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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.

Objective. To investigate the change of cerebral blood flow velocity during 4 d head-down tilt (HDT) bed rest in humans. Method. Eight healthy male volunteers were exposed to -6 degrees HDT bed rest for 4 d. Orthostatic tolerance was assessed by means of standard tilt test. Cerebral blood flow velocity in the right middle cerebral artery was measured by transcranial Doppler sonography before HDT (supine), on days 1, 3 and 4 of HDT and on day 2 post HDT. Result. After 4 d HDT, the frequency of orthostatic intolerance was significantly higher than those before HDT (P<0.05). The systolic, diastolic and mean blood velocities in the middle cerebral artery tended to decrease on days 1 and 3 of HDT, and decreased significantly on day 4 of HDT, compared with pre-HDT, and returned to basal levels on day 2 post HDT. The mean arterial blood pressure and diastolic blood pressure increased significantly, while the body weight decreased significantly during HDT. Conclusion. It is suggested that 4 d HDT may decrease cerebral blood flow velocity and increase the frequency of orthostatic intolerance. This decrease of cerebral blood flow velocity may be partially responsible for the increased risk of orthostatic intolerance.

Objective. To explore the effect of push-pull effect (PPE) simulated by lower body negative pressure (LBNP) rotating-table, and observe the physiological responses to push-pull maneuver. Method. A special LBNP rotating-table was used to simulate the push-pull maneuver. 8 healthy adults participated randomly in two experiments. One was simulated PPE test, which include a series of head-up stand (HUT, +1 Gz) for 1 min, then in head-down stand (HDT, -1 Gz) for 30 s and again in HUT combining LBNP (-50 mmHg) for 10 min. The other one was control test, which only consists of HUT combining LBNP (-50 mmHg) for 10 min. Changes of heart rate (HR), blood pressure (BP), basic impedance (Z0) , stroke output (SO) , cardiac output (CO) and total peripheral resistance (TPR) were monitored by electrical impedance instrument during the experiment. Result. During simulated PPE experiment, 3 subjects presented presyncopal symptoms, with average standing time of 8.99 +/- 1.47 min, while during control test, all the subjects completed HUT combining LBNP for 10 min. In simulated PPE experiment, as compared with HUT (control), HR, Z0 during HDT were significantly lowered, while SV and CO were increased significantly. During HUT + LBNP, HR, Z0 and TPR were significantly higher, while SV and CO were significantly lower than that of control and HDT. SBP was increased significantly than control value when "HUT + LBNP" started, but during the whole process of "HUT + LBNP ", it became significantly lowered. In control experiment, the above mentioned indexes showed the same trend of as change compared with the control, however, the percentage of the change was lower than simulated PPE test, the change percentage in HR was not including. Conclusion. After headstand, head-up stand combining LBNP caused cardiovascular function descends, the degree was larger than simple head-up stand combining LBNP. LBNP rotating-table can be used to simulated push-pull effect.

Objective: To investigate the change of human cerebral bottom arterial hemodynamics during 21 d simulated weightlessness., Method: 21 d -6 degrees head-down tilt bed rest (HDT) were used to simulate weightlessness. 6 healthy male, aged 24.8 +/- 6.1 served as subjects. Systolic blood velocity (Vs), diastolic blood velocity (Vd), mean blood velocity (Vm), pulsatility index (PI), resistance index (RI) and other indices of middle cerebral arteries (MCA), anterior cerebral artery (ACA) and posterior cerebral artery (PCA) were measured by transcranial ultrasound Doppler before HDT and on day 0 (D0), 1, 3, 7, 10, 21 of HDT. HUT +75 degrees 20 min orthostatic tolerance tests were done on day -1, 10, and 21 of HDT., Result: During HUT +75 degrees 20 min orthostatic tolerance test on day 10 and 21 of HDT, the average standing time were shorter than that of the pre-HDT values (P<0.05). On day 3 and 21 of HDT, Vs of right MCA reduced significantly than pre-HDT (P<0.05 or P<0.01). On day 1, 3, 7, 10 and 21 of HDT, Vs of right MCA were obviously lower than that on D0 (P<0.05 or P<0.01). Left MCA Vs on D0 increased significantly than that of pre-HDT (P<0.05), and both were significantly higher than those of the 3rd day of HDT (P<0.01). Right MCA Vm on the 3rd and 21st day of HDT were significantly lower than those pre-HDT and D0 (P<0.05 or P<0.01). On day 10 of HDT, Vm of right MCA were significantly reduced than that on D0 (P<0.05). Both MCA bilateral velocity difference (right Vm-left Vm) on the 3rd, 10th, 21st day of HDT, and MCA inter-hemispheric asymmetry index on the 10th, 21st day of HDT were significantly lower than that of pre-HDT (P<0.05 or P<0.01)., Conclusion: 21 d HDT bed-rest decreased orthostatic tolerance, Vs of both side MCA, and Vm of right MCA. Lower Vs of both side MCA and the inter-hemispheric asymmetry of MCA during HDT maybe responsible, in part, for the increased risk of orthostatic intolerance.

Objective. To accumulate data for further studies on the mechanisms of the decrease of cardiovascular function after weightlessness. Method. Cardiopulmonary circulatory function under supine position and head up tilting (HUT) for 20 min before and after exposure to 7 d 6 degrees head down tilt (HDT) in 6 healthy adults who aged 19-21 were measured with a XXH-2000 lesser (pulmonary) circulation and cardiac function instrument. Result. The 7 d HDT resulted in orthostatic intolerance of the subjects; the reduction of RVET (j-z) and the elevation of RPEP [RVET(Q-j)/(j - z)] indicated a decrease of the right heart function. An obvious decrease of the right heart reserves was also observed under HUT after HDT. Conclusion. hc and hc/hz were demonstrated to be useful parameters to evaluate orthostatic tolerance or to forecast orthostatic syncope. The lesser (pulmonary) circulation and cardiac function testing methods are valuable in evaluating the cardiopulmonary circulatory function during HUT.

To study the effects of -6 degrees head down tilt (HDT), upright posture and 24 h circadian rhythm on cerebral blood flow (CBF) velocity in humans, the CBF velocity was measured by use of transcranial Doppler technique in the middle cerebral artery (MCA) of 12 healthy male subjects. The results showed that the mean CBF velocity increased significantly during -6 degrees HDT and decreased during upright posture, and CBF velocity was higher in day time than at night.

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.

Electrogastography (EGG) was recorded in 15 healthy volunteers before and after meal during 21 days head down tilt -6 degrees bed rest. The results showed that nausea, distension and pain in the abdomen and loss of appetite appeared at the beginning of bed rest and body weight decreased significantly (P < 0. 01) after bed rest; Low frequency (Bradygastria) proportion of EGG (<2.4cpm) increased apparently after 8 days of bedrest, and there was significant difference (P <0.05) between preprandial and postprandial bradygastria. The dynamic parameters of bradygastria declined significantly and the rhythm of bradygastria increased with duration of bedrest. It indicates that simulated weightlessness may cause decrease of gastric rhythm and gastric motility.

Changes of microcirculation in nasal mucosa in 19 young men during 2.5 h head-down -15 degrees tilt (DHT) were observed with Laser Doppler Flowmetry. The results showed that the change of microcirculation in nasal mucosa was significant, blood volume, concentration and the velocity of blood flow increased, and distinct periodical wave of microvessels appeared during HDT. The results suggest that the change of microcirculation in nasal mucosa caused by fluid shift from the lower to the upper body is one of the important factors causing stuffy nose and breathe with a little difficulty.

To understand the changes of cardiovascular functions in the initial stage of space flight, the changes in 19 healthy young men during 2.5h head down tilt (HDT) (15 degrees) were observed with CF-II cardiovascular function detecting and diagnosing equipment. The blood pressure and sphygmogram of left radial arterial were recorded in sedentary condition and at 10th, 30th, 60th, 90th, 120th and 140th minute of HDT. The results showed that changes of cardiovascular indices during HDT can be divided into acute regulation stage (< 1h) and the regulation stage (1-2.5 h); circulatory blood volume, stroke volume and cardiac output were increased, while heart rate, pre and after load of the heart, CVP, coronary circulatory function, blood pressure and systemic vascular resistance were decreased; the vagus feedback index increased and the regulation function of vasscule decreased. Most of the changes of cardiovascular indices as reflected in the sphygmogram are in consistent with the reported result in space flight or simulated micro-G, so the sphygmogram method might be applied to space medical research.

-6 degrees head down bed rest (-6 degrees HDBR) 21d were used to simulate weightlessness. 15 healthy males, aged 19-22, were divided into 3 groups with 5 people in each group: control group (-6 degrees HDBR), hypoxia group (-6 degrees HDBR + Low Oxygen), Qigong group (-6 degrees HDBR + Qigong). The results showed that the reduction of weight, perimeter of shank, daily average cardic output, basal cardic output and the pulse pressure of the Qigong group were lower than those of the control group (P<0.05). The basal cardic output and the perimeter of shank of the Hypoxia group reduced significantly than those of the control group (P<0.05). However, the reduction of the other physiological functions of the Hypoxia group were not significantly lower than that of the control group (P>0.05). During HUT +75 degrees 20 min orthostatic tolerance test after HDBR, the parameters in the Hypoxia group were better than those in the other groups. The average standing time was also longer, and no presyncopal symptom occured.

Differentiation of syndromes during 21 d HDT -6 degrees bed rest was made in 15 healthy young men. The results indicated that the subjects showed mainly deficiency of kidney-Yin, deficiency of Yin and hyperactivity of Yang, insufficiency of spleen-Qi and blood stasis in various degrees during the bed rest. The syndromes were most serious on the 3rd day, and then deficiency of kidney and deficiency of Yin and hyperactivity of Yang became mild gradually but insufficiency of spleen-Qi and blood stasis remained the same. The pulse condition was normal through the bed rest period

To study the possible effect of simulated weightlessness on brain function state, the brain event-related potentials (ERPs) during a simple visual selective response task were compared between head down tilt (HDT) and head up tilt (HUT) in 9 normal subjects. The results were: both the target (T) and non-target (NT) flash signals induced significant slow positive potentials which were supposed to be related to the attention activity; the amplitude of the positive potentials in the frontal regions decreased significantly especially for NT-ERPs during HDT as compared with that during HUT. The data provide new evidence indicating that the ability of brain response declined during simulated weightlessness and more attention should be paid to the study of brain function during space flight.