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PubMed1997

The effect of reduced gravity on the kinematics of human walking: a test of the dynamic similarity hypothesis for locomotion.

To gain insight into the basic principles that govern the biomechanics of locomotion, we investigated the effect of reduced gravity on walking kinematics. We hypothesized that humans walk in a dynamically similar fashion at combinations of speed and simulated gravity that provide equal values of the Froude number, v2/gLleg, where v is forward speed, g is gravitational acceleration and Lleg is leg length. The Froude number has been used to predict the kinematics and kinetics of legged locomotion over a wide range of animal sizes and speeds, and thus provides a potentially unifying theory for the combined effects of speed, size and gravity on locomotion biomechanics. The occurrence of dynamic similarity at equal Froude numbers has been attributed previously to the importance of gravitational forces in determining locomotion mechanics. We simulated reduced gravity using a device that applies a nearly constant upward force to the torso while subjects walked on a treadmill. We found that at equal Froude numbers, under different levels of gravity (0.25g-1.0g), the subjects walked with nearly the same duty factor (ratio of contact time to stride time), but with relative stride lengths (Ls/Lleg, where Ls is stride length) that differed by as much as 67 %, resulting in the rejection of our hypothesis. To understand the separate effects of speed and gravity further, we compared the mechanics of walking at the same absolute speed at different levels of gravity (0.25g-1.0g). In lower gravity, subjects walked with lower duty factors (10 %) and shorter relative stride lengths (16 %). These modest changes in response to the fourfold change in gravity indicate that factors other than gravitational forces are the primary determinants of walking biomechanics.

Biomechanical Phenomena↗
PubMed2000

The independent effects of gravity and inertia on running mechanics.

It is difficult to distinguish the independent effects of gravity from those of inertia on a running animal. Simply adding mass proportionally changes both the weight (gravitational force) and mass (inertial force) of the animal. We measured ground reaction forces for eight male humans running normally at 3 m s(-)(1) and under three experimental treatments: added gravitational and inertial forces, added inertial forces and reduced gravitational forces. Subjects ran at 110, 120 and 130 % of normal weight and mass, at 110, 120 and 130 % of normal mass while maintaining 100 % normal weight, and at 25, 50 and 75 % of normal weight while maintaining 100 % normal mass. The peak active vertical forces generated changed with weight, but did not change with mass. Surprisingly, horizontal impulses changed substantially more with weight than with mass. Gravity exerted a greater influence than inertia on both vertical and horizontal forces generated against the ground during running. Subjects changed vertical and horizontal forces proportionately at corresponding times in the step cycle to maintain the orientation of the resultant vector despite a nearly threefold change in magnitude across treatments. Maintaining the orientation of the resultant vector during periods of high force generation aligns the vector with the leg to minimize muscle forces.

Adult↗
PubMed2003

Mechanosensing and mechanochemical transduction: how is mechanical energy sensed and converted into chemical energy in an extracellular matrix?

Gravity plays a central role in vertebrate development and evolution. Gravitational forces acting on mammalian tissues cause the net muscle forces required for locomotion to be higher on earth than on a body subjected to a microgravitational field. As body mass increases during development, the musculoskeleton must be able to adapt by increasing the size of its functional units. Thus mechanical forces required to do the work (mechanical energy) of locomotion must be sensed by cells and converted into chemical energy (synthesis of new tissue). Extracellular matrices (ECMs) are multicomponent tissues that transduce internal and external mechanical signals into changes in tissue structure and function through a process termed mechanochemical transduction. Under the influence of an external gravitational field, both mineralized and unmineralized vertebrate tissues exhibit internal tensile forces that serve to preserve a synthetic phenotype in the resident cell population. Application of additional external forces alters the balance between the external gravitational force and internal forces acting on resident cells leading to changes in the expression of genes and production of protein that ultimately may alter the exact structure and function of the extracellular matrix. Changes in the equilibrium between internal and external forces acting on ECMs and changes in mechanochemical transduction processes at the cellular level appear to be important mechanisms by which mammals adjust their needs to store, transmit, and dissipate energy that is required during development and for bodily movements. Mechanosensing is postulated to involve many different cellular and extracellular components. Mechanical forces cause direct stretching of protein-cell surface integrin binding sites that occur on all eukaryotic cells. Stress-induced conformational changes in the extracellular matrix may alter integrin structure and lead to activation of several secondary messenger pathways within the cell. Activation of these pathways leads to altered regulation of genes that synthesize and catabolize extracellular matrix proteins as well as to alterations in cell division. Another aspect by which mechanal signals are transduced involves deformation of gap junctions containing calcium-sensitive stretch receptors. Once activated, these channels trigger secondary messenger activation through pathways similar to those involved in integrin-dependent activation and allow cell-to-cell communications between cells with similar and different phenotypes. Another process by which mechanochemical transduction occurs is through the activation of ion channels in the cell membrane. Mechanical forces have been shown to alter cell membrane ion channel permeability associated with Ca(+2) and other ion fluxes. In addition, the application of mechanical forces to cells leads to the activation of growth factor and hormone receptors even in the absence of ligand binding. These are some of the mechanisms that have evolved in vertebrates by which cells respond to changes in external forces that lead to changes in tissue strcture and function.

Animals↗
PubMed2000

Effects of hypergravity on morphology and osteopontin expression in the rat otolith organs.

Recovery from balance disorders after spaceflight is supposed to reflect the process of readaptation to normal gravitational environment (1G) from microgravity. Linear acceleration including gravity is perceived by otolith pathways, therefore, it could be assumed that possible plastic changes in any part of otolithic pathways from the level of the vestibular periphery to the central vestibular system might be responsible for adaptive mechanisms to an altered gravitational environment. In the present study, to elucidate a role of otoconia in adaptation to altered gravity, we examined the effects of hypergravity (2G) on morphology and synthesis of saccular and utricular otoconia in young adult rats. Morphology of otoconia was examined by scanning electron microscopy. Otoconial synthesis was assessed by mRNA expression of osteopontin, a matrix protein of otoconia, in otolithic maculae as a marker of otoconial genesis determined by a real-time quantitative PCR method. The present results showed that neither otoconial morphology nor otoconial synthesis was affected by up to one week exposure to hypergravity. These findings suggest that changes in neurotransmission at the synapses of the peripheral and/or central vestibular system rather than the changes in otoconial morphology and synthesis may be involved in adaptive mechanisms to an altered gravitational environment.

Animals↗
PubMed1994

Kinetics of stipe gravitropism in the mushroom fungus Coprinus cinereus under the conditions of microgravity simulation provided by clinostat treatment.

The extent of the gravitropic response, measured as the angle of the stipe apex at maximum curvature, was dependent upon the gravitational exposure time. The reaction time did not depend on exposure time, and interruption of gravitational exposure by a period of clinostating allowed the gravitational stimulus to decay. It is concluded that the gravitropic impulse is an 'all-or-nothing' signal in Coprinus cinereus, that perception and response probably occur in the same tissue regions, and that sustained exposure to the unidirectional gravity vector is necessary for the normal gravitropic response. The presentation time was found to be 7 min. Immediately after reaching curvature, stipes placed on the clinostat after various gravity exposure times 'relaxed' by 5 degrees. This relaxation suggests that gravitropic bending is a two-stage process with an initial, reversible, phase of plastic bending followed by a 'fixation' phase providing the gravitropic stimulus has been maintained.

Coprinus↗
PubMed1999

Gravity-dependent modulation of Ia afferent in human.

Recent work has shown that the H-reflex excitability of the human soleus motoneurones is modulated in reduced gravity and accompanied by a corresponding change in electromyographic (EMG) activity during space flight mission or different gravitational load. Spinal reflexes are often viewed as stereotyped motor patterns with limited scope for modification. However, recent evidence suggests that even short-latency, largely monosynaptic reflexes show a high degree of modulation during simple human motor activities such as walking and standing, and that the pattern of modulation can be specifically altered for the different functional requirements of each activity. Capady and Stein have demonstrated that H-reflex amplitude of the soleus increases progressively during the stance phase and reaches its peak amplitude late in the stance phase during walking. However, during running, the H-reflex is found to be significantly smaller than during walking, suggestion a modified spinal reflex gain for the different functional requirements of the motor behaviors. It is well documented that gravitational loads on the human body, spinal cords are much higher during standing in the water than standing in land. Little is known about the occurrence and influence of neural modulation in spinal cord during different gravitational load, which was not induced by posture but by voluntary background activity. The purpose of the present study was consequently to investigate how to effect is controlled H-reflex modulated during reduced gravity standing in a water in normal subjects.

Adult↗
PubMed1999

Effects of gravity on development: the importance of behavior.

Organisms live in four dimensions. With the dimension of time, we recognize that each organism is a lifecycle--an expression of its development. The cycles of differentiation expressed in the timeframe of biotic evolution yields the diversity of life on Earth. Thus, phylogenesis, can be understood as alterations in developmental processes. Species of organisms are thus groupings of individuals that share developmental processes. Natural selection acts throughout the lifecycle to select for developmental features that are adoptively appropriate for the organism's immediate environment. The process of ontogeny occupies an appropriately central position in gravitational biology. The evolution of all life on Earth, and thus the evolution development took place in the presence of gravitational forces. It is thus natural and necessary for biologists to wonder and to hypothesize about the role of gravity in development. We shall discuss some of the ideas and concepts that we believe are fundamental to appreciating the place of developmental analyses in gravitational physiology. We focus on problems relevant to the effects of gravity on vestibular development, and then emphasize issues pertinent to mammalian development.

Adaptation, Physiological↗
PubMed1976

The evolutionary role of gravity.

Analysis of the part played by gravity in development in the organic world shows that this factor has had an impact on evolution. All terrestrial organisms, including man, have adapted themselves to gravity by developing a number of important features of their composition and functions. Variations of gravitational field in any direction bring about numerous changes in organisms, ranging from metabolism to changes in more conservative systems which also include hereditary structures. Gravitational forces determine the form and the size of organisms, the development of skeletal supporting organs, and energetics. The study of the role of gravity in the variability of the organic world will be of great importance for long-term systems of life support and for work on space orbital stations or at bases on the moon and planets where gravitational forces may differ greatly those from on the earth.

Adaptation, Biological↗
PubMed2004

Passive infusion: a simple delivery method for retrograde cardioplegia.

Some damage to the capillaries and increase in myocardial edema have been shown when retrograde cardioplegia perfusion pressure exceeds 40-50 mmHg, or possibly when it falls within this pressure interval. To avoid these complications, we designed a very simple delivery method for retrograde cardioplegia: passive continuous infusion by gravitational force alone. From August 2002 through April 2003, 147 patients undergoing elective coronary artery bypass surgery were randomly allocated into 2 groups. In both groups, isothermic blood cardioplegic solution was infused continuously in a retrograde fashion, after antegrade cardioplegic arrest. Group 1 (n=76) received retrograde infusion passively by gravitational force, while Group 2 (n=71) received retrograde infusion from a manually controlled pressure bag, with the pressure maintained at about 40 mmHg. Myocardial biopsy specimens were taken just before the aorta was declamped, and myocardial edema was scored upon histopathologic examination. Postoperative myocardial damage was evaluated with periodic measurements of CK-MB isoenzyme and cardiac troponin T levels. We recorded cardioplegic infusion pressures and rates, and the total amount of potassium administered. The mean cardioplegic infusion pressures and rates, total potassium levels, and cardioplegic solution amounts were significantly lower in Group 1 than Group 2. Histologic observations revealed significantly less myocardial edema in Group 1. There were no differences between groups in CK-MB isoenzyme or cardiac troponin T levels, mortality, or morbidity. Retrograde continuous infusion of isothermic blood cardioplegic solution by gravitational force alone appears to provide satisfactory myocardial protection and to eliminate the harmful effects of higher pressures upon the myocardium.

Aged↗
PubMed2004

Perception mechanism of gravistimuli in gravity resistance responses of plants.

Gravity resistance is a response that enables plants to develop against the gravitational force. Hypergravity conditions produced by centrifugation have been used to analyze the mechanisms of gravity resistance responses. Under hypergravity conditions, plants construct short and thick shoots and increase cell wall rigidity for resisting the gravitational force. Hypergravity caused a decrease in the percentage of cells with transverse microtubules, and an increase in that with longitudinal microtubules. Such a prompt reorientation of cortical microtubules is involved in the changes in morphology of shoots by gravity. Hypergravity increased cell wall rigidity by increasing the molecular mass of xyloglucans via suppression of xyloglucan breakdown as well as by the thickening of cell walls. Blocker reagents of mechanoreceptors nullified the above-mentioned changes induced by hypergravity. Gravity resistance responses were brought about normally in mutants deprived of gravitropism. This result indicates that the graviperception mechanism in gravity resistance is independent of that in gravitropism. Gravity resistance responses were brought about independently of the direction of gravistimuli, but the responses disappeared in the presence of blockers of mechanoreceptors. Thus, in gravity responses, plants may perceive the gravitational force independently of the direction of stimuli by mechanoreceptors on the plasma membrane, and may utilize the signal to construct a tough body.

Arabidopsis↗
PubMed2005

[History of ether in the 18th century: George-Louis Lesage's system of corpuscules ultramondains].

The article presents an account of Lesage's theory of corpuscules ultramondains and ether. It shows that essential attributes of the antique concept of ether still belong to his speculative physics. In accordance with this concept, Lesage understood the corpuscules ultramondains as subtle celestial matter and carriers of the primordial movements in the universe which were characterised by their proximity to the divine. On the other hand, Lesage was engaged in the contemporary debate concerning the problem of causa gravitatis. His position turns out to be halfway between dynamic corpuscularity and mechanistic physics. With the former he shared the rejection of vortex theories and the adherence to the corpuscular theory of light and the nutshell theory, with the latter the rejection of action at-a-distance and forces inherent to matter. Contrary to the accusation that he plagiarised Fatio de Duillier's theory of gravitation, it is shown that Lesage formulated a gravitational mechanism essentially different to Fatio's. Lesage used the term ether for the theory of chemical affinities. His attempt to reduce them to gravitational force failed. The complexity of chemical phenomena could not be mastered theoretically by reduction to a uniform natural force.

Chemistry↗
PubMed1978

[Comparative study of the lymphoid organs of rats aboard a space flight under weightless and artificial gravity conditions].

A comparative histological investigation of the thymus, spleen and inguinal lymph nodes has been performed in the rats flown for 18.5 days on board the biosatellite "Cosmos-936" under the conditions of weightlessness and artificial gravitation (acceleration 1 g) imitating terrestrial magnetism. It has been stated that in the animals that were under the conditions of weightless ness during the flight and were sacrificed 4.5--13 h after they have landed the Earth, accidental involution of lymphoid organs is noted with morphological signs in them of an acute stress in the form of massive degeneration of the thymus lymphocytes and neutrophilic infiltration of the spleen. In rats that during the flight were subjected to the effect of artificial gravitation there was noted neither involution of the lymphoid organs nor morphological signs of acute stress in them. One of the main cause of acute stress in the rats subjected to weightlessness during the space flight is supposed to be transition to the terrestrial gravitation.

Animals↗
PubMed1995

Asynchronous closure and leaflet impact velocity of bileaflet mechanical heart valves.

The effect of gravitational field on the asynchronous closure of four different types of bileaflet heart valves (BHV) were investigated in an in vitro mock circulation system. The experimental study involved the 29 mm St. Jude Medical Standard, 29 mm CarboMedics, 29mm Edwards-Duromedics and 29 mm Edwards-Tekna BHVs. The valves were tested in the mitral position on an inclined 45 degrees plane of the pulsatile mock flow loop. The test valves were orientated with their pivotal axis horizontal so that the gravitational vectors on the two leaflets were clearly disparate. Using a specially designed laser optical system, the time difference at which the closing leaflets made their first contacts with the valve housing was measured. The closing velocity of each leaflet was measured separately by the laser sweeping technique (LST). The experiments were conducted under physiologic ventricular and aortic pressures at the heart rates of 70, 90, and 120 beats/minute with the corresponding flow rates of 5.0, 6.0, and 7.5 liters/minute. Asynchronous closing motions were registered in all four tested BHVs. The leaflet closing motions were random in nature, but indicated clear dependency on the orientations with respect to the gravitational field. The lower leaflet which makes a generally level swing to close, was assisted initially by the gravity and was always found to close earlier than the upper leaflet, which swing upward to close. The initial closure of the upper leaflet was against the gravity which delayed the leaflet motion. Depending on the BHV designs, the time delays between the two leaflets were found to vary from beat to beat but to follow certain probability distributions. In general, the leaflet/housing contact time between the two valve leaflets exhibited the clear trend of decreasing delay time at closure with the increase of the heart rate. For each of the valves tested, the average impact velocity of the first closing leaflet was found always smaller than that of the second closing leaflet at all three heart rates tested. The impact velocities of both the BHV leaflets were found to increase with the heart rate. The difference in the closing velocities between the two leaflets decreases with the increase of the heart rate and is generally proportional to the impact time delay between the two leaflets.

Analog-Digital Conversion↗
PubMed1995

Gravity and hemineglect.

Spatial cognition requires the integration of visual inputs with proprioceptive and vestibular information about the position of the eye, the head and the body. All these sources are used by the brain to produce multiple higher-order (e.g. egocentric) representations of space, subserving accurate spatial behaviour. Such spatial representations are disrupted by unilateral cerebral damage producing neglect in the contralateral side of space. In eight brain-damaged patients with left unilateral neglect the manipulation of gravitational-otolithic information, obtained by placing patients in a supine position, produced a significant reduction of the rightward directional error in the line bisection task in all cases. This finding suggests that, in patients with neglect, gravitational information is processed in a non-symmetrical fashion, with a rightward bias towards the side of the lesion. This is the first study showing that manipulation of gravitational input affects neuropsychological disorders of visuo-spatial processing.

Aged↗
PubMed1994

Comparative assessment of the polypeptide profiles from lateral and primary roots of Phaseolus vulgaris L.

In Phaseolus vulgaris, primary roots show gravitational sensitivity soon after emerging from the seed. In contrast, lateral roots are agravitropic during early development, and become gravitropic after several cm growth. Primary and lateral root tissues were examined by polyacrylamide gel electrophoresis, coupled with western blotting techniques, to compare proteins which may contribute to the acquisition of gravitational sensitivity. Root tips and zones of cell elongation were compared for each root type, using immunological probes for calmodulin, alpha-actin, alpha-tubulin, and proteins of the plastid envelope. Lateral roots contained qualitatively less calmodulin, and showed a slightly different pattern of actin-related epitope proteins, than did primary root tissues, suggesting that polypeptide differences may contribute to the gravitational sensitivity which these root types express.

Actins↗
PubMed2006

Clinical outcome of patients with idiopathic normal pressure hydrocephalus three years after shunt implantation.

OBJECTIVE: To investigate the outcomes of surgical treatment of idiopathic normal pressure hydrocephalus (iNPH). PATIENTS AND METHODS: We prospectively investigated 51 patients treated for iNPH by insertion of a ventriculoperitoneal shunt with gravitational valve. RESULTS: The proportion of excellent, good, and satisfactory outcomes immediately following surgery was 80%; the same clinical outcome was later verified in 67% of patients on average of 34 months postoperatively. These results are similar to those reported in the literature. Ventricle volume decreased minimally during the course of treatment using Evans' index, which was concordant with recent literature and with current understanding of hydrocephalus treatment. CONCLUSIONS: A gravitational valve for treatment of iNPH is the logical implementation of current knowledge of the pathophysiology of this illness enabling us to solve the problem of cerebrospinal fluid drainage with the lowest possible opening pressure while simultaneously protecting from overdrainage. The use of programmable valves, in combination with a gravitational component, is the next evolutionary stage, potentially making revision operations unnecessary.

Adult↗
PubMed1995

The hybrid mass-spring pendulum model of human leg swinging: stiffness in the control of cycle period.

Human leg swinging is modeled as the harmonic motion of a hybrid mass-spring pendulum. The cycle period is determined by a gravitational component and an elastic component, which is provided by the attachment of a soft-tissue/muscular spring of variable stiffness. To confirm that the stiffness of the spring changes with alterations in the inertial properties of the oscillator and that stiffness is relevant for the control of cycle period, we conducted this study in which the simple pendulum equivalent length was experimentally manipulated by adding mass to the ankle of a comfortably swinging leg. Twenty-four young, healthy adults were videotaped as they swung their right leg under four conditions: no added mass and with masses of 2.27, 4.55, and 6.82kg added to the ankle. Strong, linear relationships between the acceleration and displacement of the swinging leg within subjects and conditions were found, confirming the motion's harmonic nature. Cycle period significantly increased with the added mass. However, the observed increases were not as large as would be predicted by the induced changes in the gravitational component alone. These differences were interpreted as being due to increases in the active muscular stiffness. Significant linear increases in the elastic component (and hence stiffness) were demonstrated with increases in the simple pendulum equivalent length in 20 of the individual subjects, with r2 values ranging between 0.89 and 0.99. Significant linear relationships were also demonstrated between the elastic and gravitational components in 22 subjects, with individual r2 values between 0.90 and 0.99.(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration↗
PubMed1991

Human ocular torsional position before and after unilateral vestibular neurectomy.

The static ocular torsional position of both eyes of 23 patients was measured by means of fundus photographs one day before and one week after unilateral vestibular neurectomy for the treatment of acoustic neuroma, Ménière's disease or paroxysmal vertigo. The results showed that in all patients the vestibular neurectomy caused both eyes to tort (i.e. to roll around the visual axis) toward the side of the neurectomy when measured one week after operation. The extent of this torsion was an average of 9.5 degrees one week after operation and there was no statistically significant difference in the average magnitude of the torsion in the two eyes. In 8 of these patients, additional measurements were made at intervals up to one year after operation and it was found that in these patients there is a significant reduction in torsion over time from an average of 10.2 degrees one week after operation to an average of 2.8 degrees by 16 weeks after operation. The change in torsional eye position following the neurectomy was accompanied by a change in the perceived visual orientation of a small (9.5 degrees visual angle) illuminated horizontal line at a straight ahead eye level position in an otherwise completely darkened room. One week after operation when asked to adjust the line to the perceived gravitational horizontal by rotating it in roll (i.e. around an X axis), patients who had had a right vestibular neurectomy consistently set the line so that the right side of the line (from the patient's point of view) was below the true gravitational horizontal. Similarly patients after a left neurectomy consistently set the line so that the left side of the line was below the true gravitational horizontal. There is a high correlation (r = 0.95) between the direction and magnitude of the change in torsional eye position and the direction and magnitude of the change in the perceived visual horizontal one week after operation.(ABSTRACT TRUNCATED AT 250 WORDS)

Eye Movements↗

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