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At least 811 records · Page 45Linked to original sources

PubMed2001

[Physiology of vertebrates under micro-gravity with special reference to the Ca metabolism].

On April 12, 1961, Major Yurii A. Gagarin of the former-U.S.S.R. Air Force circled the Earth in a spacecraft named "Vostok", a word which means "east". He spent 1 hour and 48 minutes in space. Since then, the U.S.S.R. and the U.S.A. have sent many astronauts into space. In one case, the stay in space exceeded a year in length, reaching 438 days. Through these experiences, it became clear that micro-gravity caused various problems in human physiology. One of the most serious problems was the loss of Ca from bones, as a result of the negative expenditure of Ca. Under 1G on the ground, bone absorption and bone formation proceed in accordance. Under micro-gravity, however, this balance is broken. Although this phenomenon has been widely analyzed from the viewpoint of molecular biology as well, studies to clarify the mechanism that causes the disorder of Ca metabolism in bones have just started. At present, no perfect treatment to prevent the loss of Ca from bones is available.

Adaptation, Physiological↗

PubMed1998

Balance retraining in a hemiparetic patient using center of gravity biofeedback: a single-case study.

A single-subject experimental design was used to evaluate the effects of center of gravity biofeedback on retraining balance control in a 72-yr.-old male hemiparetic patient. For both assessment and training the subject stood on dual force-plates enclosed on three sides by a visual surround. A 4-wk. training period consisted of subject-initiated shifts in body weight to control movement of a real-time computer display of the subject's center of gravity. A Sensory Organization Test and evaluation of weight distribution indicated that biofeedback retraining positively affected balance control during dynamic conditions and when the ground support moved forward.

Aged↗

PubMedDate not supplied

Computer calculation of movement of body's center of gravity.

The movement of the body's center of gravity was calculated in normal subjects and in vertiginous patients by using a strain gauge platform system and a ditigal computer. The total length of the loci traced by the center of gravity in 40 normal subjects during normal standing for 1 minute was 52.0 +/- 18.5 cm with eyes open, and 81.5 +/- 52.3 cm with eyes closed. The ratio of the total length with the eyes closed compared with that with the eyes open during normal standing for 1 minute was 1.56 +/- 0.56. The time course of the length of the locus was calculated every 10 seconds, and characteric curves were obtained. The dependability of this test appeared to be fairly accurate and the usefulness of this technique for the diagnosis of vertiginous or ataxic diseases is recommended.

Adolescent↗

PubMed1998

[Optokinetic nystagmus under prolonged alteration in the direction of gravity].

Optokinetic Nystagmus (OKN) exhibit different responses depending on the direction of gravity, with respect to head and body. In 13 normal healthy volunteers (10 experimental subjects and 3 controls), we studied the OKN evoked by horizontal and vertical stimuli, in upright, side-lateral, and repeated upright positions during a long time course of six test stages. Stage 1 was an upright sitting position. Stage 2 was a 90-degree recumbent lateral position immediately after Stage 1. Stage 3 was the same position as in Stage 2, but 2h later. Stage 4 was the same position, another 2h later (total of 4h). Stage 5 was a return to the upright position (the same as Stage 1) immediately after Stage 4. Stage 6 was a return to the same upright position, 2h after Stage 5. The results showed continuous modifications of OKN. A lateral tilt produced different effects on the horizontal and vertical optokinetic oculomotor systems. The gain in horizontal OKN (HOKN) decreased during Stages 2-4 with time, and returned to normal in Stages 5 and 6. As for vertical OKN (VOKN), the gain of upward (the direction by slow phase) OKN increased during Stages 2-4, and returned to normal in Stages 5 and 6. But the gain of downward OKN did not show any clear modulation. We showed that the change in gravity direction has a clear effect on OKN, and that it takes some time to reach the maximal and desirable level of modification. The difference in time-dependent modifications between HOKN and VOKN should be due to the difference in OKN-producing mechanisms and velocity storage systems.

Adolescent↗

PubMed2000

The experience of nausea during sustained hyper-gravity flight with negligible angular velocity.

BACKGROUND: The purpose of this study was to investigate nausea and vomiting during hyper-gravity flight at a slow rate of turn. During head-movements under these conditions, the semi-circular canals of the vestibular system function normally whereas the otoliths experience a G-excess effect, displacing further and moving faster than in a 1 G field. HYPOTHESIS: Nausea and vomiting are greater during hyper-gravity flight compared with historical data collected in a 1 G field at a similar rate of turn. METHODS: There were 27 subjects who were exposed to 1.8 G (hyper-G) during a slow rate turn on three NASA KC-135 flights. Subjects participated in one of three experimental periods, each period consisting of two 5.5-min hyper-G runs: 1) rest, with only incidental head movements; 2) active roll and pitch head movements; or 3) passive roll head movements. Subjective symptom data were collected pre-flight, following each experimental period and post-flight using a standardized nausea questionnaire. Electrogastrograms were obtained from eight subjects. RESULTS: Seven subjects (26%) vomited during the flight. Nausea initially increased but was then stable throughout the flight. Nausea appeared highest during active head movements. In subjects who vomited, greater gastrointestinal distress and somatic distress were reported. CONCLUSIONS: The levels of nausea and vomiting observed during hyper-G cannot be explained by Coriolis cross coupling and are likely due to the G-excess effect on the otoliths. The nausea profiles observed in individuals who vomit during hyper-G appear similar to those previously observed during nausea produced by an optokinetic drum stimulus in a 1-G field.

Adult↗

PubMedDate not supplied

[Eye movements occurring during head rotation on artificial gravity stands].

On the basis of previously advanced theories the direction and pattern of eye movements induced by stimulation of semicircular canals onboard artificial gravity stations are predicted. The resulting data are important to describe expected disorientation illusions of vestibular origin as well as vestibular effects on the visual functions of tracking and fixation onboard artificial gravity stations.

Eye Movements↗

PubMed2001

A gravity-independent constant force resistive exercise unit.

This study designed, developed and tested a novel, practical, gravity-independent exercise machine, the Constant Force Resistance Exercise Unit (CFREU). A CFREU prototype was designed and built according to National Aeronautic and Space Administration (NASA) hardware and physiological requirements, and was evaluated for potential exercise countermeasure viability. Life cycle data exhibit lower life than required by NASA guidelines; however, current CFREU re-designs are addressing this issue. Electromyography (EMG) data indicate that the CFREU used on the ground and in microgravity during exercise is capable of providing forces on the muscles that are similar to a standard free-weight machine used in gravity. Given the results of this study, the CFREU has proven to be a viable potential resistive exercise countermeasure to the deconditioning of the musculoskeletal system in microgravity.

Adult↗

PubMed2001

Small diameter gravity sewers: self-cleansing conditions and aspects of wastewater quality.

The construction of conventional sewerage systems in small communities, with pipes laid on a uniform slope and manholes regularly spaced, is sometimes not economically feasible, because of the high costs of sewer installation. Under those circumstances, the small diameter gravity sewers (SDGS) have often proven to be substantially less costly than conventional sewers. Typically, in SDGS systems the wastewater from one or more households is discharged into an interceptor tank (or a single compartment septic tank). The settled effluent is discharged afterwards into small diameter sewers operating under gravity. In this paper, special emphasis is given to the analysis of self-cleansing conditions and to the analysis of risks of sulphide generation and occurrence of septic conditions in SDGS systems. For the evaluation of the self-cleansing conditions, the critical velocity and the critical shear stress were computed according to the Shields equation. The forecasting of dissolved oxygen concentrations and sulphide build-up along the lines, for different flow conditions, was done running an established wastewater quality model.

Equipment Design↗

PubMed1988

Does vector-free gravity simulate microgravity? Functional and morphologic attributes of clinorotated nerve and muscle grown in cell culture.

Cocultured Xenopus neurons and myocytes were subjected to non-vectorial gravity by clinostat rotation to determine if microgravity, during space flights, may affect cell development and communications. Clinorotated cells showed changes consistent with the hypothesis that cell differentiation, in microgravity, is altered by interference with cytoskeleton-related mechanisms. We found: increases in the myocyte and its nuclear area, "fragmentation" of nucleoli, appearance of neuritic "aneurysms", decreased growth in the presence of "trophic" factors, and decreased yolk utilization. The effects were most notable at 1-10 rpm and depended on the onset and duration of rotation. Some parameters returned to near control values within 48 hrs after cessation of rotation. Cells from cultures rotated at higher speeds (>50 rpm) appeared comparable to controls. Compensation by centrifugal forces may account for this finding. Our data are consistent, in principle, with effects on other, flighted cells and suggest that "vector-free" gravity may simulate certain aspects of microgravity. The distribution of acetylcholine receptor aggregates, on myocytes, was also altered. This indicates that brain development, in microgravity, may also be affected.

Animals↗

PubMed1997

Changes in gravity influence rat postnatal motor system development: from simulation to space flight.

Our research examines the role of the environment in postnatal nervous system development. Recently we have been studying the effects of changes in gravity on the motor system of rats from postnatal day (P) 2 to 31 using kinematic analysis of swimming, walking, and righting reflexes. Using the tail suspension model of weightlessness we identified sensitive and critical periods of motor system development corresponding to the time during which a motor skill is first achieved. Motor performance in suspended animals was marked by slow swimming, walking, and air-righting, all of which were characterized by hindlimb extension. (Walton et al, Neurosci. 52,763,1992). The critical periods identified in these studies contributed to determining the age of animals for a small payload, NIH.R3. This 9-day mission (STS-72) included 2 litters at P5, P7, or P15 at launch. The P7-16 and P15-24 groups were studied post-flight. On the landing day (R+0) surface righting, swimming and walking were slower in flight compared to control animals. Differences were more marked in the younger animals and the hindlimbs were more affected than the forelimbs with marked, prolonged extension of, at least, the ankle joint angle. Readaptation to 1G was slower in the P7-16 group with righting reflexes adapting first, walking last. We have shown that gravity is an important factor in postnatal nervous system development and that its affect depends on the age of the animal, duration of the perturbation, and the motor function studied.

Animals↗

PubMedDate not supplied

An overview of the cosmic dust analogue material production in reduced gravity: the STARDUST experience.

The formation, properties and chemical dynamics of microparticles are important in a wide variety of technical and scientific fields including synthesis of semiconductor crystals from the vapour, heterogeneous chemistry in the stratosphere and the formation of cosmic dust surrounding the stars. Gravitational effects on particle formation from vapors include gas convection and buoyancy and particle sedimentation. These processes can be significantly reduced by studying condensation and agglomeration of particles in microgravity. In addition, to accurately simulate particle formation near stars, which takes place under low gravity conditions, studies in microgravity are desired. We report here the STARDUST experience, a recent collaborative effort that brings together a successful American program of microgravity experiments on particle formation aboard NASA KC-135 Reduced Gravity Research Aircraft and several Italian research groups with expertise in microgravity research and astrophysical dust formation. The program goal is to study the formation and properties of high temperature particles and gases that are of interest in astrophysics and planetary science. To do so we are developing techniques that are generally applicable to study particle formation and properties, taking advantage of the microgravity environment to allow accurate control of system parameters.

Astronomy↗

PubMed1997

Age-related changes in postural control associated with location of the center of gravity and foot pressure.

The purpose of this study was to assess the limitations of the head and lumbar movements in relation to the center of gravity which is needed to maintain standing balance with aging. The subjects of the study were 22 healthy volunteers. The subjects were divided into two age categories, the young group (mean 21.7 +/- 2.9 years, 7 males and 6 females); and the elderly group (mean 71.3 +/-2.6 years, 3 males and 4 females). The instruments for measuring lumbar and head movements and the center of pressure (COP) were a three-dimensional motion analysis system and a force plate. In addition, the peak foot pressure was measured during standing using the F-Scan system. The subjects were first asked to stand relaxed for 10 s. They then shifted from the starting position to the four directions (sways); anterior, posterior, right, and left. They tried to maintain standing balance at the maximal possible distance position for each sway for 10 seconds. Analyzing parameters were performed by measuring the average maximal linear displacement (cm) of the head and lumbar markers, the COP (cm), and the peak foot pressure (percent of body weight per squared centimeters; BW%/cm2) in each subject. The data of the young group for lumbar maximal displacement were greater than those of the elderly group in the anterior, posterior, and lateral sways. A significant difference between the young and elderly data was found in the posterior sway. According to the data of the head's maximal displacement, the elderly group was greater than the young group in all sways except for the anterior side. For the data of peak foot pressure in the posterior sway, the elderly group's data was greater than the young group's data. The forefoot area data of the young group was significantly greater than that of the elderly group and the heel area data of the elderly was significantly greater than that of the young group in the right sway. The results suggest that evaluating the maximal displacement of head and lumbar positions and toe's activity in the forefoot are all important factors associated with the center of gravity in healthy adults.

Adolescent↗

PubMed1999

[Ontogenesis of human motor-ability to control the position of the centre of gravity].

Knowledge of the basic principles of biomechanics makes it possible to understand the complex problem of ontogenesis of human movement. The ontogenesis of human motor can be characterized as acquisition of the ability to find a centre of gravity and to maintain or intentionally alter its position in space. This is made possible by intentional change of the tightness of connecting segments by controlled muscular activity and the use of external forces. The CNS controls the position of the centre of gravity via coordinated muscular activity.

Biomechanical Phenomena↗

PubMed1999

A plant's response to gravity as a wave phenomenon.

In 1988 I discovered low velocity longitudinal waves plants. These waves are called W-waves because they were first found by probing freshly cut live wood. The initial velocity for these waves was found to be close to 1 m/s. These waves don't appear to be explicitly electromagnetic but in live materials they shift charge because charge is free to move. These waves usually appear as standing waves so that with multiple probes or probing one can often find evidence for a standing wave in plant materials with charge located in periodically spaced piles. It appears likely that standing waves are largely responsible the placement of structures such as branches or leaves. The standing waves also appear to have an important influence on determining the size and shape of cells and shorter wavelengths are hypothesized to be important in determining cell structure. It is the authors opinion that W-waves are just a macroscopic extension of quantum waves (which determine the structure of matter) with a continuous connection with the microscopic. Th waves are also found outside of plants traveling with much larger velocities (v), however. W-waves appear to have many unique frequencies (f). These frequencies can be measured electronically, by beating with weak electromagnetic signals, and directly with a low frequency, spectrum analyzer. One can also measure plant internodal spacings (i) and use these measurements to calculate the same characteristic plant frequencies using a previously measured wave velocity. A frequency for a particular spacing is given by f=v/2i. Characteristic plant frequencies repeat from plant to plant. For this paper the most important result is that W-waves seem to be influenced tremendously by the gravitational field. The velocity of these waves within a plant may be different depending on whether they are traveling along the gravitational field or perpendicular to it or anywhere in between. Also it appears that the frequencies of the waves are shifted to lower waves when traveling along the gravitational field as compared to traveling perpendicular to the gravitational field. Both effects may complete the picture. Gravity has a very large influence on frequencies appearing to reduce frequencies to lower values by as much as a factor of one third (or even a smaller fraction) in live plant material. This results in cell lengths and internodal spacings being up to three (or even more) times longer parallel to the gravitational field compared to perpendicular to the gravitational field. Cell lengths and internodal spacings take on immediate values between vertical and horizontal. If the gravitational field is missing or nearly so as with microgravity, the cell is missing the gravity references that determine its shape, for example. It appears that plant parts grow at discrete angles to the gravitational field. All these features constitute overwhelming proof that plants are wave operated with the characteristics of the waves involved very much influenced by the gravitational field.

Biophysical Phenomena↗

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↗

PubMed1998

[Identification of gravity-related esterases (grEST1 and grEST2) in carrot callus cells].

A horizontal clinostat which mimics the microgravity in space was used to study its effects on carrot cells. After using boric acid buffer (pH 8.8) as extraction medium, PAGE pattern of esterase isozymes of carrot callus cells displayed 8 bands of which the activities of only 2 were affected by microgravity. They were named grEST1 and grEST2, where grEST stands for gravity-related esterase. The rates of increase in activity of them in carrot cells when cultured on a rotating horizontal clinostat were lower than that cultured in normal gravitational environments, and the difference increased with the culture time. The activities of grEST1 and grEST2 in carrot callus cells subjected to horizontal rotation were found to return to their original levels after being placed under normal gravity (1 x g) for 7 days. We suggest that the effect of simulated microgravity conditions on grEST1 and grEST2 activities in carrot callus cells is through affecting their synthesis. In addition, the activities of grEST1 and grEST2 were not inhibited by eserine, acetylcholine iodide, diisopropyl fluorophosphate and p-chloromercuribenzoate, which indicates that they are acetylesterases.

Acetylcholine↗

PubMed1975

Scales of gravity in head injury.

From the head injury onward the victim loses control over his own existence and starts a long journey through the various fields of forces determining his destiny until he can reassume control. Scales of gravity applied at different points in time vary and sometimes contradict each other. The vital scale is an immediate emergency scale, determined by the need to save a life, observe and treat a coma, and detect early complications, and the criteria are those of intensive care, surgery, and neurosurgery. The neurological and neuropsychological scale established towards the end of the first hospitalisation, assesses brain damage by neurological investigations, ophthalmological and otological tests and a neuropsychological evaluation. First individual psychiatric reactions appear at this stage. The psychosocial scale should consider information provided by previous scales, but also evaluate pre- and post-traumatic personality, family setting, social, legal, administrative and economic realities, residual skills, previous profession, possibilities of reinstatement and above all, motivation. Probably the neurological and neuropsychological scale provide the best common point of reference for a global assessment. These scales of gravity are examined in their relationship to traditional clinical thinking in different countries. A prospective and descriptive system of a "European" cofification as proposed within the framework of the European Communities is described.

Brain Injuries↗