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At least 343 records · Page 19Linked to original sources
PubMed2005

Effect of low gravitational stimulation on the perception of target elevation: role of spatial expertise.

To examine the interindividual differences in the judgment of the visually perceived eye level (VPEL-upright position) and of the visually perceived apparent zenith (VPAZ-supine position) when the subject is subjected to low gravitational-inertial force (GIF), we independently altered GIF in two different populations: control subjects and spatial experts. Subjects were instructed to set a luminous target to the eye level while they were in total darkness and motionless or undergoing low radial acceleration with respect to the threshold of the otolithic system (0.015-1.67 m/sec2 for the VPEL and 0.55-2.19 m/sec2 for the VPAZ, respectively). Results showed that (1) low GIFs, close to those met during daily life, induced an eye level lowering in the upright and supine positions for the control group, and (2) the spatial expertise modified the influence of low GIF. Whereas an oculogravic illusion was found for the control group, this phenomenon was absent (VPAZ) or weaker (VPEL) for the spatial experts. Thus, the relations that the subjects maintain with their spatial environment and the knowledge acquired through experience modify the processing of sensory information and the perceptive construction resulting from it. The interindividual differences in sensitivity to the oculogravic illusion are discussed in terms of sensory dominance and of a better efficiency in the use of the available sensory information.

Gravitation↗
PubMed1997

Digging behaviour and responses to photic and gravitational cues as elements of escape behaviour of bumblebees.

We have investigated escape behaviour of workers of two bumblebee species, Bombus terrestris and B. pascuorum, when confined to test tubes plugged with soil and either exposed to sunlight or kept in darkness. In both these situations B. terrestris performed better (i.e. escaped after a shorter time) than B. pascuorum. B. terrestris (but not B. pascuorum) also performed better in darkness than in tubes exposed to sunlight. This implies that in both situations B. terrestris showed higher readiness to dig than B. pascuorum, and that in tubes exposed to sunlight only B. terrestris showed high readiness to display photopositive behaviour as well. B. pascuorum displayed, however, photopositive behaviour in another escape situation: when released in a dark room in front of a vertical array of four sources of white light. In that situation, B. pascuorum also displayed the tendency to fly upwards, based most probably on responses to gravitational cues.

Animals↗
PubMed2001

[Tilt test and orthostatic intolerance: abnormalities in the neural sympathetic response to gravitational stimulus].

In the present manuscript the different methodologies aimed at assessing the autonomic profile in humans during a gravitational stimulus have been described. In addition, strengths and drawbacks of the tilt test in relation to occasional orthostatic intolerance were addressed. Finally, different autonomic abnormalities underlying occasional and chronic orthostatic intolerance syndromes have been schematically highlighted. The direct recording of the neural sympathetic discharge from the peroneal nerve (MSNA), in spite of its invasive nature, still represents the recognized reference to quantify the changes in the sympathetic activity to the vessels attending postural modifications. The increase of plasma norepinephrine during a tilt test is achieved by both an increase in plasma spillover and a concomitant decrease in systemic clearance. Changes in the indices of cardiac sympathetic and vagal modulation may also be quantified during a tilt test by power spectrum analysis of RR interval variability. The spectral markers of cardiac autonomic control, if evaluated concomitantly with MSNA, may contribute to assess abnormalities in the regional distribution of the sympathetic activity to the heart and the vessels. The capability of the tilt test of reproducing a vasovagal event or of inducing "false positive responses" seems to be markedly affected by the age, thus suggesting that additional or different etiopathogenetic mechanisms might be involved in the loss of consciousness in older as compared to younger subjects. In subjects suffering from occasional or habitual neurally mediated syncope an increase or, respectively, a decrease in cardiac and vascular sympathetic modulation has been documented before the loss of consciousness. In patients with pure autonomic failure, a global dysautonomia affecting both the sympathetic and the vagal modulation to the heart, seems to be present. In chronic orthostatic intolerance, the most common form of dysautonomia of young women, an abnormal regional distribution of sympathetic activity has been hypothesized during up-right posture. Indeed, during standing a blunted increase of sympathetic activity to the vessels is attended by a cardiac sympathetic overactivity leading to an exaggerated tachycardia.

Chronic Disease↗
PubMed1991

Issues in human gravitational physiology: a medical perspective on gravity and the cell.

There are many interacting factors that contribute to understanding the effects of gravity and microgravity on human gravitational physiology. Medical practitioners are interested in maintaining human health and performance in the space environment and thus have concerns regarding what biological questions should be addressed during human space excursions. Communication between disciplines and subdisciplines and creation of a common language and perspective must be determined for knowledge to progress. There is a need for increased experimentation supplying a solid data bank to aid in answering biological questions. Perhaps simple things may be as important as complicated discoveries when learning how biological adaptation has occurred.

Adaptation, Physiological↗
PubMed1992

Centrifuges: evolution of their uses in plant gravitational biology and new directions for research on the ground and in spaceflight.

The use of centrifugation as a tool for exploring qualitative and quantitative features of plant responses to gravity and to other body forces can be traced to plant scientists' early 19th century experiments. To study how plants perceive and respond to gravitational stimuli requires experimental manipulation of the force or acceleration vector direction and magnitude. As technology advanced, especially during the past half-century, so did the sophistication of experimental designs and of the scientific questions that could be addressed. The most significant improvement in methodology probably will prove to be attainment of experimental access to the hypogravity range of inertial accelerations by the combination of centrifugation and spaceflight.

Acceleration↗
PubMed1992

The fast rotating clinostat: a history of its use in gravitational biology and a comparison of ground-based and flight experiment results.

The fast rotating clinostat has been used in gravitational biology since 1965 to investigate effects of simulated microgravity. Using a microscope, the behavior of cells and organelles within the cells under microgravity conditions can be directly observed during rotation. Experiments with several mammalian cells and unicellular organisms have shown that different cellular functions are affected in simulated microgravity. Almost no changes were noted in the area of developmental biology. A comparison of results from the fast rotating clinostat and flight experiments reveals that the clinostat is a valuable tool to evaluate an organism's sensitivity to gravity changes. Therefore, a biological object proposed for a flight experiment should first be investigated in the clinostat before it is selected. This is especially true in the use of single cells and unicellular organisms.

Animals↗
PubMed1992

The NASA Specialized Center of Research and Training (NSCORT) in Gravitational Biology.

The Life Sciences Division of NASA has initiated a NASA Specialized Centers of Research and Training (NSCORT) program. Three Centers were designated in late 1990, as the culmination of an in-depth peer review analysis of proposals from universities across the nation and around the world. Kansas State University was selected as the NSCORT in Gravitational Biology. This Center is headquartered in the KSU Division of Biology and has a research, training, and outreach function that focuses on cellular and developmental biology.

Biological Science Disciplines↗
PubMed1993

Isolation of the physiological regulation component of the arterial pressure time variation after postural stresses in by a model of the gravitational and arterial kinking effects.

Prompt active postural manoeuvres induce an immediate arterial pressure variation followed by a period of regulation. For the squatting manoeuvre, initial hypertension was explained by a rise of cardiac filling pressure due to "squeezing blood out of the veins of the legs", leading to an increase in stroke output by Frank-Starling mechanism. For a minor part, it was also explained by "kinking" of the femoral arteries. O'Donnel and Mc Ilroy observed an increase in central blood volume and accepted the idea of a rise of cardiac filling. However, they did not observe so consistent circulatory variations when postural changes were realized in a water tank. Therefore, they concluded that kinking of the arteries and veins of the legs could not be very important. Moreover, the immediate pressure variations, most often appearing in the first beat succeeding the postural manoeuvres cannot be easily explained by the previously invoked modifications of cardiac filling pressures. When Hoffman et al lifted dogs until they stood erect, the right ventricular stroke volume usually fell in the first beat after the postural change, but the left ventricular stroke volume did not fall for another 1-3 beats. When the dogs were rapidly lowered to standing on four legs again, a delay of 2-3 beats was also observed. Thus, another interpretation of immediate hypotension must be added. It should especially take into account the natural gravitational fluid mechanics phenomena imposed to the arterial blood. Besides, to allow the investigation of the orthostatic regulation of arterial blood pressure, it would be necessary to separate the cardiovascular regulation component of the arterial pressure time course from the pressure evolution that would naturally appear in the network without physiological contribution. It is the aim of this study.

Blood Pressure↗
PubMed1995

Exercise with and without gravitational gradient: evaluation with the new random access mass spectrometer (RAMS).

Gravity adds about 40-50 mmHg perfusion pressure to the arterial supply of the quadriceps muscles in the upright posture. This could have important implications in supply of blood flow during exercise. Recently, we have shown that when subjects exercise in the supine posture the rate of increase in VO2 is considerably slower then when cycling exercise takes place in the upright posture. The most probable explanation for this slower adaptation was the altered perfusion gradient. Indeed, when the perfusion gradient from heart to legs was restored by placing the lower part of the body of supine subjects in a negative pressure chamber, the rate of increase in VO2 returned to upright values. The hypothesis advanced from these studies was that skeletal muscle blood flow was reduced at the onset of supine exercise. Exercise in the microgravity environment of space should be similar to that in the supine posture. The only experiments conducted in space to this date that have addressed the question of cardiorespiratory adaptation to changing work rates were performed on the German D2 mission using the methodology proposed by Stegemann and colleagues. To conduct these experiments, it is necessary to utilize sensitive breath-by-breath technology. Recently, NASA and the Russian space programs have commissioned a new mass spectrometer based system as part of the GASMAP project. It was the purpose of this study to evaluate the new mass spectrometer under conditions in which the gravitational effects on the cardiorespiratory response were being challenged.

Adult↗
PubMed1994

Gravitational biology of mushrooms: a flow-chart approach to characterising processes and mechanisms.

Flow charts are presented which systematise recently published work on gravitropic responses of the mushroom stipe of Coprinus cinereus. The hypothetical model represented by the charts suggests that the meiotic division is a pivotal point in the gravitational biology of the mushroom fruit body. The unilateral gravity vector seems to be required for formation of the tissues in which meiosis normally occurs, and stipes become gravitropically competent only after onset of meiosis. The gravitropism flow-chart also indicates that two signals emanate from the upper regions of the stipe, one promotes the process of gravitropic bending, and is followed by a second signal which compensates for excess bending and adjusts the stipe apex to the vertical. Formalisation of the various observations into flow-charts, even though comparatively simple at the moment, facilitates comparison with other species and concentrates attention on aspects requiring further experimental analysis.

Calcium↗
PubMed1998

[Assessment of responsiveness of spontaneous baroreceptor-heart rate reflex under gravitational stress].

Beat by beat arterial blood pressure was measured using Finapres 2300 monitor. Sequences of 3 or more beats with systolic pressure and next beat interval changed in the same direction were identified as baroreflex sequences from 6-min data segments. A linear regression was applied to each sequence and the slope (correlation coefficient > or = 0.85) was taken as a measure of the baroreflex response slope (BRS). The changes in mean BRS during + 65 degrees head-up tilt (HUT), -6.67 kPa lower body negative pressure (LBNP) and 16 days -6 degrees head-down tilt (HDT) bed rest were observed. The results showed that there was a significant decrease in the mean BRS during LBNP or HUT as compared with that of the supine control, though the blood pressure responses differed. The mean BRS was also significantly decreased during bed rest. It suggests that the responsiveness of spontaneous baroreceptor-heart rate reflex can be evaluated in humans under gravitational stress.

Adaptation, Physiological↗
PubMed1975

[Effect of gravitational loads and hypokinesia on the structure of the blood vessels of the tongue in the rabbit].

The vessels of the tongue were studied in 120 rabbits in 5 series of experiments methods of injection, clearing, rentgenography, silver nitrate impregnation after V. V. Kuprijanov and a histological method. The animals were rotated in a centrifuge with a 1 m radius. For hypokinesia the animals were placed in small cages. Gravitation stress mainly caused changes in the capillary-venous part of the circulatory bed (dilatation of vessels). Under conditions of hypokinesia morphological changes were most pronounced in terminal portions of the arterial part of the bed, arterioles and precapillaries. Successive exposure to both factors caused no specific changes. Preliminary training to stressess failed to prevent the appearance of considerable morphological changes in blood vessels of the tongue.

Animals↗
PubMed1975

[Effect of transverse gravitational loads on the vessels of the retinal membrane of the rabbit eyeball].

Changes in the eye ball retina were studied in 3 series of experiments in cleared preparations after exposure of the animal to gravitation stress of transversal direction. Prolonged single functionally endurable stress of ventro-dorsal direction (10 units/3 min) caused dilatation of the retina vessels, worse filling of peripheral parts of the circulatory bed, uneven staining of the vascular wall, constriction and dilatation along the course of the vessel. More continuous exposure to the same value of stresses (10 units up to the animal's death) resulted in a pressor effect; qualitative changes in the vessels increased. Within 1,5 hour after a 3-minute-long exposure to stress the vascular bed still remained unchanged. The diameter of vessels approached normal while the general quantity of vessels was decreased and qualitative changes were well pronounced.

Animals↗
PubMed1975

[Effect of longitudinal gravitational loads on the structure of the wall of the vertebral artery].

A single exposure to the greatest endurable gravitation stress causes such changes in the wall of the vertebral artery as division into layers, oedema, vacuolization of smooth muscle cells. Repeated exposure according to a training schedule resulted in reconstruction of the vascular wall (division of the medial sheath of the artery into several muscular layers). Concentration of smooth muscle cells in "layers" increased when training was after a "cumulative" schedule. Under conditions of increasing cumulative effect the collagenization of the media and dystrophy of the muscular and elastic tissue began. The greatest changes in the arterial wall took place in the upper parts of the vertebral artery at the level of the 2nd and 3d cervical vertebra.

Adaptation, Physiological↗
PubMed1975

[Effect of gravitational loads in different directions on the structure of the lymphatic bed of the pelvic extremities in the rabbit in vivo].

The method of lymphorentgenography was used in order to study alterations in the lymph vessels of pelvic extremities of rabbits at different terms (from 1 week up to 6 months) after exposure to gravitation stresses of different directions, value and duration. After exposure to stresses of cranio-caudal direction the amount of vessels increased. They had weel pronounced sinuosity and clearly protruding valves. The diameter of the vessels was more than normal and was equal to 0,3-0,8 mm. Popliteal lymph nodes were also increased up to 12,6-6,7 mm. Within 6 months after stresses these changes retained. Stresses of caudal-cranial direction during all periods of observation (from 1 week up to 6 months) caused dilatation of vessels (0,3-0,6 mm), their sinuosity and enlargement of popliteal lymph nodes up to 10,5-6,2 mm. All these changes returned to normality within 6 months. Thus, most pronounced and resistant morphological changes of the lymphatic bed were caused by greatest endurable stresses of cranio-caudal direction.

Animals↗
PubMed1966

On the thresholds of gravitational force perception by plants.

Changes in growth and development of plants in "weightless" environments is a focus of several biosatellite projects. Implicit in experimental designs is the consideration that the force vectors from vibration and vehicular spin are near or below the thresholds of perception. Thresholds of 10(-3) x g have been assigned based upon results from centrifugal stimulation of organs essentially fixed with respect to earth gravity. A value of 2 x 10(-5) x g was derived from vibrational (discontinuous) acceleration of a clinostat wire on which seedlings were mounted. We have developed apparatus that will enable the imposition upon seedlings of a continuous centrifugal force of constant sign concomitant with the nullification of the directional component of earth gravity. Recent experiments evaluating the responses of Avena roots and shoots in such apparatus indicate a threshold on the order of 10(-3)-10(-2) x g. These values are supported by results of experiments where organs were grown on clinostats whose rotational axes were at various tilt angles with respect to earth gravity; this technique enables minute increments of longitudinal gravitational stimulation as a vector function of the tilt angle, concomitant with compensation for earth gravity. We will discuss the possibility that assigned thresholds of micro-g magnitude are derived as a consequence of undefined forces that are artifacts of apparatus function.

Acceleration↗
PubMed2002

Changes of decartograms under gravitational acceleration and microgravity.

The Decarto technique was used to study the orthogonal ECGs recorded in 23 subjects during parabolic flights (44 records). A parameter of the instantaneous decartograms, namely the activation area (AA), which is the total area of the depolarization front projection on the image sphere, was analyzed. We compared the values of AA during the periods of horizontal flight, upward parts of all parabolas, and the initial 10 s of microgravity of all parabolas. According to the characteristics of the vectorcardiograms and AA, all subjects were subdivided into 3 groups: with increased electric activity of the right ventricle (I), the left ventricle (II) and both ventricles (III). Changes of AA with change of gravitational levels in these groups showed some differences. In groups I and II, the AA of the initial part of the QRS complex increased during microgravity and decreased during hypergravity. In group III it decreased during microgravity and changed variously during hypergravity. The AA of the middle part of the QRS complex decreased during microgravity and increased during hypergravity, and these changes were more pronounced in group III. The changes of AA in groups I and II may be explained by the Brody effect. In group III, AA seems to be influenced by some additional factors, possibly by changes in the intramyocardial or intraventricular blood volume. The AA of the last part of the QRS complex increased during microgravity and decreased during hypergravity in all groups. This may be explained by an effect of mutual neutralization of depolarization fronts related to the changes of the QRS duration.(Fig. 3, Ref. 4)

Acceleration↗
PubMed2000

Modelling the neuromechanical events of locomotion at varying gravitational levels.

The purpose of the present study was to determine the feasibility of using a neuromechanical model of human locomotion based on a model previously published by Taga et al. to simulate gait at various speeds and gravitational levels. The results indicate that this model may be appropriate for studying walking at 1 G but not for higher speed or lower G locomotion.

Biomechanical Phenomena↗