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At least 19 recordsLinked to original sources
PubMed2002

[Changes of leg compliance during weightlessness or simulated weightlessness].

Weightlessness or simulated weightlessness causes increase of leg compliance. It leads to more blood pooling in the legs and less blood returning to the heart during orthostatic test, which may partly explain the occurrence of orthostatic intolerance induced by weightlessness or simulated weightlessness. This article is a review covering published materials about the methods of measurement, mechanisms and countermeasures of the increase of leg compliance during weightlessness or simulated weightlessness.

Compliance↗
PubMed2000

[Changes of learning and memory function under weightlessness or simulated weightlessness].

The work efficiency of astronauts has an intimate connection with the brain function state during space flight. The research results of the learning and memory mechanism of the brain in recent years were introduced. The effects of weightlessness or simulated weightlessness on brain's learning, memory, focused attention and many other higher neural activities and on the relative neural transmitters were summarized. Several research aspects were put forward in the future.

Aerospace Medicine↗
PubMed1999

[The effect of weightlessness and simulated weightlessness on the expression of genes].

The research results of the relationship between gene expression and weightlessness or simulated weightlessness were studied. The influence of weight on the expression of genes in central nervous system were summarized in three aspects. It can be concluded that the expression of genes in central nervous system were precisely regulated by weight. It was important to study the effects of microweight on central nervous system in the molecular level.

Aerospace Medicine↗
PubMed1988

Correlation of macro and micro cardiovascular function during weightlessness and simulated weightlessness.

The investigation of cardiovascular function necessarily involves a consideration of the exchange of substances at the capillary. If cardiovascular function is compromised or in any way altered during exposure to zero gravity in space, then it stands to reason that microvascular function is also modified. We have shown that an increase in cardiac output similar to that reported during simulated weightlessness is associated with a doubling of the number of post-capillary venules and a reduction in the number of arterioles by 35%. If the weightlessness of space travel produces similar changes in cardiopulmonary volume and cardiac output, a reasonable expectation is that astronauts will undergo venous neovascularization. We have developed an animal model in which to correlate microvascular and systemic cardiovascular function. The microcirculatory preparation consists of a lightweight, thermo-neutral chamber implanted around intact skeletal muscle on the back of a rat. Using this technique, the performed microvasculature of the cutaneous maximus muscle may be observed in the conscious, unanesthetized animal. Microcirculatory variables which may be obtained include venular and arteriolar numbers, lengths and diameters, single vessel flow velocities, vasomotion, capillary hematocrit anastomoses and orders of branching. Systemic hemodynamic monitoring of cardiac output by electromagnetic flowmetry, and arterial and venous pressures allows correlation of macro- and microcirculatory changes at the same time, in the same animal. Observed and calculated hemodynamic variables also include pulse pressure, heart rate, stroke volume, total peripheral resistance, aortic compliance, minute work, peak aortic flow velocity and systolic time interval. In this manner, an integrated assessment of total cardiovascular function may be obtained in the same animal without the complicating influence of anesthetics.

Animals↗
PubMed2000

[Changes of cerebral circulation during weightlessness or simulated weightlessness].

The results about studies on changes of the cerebral circulation during weightlessness/simulated weightlessness were reviewed in this paper. The possible influencing mechanism of weightlessness on cerebral circulation and its physiological significance were summarized. It could be concluded that the changes of cerebral circulation were the results of self-regulation of the brain to maintain its normal function, and it might play an important role in the genesis of postflight orthostatic intolerance.

Aerospace Medicine↗
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↗
PubMed2005

[Effects of simulated weightlessness on rats mandible, lumbar vertebra and femur].

OBJECTIVE: To observe the effect of weightlessness simulation on rats mandible, lumbar vertebra and femur. METHOD: Twenty five Wistar rats were randomly arranged into control group (n=10) and tail-suspension group (n=15 rats). The experiment lasted for 28 d. Then the mandible, lumbar vertebra and femur were excised and the histological structure of condylar process of mandible, molar and premolar area of mandible body, first lumbar, head, middle segment and condyle of femur were examined. RESULT: After tail-suspension there was no distinct change in bone density and bone mass of condylar process. But the degree of interlacement of trabecular bone increased. The bone substance of mandible was very dense in both control and experimental groups. There was no stimulated difference of bone structure and bone mass between the two groups. There was no marked change in the thickness of periodontal membrane. The bone lamella in premolar area of experimental group arranged regularly. And its maturity was higher than that in molar area. The line of bone hyperplasia in molar area of experimental group arranged disorderly and irregularly, which means that much bone remodeling occurred. The component of trabecular bone decreased in femur and lumbar vertebra and the thickness was uneven. The interlacement and connection among trabecular bones was poor. CONCLUSION: Four weeks of stimulated weightlessness can lead to osteoporosis in acantha and femur [correction of feurar] but has no distinct effect on mandible.

Animals↗
PubMed1995

Central and peripheral sympathetic activities in rats during recovery from simulated weightlessness.

Rats were tail suspended, keeping their forelimbs weight bearing for 14 days, and then allowed to recover for a short (6-h) or a long (24-h) period to assess the behavior of the sympathetic nervous system after weightless simulation. Sympathetic activity was determined by measuring norepinephrine (NE) turnover in the brain stem cell groups involved in central blood pressure control and in organs playing a key role in the cardiovascular regulation (heart and kidneys). The NE turnover was greatly reduced in the rostral (-56%; P < 0.001) and caudal (-73%; P < 0.001) A2 nucleus of suspended rats but was unchanged in the A1, A5, and A6 cell groups compared with attached rats. The NE turnover in the cardiac atria (-34%; P < 0.001) and ventricles (-35%; P < 0.001) and kidneys (-31%; P < 0.001) was decreased after suspension. The central and peripheral sympathetic activities returned to normal within 24 h of release from suspension, but there was hyperactivity after 6 h of recovery. This raises the problem of interpreting the results obtained in animals killed a few hours after return from spaceflight.

Animals↗
PubMed1997

Orthostatic tests after a 4-day confinement or simulated weightlessness.

Besides microgravity, inactivity is likely to play a role in the cardiovascular deconditioning after space flights and weightlessness simulations. The aim of the study was to compare the effects of a 4-day head-down bed rest (HDBR) (-6 degrees) and a 4-day confinement (C) on cardiovascular responses to orthostatic stress. Eight male subjects underwent head-up tilt (HUT) (+60 degrees) and lower-body negative pressure (LBNP) (-20, -30, -40 and -50 mmHg) before (D-1) and at the end (R1) of each situation. Blood pressure, heart rate variability (HRV) and spontaneous baroreflex slope (SBS) were determined. The HDBR reduced orthostatic tolerance, as five subjects presented orthostatic hypotension during the HUT at R1, compared with two subjects at D-1. These same two subjects presented orthostatic hypotension after confinement. The main findings, after HDBR, included reductions in RR interval and total spectral power and a decrease in the parasympathetic indicator (PNS) in favour of a decrease in vagal tone; the increase in the sympathetic indicator (SNS) was not significant. After confinement, the RR interval was also significantly reduced and PNS decreased, but not significantly. RR interval and PNS were further reduced during HUT and LBNP, reflecting a withdrawal of parasympathetic activity. SBS was reduced after HDBR (P < 0.05) and confinement (P = 0.05), with a further reduction during HUT and LBNP without difference between D-1 and R1. This experiment showed that a 4-day HDBR leads to impaired baroreflex function and changes in autonomic balance, which may contribute to orthostatic intolerance. Although less significant, similar patterns of changes in the autonomic nervous system were observed after confinement, suggesting an influence of the inactivity in cardiovascular deconditioning.

Adult↗
PubMed1983

Fluid shifts in vascular and extravascular spaces during and after simulated weightlessness.

To simulate weightlessness in a normal-gravity environment, eight male subjects were tilted 5 degrees head-down for 8 h to determine vascular and extravascular shifts of fluid. Most of the initial loss of leg volume during head-down tilt represented a passive shift of venous blood toward the head. Facial edema, headache, nasal congestion, and a pronounced diuresis were associated with this redistribution of blood volume. As measured by the wick-catheter technique during head-down tilt, interstitial fluid pressure in lower-leg muscle and overlying subcutaneous tissues decreased by 7.4 and 4.4 mmHg, respectively. Interstitial fluid was shifted from the lower legs at a rate of 12 ml X h-1. Dehydration of lower-leg tissues probably resulted from decreased capillary blood pressure within these tissues during tilt. Other transcapillary pressures were unchanged. The abrupt alterations in local blood pressure upon changes in body posture were probably sufficient to explain all shifts of vascular and extravascular fluid. In this regard, countermeasures may be necessary to maintain precapillary-muscle tone during long space flights in order to prevent swelling of lower-leg tissues upon readjustment to Earth's gravity.

Airway Obstruction↗
PubMed2003

[Weightlessness or weightlessness simulation and vascular remodeling].

Weightlessness is inavoidable during spaceflight. It brings profound physiological effects on human body. Vascular remodeling is one of the important changes of cardiovascular system caused by weightlessness or simulated weightlessness. The paper summarized the studies on the effects of weightlessness or weightlessness simulation on vascular remodeling in recent years. The emergence and development of the concept of vascular remodeling were briefly reviewed. The advances of study on vascular remodeling in recent years was briefly discussed with the points focused on the effects of weightlessness or weightlessness simulation on cardiovascular remodeling and its mechanism. It is proposed that cardiovascular remodeling might be important in studying the causes of orthostatic intolerance after spaceflight.

Adaptation, Physiological↗
PubMed2002

[Effects of simulated weightlessness on EEG frequency fluctuation characteristics].

Objective. To develop a method of EEG monitoring under special environment, which is of value for astronauts selection and training. Method. Weightlessness was simulated by means of -6 degrees head down bed rest (HDBR). Rest EEG was recorded in 12 male subjects (aged 18-22) with eyes-closed and then analyzed by means of EEG frequency-fluctuation analysis system. Result. Before HDBR, the dominant order at parietal and occiput was 10, 9, 11 Hz; At frontal and temporal regions 9 Hz competed with 10 Hz for the main dominant component, while the third was 7 Hz. During HDBR, reversible changes of position and interrelation between 7, 8, 9, 10, 11 and 12 Hz appeared, and the frequency components and their regions involved spread gradually. The probability of 7 Hz and 8 Hz dominance increased, while 10 Hz and 11 Hz dominance decreased. At parietal, occiput and post-temporal regions, 9 Hz competed with 10 Hz for the main dominant component, the third was 7 Hz. At frontal and pre-temporal regions, 9 Hz occupied the main dominant position, while the second was 7 Hz (at right-frontal regions, it even occupied the main dominant position), the third was 10 Hz. Conclusion. Simulated weightlessness cause change of EEG dominant-frequency fluctuation competitive structure significantly. Brain adaptation function decrease, and headache can be easily induced. There exists a potential influence on brain function.

Adolescent↗
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↗
PubMed1997

[Thermoregulation under simulated weightlessness].

The effect of simulated weightlessness on thermoregulation was studied in 5 subjects. The experiment consisted of 3d baseline measurements, 7d head-down bed rest and 2d recovery. Circadian rhythm was assessed by continuous measurements of rectal temperature and skin temperature with 2h intervals. Heat Stress Protein 70 (HSP70) was measured by Western-blot Dot method and the facial surface temperature distribution was measured by HR-2 infrared thermography. The results showed that rectal temperature keeps the wake-sleep variation, but the circadian rhythm changed during bed rest, and the change of rectum temperature rhythm appeared mainly in the early-days of bed rest; HSP70 and facial surface temperature increased during bed rest.

Bed Rest↗
PubMed2001

[Heat stress-induced HSP70 expression in heart and vessels of simulated weightless rats].

To examine the effect of simulated weightlessness on inducible HSP70 expression in the heart and vessel tissues of rats, a tail-suspension rat model was used to simulate weightlessness. HSP72 mRNA and HSP70 expression in heart and vessel tissues of both simulated weightless and control rats exposed to heat stress (ambient temperature, Ta = 43 degrees C) and recovered at Ta of 25 degrees C for 1 h (CON-H1, SUS-H1) or 2 h (CON-H2, SUS-H2) were analyzed using Northern blot and Western blot. The expression of HSP72 mRNA in the myocardium significantly decreased in SUS-H2, as compared with that of CON-H2 rats. The amount of HSP72 in the myocardium tended to decrease in both SUS-H1 and SUS-H2 groups, as compared with the corresponding control groups, but the differences were not statistically significant. The levels of inducible HSP70 expression in the vessels were related with their anatomical locations, for that the expression of both HSP72 mRNA and HSP72 significantly increased in basilar arteries, whereas it showed a slight decline in femoral arteries. The blunted HSP70 expression in myocardium suggests that simulated weightlessness may induce myocardial changes similar to those in aging. However, the HSP70 expression changes in arteries are in accord with the trend of differential adaptation changes in vessels to simulated weightlessness.

Animals↗
PubMedDate not supplied

[Energy-metabolism enzymes during combined exposure of the body to simulated weightlessness and gravitational overloads].

Exposure to simulated weightlessness (7-day water immersion and 7-day head-down tilt) caused a decrease in the activity of malate (MDH) and isocitrate dehydrogenase (ICDH), and creatine phosphokinase dehydrogenase (ICDH), and creatine phosphokinase (CPK) at the expense of its MM isoform whereas the activity of alanine (ALT) and aspartate aminotransferase (AST) and pattern of distribution of MDH isoforms remained unchanged. Exposure to acceleration of +3 Gz before and after simulated weightlessness revealed similar changes in the activity of MDH, ICDH, ALT, AST and MDH cytoplasmic fractions. However, the higher increase in the enzyme activity after simulated weightlessness may give evidence for a greater change in cell membrane permeability during acceleration effects that followed simulated weightlessness.

Bed Rest↗
PubMed1997

Effects of Chinese herb medicine on improving the circulation of rabbits under simulated weightlessness.

In order to find out the effects of Chinese herb medicine on improving the functional state of blood circulation under weightlessness (WL) or simulated weightlessness (SWL), five experiments (building the SWL animal model and determining the treatment based on the differentiation of symptoms and signs, selecting herb medicine, determining the dosage of Chinese herb medicine, pharmacological text and toxicological experiment of (DH) were accomplished. Two kinds of Chinese herb medicine(CQ and DH) having the effects of improving the circulatory conditions of rabbits in SWL were selected. SWL animal model, space blood stasis and mechanism and effects of Chinese herb medicine were discussed.

Animals↗
PubMed1999

[Changes in lumen diameters of vessels in arteriolar network in rat soleus muscle after simulated weightlessness].

Objective. To elucidate whether simulated weightlessness can induce changes in lumen diameters of vessels in arteriolar networks in hindlimb muscles and whether these changes are reversible. Method. Changes in lumen diameters of the vessels in the arteriolar network in soleus muscle of 4 wk tail-suspended (SUS-4), 1 wk (REC-1) and 5 wk (REC-5) recovered rats were examined and compared with that of control (CON) rats by use of the method of intra-arterial infusion of a carbon suspension. Result. The lumen diameters of the feeding arteries and arcade arterioles, and the transverse arterioles of the order of both V and II in the SUS-4 group were reduced by 31%, 29%, 28%, and 41%, respectively, as compared with that of the CON group (P<0.01). The diameters of these arterioles in REC-1 group were partially restored but remained significantly less than that of the CON group (P<0.05, or P<0.01). In REC-5 group, except for the transverse arterioles of order II, the diameters of all the other arterioles were fully recovered. Conclusion. These findings indicate that a 4 wk simulated weightlessness might induce atrophic changes in the arterioles of the hindlimb muscles. It also suggests that structural changes in arteriolar network might be an important mechanism accounting for postflight orthostatic intolerance.

Animals↗