Effect of thigh cuffs on haemodynamic changes of the middle cerebral artery and on orthostatic intolerance induced by 10 days head-down bed rest.

Thigh cuffs are used by cosmonauts to limit fluid shift during space flight, but the appropriate level of cuff pressure and the duration of application to optimize their beneficial effects require further detailed investigations. In the present study, 10 days head-down tilt (HDT) bed rest was performed to assess the effects of thigh cuffs (40 mmHg, 10 h/day) on haemodynamic changes of the middle cerebral artery (MCA) and on orthostatic tolerance in six healthy male volunteers. Another six healthy male volunteers without thigh cuffs served as the control group. Haemodynamic parameters of the MCA were measured using transcranial Doppler. Orthostatic tolerance was assessed before and after HDT. After HDT, the mean upright time in the control and thigh cuff groups was 14.0 +/- 4.1 and 19.2 +/- 0.7 min, respectively. Compared with values before HDT, the percentage increase in heart rate from baseline in the upright position after HDT was significantly higher in the control group and the percentage change from baseline of mean diastolic arterial blood decreased more after HDT in this group. In the control group, systolic blood velocity (Vs) and mean blood velocity (Vm) of the right MCA decreased significantly during HDT. In the thigh cuffs group, the Vs of the right MCA decreased significantly on Days 3 and 7 of HDT and the Vm of the right MCA decreased significantly on Day 7 of HDT. The results indicate that daily use of thigh cuffs during 10 days of HDT does not completely prevent the decrease in haemodynamics of the right MCA, but is effective in preventing orthostatic intolerance.

[Repeated body position change training can improve human head-down tilt tolerance].

AIM: To verify the hypothesis that repeated body position change training can improve human head-down tilt (HDT) tolerance. METHODS: Six young healthy subjects were trained with repeated position change for 9 times and 11 days according to protocol of alternative head-down and head-up tilts, each time of training lasted for about 35 min. Their HDT tolerance (- 30 degrees/30 min) were determined before and after training. RESULTS: (1) Compared with the data before training, subjects' symptom scores during HDT test after training decreased significantly (6.00 +/- 3.79 vs 1.00 +/- 0.63, P < 0.05), magnitude of the decreased heart rate increased significantly (-0.6 +/- 2.5 vs -4.4 +/- 3.6, P < 0.01). (2) Before training, blood flow volume of internal jugular vein (IJV) during HDT decreased significantly and that of internal carotid artery (ICA) increased significantly at the beginning period of HDT compared with pre-HDT (P < 0.01), while blood flow volume of the common carotid artery (CCA) presented increasing trend. After training, there was no significant difference in blood flow volume of IJV between during HDT and pre-HDT, that of ICA and CCA presented decreasing trend in the final period of HDT compared with Pre-HDT. CONCLUSION: Repeated body position change training can improve human head-down tilt tolerance. And its main causation is that headward shift of blood volume is restrained to some extend during HDT after training.

Compliance changes in femoral veins of rabbits after 21 days of simulated weightlessness.

Increased venous compliance in lower limbs may be contributed to postflight orthostatic intolerance; however, direct animal studies to address the changes of venous compliance to microgravity have been rare. The purpose of this study was to determine compliance changes in femoral veins of rabbits after 21 days of head-down rest. Head-down rest -20 dgrees rabbit model was used to simulate weightlessness. 24 healthy male New Zealand Rabbits were randomly divided into 21 days of head-down rest group (HDR), horizontal immobilization group (HIG) and Ctrl group (Ctrl), with 8 in each. We constructed pressure-volume relationships from femoral veins in vivo for all groups after simulation by changing the venous internal volume and measuring the corresponding pressure. Microstructure of femoral vein wall in 3 groups was observed. Compared among the groups, the corresponding intravenous pressure of Ctrl was the highest when intravenous volume was expanded and HDR was the lowest. The parameter 3 , and P 2 in quadratic equations of femoral venous P-V relationship of HDR group were significantly higher than these values of HIG group and Ctrl group. The structure of femoral vein wall of HDR rabbits changed significantly, outlines of some endothelium cells (EC) became short and columnar or cubic, some of EC fell off and smooth muscle layer became thinner. These results indicate that, the femoral venous compliance increased after weightlessness simulation. This may partially underlie the mechanism of orthostatic hypotension seen in astronauts during an orthostatic stress after exposure to microgravity.

[Dynamic responses of human body and human surrogate to different impacts under 30 degrees supine position].

OBJECTIVE: To study the difference between the dynamic responses of human body and human surrogate under 30 degrees supine position, and to discuss impact probability of substituting human body with human surrogate in impact tests. METHOD: Five volunteers experienced half-sine impact pulses, averaged 4.76, 8.96, 11.33 G, lasting for 40-60 ms on an impact tower. The human surrogate was exposed to half-sine impact pulses, averaged 6.77, 10.39, 16.93, 21.11, 24.98, 31.11 G, lasting for 40-60 ms, two times for each G level. ECG changes of the volunteers were continuously monitored before, during and after each impact. RESULT: Output responses at forehead and chest of human body and human surrogate increased with input increments. But there was obvious difference of the dynamic responses between human body and the surrogate to impact of low G levels. Heart rate of each volunteer had temporary increase during the process of impact, and returned to normal level soon after the impact. CONCLUSION: There is difference in a certain extend between the dynamic responses of human body and human surrogate. The ECG changes are induced mainly by mental stress during process of impact.

Effect of lower-body negative pressure on cerebral blood flow velocity during 21 days head-down tilt bed rest.

BACKGROUND: The purpose of this study was to investigate cerebral blood flow (CBF) velocity in humans during 21 days of head-down tilt (HDT) bed rest with and without lower-body negative pressure (LBNP). MATERIAL/METHODS: Twelve healthy male volunteers were exposed to -6 degrees HDT bed rest for 21 days. Six subjects received -30 mmHg LBNP sessions for 1 h per day from the 1st to the 7th day and from the 15th to the 21st day of HDT, and six others served as controls. CBF velocity was measured by use of the transcranial Doppler technique in the right middle cerebral artery before and during HDT. RESULTS: In the control group, mean and systolic CBF velocities decreased on day 1 of HDT compared with the pre-HDT value, and dropped further on day 3 of HDT, then remained significantly below the pre-HDT baseline on days 7 and 10 of HDT, and reached a minimum value on day 21 of HDT. In the LBNP group, mean and systolic CBF velocities decreased significantly on day 1 of HDT compared with the pre-HDT value, and remained lowered throughout HDT. Diastolic CBF showed no significant change throughout HDT in both groups. There were no significant differences in these parameters between the two groups. CONCLUSIONS: The results of this study suggest that CBF velocity is reduced during 21 days of HDT, and brief daily LBNP sessions used in the first and last weeks of 21-day HDT bed rest does not improve CBF velocity.

[Changes of ERK1/2 in femoral arteries of tail-suspended rats and their effects on contractility].

OBJECTIVE: To study changes of extracellular signal-regulated kinase 1 and 2 (ERK1/2) in femoral arteries of tail-suspended rats and their effects on contractility. METHOD: Microgravity was simulated by elevating the hindquarters of Wistar rats to produce hindlimb unweighting (HU). In the absence or presence of prazosin and PD98059 respectively, isometric tension of vessel rings from femoral arteries in response to norepinephrine (NE) was determined by in vitro perfusion technique; Basal total ERK1/2 level and phosphorylated ERK1/2 level stimulated by norepinephrine in the absence or presence of prazosin and PD98059 respectively were detected by Western blotting-enhanced chemically lightening system. RESULT: The maximal contractile response to NE was significantly lower in femoral arterial rings from 14 day-HU rats as compared with those in control rats. PD98059 caused a marked inhibition of NE-induced maximum contractile response in both control and HU femoral arterial rings. Moreover, the effect of inhibition was more significant in control rats than that in HU rats. Prazosin caused a right shift of the concentration-response curves (CRCs) to NE in both control and HU rats, but no difference was found between the two groups for the PA2 of prazosin calculated by Schild analysis, which showed that the sensitivity of alpha1 adrenoceptor was not changed by HU. After 7d-recovery, the difference of contractile response of femoral arterial rings to NE between recovered group and control group was nonsignificant. Data from Western blotting showed that basal total ERK1/2 levels were elevated in femoral arterial rings from 14d-HU rats as compared with those in control rats, but the levels of basal and NE-stimulated phosphorylated ERK1/2 were higher in control as compared with HU rats. After 7d recovery, the basal total ERK1/2 level and phosphorylated ERK1/2 level were not different from control. CONCLUSION: Microgravity simulated by 14d-HU can induce abnormality of MAPK/ERK pathway, which may contribute to declined contractile response of femoral vessel rings to NE.

[Role of ROK in contraction of rat femoral arteries after 14 d tail suspension].

OBJECTIVE: To determine the role of Rho associated kinase (ROK) in contraction of rat femoral arteries after 14 d tail suspension. METHOD: Male Wistar rats were randomly divided into control group (CON) and 14 d -30 degrees tail suspension group (TS14d). Analysis was performed on the contractile responses of perfused femoral arterial rings from both TS14d and CON rats to KCl, phenylephrine (PE), and U-46619 in the presence of Y-27632. RESULT: Arterial rings from TS14d rats displayed a reduced contractile response to KCl and PE but not significantly to U-46619. In the response to KCl, Y-27632 caused a concentration-dependent relaxation and significantly larger decrease of contraction in tissues from TS14d rats. Y27632 nearly abolished the tonic component of KCl-induced contraction when its dose was increased from 10(-6)mol/L to 10(-5) mol/L. It had also an inhibitive effect on the PE and U-46619-induced contraction and caused significantly larger decrease in U-46619 but not in KCl or PE induced contraction in tissues from TS14d rats. CONCLUSION: ROK activity may be enhanced and play a compensational role in rat femoral arteries after TS14d.

[Changes of reactivity of rabbit femoral venous rings after 21 d simulated weightlessness].

OBJECTIVE: To study the effects of simulated weightlessness on reactivity of leg veins. METHOD: Vascular bathing technique was used to measure the contractile responses of rabbit femoral venous rings to Ht, PE and KCl, and the dilatory responses to ACh and SNP after horizontal confinement or head-down tilt confinement for 21 d. RESULT: After simulated weightlessness for 21 d, the contractile response of rabbit femoral venous rings to higher concentrations of PE and KCl decreased significantly (P<0.05); the contractile response to Ht also decreased, but not significantly (P>0.05); the dilatory responses to ACh and SNP did not change significantly in both groups. CONCLUSION: Contractile response of rabbit femoral vein decreased after simulated weightlessness for 21 d, which might partly explain the occurrence of orthostatic intolerance in men after space flight.

Effect of lower body negative pressure on orthostatic tolerance and cardiac function during 21 days head-down tilt bed rest.

The purpose of the present study was to investigate the changes of orthostatic tolerance and cardiac function during 21 d head-down tilt (HDT) bed rest and effect of lower body negative pressure in the first and the last week in humans. Twelve healthy male volunteers were exposed to -6 degrees HDT bed rest for 21 d. Six subjects received -30 mmHg LBNP sessions for 1 h per day from the 1st to the 7th day and from the 15th to the 21st day of the HDT, and six others served as control. Orthostatic tolerance was assessed by means of standard tilt test. Stroke volume (SV), cardiac output (CO), preejection period (PEP) and left ventricular ejection time (LVET) were measured before and during HDT. Before HDT, all the subjects in the two groups completed the tilt tests. After 10 d and 21 d of HDT, all the 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 (15.0 +/- 3.2 min) was significantly shorter than those in the LBNP group (19.7 +/- 0.9 min). SV and CO decreased significantly in the control group on days 3 and 10 of HDT, but remained unchanged throughout HDT in the LBNP group. A significant increase in PEP/LVET was observed on days 3 and 14 of HDT in both groups. The PEP/LVET in the LBNP group was significantly lower on day 3 of HDT, while LVET in the LBNP group was significantly higher on days 3, 7 and 14 of HDT than those in the control group. The results of this study suggest that brief daily LBNP sessions used in the first and the last weeks of 21 d HDT bed rest were effective in diminished the effect of head-down tilt on orthostatic tolerance, and LBNP might partially improve cardiac pumping function and cardiac systole function.

[Human-centered ergonomical study and applications in manned spacecraft project of China].

High G and weightlessness are two important environment factors that are unavoidable during spaceflight. They will bring key effects on astronauts' posture and working efficiency. In this paper, on the basis of experience of China first manned spacecraft project in the past 10 years, the concept of space ergonomics and its role in the project were reviewed. Ergonomic research items and corresponding methods were systematically analyzed with astronauts' working state, and ergonomic evaluation types and approaches were discussed with some given cases being used in the project. Finally, some suggestions were proposed on space man-machine system development according to recent ergonomic trend in space ergonomics and the basis of experience of first manned spacecraft project.

[Effects of simulated microgravity on cardiovascular function and counter effect of lower body negative pressure].

Studies on effect of simulated microgravity on cardiovascular function and counter effect of lower body negative pressure (LBNP) in recent years were summarized. The mechanism of simulated microgravity induced orthostatic intolerance may involve the reduction of cardiovascular function and cerebral blood flow, and endocrine changes. The significance of mathematical model in the study of mechanism of microgravity induced orthostatic intolerance was also discussed. The counter effect of LBNP was emphasized.

[Effects of 21 d -6 degrees bed rest on diastolic function of human left ventricle].

Objective. To investigate the effects of head down bed rest (HDBR), the simulated weightlessness, on the diastolic function of human left ventricle, and to discuss its role in cardiovascular deconditioning after space flight. Method. Six healthy young volunteers were subjected to -6 degrees HDBR for 21 d. Ultrasound Doppler technique was used to examine the changes of the diastolic function before, on the 10th, and 21st day during and 2nd day after HDBR. The orthostatic tolerance was also tested before and after HDBR. Result. Peak E-wave velocity (PEV) , peak A-wave velocity (PAV) , and velocity total integration of E-wave (VTI E), were significantly decreased (P<0.05) on the 10th and 21st day during and the 2nd day after HDBR, and velocity, total integration of A-wave (VTI A), ratio of E/A, and ratio of VTI E/A were also decreased, but did not reach the significant level (P>0.05). None of the six subjects passed the orthostatic tolerance test after HDBR. Conclusion. Simulated weightlessness can induce marked decline in diastolic function of human left ventricle.

[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.

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.

Effects of repeated brain ischemia induced by rapid lower body negative pressure on brain water and Na+,K+-ATPase activity in rats.

BACKGROUND: It has been demonstrated that during +Gz exposure cerebral blood flow is significantly reduced resulting in brain ischemia. Animal centrifuge models are commonly used to investigate the mechanisms of +Gz-induced loss of consciousness (G-LOC) and their pathophysiological effects on the brain. These dynamic models are limited because we currently are unable to obtain accurate measures of membrane ion flux or single cell electrophysiological responses from animals under centrifugation. HYPOTHESIS: The aim of the present study was to develop a non-centrifuge animal model of short-term, repeatable and complete brain ischemia using a rodent lower body negative pressure (LBNP), and to investigate the effects of repeated complete brain ischemia induced by LBNP on brain Na+,K+-ATPase activity, Na+, K+ and water contents in rats. METHODS: Eight anesthetized rats were exposed randomly to LBNP of -2.67 kPa, -4.00 kPa, and -5.33 kPa, respectively, at the rate of -0.67 kPa x s(-1). The pressure rapidly returned to control level when EEG became isoelectric (flat). The mean arterial BP (MAP), EEG and ECG were recorded. Twenty-one rats were divided randomly into control, single LBNP exposure, and three LBNP exposures groups (n = 7 in each group). Brain samples were analyzed for Na+,K+-ATPase activity, Na+, K+ and water contents 1 h after single and three 2-min LBNP exposures (-4.00 kPa at a rate of 0.67 kPa x s(-1)), respectively. RESULTS: MAP decreased rapidly during LBNP exposure. The mean time to isoelectric EEG was 41.33 +/- 11.48, 30.67 +/- 3.88 and 25.67 +/- 3.45 s during -2.67, -4.00 and -5.33 kPa LBNP, respectively. Heart rate (HR) significantly decreased when EEG became isoelectric. MAP, HR and EEG rapidly returned after releasing LBNP. The brain Na+,K-ATPase activity decreased significantly after single LBNP exposure and decreased further after three LBNP exposures. The brain K+, Na+ and water contents increased significantly after three LBNP exposures. CONCLUSIONS: A rat model of short-term, repeatable brain ischemia was developed using rapid LBNP. Three -4.00 kPa LBNP exposures (2 min each) cause a significant reduction in brain Na+,K+-ATPase activity and brain edema in rats.

[Review of influence of landing impact on human body (correction of boby) and its medical evaluation].

Landing impact is the dynamic factor that manned spaceship will inevitably meet after the mission has been completed, and impact force may cause damages to human tissues [correction of tissuses] and organs, even death. This paper described the characteristics of pathological and dynamic response of human body to landing impact, and discussed various related factors such as impact angle, fetters, design of cushion, harness and terrain condition. Medical evaluation of +Gx, +Gz, +/- Gy impacts were summarized.

[Probe into characteristics of Taraxacum mongolicum ultramicro-power].

OBJECTIVE: To observe and study the tissue characteristics of T. mongolicum ultramicro-power and dissolving-out characteristics of effective compositions. METHOD: By microscopic observation and thin-layer chromatography. RESULT: Nearly all cell walls of T. mongolicum are broken and dissolving-out characteristics of effective compositions are remarkably improved, after it is ultramicro-porphyrized.