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PubMed2000

[Effects of different training methods on cardiovascular autonomic regulation during bedrest].

Objective. To investigate the effects of different training methods on cardiovascular autonomic regulation under bedrest. Method. 15 healthy male volunteers aged 19-22 participated tests in head-down tilt (HDT) -6 degrees bedrest in order to observe the changes of cardiovascular system under simulated weightlessness. They were divided into control (5 men), hypoxia training (5 men) and Fangsong training (5 men) groups. 24 h dynamic ECG were recorded on the 2nd day of pre-bedrest, on the 3rd, 14th and 18th day of bedrest and on the 7th day of the post- bedrest. All spectra were estimated from entire 24 h HRV, before, during and after Fangsong and hypoxia training by autoregressive (AR) modeling method. Normalized low-frequency (LF%) was a quantitative marker of cardiac sympathetic activity, normalized high-frequency (HF%) reflected the changes in cardiac vagal activity, and LF/HF was considered to be related to sympathovagal balance or sympathetic activity. Result. In control group, LF% and HF% were all significantly reduced (P<0.05), LF/HL showed no significant changed during bedrest. In Fangsong group, HF% increased markedly (P< 0.05), while in hypoxia group, LF% increased markedly (P< 0.05). Conclusion. Fangsong training counteracted markedly the reduction in vagal activity, while hypoxia training counteracted markedly the decrease in sympathetic activity. It was possible that HRV indices could be used to evaluate the efficiency of countermeasures counteracting the adverse effects of weightlessness.

Adaptation, Physiological↗
PubMed2000

[Effects of intermittent +45 degrees head-up-tilt on mechanical parameters of femoral (correction of femural) bone in tail-suspended rats].

Objective. To study the effects of different intermittent +45 degrees head-up-tilt (IHUT) on tail-suspended rats. Method. 28 male SD rats were randomly and equally divided into: control group (C), tail-suspended group (S), IHUT 2 h group (H2), and IHUT 4 h group (H4). On the basis of tail-suspension to simulate weightlessness, H rats were given 2 h or 4 h IHUT each day. The effects of 3 wk IHUT on tail-suspended rats were evaluated by measuring physical and mechanical parameters of the femur. Result. Femoral mass (fresh, dry and ash), diameter, and density (fresh, except H2 group) in S, H2 and H4 rats were declined significantly compared to C rats (P<0.01 or P<0.05). Diameter (P<0.05) and density of femur (P<0.01) in H2 rats were significantly improved compared to S rats. Compared to C rats, the strength and stiffness of femora were obviously weakened (P<0.01) in S rats. Elastic load in H2 rats improved markedly (P<0.05) than those in S group; in H4 group, elastic load, maximum load, and bending toughness coefficient improved significantly (P< 0.01 or P<0.05). Conclusion. Using IHUT, mechanical parameters of weight bearing bones of tail-suspended rats can be improved apparently, by extending the exposure time, mechanical parameters can be improved.

Animals↗
PubMed2002

Effect of lower body negative pressure against orthostatic intolerance induced by 21 days head-down tilt bed rest.

BACKGROUND: Exposure to actual or simulated weightlessness is known to induce orthostatic intolerance in humans. Many different methods have been suggested to counteract orthostatic hypotension. The repetitive or prolonged application of lower body negative pressure (LBNP) has shown beneficial effects to counter orthostatic intolerance, but devoting so much time to countermeasures is not compatible with space mission objectives or costs. The purpose of the present study was to assess the effects of brief LBNP sessions against orthostatic intolerance during a 21-d head-down tilt (HDT) bed rest. METHODS: There were 12 healthy male volunteers who were exposed to -6 degrees HDT bed rest for 21 d. Six subjects received -30 mm Hg LBNP sessions for 1 h x d(-1) from day 15 to day 21 of the HDT, and six others served as control. Orthostatic tolerance was assessed by means of standard tilt test. RESULTS: Before HDT, all the subjects in the two groups completed the tilt tests. After 21 d of HDT, five subjects of the control group and one subject of the LBNP group could not complete the tilt test due to presyncopal or syncopal symptoms. The mean upright time in the control group 13.0 +/- 4.0 min) was significantly shorter (p < 0.05) than that in the LBNP group (19.0 +/- 2.2 min). Body weight decreased significantly in the control group during HDT, while increasing significantly on day 21 of HDT in the LBNP group. Urine volume increased on days 15-21 of HDT in the control group, but remained unchanged throughout HDT in the LBNP group. A significant decrease in cardiac output and cardiac index, and a significant increase in total peripheral resistance, pre-ejection period, plasma renin activity, aldosterone, and prostaglandin 12 were observed during HDT in both groups. There were no significant differences in these parameters between the two groups. CONCLUSIONS: Brief daily LBNP sessions were effective in preventing orthostatic intolerance induced by 21 d HDT bed rest. However, it did not improve cardiac pump and systolic functions and did not preserve volume regulating hormones.

Adult↗
PubMed2000

[Hemodynamic changes of pulmonary circulation during HDT -30 degrees].

OBJECTIVE: To study the hemodynamic changes of pulmonary circulation during simulated weightlessness. METHOD: 12 subjects were studied using echocardiography and electrocardiography during head-down tilt (HDT) of -30 degrees lasting for 45 min. RESULT: Right ventricular ejection time increased significantly (P<0.05); peak velocity of pulmonary arterial blood flow decreased significantly (P<0.05); acceleration time of pulmonary arterial blood flow did not change significantly; significant decrease of right ventricular output occurred at the 10th minute and the 30th minute (P<0.05); pre-ejection period significantly decreased at the 30th minute and recovery. Heart rate, mean velocity of pulmonary arterial blood flow, and acceleration of pulmonary arterial blood flow did not change significantly; left ventricular cardiac output, stroke volume and blood pressure remained constant throughout the experiment. CONCLUSION: Changes of the parameters of pulmonary circulation suggested that pulmonary resistance increased, and the increase of pulmonary resistance maybe be the direct cause of the increase of pulmonary arterial pressure.

Adult↗
PubMed2002

[Changes of serum alkaline phosphatase and electrolytes during 21 d head down bed-rest].

Objective. To investigate the effect of simulated weightlessness on serum alkaline phosphatase (ALP), calcium, magnesium, chlorine and phosphorus. Method. 6 healthy males, aged 24.8 +/- 6.1, were exposed to -6 degrees HDT bed rest for 21 d. Activity of serum alkaline phosphatase, serum contents of calcium (Ca), magnesium (Mg), chlorine (Cl) and phosphorus (P) ions were assayed before HDT (d-3), on the 3rd, 10th and 21st day during HDT and after HDT (d+2). Ca was measured by methyl thymol blue method, P was determined with ultraviolet spectrophotography, determination of Mg and Cl were made with enzyme method, ALP was examined with 4-nitrobenzene phosphate method. Result. Serum Ca2+ levels were significantly higher at d10, d2l and d+2 than the value of d-3 (P<0.01). P3+ levels declined significantly on d2l as compared with d-3 (P<0.01). During the HDT and after HDT, Mg2+ declined to a level below that before HDT (P<0.05 or P<0.01). Cl- were significantly higher at d2l and d+2 than the value of d-3 (P<0.01). ALP level was higher on d2l than on d-3 (P<0.01). Conclusion. 21 d HDT induced increase of Ca, Cl, ALP, and decline of Mg and P. The changes may reflect the imbalance of metabolism.

Adult↗
PubMed1999

[Differentiated remodeling changes of medium-sized arteries from different body parts in tail-suspended rats and their reversibility].

Objective. The aim of the present study was to test whether medium-sized arteries in different body parts are differentially directed to achieve stimulus-specific remodeling to adapt local hemodynamic changes induced by tail-suspension, and to examine whether these structural changes are reversible. Method. Morphological changes of femoral, anterior tibial, common carotid, and basilar arteries from 4 wk tail-suspended (SUS-4), 1 wk recovered (REC-1), and control (CON) rats were studied using van Gieson-Orcein staining method. Result. For the hindquarter arteries, like the femoral and anterior tibial arteries, the lumen diameter (d) and medial tissue area (A) of SUS-4 group were significantly decreased (P<0.05, P<0.01) as compared with that of CON group, and that of REC-1 group were not fully recovered though the differences were not significant. With respect to arteries in the neck region and the brain, the remodeling changes were just in an opposite direction. In SUS-4 group, the d and A of both common carotid and basilar arteries were significantly increased (P<0.05, P<0.01) as compared with that of CON, and not fully restored after 1 wk recovery. Conclusion. The structures of medium-sized arteries in different body parts remodel differentially in response to local hemodynamic changes during simulated weightlessness and these changes were reversible.

Adaptation, Physiological↗
PubMed2002

[Effects of Qiang Gu Kang Wei compound on hemorheology in tail-suspended rats].

Objective. To investigate the effects of Qiang Gu Kang Wei compound on hemorheology in tail-suspended rats. Method. Rats were tail-suspended (-30 degrees) for 21 d to simulate weightlessness. The effect of the compound on erythrocyte sedimentation rate (ESR), hematocrit value (HCT), plasma fibrinogen content (PFC), blood viscosity, red blood cells deformability and erythrocytes aggregation were examined. Result. PFC, whole blood reducing viscosity (eta h), whole blood viscosity (eta b), erythrocyte rigid index (IR) and maximum aggregation index (MAXD) increased significantly (P<0.01 or P<0.05 ) and maximum deformity index (DImax) (P<0.01) decreased significantly in suspended rats as compared with the normal control. Different doses of the compound showed different effects. The small dose group (10 g/kg) inhabited eta h and eta b (P<0.01 or P<0.05) of all shear rates, abnormal IR and MAXD (P<0.01); The middle dose group (20 g/kg) decreased PFC (P<0.01); The big dose group (30 g/kg) inhabited eta h and eta b (P<0.01 or P<0.05) of high shear rates, decreased IR (P<0.01), and improved DImax (P<0.01). Conclusion. This compound could improve hemorheology in tail-suspended rats. But there was no concentration-dependence.

Animals↗
PubMed2001

Effects of long-duration bed rest on structural compartments of m. soleus in man.

Magnetic resonance imaging (MRI), histomorphometry and electron microscopy of muscle demonstrate that long-term exposure to actual or simulated weightlessness (including head down bed rest) leads to decreased volume of antigravity muscles in mammals. In muscles interbundle space is occupied by the connective tissue. Rat studies show that hindlimb unloading induces muscle fiber atrophy along with increase in muscle non-fiber connective tissue compartment. Beside that, usually 20% of the muscle fiber volume is comprised by non-contractile (non-myofibrillar) compartment. The aim of the present study was to compare changes in muscle volume, and in muscle fiber size with alterations in myofibrillar apparatus, and in connective tissue compartment in human m. soleus under conditions of 120 day long head down bed rest (HDBR).

Adult↗
PubMed2000

Vasoconstrictor responsiveness of hind body vascular beds is diminished in tail-suspended rats.

It is well known that the mechanisms of occurrence of orthostatic intolerance induced by exposure to microgravity deal with multiple factors including alterations of arteries. In the previous works, the diminished contractile responsiveness of abdominal aorta and hind body medium-sized conduit arteries, mesenteric artery and femoral artery, were observed in tail-suspended rats, and the data showed that the femoral artery have subjected to the greatest changes. These results suggested that the vasoreactivity of resistance vessels might be affected by the real or simulated microgravity. Since the arterioles are the main site of peripheral resistance and of its regulation. Therefore, changes in responsiveness of arteriolar network, especially in the lower/hind body region, would be of primary importance in the genesis of postflight orthostatic intolerance. The aim of the present work was to examine whether simulated weightlessness may lead to an impairment in vasoconstrictor responsiveness in hind body vascular beds.

Animals↗
PubMed2003

[Changes of osteocalcin in bone and bone marrow in tail suspended rats].

OBJECTIVE: To study osteocalcin [correction of osteocakin] (OC) changes in bone and marrow and calcium deposition in bone and cartilage under simulated weightlessness. METHOD: Twenty SD rats were randomly divided into 14 d and 28 d tail suspension group and 2 corresponding control groups. Histological samples were in situ hybridized and trichrome stained. RESULT: OC expression of bone and marrow of rats were lower in tail suspended rats than that in the control (P<0.05). OC expression in 14 d tail suspended rats were higher than that in 28 d tail suspended group (P<0.05). Mineralization was inhibited, and demineralization of femur [correction of furmer] and cartilage mineralized matrix was prominent. Demineralization was more prominent in 28 d group. CONCLUSION: OC levels in bone and marrow of rats were lower after tail suspension. Calcium deposition was inhibited in bone and cartilage. Demineralization was prominent after long term hindlimb unloading.

Animals↗
PubMed2004

[Effects of Chinese herb compound on myocardial SDH, ATP-ase and energy reserves in tail-suspended rats].

OBJECTIVE: To investigate effects of Chinese herb compound on myocardial SDH, ATP-ase and energy reserves in tail-suspended rats. METHOD: Male SD rats were randomly divided into three groups (n=10 each): (A) normal control group; (B) tail-suspended group; (C) tail-suspended + Chinese Medical herb compound group. Rats in group B and C were tail-suspended (-30 degrees) for 5 d to simulate weightlessness. All rats B were decapitated after the experiment. Myocardial SDH (method of Anderson N-BT), ATP-ase (method of Wachstein and Meisel) and energy reserves (method of HPLC) were examined. RESULT: Compared with rats in groups A and C, SDH activity increased, SDH staining deepened, value of OD SDH enhanced, ATP-ase activity and OD value increased and enhanced significantly (P<0.01) but value of myocardial energy reserves decreased in group B rats. CONCLUSION: Tail-suspension strengthens compensatory oxidation metabolism of cardiac muscle and activates SDH and ATP-ase, at the same time decrease, myocardial energy reserves. Normal are maintained the low level of metabolism by the medical herb compound used which shows a protecting effects through mitigation, tranguilization and replenishment of Qi.

Adenosine Triphosphatases↗
PubMed2004

Vascular endothelial growth factor inhibits programmed cell death of endothelial cells induced by clinorotation.

The principal aim of this study was to investigate short- and long-term effects of clinorotation on human endothelial cells (EA hy 926 cell line) using a three-dimensional random positioning machine. Moreover, the impact of vascular endothelial growth factor (VEGF) was addressed. Immediately, within one hour and after four and twenty-four hours an increase of apoptotic cells was detected. VEGF significantly inhibited the amount of apoptotic endothelial cells (EC). VEGF reduced the amount of fas-positive EC. Moreover, after 24 hours, proliferating EC grew in form of three-dimensional multicellular spheroids and also as monolayers. The initially formed spheroids (maximum diameter 3 mm) remained stable up to the 15th day of clinorotation. Some spheroids revealed tubular structures. In addition, a clear increase of extracellular matrix proteins such as osteopontin and fibronectin was measured. The three-dimensional clinostat represents an important tool for cell biological experiments. VEGF significantly attenuated the changes of endothelial cells induced by simulated weightlessness in a cell protective manner.

Apoptosis↗
PubMed1995

Effects of 28-day head-down tilt with and without countermeasures on lower body negative pressure responses.

This study was performed to determine the effects of 28 d of head-down tilt (HDT) (simulated weightlessness) on cardiovascular responses to orthostatic stress induced by lower body negative pressure (LBNP) (before, during, and after HDT) and +60 degrees head-up tilt (before and after HDT) in 12 subjects. Half of them underwent countermeasures (CM) of regular muscular exercise (isometric and isokinetic training) and LBNP sessions (-30 mm Hg) as generally performed during spaceflight; the other six were a control group (C). The countermeasure effect on the orthostatic responses to LBNP and tilt test was assessed by studying the changes after HDT in the two groups. Essentially, blood pressure was better maintained in group CM in the tilt test after HDT (MBP at the end of the tilt vs. baseline value: +16% (CM); -19% (C)). LBNP and muscular exercise may have contributed to this improvement. One of the probable contributing factors is the relative conservation of plasma volume, at the end of HDT, in group CM (-2.2%), compared to group C (-11.2%). Transcranial Doppler (TCD) recordings of middle cerebral artery (MCA) velocities permitted indirect evaluation of cerebral blood flow changes during the orthostatic tests. MCA velocities decreased significantly although slightly (-7 to -12%) during LBNP sessions without changes along the HDT showing that the cerebral circulation was well preserved in each group. On the other hand, subjects undergoing presyncopal symptoms presented a drop in MCA velocities, suggesting a decrease in cerebral blood flow.

Adult↗
PubMed1996

Effects of head down tilt on hemodynamics, fluid volumes, and plasma Na-K pump inhibitor in rats.

BACKGROUND: Hindquarter suspension in rats has been used as a model of simulated weightlessness (SW) for ground based study of the effects of microgravity on the cardiovascular system (CVS). METHODS: Using this rat model of SW we tested the hypothesis that CVS deconditioning following spaceflight results, in part, from a decrease in the circulating concentration of sodium-potassium pump inhibitor (SPI). Control rats similarly prepared were not suspended. RESULTS: During the first hour of suspension, central venous pressure (CVP), blood pressure (BP), heart rate (HR), cardiac output (CO), plasma volume (PV), extracellular fluid volume (ECFV), urine output (UV), atrial natriuretic peptide (ANP), and the plasma level of SPI increased. Plasma renin activity (PRA) and myocardial Na+, K(+)-ATPase activity (NKA) decreased. By the end of 4 h of SW, the changes in CVP, BP, HR, ECFV, and UV persisted, but PV, plasma ANP and SPI, and myocardial NKA activity returned to control levels. By the end of 1 d of SW, ECFV and plasma SPI levels had decreased but the myocardial NKA had not increased. At day 4, CVP and BP were the same as in control sham treated rats. Plasma SPI levels were decreased at day 4 but the myocardial NKA was not different, whereas renal NKA was increased. At day 7, myocardial NKA and renal NKA were increased and vascular smooth muscle cell (VSMC) membrane potentials were hyperpolarized. CONCLUSIONS: These data indicate that prolonged SW causes a decrease in plasma SPI level which, by hyperpolarizing VSMC, may play a role in the CVS deconditioning seen in astronauts following spaceflight.

Animals↗
PubMed1998

[Problem of orthostatic intolerance in astronauts and perspectives for its pharmacological prevention].

Double-blind placebo-controlled method was applied to study venoconstrictor agent Dihydroergotamine effects on orthostatic tolerance in 8 healthy male-volunteers after 6-hour exposure to antiorthostatic stress (-6 degrees). The drug was able to induce blood centralization and diuresis additional to those caused by the simulated microgravity per se and failed to prevent the orthostatic intolerance. In 6 subjects the studies were repeated with the occlusive cuffs used in order to prevent venous blood return from the vascular bed of the lower limbs during 0-gravity simulation. The occlusive cuffs were shown to eliminate the additional drug-induced blood centralization and diuresis. Orthostatic tolerance in this case occurred to be less affected than in the case of no countermeasure used or in the case when dihydroergotamine was used alone. Thus, it was shown that mechanical prevention of the drug-induced blood centralization from being realized in 0-gravity simulation must be considered as the requirement necessary to permit the drug to perform its beneficial effect on the orthostatic tolerance after the real or simulated weightlessness.

Adult↗
PubMed2006

Effects of altered gravity on the actin and microtubule cytoskeleton of human SH-SY5Y neuroblastoma cells.

Human SH-SY5Y neuroblastoma cells were used to study the effects of altered gravity on the actin and microtubule cytoskeleton dynamics. A cholinergic stimulation of the cells during a 6 min period of changing gravity (3 parabolas) resulted in an enhanced actin-driven protrusion of evoked lamellipodia. Likewise, the spontaneous protrusive activity of nonactivated cells was promoted during exposure to changing gravity (6 up to 31 parabolas). Ground-based experiments revealed a similar enhancement of the spontaneous and evoked lamellar protrusive activity when the cells were kept at 2 g hypergravity for at least 6 min. This gravity response was independent of the direction of the acceleration vector in respect to the cells. Exposure of the cells to "simulated weightlessness" (clinorotation) had no obvious influence on this type of lamellar actin cytoskeleton dynamics. A 20 min exposure of the cells to simulated weightlessness or to changing gravity (6 to 31 parabolas) - but not to 2 g (hypergravity, centrifugation) - resulted in an altered arrangement of microtubules indicated by bending, turning, and loop formation. A similar altered arrangement was shown by microtubules which had polymerized into lamellipodia after release from a taxol block at simulated weightlessness (clinorotation) or during changing gravity (5 parabolas). Our data suggest that in human SH-SY5Y neuroblastoma cells, microgravity affects the dynamics and spatial arrangement of microtubules but has no influence on the Rac-controlled lamellar actin cytoskeleton dynamics and cell spreading. The latter, however, seems to be promoted at hypergravity.

Acetylcholine↗
PubMed2004

[Influence of 100 Hz sinusoidal vibration on muscle spindle afferents of soleus muscles in suspended situation rat].

OBJECTIVE: To study influence of 100 Hz sinusoidal vibration on muscle spindle afferents discharges of rat soleus muscles in simulated-weightlessness situation. METHOD: The tail-suspended rat model was used to simulate weightlessness, and 100 Hz sinusoidal vibration was performed by a vibrator. Unit activity was recorded electrophysiologically from the centrally cut filaments of the spinal dorsal roots innervating muscle spindles of the rat soleus muscle; then observation on the changes in afferent discharges from muscle spindle in a rat soleus muscles were made after 7 d. RESULT: 1) Compared with control muscle spindle afferents discharges of rat soleus muscles decreased after 7 d tail-suspension (P<0.05). 2) Compared with suspension the afferent discharges from soleus muscle spindles increased after 7 d tail-suspension with 100 Hz sinusoidal vibration. CONCLUSION: Sinusoidal vibration (100 Hz; 300 micrometers) can selectively activate muscle spindles. Muscle spindle afferent input of the suspended rats increased after the application of 7 d 100 Hz sinusoidal vibration.

Afferent Pathways↗
PubMed2003

[Effects of spirulina on serum lipids, erythrocyte membrane fluidity and vascular endothelial cells in tail-suspended rats].

OBJECTIVE: To study the changes of erythrocyte membrane fluidity, serum lipid and vascular endothelial cell caused by simulated weightlessness in rats and the beneficial effect of spirulina. METHOD: Thirty male SD rats were divided into 3 groups: free control group (group A) and two simulated weightlessness groups (groups B, C). Rats in group A and B were fed with normal forage, and the rats in group C were fed with normal forage supplemented with 5% (W/W) spirulina. Water was taken ad libitum. RESULT: Levels of serum CHO, HDL, TG, HDL-C/CHO and erythrocyte membrane fluidity decreased significantly, and number of vascular endothelial cells in plasma increased markedly in group B as compared with those in group A; The ratio of LDL-C/HDL-C, and atherosclerosis index (AI) decreased, number of vascular endothelial cells significantly lowered; level of CHO, HDL-C and value of the IDmax of plasma as well as erythrocyte membrane fluidity remarkedly increased in group C compared with those in group B. CONCLUSION: Spirulina can improve the physiological conditions of erythrocyte membrane fluidity, serum lipid and vascular endothelial cell caused by simulated weightlessness in rats.

Animals↗