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At least 235 records · Page 13Linked to original sources
PubMed1987

Fluid control mechanisms in weightlessness.

Experiments performed on Space Shuttle flights have emphasized study of the earliest effects of the cephalad fluid shift resulting from microgravity. Analysis of one subject's urine collected during flight showed that a sharp increase in antidiuretic hormone occurred within 2 h of launch, followed by an increase in cortisol excretion. Although this subject had symptoms of the space adaptation syndrome (SAS), inflight data from Spacelab missions suggested that these transient changes were not caused by SAS. Unpaired t-tests and Mann-Whitney tests showed that before and after flight, plasma thyroxine and urine osmolality were significantly higher in Shuttle crewmembers who exhibited more severe symptoms of SAS than in asymptomatic crewmembers. Collection of inflight data from more crewmembers should allow distinction between the effects of SAS and effects of weightlessness, and in the future several additional fluid regulation hormones will be measured in samples from crewmembers for a more complete understanding of fluid control during weightlessness.

Adaptation, Physiological↗
PubMed1987

Logistic risk model for the unique effects of inherent aerobic capacity on +Gz tolerance before and after simulated weightlessness.

Small sample size (n less than 10) and inappropriate analysis of multivariate data have hindered previous attempts to describe which physiologic and demographic variables are most important in determining how long humans can tolerate acceleration. Data from previous centrifuge studies conducted at NASA/Ames Research Center, utilizing a 7-14 d bed rest protocol to simulate weightlessness, were included in the current investigation. After review, data on 25 women and 22 men were available for analysis. Study variables included gender, age, weight, height, percent body fat, resting heart rate, mean arterial pressure, VO2max, and plasma volume. Since the dependent variable was time to greyout (failure), two contemporary biostatistical modeling procedures (proportional hazard and logistic discriminant function) were used to estimate risk, given a particular subject's profile. After adjusting for pre-bed-rest tolerance time, none of the profile variables remained in the risk equation for post-bed-rest tolerance greyout. However, prior to bed rest, risk of greyout could be predicted with 91% accuracy. All of the profile variables except weight, MAP, and those related to inherent aerobic capacity (VO2max, percent body fat, resting heart rate) entered the risk equation for pre-bed-rest greyout. A cross-validation using 24 new subjects indicated a very stable model for risk prediction, accurate within 5% of the original equation. The result for the inherent fitness variables is significant in that a consensus as to whether an increased aerobic capacity is beneficial or detrimental has not been satisfactorily established. We conclude that tolerance to +Gz acceleration before and after simulated weightlessness is independent of inherent aerobic fitness.

Acceleration↗
PubMed1986

Osteoblast histogenesis in periodontal ligament and tibial metaphysis during simulated weightlessness.

According to nuclear size, fibroblast-like cells adjacent to bone surfaces in the periodontal ligament (PDL) and tibial primary spongiosa (PS) were classified as less differentiated progenitors and committed osteoprogenitors (A/A'), nonosteogenic cells (B), or preosteoblasts (C/D). The ratio of A/A' to C/D cells reflects osteogenic status of bone lining tissue. When 83-day-old rats were subjected to simulated weightlessness (S-W) for 17 d and examined for changes in osteoblast histogenesis, PDL and PS cell populations increased in A/A' cells (p less than 0.01; less than 0.05) but decreased in C/D cells (p less than 0.01; less than 0.05) compared to controls. These data indicate that the nuclear volume method, originally developed in PDL, can also be used to assess osteoblast histogenesis in PS of long bones, and that simulated weightlessness in the present experimental context interferes with osteoblast histogenesis. Since the surfaces of both weightbearing (PS) and nonweightbearing (PDL) bones were affected, systemic factors appear important in the gravity-related mechanism of osteoblast histogenesis. Although unloading of the tibia and cephalad fluid shifts occur during S-W, the data attained in this experiment could also be explained by stress and/or cessation of growth in the S-W rats.

Animals↗
PubMed1987

Skeletal response to simulated weightlessness: a comparison of suspension techniques.

The skeletal response to simulated weightlessness was studied in rats subjected to two different methods of suspension. Skeletal unloading of the hind limbs for a two week period was achieved by use of either a back harness or tail traction. In comparison to pair-fed control rats, back-suspended rats failed to gain weight whereas tail-suspended rats exhibited normal weight gain. Quantitative bone histomorphometry revealed marked skeletal abnormalities in the proximal tibial metaphysis of back-suspended rats. Loss of trabecular bone mass in these animals was due to a combination of depressed longitudinal bone growth, decreased bone formation, and increased bone resorption. In contrast, the proximal tibia of tail-suspended rats was relatively normal by these histologic criteria. However, a significant reduction in trabecular bone volume occurred during 2 weeks of tail suspension, possibly due to a transient inhibition of bone formation during the early stages of skeletal unloading. Lack of weight gain in back-suspended rats may be indicative of a pronounced stress response during which corticosteroids adversely affected the skeleton. Maintenance of normal weight gain by tail-suspended rats provides evidence for the less traumatic nature of this method of suspension. Our findings indicate that tail suspension may be a more appropriate model for evaluating the effects of simulated weightlessness on skeletal homeostasis.

Adipose Tissue↗
PubMedDate not supplied

[Structure of the vestibular apparatus and ionic composition of the body of Xenopus laevis larvae as affected by weightlessness].

Clawed frog larvae (stages 45-46) that developed for 9 and 8 days beginning with the blastula and tail bud stages, respectively, in the weightless state were investigated. Scanning microscopy of the larval labyrinths did not reveal significant qualitative changes in the receptor and supporting cells of the maculae and in the otolith membrane. Determination of the electrolyte composition (Na, K, Ca, Mg) of the larval body showed no significant changes in the relative content of these elements. The morphometric examinations indicated an increase of the size of the utricular otoliths by 1.3 times as a result of exposure to weightlessness. There was a tendency for a greater asymmetry between the left and right otoliths in the same larva.

Animals↗
PubMedDate not supplied

[Effect of human body position and its holding on the level of manifestation of spatial illusions in weightlessness].

Test subjects were exposed to short-term weightlessness in various positions: standing, seated, supine in the cosmonaut's chair and on the flat surface, with the head kept straight ahead, bent forward or backward. Their susceptibility to illusionary sensations was measured. It was found that the development of spatial illusions in the weightless state was not correlated with body position, head position relative to the torso or restraint type.

Humans↗
PubMedDate not supplied

[Interrelationship between pulse filling of earlobe vessels and cardiac extrasystole during "head--foot" loading following exposure to simulated weightlessness].

The relationship between changes in the pulse blood filling of earlobe vessels and cardiac arrhythmias was studied in 91 manned experiments during which test subjects were exposed to simulated weightlessness and then to acceleration of +3 Gz for 5 min in a 7.25 m arm centrifuge. The studies demonstrated that the vascular type of functional decompensation may transform into the cardiac type in normal men during recovery from an exposure to +3 Gz and simulated weightlessness. This may be of theoretical and practical importance for space programs.

Adult↗
PubMedDate not supplied

[Combined action of weightlessness and ionizing radiation on the body of rats (based on data from morphological studies)].

The combined effect of weightlessness and ionizing radiation (24 hour exposure to Cs-137 at a total dose of 800 rad) was investigated morphologically in Cosmos-690 flight, synchronous and vivarium rats. Irradiation-induced lesions prevailed in both groups of rats. Comparative study of changes in flight and control rats showed that weightlessness and other space flight factors did not induce any new, previously unknown effects as compared with the exposure on the Earth; they did not exert a significantly aggravating effect on the development of radiation-induced lesions.

Adrenal Glands↗
PubMedDate not supplied

[Effect of blood redistribution on illusional sensations of spatial position in weightlessness].

The study was performed onboard a specially equipped aircraft which allowed zero-g and high-g studies. Blood redistribution was produced using a tilt table (-30 degrees) and a LBNP device. Illusionary sensations were measured by a Birtok unit and subjective reports of the test subjects. In the head-down position the feeling of blood rush to the head disappeared as soon as the weightless state was reached. In most cases illusionary sensations were similar to those in the horizontal position. When exposed to LBNP tests, the subjects developed no illusionary sensations during horizontal flight and felt their upper body going upwards and legs going downwards in the weightless state. Thus, illusionary sensations of the spatial position depend at large on blood redistribution in the human body.

Aerospace Medicine↗
PubMed1983

Effect of weightlessness on myofibrillar proteins of rat skeletal muscles with different functions in experiment of biosatellite "Cosmos-1129".

The composition of contractile and regulatory proteins was studied in rat muscles with different functions. The rats were exposed to weightlessness for 18.5 days during a space journey in biosatellite Cosmos-1129. Under the effect of weightlessness the myosin light chain composition changed, the quantity of myosin LC-3 subunits increased in the soleus and extensor digitorum longus (EDL) while it decreased in the triceps and brachialis muscles. The experiments showed changes in the subunit composition of the TN-TM complex, too. The results obtained are in favour of a possible adequate transformation of fibril phenotypes of some (antigravitational) muscles under the effect of spaceflight.

Animals↗
PubMedDate not supplied

[Vestibular apparatus study of the toad, Xenopus laevis, and rats under prolonged weightlessness].

Fertilized eggs of the clawed toad Xenopus laevis were placed aboard of orbital laboratory of "Salut-6" spacecraft where they developed for 20 days at temperature 15 degrees C. The larvae were fixed in weightlessness. Light and electronmicroscopic studies revealed undisturbed structure on the saccular and utricular maculae and otolith membranes. Some ultrastructural abnormalities were found in the inner ear of adult rats after 20 days of weightlessness ("Kosmos-936").

Animals↗
PubMed1981

In vivo bone strain measurements: clinical results, animal experiments, and a proposal for a study of bone demineralization in weightlessness.

An extensive review of the literature of the aetiology of bone demineralization in weightlessness underline the prevalent effect of mechanical stimulations on bone structure and metabolism. The accurate determination of the mechanical environment of bone can be realized using strain gauges. The results of more than 10 years of clinical application of bone strain measurements demonstrate the interest of this technic. We designed an implantable bone strain transducer composed of a strain gauge embedded in epoxy resin and surrounded by a porous shell. The fixation of the transducer is by bone ingrowth. Results on animals and an acute experimentation on man are presented. The objective of our study in space is to compare the mechanical response of bones of an animal or of a human submitted to normal 1-G gravity and to weightlessness. The average amount of bone strains and their variations during specific movements can be compared.

Aerospace Medicine↗
PubMedDate not supplied

[Reproduction and mutability of the flour beetle in weightlessness (experiments on the Saliut-6 orbital station)].

Experiments with the flour beetle Tribolium castaneus showed that in weightlessness these insects completed their cycle of development--from fertilization to the emergence of mature imago of the next generation--in the normal way. Survival of specimens, densities of cultures, duration of development and frequency of morphoses in flight and control studies were similar. Exposure to weightlessness did not increase the number of genetic changes.

Animals↗
PubMedDate not supplied

[Cathepsin activity of skeletal muscle and myocardial myofibrils after exposure to weightlessness and G force].

The rats flown on board Cosmos-605 and exposed to a synchronous experiment for 22 days showed an increased activity of myofibrillar cathepsins in skeletal muscles of different groups. In the flight rats the increase was greater than in the synchronous ground-based animals. This suggests a significant effect of weightlessness on the cathepsic activity. The parameter was partly normalized at R + 25 or 26. The exposure of rats to accelerations of 4 and 5 G for 20 min daily during 2 weeks also increased the cathepsic activity of skeletal and myocardial myofibers. The parameter returned to normal a month after completion of acceleration exposures. Thus, changes in the proteolytic activity of myofibers of different muscles induced by weightlessness and acceleration are reversible. The significance of changes in the muscle tension as related to the mechanism of stimulation of proteolytic reactions is discussed.

Animals↗
PubMed1980

Simulated weightlessness: effects of bioenergetic balance.

As a prelude to a flight experiment, an attempt was made to separate energy requirements associated with gravity from all other metabolic needs. The biological effects of weightlessness were simulated by suspending animals in a harness so that antigravity muscles were not supporting the body. Twelve pairs of rats were allowed to adapt to wearing a harness for 5 d. Experimental animals were then suspended in harness for 7 d followed by recovery for 7 d. Control animals were harnessed but never suspended. VO2, VCO2 and rate of 14CO2 expiration from radio-labeled glucose were monitored on selected days. Food intake and body mass were recorded daily. Metabolic rate decreased in experimental animals during 7 d of suspension and returned to normal during recovery. Although some of the metabolic changes may have related to variation in food intake, simulated weightlessness appears to directly affect bioenergetic balance.

Animals↗
PubMed1980

Effect of simulated weightlessness on the immune system in rats.

Rats suspended in a model system designed to simulate many aspects of weightlessness were immunized with sheep red blood cells. Parameters measured on these and control rats included titers of anti-sheep red blood cell antibodies, serum immunoglobulin levels, spleen and thymus weights, hematocrits, and leukocyte differential counts on peripheral blood. No significant differences were found between test and weight-bearing, harnessed controls; however, the thymuses of animals in both these groups were significantly smaller than untreated cage controls. The lack of an effect of simulated weightlessness on the immune system is an interesting result, and its significance is discussed.

Animals↗
PubMedDate not supplied

[Effect of weightlessness and an artificial gravitational force on the ion-regulating function of the kidney in rats].

Weightless rats showed greater changes in the fluidelectrolyte metabolism and ion regulatory function of the kidneys than centrifuged rats. During water loads they exhibited an increased sodium excretion. During potassium loads they displayed a higher potassium excretion. The study of electrolyte composition of different kidney segments demonstrated a reduced potassium content in the wet cortical and medullary matter due to elevated tissue hydration. Kidney microdissection did not reveal any structural differences in nephrons of the weightless and centrifuged rats.

Animals↗
PubMedDate not supplied

[Theoretical values for left ventricular ejection time during weightlessness].

The relationship between duration of blood ejection and cardiac cycle at rest can be well described by a linear function. This relationship is maintained in weightlessness as well. The derived formula used in calculations of the theoretical values of the ejection phase during an exposure to LBNP makes it possible to predict LBNP test tolerance in the weightless state. The level of deviation of factual values of heart rate from theoretical values may be an additional index to be used in assessing health status of crewmembers inflight.

Heart Ventricles↗