Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “WEIGHTLESSNESS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 253 records · Page 14Linked to original sources
PubMed1993

[The effect of weightlessness on amphibians. The ultimobranchial body].

C-cells of Pleurodeles waltilii ultimobranchial bodies (ULT) were studied after a series of two-week spaceflight on the biosatellites. It was shown that under conditions of weightlessness the hypertrophy of ULT and calcitonin secretion activation occurred. Calcitonin accumulated into the ULT which resulted in metaplasia of the surrounding tissues, organ calcification and C-cells death. After landing, the regenerative processes which were not manifest in weightlessness occurred. They were similar to those of embryonic development of the organ.

Adaptation, Physiological↗
PubMed1993

[The effect of weightlessness on amphibians. The skeleton and mineral metabolism].

The visceral and somatic skeleton of Pleurodeles waltilii was investigated after a series of two-week space flights on the biosatellites. It was shown that under conditions of weightlessness osteoporosis of the skeleton and its demineralisation were stimulated. In weightlessness, calcium, phosphorus and sulfur were lost and potassium accumulated. Trabeculae of endochondral part of the extremity bones were destroyed by osteoclasts. Proliferation of osteoclasts was disrupted, appositional growth stopped, and the cartilage of hyoid system was resorbed. Skeleton readaptation during two months did not result in the complete regeneration of morphological structure of the bones.

Adaptation, Physiological↗
PubMed1994

Health care during prolonged weightlessness in humans.

The demands for accumulation of knowledge about the human adaptation to weightlessness of long duration and the implications for the health and well-being of the astronaut have become increasingly important also for the international space programmes which are under development. The health care during long duration space-flights starts already with the selection where professional, psychological and medical criteria are considered. Space flights in low earth orbit have not been extended beyond 1 year, so the predictable value for long term space flights is limited, because e.g. Mission to Mars will last from 1.5 to 3 years, depending on the position of the planets, the space vehicle etc. The long duration and the enormous distance covered will induce very special and until now unknown effects on the human psychology which might be seen as the one single major factor which might be prohibitive for such long duration flights. The Moon base will bring further knowledge useful for long duration space flights in the field of medical care in general, but also with regard to the development of countermeasures against the adverse effects of weightlessness on the human body. The Moon's gravitational field of 0.16 G makes it possible to study this as a threshold in the adaptation processes.

Aerospace Medicine↗
PubMed1999

Contributory factors to orthostatic intolerance after simulated weightlessness.

Various factors may contribute to orthostatic intolerance (OI) observed after space flights or simulated weightlessness such as bed rest experiments: individual physical and physiological factors (arterial blood pressure (BP), height), physiological changes induced by real or simulated weightlessness (hypovolaemia, increase in venous distensibility), and space flight or simulation conditions (duration and counter-measure application). Our purpose was to test which of these factors were dominant in contributing to the OI. This was assessed in 47 healthy men participating in bed rest experiments of 4, 14, 28, 30 and 42 days, with or without counter-measures (medical stockings, lower-body negative pressure (LBNP), LBNP + muscular exercise). Nineteen subjects did not finish the orthostatic test (60 degrees head-up tilt or stand test) after bed rest. The occurrence of OI was associated with greater height, low resting BP, greater changes in resting lower-limb venous distensibility throughout the bed rest, and absence of counter-measures.

Adult↗
PubMed2003

FPGA implementation of a pyramidal Weightless Neural Networks learning system.

A hardware architecture of a Probabilistic Logic Neuron (PLN) is presented. The suggested model facilitates the on-chip learning of pyramidal Weightless Neural Networks using a modified probabilistic search reward/penalty training algorithm. The penalization strategy of the training algorithm depends on a predefined parameter called the probabilistic search interval. A complete Weightless Neural Network (WNN) learning system is modeled and implemented on Xilinx XC4005E Field Programmable Gate Array (FPGA), allowing its architecture to be configurable. Various experiments have been conducted to examine the feasibility and performance of the WNN learning system. Results show that the system has a fast convergence rate and good generalization ability.

Algorithms↗
PubMed2002

Changes in potassium currents of vascular smooth muscle cells from hindquarter arteries of 4-wk simulated weightlessness rats.

It has been reported by Delp et al and Ma J et al that the vasoreactivity of hindquarter vessels from simulated weightless rats decreased. Many factors may contribute to the depressed vasoreactivity. Because the potassium channels play an important role in regulating the resting potential and contribute to the action of some vasoactive substances, we speculated that the changes of potassium channels may be an electro-physiological mechanism involved in the depressed vasoreactivity of hindquarter vessels due to simulated weightlessness.

Journal Article↗
PubMed1967

Cardiovascular studies during and following simulation and weightlessness.

Two major characteristics of space flight may be simulated to some degree by bed rest and by water immersion. These are inactivity and the lack of the hydrostatic stress on the systematic circulation. Studies prior to the advent of space flight led to the prediction of orthostatic intolerance, muscular weakness, and calcium loss. Prolonged space flight has heightened the interest in these simulations to provide information concerning the temporal cause of the "deconditioning" or disuse syndrome and the value of simulation for testing the effectiveness of remedial measures. This report will evaluate the extent to which the simulation appears valid. In its gross effects, orthostatic intolerance can be studied with respect to its temporal course, etiology and effectiveness of remedial measures. The intolerance develops more rapidly during water immersion with respect to cause as well as effect. The short term of immersion studies does not allow study of the secondary change in blood volume due to red cell mass changes, Remedial measures seem clearly defined in water immersion simulation and less clear in bed rest. Measures of venous pooling following water immersion appear different than those obtained following weightlessness. There also appear to be differences in the results of evaluation of protective devices and measures and in the time course of development and recovery of orthostatic intolerance. Correlates of the cardiovascular responses such as muscle tone, skeletal strength, and endocrine change (catecholamines, vasopressin and aldosterone) suggest a marked alteration in physiology during hypodynamic status. To date, work on exposure to increased G force has provided only extrapolated data concerning metabolic requirements.

Bed Rest↗
PubMed1999

[The progress in research on changes of central venous pressure under simulated weightlessness and microgravity].

One of the most profound circulatory changes that occur in man during exposure to microgravity is a cephalad redistribution of fluid. Central venous pressure (CVP) is not only an important standard for determining the cephalad redistribution of fluid but also the unique valuable means for measuring continuously cardiac filling pressure under simulated weightlessness (SW) and microgravity, and has a relationship with neurohumoral [correction of nerohumoral] regulation. With the development of manned spaceflight, the researches in space suggested that CVP did not increase, which is directly contradictory to the previous results under SW. This paper mainly discusses the changes of CVP and the effects of countermeasures on CVP under SW and microgravity, and the mechanisms of decreased CVP under microgravity. It is postulated that more suitable SW models, more studies about the area of low pressure including especially pulmonary circulation, and comprehensive studies in multiple systems are needed.

Cardiovascular Deconditioning↗
PubMed1979

A review of the consequences of fluid and electrolyte shifts in weightlessness.

This review describes the renal-endocrine mechanisms related to the early losses of fluid-electrolytes from the body during weightlessness as well as their contribution to longer term adaptation of fluid-electrolyte balance. The hypotheses presented were generated by a systematic analysis of body fluid and renal dynamics observed under conditions of actual and simulated spaceflight. These have increased our understanding of the effects of acute headward fluid shifts on renal excretion, the factors promoting excess sodium excretion and the regulation of extracellular fluid composition.

Adaptation, Physiological↗
PubMed1979

A mathematical and experimental simulation of the hematological response to weightlessness.

Two ground-based methods of weightlessness simulation--a computer model of erythropoiesis feedback regulation and bedrest--were used to investigate the mechanisms which lead to loss of red cell mass during spaceflight. Both methods were used to simulate the first Skylab mission of 28 days. Human bedrest subjects lose red cell mass linearly with time and in this study the loss was 6.7% at the end of four weeks (compared to 14% in Skylab). Postbedrest recovery of red cell mass was delayed for two weeks during which time a further decline in this quantity was noted. This is consistent with the first Skylab mission but not with the two longer flights of two and three months. Hemoconcentration, observed early in the study, was essentially maintained despite red cell loss because of continued loss of plasma volume. The computer model, using the time-varying hematocrit data to estimate red cell production rates, predicted dynamic behavior of plasma volume and red cell mass that was in close agreement with the measured values. The results support the hypothesis that red cell loss during supine bedrest is a normal physiological feedback process in response to hemoconcentration enhanced tissue oxygenation and suppression of red cell production. In contrast, the delayed postbedrest recovery of red cell mass was more difficult to explain, especially in the light of enhanced reticulocyte indices observed at the onset on ambulation. Model simulation suggested the possibilities, still to be experimentally demonstrated, that this period was marked by some combination of increased oxygen-hemoglobin affinity, small reductions in mean red cell life span, ineffective erythropoiesis, or abnormal reticulocytosis. The question of whether hemoconcentration is the sole contributor to spaceflight red cell losses also remains to be resolved.

Bed Rest↗
PubMed1990

Cardiovascular deconditioning during weightlessness simulation and the use of lower body negative pressure as a countermeasure to orthostatic intolerance.

The cardiovascular function is one of the main disturbed by weightlessness: it is particularly affected by the astronaut's return to Earth, where symptoms linked to the cardiovascular deconditioning syndrom appear in the following forms: (1) orthostatic intolerance with its risk of syncope: (2) higher submaximal oxygen consumption for an equivalent work load. Lower Body Negative Pressure (LBNP) is intended to stimulate the venous system of the lower limbs; however, the specific effects of periodical LBNP sessions on the orthostatic intolerance have never been studied. With this objective in mind, 5 volunteers took part in two recent antiorthostatic bedrest experiments for 30 days. In the first experiment 3 subjects were submitted to several sessions of LBNP experiment per day and 2 others were controls; in the second experiment the LBNP group of the 1st one became controls and vice-versa. Two orthostatic investigations were performed: (1) 5 days before the bedrest; (2) at the end of the 30 day bedrest period. The results showed: (1) when the subjects were control, a high orthostatic intolerance post bedrest with 3 syncopes and one presyncopal state during the first minutes of the tilt test; (2) when the subjects were submitted to LBNP sessions, no orthostatic intolerance.

Adult↗
PubMed1994

Diuretic as a means for rapid adaptation to weightlessness.

In a number of flights, cosmonauts and astronauts have experienced aggravation of their health status and general condition in the initial hours and days in a weightless environment. One of the trigger mechanisms for the onset of these unfavourable conditions at the start of space flight is a redistribution of body fluids and a blood shift towards the head. To ensure controlled hypohydration as a countermeasure to the deleterious effects of 0-g and to investigate the feasibility to control adaptation, six cosmonauts were administered lasix once a day during the first 3 days of a mission. All data of the experiment (correction test, questionnaire, hematocrit) were recorded on a special form in the logbook and transmitted to the control centre for processing. Results showed that the diuretic weakened the sensation of discomfort and improved the cosmonauts' general condition. Objective indices of the correction test indicate an increased work ability of cosmonauts. After hypohydration, circulating plasma volumes in the group were reduced by 6.8 + 1.0% on average.

Adaptation, Physiological↗
PubMedDate not supplied

Countermeasure of the negative effects of weightlessness on physical systems in long-term space flights.

The system of countermeasure of microgravity effects has been developed in Russia that allowed to perform safely long-term space flights. This system that includes different means and methods such as special regimens of physical exercises, axial loading ("Pingiun") and antigravity suits, low body negative pressure device (LBNP, "Chibis") and "cuffs" and others has been used with certain variations at certain stages of flight in 27 successfully accomplished space flights that lasted from 60 to 439 days. The pre-, in- and postflight studies performed in 57 crew members of these flights have shown that the system of countermeasure is effective in preventing or diminishing to a great extent almost all the negative effects of weightlessness in flights of a year and more duration and that the intensity and duration of changes recorded in different body systems after flights do not correlate significantly to flight durations, correlating strongly to the volume and intensity of physical exercises used during flight and especially during concluding stage of it.

Aerospace Medicine↗
PubMed1981

The action of simulated and true weightlessness on the digestive tract of rats.

Rats on board the Soviet Cosmos 936 satellite for l8 1/2 days showed a decreased glycoprotein secretion from the salivary mucous glands, stomach and intestine, and an increased leucine aminopeptidase and acid phosphatase content from the small intestine. Grimelius positive cells were activated. One group of rats were centrifuged at 1 g during the flight to simulate terrestrial gravity. Some investigations have suggested that under these conditions muscular and cardiac disorders diminished. In the digestive tract the benefits of centrifugation at 1 g are minimal and limited to a few glycoprotein components. The digestive changes are probably the expression of a stress response, unrelated to weightlessness. Similar changes, concomitant with a glycocorticoid hypersecretion, were found in rats after 15 days of hypokinesia on Earth. These digestive changes persisted even in adrenalectomized rats.

Acid Phosphatase↗
PubMed1986

Confirmation of gravisensitivity in the slime mold Physarum polycephalum under near weightlessness.

We have investigated Physarum polycephalum, a unicellular organism with no special gravity receptors, on its ability to react to gravity. The first experiments were 0 g-simulation experiments on the fast-rotating clinostat conducted with plasmodial strands of this acellular slime mold. In these earth-bound experiments the observed parameters were periodicity of the contractions and dilatations of the strand's ectoplasm as well as the periodicity and velocity of the striking cytoplasmic (endoplasmic) shuttle streaming. During 0 g-simulation these parameters showed significant changes indicating the existence of a gravisensitivity of the slime mold. The Space-Shuttle experiment (ESA-Biorack in D 1-Mission) should demonstrate the validity of the 0 g-simulation on the fast-rotating clinostat. The experiment was designed in a way enabling the registration of the same parameters as on the clinostat (using the light microscope in combination with a photo diode and a cinecamera). Only one of the two planned measurement sessions was fully successful and provided us with data confirming the results gained on the fast-rotating clinostat: The slime mold showed under real near weightlessness in the D 1-Space Shuttle Mission a transient frequency increase in tis contraction rhythmicity and a (steady) increase in the streaming velocity of its endoplasm.

Animals↗
PubMed1996

Early development in aquatic vertebrates in near weightlessness during the D-2 Mission STATEX project.

Aboard the German-Spacelab-Mission D-2 the project "Gravity Perception and Neuronal Plasticity (STATEX II)" was performed. STATEX is for STATolith EXperiment. Objects were growing tadpoles of the South African Toad (Xenopus laevis D.) and a juvenile cichlid fish (Oreochromis mossambicus). The results give a broader base for the understanding of how environmental stimuli (e.g. linear accelerations) affect the development and function of the gravity perceiving systems in these two vertebrates. These systems are accepted as models for the human vestibulum. Results of experiments in hyper-g (up to 5 g), simulated weightlessness (Fast-rotating-clinostat) and parabolic flights are compared and discussed.

Animals↗
PubMed1979

Prophylactic [correction of prophylatic] effects of intermittent acceleration against physiological deconditioning in simulated weightlessness.

The prophylactic effect on adult human males of intermittent acceleration against physiological deconditioning in weightlessness simulated by water immersion was studied at +0.8, +1.2, and +1.6 g. These prophylactic exposures reduced renal excretion of fluid and plasma volume changes, and increased venous compliance and the time at which the subjects could tolerate an acceleration field of +3 g.

Acceleration↗
PubMed2002

Clinorotation-induced weightlessness influences the cytoskeleton of glial cells in culture.

During and after spaceflight astronauts experience neurophysiological alterations. To investigate if the impairment observed might be traced back to cytomorphology, we undertook a ground based research using a random positioning machine (clinostat) as a simulation method for microgravity. The outcome of the study was represented by cytoskeletal changes occurring in cultured glial cells (C(6) line) after 15 min, 30 min, 1 h, 20 h and 32 h under simulated microgravity. Glia is fundamental for brain function and it is essential for the normal health of the entire nervous system. Our data showed that after 30 min under simulated microgravity the cytoskeleton was damaged: microfilaments (F-actin) and intermediate filaments (Vimentin, Glial Fibrillary Acidic Proteins GFAP) were highly disorganised, microtubules (alpha-tubulin) lost their radial array, the overall cellular shape was deteriorated, and the nuclei showed altered chromatin condensations and DNA fragmentation. This feature got less dramatic after 20 h of simulated microgravity when glial cells appeared to reorganise their cytoskeleton and mitotic figures were present. The research was carried out by immunohistochemistry using antibodies to alpha-tubulin, vimentin and GFAP, and cytochemical labelling of F-actin (Phalloidin-TRIC). The nuclei were stained with propidium iodide or 4,6-diamidino-2-phenylindole dihydrochloride (DAPI). The cells were observed at the conventional and/or the confocal laser scanning microscope. Samples were also observed at the scanning electron microscope (SEM). Our data showed that in weightlessness alterations occur already visible at the scale of the single cell; if this may lead to the neurophysiological problems observed in flight is yet to be established.

Actins↗