell distribution within the defect. Using an ex vivo bovine model, the orientation relative to gravity of a repaired full-thickness articular cartilage defect was found to affect the initial distribution of transplanted chondrocytes, prelabeled with 3H-thymidine. After 4 hours, the injected cells (3H-radioactivity) were primarily at the base of the defect (79%) in samples oriented in the up position, primarily at the dependent semicylindrical half of the defect (83%) in samples oriented to the side, and primarily at the periosteal top of the defect (78%) in samples oriented upside-down. Subsequently, the cell distribution remained unchanged after reorientation into other positions. These results indicate that injected chondrocytes localize under the influence of gravity within the initial few hours after injection. Therefore, the defect orientation during this time can be an important factor in the uniformity of cell distribution in the autologous chondrocyte implantation procedure and may be an important determinant of the ultimate clinical outcome.

Analysis of Variance↗

PubMed1976

Role of gravity in prism ballasting.

One of the techniques commonly used in stabilizing the rotation of a contact lens is prism ballasting. The idea is to gain stabilization by the action of gravity pulling on the base of the prism. The determination of just how much prism is necessary in any particular case is usually made empirically, gradually increasing prism amount when more stability is required. This paper will present the results of a mathematical investigation which demonstrates that gravity forces alone do not play the major role in the stabilization of prism ballasted lenses. It is hoped that this preliminary analysis will stimulate further theoretical work of a similar nature, in the growing field of contact lenses.

Contact Lenses↗

PubMedDate not supplied

Gravity-dependent distribution of retinal pigment epithelial cells dispersed into the vitreous cavity.

Release of viable retinal pigment epithelial (RPE) cells into vitreous cavity and subsequent attachment to the retina may be the first steps in the occurrence of macular pucker and proliferative vitreoretinopathy (PVR) complicating rhegmatogenous retinal detachment. Gravity and post-operative position of the patient together may influence where the cells settle, and, thereby, the location of subsequent membrane formation. To study the effect of gravity on the location of RPE cell attachment, 3H-thymidine-labelled RPE cells were injected into 12 enucleated pig eyes after vitrectomy performed to create a posterior vitreous detachment. The eyes were then positioned to make either the macula or the inferior retina gravitationally dependent. Radioactivity was later measured from several locations on the retina to indicate the proportion of cells attached in each location. Radioactivity measured from the dependent part of the globe (mean 5985 +/- 1728) was always greater than that from other parts (mean 389 +/- 79). The experiment was repeated in live pig eyes with identical results. These findings suggest that patient positioning may affect the location of cellular membrane formation and subsequent retinal traction.

Animals↗

PubMed2006

Gravity line analysis in adult volunteers: age-related correlation with spinal parameters, pelvic parameters, and foot position.

STUDY DESIGN: Prospective radiographic and forceplate analysis in adult volunteers. OBJECTIVE: Assess gravity line (GL) location and foot position regarding anatomic spinal structures to evaluate key correlations and age-related changes in balance. SUMMARY OF BACKGROUND DATA: Global spinal balance is commonly assessed by the C7 plumbline. This radiographic parameter does not offer information on foot position or forces transmitted, and poor correlation with the true GL has been demonstrated. METHODS: A total of 75 asymptomatic adult volunteers were equally distributed into three age groups. Full length, free-standing spine radiographs were obtained with simultaneous acquisition of GL and feet location (forceplate). GL and heels were projected on each radiograph to compute their distance from anatomic entities and to investigate correlations with radiologic parameters and age-related changes. RESULTS: In this study group, advancing age led to a significant increase in thoracic kyphosis. The plumbline from C7 shifted anteriorly with age. In the sagittal plane, the GL was anterior to the vertebral column for all groups. With age, the GL location regarding the heels remained constant, while the pelvis moved posteriorly toward the heels and underwent a small retroversion (increasing pelvic tilt). The acetabulum was the most reliable radiographic marker of the GL location. CONCLUSIONS: This quantitative study in volunteers reveals clear age-related changes in the spino-pelvic association and offers quantitative support to the "cone of economy" concept proposed by Dubousset. The pelvis can be seen as a regulator to help maintain a rather fixed GL-heel association with age-related changes in the spinal column. Further study in patients suffering from deformity can confirm the importance of radiographic-gravity line correlations and enhance our understanding of optimal balance.

Adult↗

PubMed1991

Evolution of bioconvective patterns in variable gravity.

Measurements are reported of the evolution of bioconvective patterns in shallow, dense cultures of microorganisms subjected to varying gravity. Various statistical properties of this random, quasi-two-dimensional structure have been found: Aboav's law is obeyed, the average vertex angles follow predictions for regular polygons, and the area of a pattern varies linearly with its number of sides. As gravity varies between 1 g and 1.8g (g = 9.8 m s-1), these statistical properties continue to hold despite a tripling of the number of polygons and a reduced average polygon dimension by a third. This work compares with experiments on soap foams, Langmuir monolayer foams, metal grains, and simulations.

Animals↗

PubMed1999

Theory of creeping gravity currents of a non-Newtonian liquid.

Recently several experiments on creeping gravity currents have been performed, using highly viscous silicone oils and putties. The interpretation of the experiments relies on the available theoretical results that were obtained by means of the lubrication approximation with the assumption of a Newtonian rheology. Since very viscous fluids are usually non-Newtonian, an extension of the theory to include non-Newtonian effects is needed. We derive the governing equations for unidirectional and axisymmetric creeping gravity currents of a non-Newtonian liquid with a power-law rheology, generalizing the usual lubrication approximation. The equations differ from those for Newtonian liquids, being nonlinear in the spatial derivative of the thickness of the current. Similarity solutions for currents whose volume varies as a power of time are obtained. For the spread of a constant volume of liquid, analytic solutions are found that are in good agreement with experiment. We also derive solutions of the waiting-time type, as well as those describing steady flows from a constant source to a sink. General traveling-wave solutions are given, and analytic formulas for a simple case are derived. A phase plane formalism that allows the systematic derivation of self-similar solutions is introduced. The application of the Boltzmann transform is briefly discussed. All the self-similar solutions obtained here have their counterparts in Newtonian flows, as should be expected because the power-law rheology involves a single-dimensional parameter as the Newtonian constitutive relation. Thus one finds similarity solutions whenever the analogous Newtonian problem is self-similar, but now the spreading relations are rheology-dependent. In most cases this dependence is weak but leads to significant differences easily detected in experiments. The present results may also be of interest for geophysics since the lithosphere deforms according to an average power-law rheology.

Journal Article↗

PubMed2001

Effects of gravity and nonlinearity on the waves in the granular chain.

The solitary signal observed in a horizontal granular chain changes its speed and form due to gravity in a vertical chain. We find that all the propagating signals in a vertical chain follow power laws in depth for propagating speed, grain velocity, amplitude, and width. This stems from the power-law type changing of elastic properties in a medium under gravity. The propagation may be separated into two types according to the behavior of the power-law exponents, depending on the strength of the nonlinearity. We show that the power-law exponents are constants in the strength of the impulse in the weakly nonlinear regime, while they depend on the strength of the impulse in the strongly nonlinear regime. We derive power-law exponents for the weakly nonlinear regime analytically and try to understand the behaviors of the strongly nonlinear regime through analytical treatment.

Journal Article↗

PubMed2002

Wave drag due to generation of capillary-gravity surface waves.

The onset of the wave resistance via the generation of capillary-gravity waves by a small object moving with a velocity V is investigated experimentally. Due to the existence of a minimum phase velocity V(c) for surface waves, the problem is similar to the generation of rotons in superfluid helium near their minimum. In both cases, waves or rotons are produced at V>V(c) due to Cherenkov radiation. We find that the transition to the wave drag state is continuous: in the vicinity of the bifurcation the wave resistance force is proportional to sqrt[V-V(c)] for various fluids. This observation contradicts the theory of Raphaël and de Gennes. We also find that the reduced wave drag force for different fluids and different ball size may be scaled in such a way that all the data collapse on a single curve. The capillary-gravity wave pattern and the shape of the wave-generating region are investigated both experimentally and theoretically. Good agreement between the theory and the experimental data is found in this case.

Journal Article↗

PubMed2004

Nonlinear dynamics of gravity and matter creation in a cosmology with an unbounded Hamiltonian.

Nonlinear dynamics and stability properties of a cosmological model of spatially homogeneous coupled gravity and matter fields is analyzed using methods of classical mechanics. The system exhibits regions of chaos and dramatic changes in structural stability as the strength of the coupling between the fields is varied. Numerical simulations suggest that Hamiltonian systems with structure appropriate for describing matter-gravity interaction constitute a new class of nonlinear systems with very unusual and rich dynamics.

Journal Article↗

PubMed2006

Creeping granular motion under variable gravity levels.

In a rotating tumbler that is more than one-half filled with a granular material, a core of material forms that should ideally rotate with the tumbler. However, the core rotates slightly faster than the tumbler (precession) and decreases in size (erosion). The precession and erosion of the core provide a measure of the creeping granular motion that occurs beneath a continuously flowing flat surface layer. Since the effect of gravity on the subsurface flow has not been explored, experiments were performed in a 63% to 83% full granular tumbler mounted in a large centrifuge that can provide very high g-levels. Two colors of 0.5 mm glass beads were filled side by side to mark a vertical line in the 45 mm radius quasi-two-dimensional tumbler. The rotation of the core with respect to the tumbler (precession) and the decrease in the size of the core (erosion) were monitored over 250 tumbler revolutions at accelerations between 1g and 12g. The flowing layer thickness is essentially independent of the g-level for identical Froude numbers, and the shear rate in the flowing layer increases with increasing g-level. The degree of core precession increases with the g-level, while the core erosion is essentially independent of the g-level. Based on a theory for core precession and erosion, the increased precession is likely a consequence of the higher shear rate. Core erosion, on the other hand, is related to the creep region decay constant, which is connected with slow diffusion in the bed and unaffected by gravity.

Journal Article↗

PubMed2000

Thermalization of a two-phase fluid in low gravity: heat transferred from cold to Hot

We present an experimental study of the thermal response to a positive temperature quench in two-phase fluid SF6 in low gravity for temperature ranging from 10.1 to 0.1 K from the critical temperature. The temperature was measured simultaneously in the gas, the liquid, and the cell wall by thermistors and the density distribution was observed by interferometry. During the quench the gas temperature considerably exceeded the temperature of the heating walls (overheating up to 23%). This striking observation is discussed in the light of the adiabatic heat transfer in this highly compressible fluid while the key role of the localization in low gravity of the gas and liquid phases is revealed.

Journal Article↗