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Results for “Gravity, Altered”

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PubMed1985

[Determination of double bonds in the lipid fraction of blood plasma in burn patients using the ADS-4M apparatus].

An ADS-4M analyser was employed to study the diagnostic potentialities of the method for determination of double bonds (DB) in lipids of the burnt's blood as a rapid method for revealing alterations in unsaturated fatty acids (USFA). The method was tried in 25 patients with varying gravity of burn injury and in 15 healthy subjects with a purpose of establishing the norm. It was discovered that in patients with burn, the number of DB differed from normal depending on the disease gravity. The time course of changes in the number of DB attests to the necessity of the use of the method under consideration for evaluating abnormalities in the content of USFA.

Adolescent↗

PubMed2000

Nociceptive responses and immunohistochemical changes in the rat brain under gravity stress.

It is well known that exposure to various stresses leads to pain suppression in animals. However, there is no report about the effects of gravitational alteration to serve as a kind of stress. The purpose of the present study is to clarify the effect of hypergravity (2 G) on the nociceptive responses and histochemical changes in rats. We examined the level of the threshold of withdrawal reflex against the noxious [correction of noxicious] stimulation in rats that were exposed to 2 G. Data show that the 2 G exposure elevates the nociceptive threshold. We have demonstrated for the first time that gravity change induces analgesic effects on rats in concomitant with c-fos induction in the arcuate, and paraventricular nuclei of rat hypothalamus. Gravity change acts as a kind of stress in rats.

Analgesia↗

PubMed1997

Molecular genetic analysis of plant gravitropism.

The analysis of mutants is a powerful approach for elucidating the components of complex biological processes. A growing number of mutants have been isolated which affect plant gravitropism and the classes of mutants found thus far provide important information about the gravity response mechanism. The wide variety of mutants isolated, especially in Arabidopsis, indicates that gravitropism is a complex, multi-step process. The existence of mutants altered in either root gravitropism alone, shoot gravitropism alone, or both indicates that the root and shoot gravitropic mechanisms have both separate and common steps. Reduced starch mutants have confirmed the role of amyloplasts in sensing the gravity signal. The hormone auxin is thought to act as the transducing signal between the sites of gravity perception (the starch parenchyma cells surrounding the vascular tissue in shoots and the columella cells of root caps) and asymmetric growth (the epidermal cells of the elongation zone(s) of each organ). To date, all mutants that are resistant to high concentrations of auxin have also been found to exhibit a reduced gravitropic response, thus supporting the role of auxin. Not all gravitropic mutants are auxin-resistant, however, indicating that there are additional steps which do not involve auxin. Studies with mutants of tomato which exhibit either reduced or reversed gravitropic responses further support the role of auxin redistribution in gravitropism and suggest that both red light and cytokinin interact with gravitropism through controlling lateral auxin transport. Plant responses to gravity thus likely involve changes in both auxin transport and sensitivity.

Arabidopsis↗

PubMed1987

The influence of gravity on horizontal and vertical vestibulo-ocular and optokinetic reflexes in the rabbit.

The influence of the linear acceleration of gravity on the vertical and horizontal vestibulo-ocular reflexes (VVOR, HVOR) as well as the vertical and horizontal optokinetic reflexes (VOKR, HOKR) has been examined in rabbits. Rabbits were mounted in a biaxial rate table in front of a rear projection tangent screen. Eye movements were measured with a light projection technique. The HVOR, VVOR, HOKR and VOKR were measured in rabbits which were maintained both prone and supine. The gain of the HVOR for the supine orientation was reduced at all frequencies tested (0.01-0.80 Hz). Similarly there was a reduction in the gain of the HOKR. By contrast, the gain of the VVOR in the supine orientation was enhanced over a lower range of frequencies (0.02-0.04 Hz) and reduced at higher frequencies (0.10-0.80 Hz). The gain of the VOKR was not reduced in the supine orientation. The range of eye positions over which compensatory eye movements occurred was restricted in the supine orientation. The altered orientation of the medio-laterally polarized hair cells of the utricular maculae with respect to gravity in the supine orientation may cause postural instability and facilitate 'righting reflexes'. A reduction in the gains of the HVOR, VVOR and HOKR caused by linear accelerations in the sagittal plane during locomotion may decrease automatic postural responses during certain movements in which these automatic postural adjustments would not necessarily be adaptive.

Animals↗

PubMedDate not supplied

Does head-down tilt simulate zero gravity?

Six anesthetized female rhesus monkeys were studied to determine the effect of head-down tilt on renal function. Head-down tilt is believed to simulate zero gravity. Some animals were tilted from 0 degree to -5 degrees or -10 degrees and others from +10 degrees to -10 degrees. None of these maneuvers consistently altered renal function. These results are in accord with those reported in early literature for the human but contrary to more recent reports. The interpretation of the latter are seriously hampered by experimental design. If indeed zero gravity translocates blood to the thorax with a resultant diuresis and natriuresis, head-down tilt is not an appropriate model for weightlessness.

Animals↗

PubMed1998

The effect of gravity on human recognition of disoriented objects.

The role of non-visual cues, and particularly of signals tied to the direction of gravity, in the mechanisms of recognition of disoriented objects is reviewed. In spite of a limited number of studies, object recognition does not seem dramatically altered by weightlessness and astronauts can adapt to this novel environment. Particularly, mental rotation strategy can still be used in weightlessness with dynamic parameters relatively unchanged. Similarly, spatial coordinate assignment can be performed adequately under different gravitational conditions. However, signals related to gravity direction seem to be integrated in the early stages of visual processing. Thus, performances in symmetry detection tasks and visual search tasks are influenced by the gravito-inertial conditions in which experience are done. Functional roles of such a multisensory convergence on cortical visual neurons, partly confirmed by neurophysiological studies, are proposed.

Form Perception↗

PubMed1996

Modulation of vergence by off-vertical yaw axis rotation in the monkey: normal characteristics and effects of space flight.

Horizontal movements of both eyes were recorded simultaneously using scleral search coils in 2 rhesus monkeys before and after the COSMOS 2229 space-flight of 1992-1993. Another 9 monkeys were tested at comparable time intervals and served as controls. Ocular vergence, defined as the difference in horizontal position between the left and right eyes, was measured during off-vertical yaw axis rotation (OVAR) in darkness. Vergence was modulated sinusoidally as a function of head position with regard to gravity during OVAR. The amplitude of peak-to-peak modulation increased with increments in tilt of the angle of the rotational axis (OVAR tilt angle) that ranged from 15 degrees to 90 degrees. Of the 11 monkeys tested, 1 had no measurable modulation in vergence. In the other 10, the mean amplitude of the peak to peak modulation was 5.5 degrees +/- 1.3 degrees at 90 degrees tilt. Each of these monkeys had maximal vergence when its nose was pointed close to upward (gravity back; mean phase: -0.9 degree +/- 26 degrees). After space flight, the modulation in vergence was reduced by over 50% for the two flight monkeys, but the phase of vergence modulation was not altered. The reduction in vergence modulation was sustained for the 11-day postflight testing period. We conclude that changes in vergence are induced in monkeys by the sinusoidal component of gravity acting along the naso-occipital axis during yaw axis OVAR, and that the modulation of the vergence reflex is significantly less sensitive to linear acceleration after space flight.

Animals↗

PubMed1982

Postural response of the head to bite opening in adult males.

The postural position of the head is a resultant of muscular interactions and reactions, influenced by gravity and functional demands. In order to investigate possible postural adaptation of the head to an altered functional status, a standard degree of jaw opening was produced by mechanical means in the mouths of thirty young males. There was an extension of the head associated with the jaw separation. In the majority of cases, a recovery to approximately the original posture resulted within 1 hour after removal of the bite-opening device.

Adaptation, Physiological↗

PubMed1989

The biological clock of Neurospora in a microgravity environment.

The circadian rhythm of conidiation in Neurospora crassa is thought to be an endogenously derived circadian oscillation; however, several investigators have suggested that circadian rhythms may, instead, be driven by some geophysical time cue(s). An experiment was conducted on space shuttle flight STS-9 in order to test this hypothesis; during the first 7-8 cycles in space, there were several minor alterations observed in the conidiation rhythm, including an increase in the period of the oscillation, an increase in the variability of the growth rate and a diminished rhythm amplitude, which eventually damped out in 25% of the flight tubes. On day seven of flight, the tubes were exposed to light while their growth fronts were marked. Some aspect of the marking process reinstated a robust rhythm in all the tubes which continued throughout the remainder of the flight. These results from the last 86 hours of flight demonstrated that the rhythm can persist in space. Since the aberrant rhythmicity occurred prior to the marking procedure, but not after, it was hypothesized that the damping on STS-9 may have resulted from the hypergravity pulse of launch. To test this hypothesis, we conducted investigations into the effects of altered gravitational forces on conidiation. Exposure to hypergravity (via centrifugation), simulated microgravity (via the use of a clinostat) and altered orientations (via alterations in the vector of a 1 g force) were used to examine the effects of gravity upon the circadian rhythm of conidiation.

Biological Clocks↗

PubMed1996

The role of signal systems in cell gravisensitivity.

Reception of physical environmental signals caused by alteration of the gravitation field leads to the shift of morpho-physiological cell characteristics. The gravity influence on a cell may be direct or non direct, its extent varying in dependence of the cell model applied. Direct influences are more pronounced in vitro, while non direct influences are usually expressed in the community of unicellular organisms (in vivo). Gravity affects morphogenesis processes, such as locomotion, adhesion, intercellular contacts, etc. At the same time, all the processes named are under control of cell integral systems of the signal transduction. Minor disturbances in this system coming from the environment, due to amplification, may provide significant modulations of the signals. So, studies of this system at the level of molecular cell reception is of great interest. Results of flight and model experiments are discussed in the present manuscript.

Animals↗

PubMed2004

The usefulness of computerized dynamic posturography for the study of equilibrium in patients with Meniere's disease: correlation with clinical and audiologic data.

The use of computerized dynamic posturogaphy (CDP) in the evaluation of patients with balance alterations not only allows quantification of the subject's capacity to maintain a stable centre of gravity, but also analysis of the degree to which the subject is able to use different types of sensory information. The present study investigated the possible use of CDP for clinical staging of vestibular diseases, specifically Meniere's disease (MD). We applied CDP sensory organization tests to 75 patients with definitive MD (AAO-HNS 1995 criteria). A total of 98 CDP sessions were included in the analysis, which focused on four CDP parameters specifically related to vestibular function (condition-5 score, condition-6 score, overall balance score, and VEST, a measure of the relative importance of vestibular information for maintenance of balance). We found a statistically significant relationship between audiometric hearing threshold and CDP scores, especially in patients with audiometrically advanced disease. In addition, CDP scores showed statistically significant variation with time elapsed since the last typical vertigo attack, suggesting that patients can be usefully grouped into three MD activity-level categories: recent post-attack (less than 1 week since last vertigo attack), late post-attack (1 week - 60 days since last attack), and inactive MD (more than 60 days since last attack). On the basis of these results, we propose expected ranges for each of the four CDP parameters in each of the three MD activity-level categories, allowing staging in terms of balance and posture. This staging system complements existing staging systems (based on audiometric criteria, and on subjective assessment of the severity of vertigo attacks and their implications for quality of life).

Adult↗

PubMed2026

Lower-limb electromyographic responses across four recumbent cycling configurations in healthy young men.

Recumbent cycling provides an adjustable configuration in which backrest angle and crank-axis height can alter lower-limb loading. Backrest angle changes the orientation of the active musculature relative to gravity, whereas crank-axis height modifies the foot-pedal interface and the ankle lever arm. Whether such positioning is associated with differences in lower-limb electromyographic (EMG) activation across both factors together has not been examined. Using a randomized crossover design, fifty-nine healthy young men cycled at 100 W and 50 rpm under four conditions combining two backrest angles (30°, 75°) and two crank-axis heights (Rh, high, 77 cm; Rl, low, 45 cm). Surface EMG from the rectus femoris (RF), biceps femoris (BF), and gastrocnemius medialis (GAS) was analyzed for root mean square (RMS) amplitude, absolute onset sequence, and relative recruitment timing (%Sequence, derived using Telescan software and referenced to RF). RMS amplitude did not differ across conditions for any muscle (all p ≥ 0.356), and absolute onset sequence showed no condition effect (all p ≥ 0.197). For GAS %Sequence, the Greenhouse-Geisser-corrected omnibus test was significant (F(1.32, 76.56) = 28.45, p < 0.001), driven by a within-30° contrast in which %Sequence was lower under Rl than Rh (paired t(58) = 10.39, Holm-adjusted p < 0.0001; mean difference 22.0 percentage points, 95 % CI [17.8, 26.3]; dz = 1.35). Because %Sequence is referenced to RF, this exploratory shift should be interpreted cautiously. Lower-limb activation may be constrained by the closed-chain nature of pedaling, whereas distal recruitment timing may be sensitive to crank-axis height and the foot-pedal interface.

Humans↗

PubMed1996

Differential proton secretion in the apical elongation zone caused by gravistimulation is induced by a signal from the root cap.

The extracellular proton activity along primary roots of Phleum pratense L. was measured using proton-selective microelectrodes. Removal of the root cap caused a reduction of the proton influx in the transitional region between the meristem and the apical elongation zone of the vertical root and inhibited the development of pH differences between the physically upper and lower flanks of the gravistimulated root. Disruption of the actin filament system of the root with 5 mmol m-3 cytochalasin D did not result in an altered proton flux and pH pattern compared with untreated vertical control roots, but inhibited the gravity-induced development of pH differences between the physically upper and lower root flanks as well as gravitropic curvature. These results provide evidence that pH changes following gravistimulation are induced by a signal transmitted from the root cap and that the actin filament system is involved in the gravity perception/transduction mechanism.

Cytochalasin D↗

PubMed1991

Valgus stability of the elbow. A definition of primary and secondary constraints.

The stabilizing structures of the elbow that resist valgus stress were studied with a tracking device in a model simulating active motion and muscle activity. By varying the order of serial release of the medial collateral ligament complex and removal of the radial head, each structure's contribution to valgus stability against the effect of gravity was determined. In the otherwise intact elbow, absence of the radial head does not significantly alter the three-dimensional characteristics of motion in the elbow joint. Isolated medial collateral release, on the other hand, causes increases in abduction rotation of about 6 degrees-8 degrees in magnitude. Releasing both structures results in gross abduction laxity and elbow subluxation. This study defines the medial collateral ligament (MCL) as the primary constraint of the elbow joint to valgus stress and the radial head as a secondary constraint. This definition facilitates the proper management of patients with radial head fractures and MCL disruption. The comminuted radial head fracture uncomplicated by MCL insufficiency should be treated by excision without the need for an implant and without concern of altering the normal kinematics of the elbow.

Biomechanical Phenomena↗

PubMed1990

[Autonomic regulation in the acute period of tick-borne encephalitis in children].

The clinico-epidemiological analysis and comparison of the data of a comprehensive study of suprasegmental vegetative regulation revealed an appreciable tension of the adaptation mechanisms in the acute period in 55 children with the meningeal form of tick-borne encephalitis (TE). Alterations in vegetative regulation in children suffering from TE were found to be coupled with impairment of the stem-hemispheric interrelations, reduction in the level of nonspecific activation, rise of convulsive preparedness of the brain. A correlation was established between alterations in the main parameters of variational cardiointervalography, character of brain bioelectric activity and the disease gravity. The data obtained can be employed as criteria for predicting the disease outcome and assessment of TE treatment in children.

Action Potentials↗

PubMed1977

Nasolacrimal duct reconstruction with the nasolacrimal duct prosthesis: an alternative to standard dacryocystorhinostomy.

For many years the standard surgical treatment for chronic dacryocystitis has been the edge-to-edge anastomosis of the lacrimal sac mucosa to nasal mucosa over the margins of a hole made through the lacrimal bone. Failures of this standard procedure have been attributed to many factors and complications frequently require reoperation. The procedure described in this paper was developed as a means of overcoming some of these difficulties. It provides a normal, gravity draining, nasolacrimal duct system without pooling and not requiring destruction of the lacrimal bone or alteration of normal anatomy. It consists of the implantation of a permanent indwelling nasolacrimal duct prosthesis (available from Concept, Inc., Clearwater, FL) from the base of the sac through the interosseous canal into the vault of the inferior nasal meatus. Because it does not involve bypassing the normal lacrimal drainage system, the technique is more simple and less traumatic. This method of reconstruction of the nasolacrimal duct has converted a major hour and a half procedure into a 15 minute operation. Because normal anatomic relationships are retained, the nasolacrimal duct prostheis gives reasonable assurance of permanent drainage and is recommended as a primary procedure of choice.

Dacryocystitis↗

PubMed1984

[Disorders of microcirculation in patients with acute surgical diseases of the biliary tract].

The authors provide the results of studying the microcirculation in 85 patients with acute cholecystitis and 56 patients with mechanical jaundice caused by choledocholithiasis. The data were obtained with the aid of bulbar capillaroscopy during conservative and surgical treatment. Considerable alterations were detected in all the components of the microcirculation (perivascular, vascular, intravascular), correlating with the gravity of destructive lesions in the gallbladder, duration and degree of jaundice. The times and degree of the normalization of microcirculatory disorders were defined.

Adult↗

PubMed2006

Reduction of anabolic signals and alteration of osteoblast nuclear morphology in microgravity.

Bone loss has been repeatedly documented in astronauts after flight, yet little is known about the mechanism of bone loss in space flight. Osteoblasts were activated during space flight in microgravity (microg) with and without a 1 gravity (1 g) field and 24 genes were analyzed for early induction. Induction of proliferating cell nuclear antigen (PCNA), transforming growth factor beta (TGFbeta), cyclo-oxygenase-2 (cox-2), cpla2, osteocalcin (OC), c-myc, fibroblast growth factor-2 (fgf-2), bcl2, bax, and fgf-2 message as well as FGF-2 protein were significantly depressed in microg when compared to ground (gr). Artificial onboard gravity normalized the induction of c-myc, cox-2, TGFbeta, bax, bcl2, and fgf-2 message as well as FGF-2 protein synthesis in spaceflight samples. In normal gravity, FGF-2 induces bcl2 expression; we found that bcl2 expression was significantly reduced in microgravity conditions. Since nuclear shape is known to elongate in the absence of mitogens like FGF-2, we used high-resolution image-based morphometry to characterize changes in osteoblast nuclear architecture under microgravity, 1 g flight, and ground conditions. Besides changes in cell shape (roundish/elliptic), other high-resolution analyses show clear influences of gravity on the inner nuclear structure. These changes occur in the texture, arrangement, and contrast of nuclear particles and mathematical modeling defines the single cell classification of the osteoblasts. Changes in nuclear structure were evident as early as 24 h after exposure to microgravity. This documented alteration in nuclear architecture may be a direct result of decreased expression of autocrine and cell cycle genes, suggesting an inhibition of anabolic response in microg. Life on this planet has evolved in a normal gravity field and these data suggest that gravity plays a significant role in regulation of osteoblast transcription.

3T3 Cells↗