Cardiac Function And Cerebral Blood Flow Following 60 Days Head-down Tilt With And Without Chinese Herbal Medicine And Vibration Countermeasures

Space flight is a unique environment that poses several physiological challenges to the human body. The weightless environment of space flight causes serious adaptive changes in cardiovascular function, and nearly all crew members develop cardiovascular deconditioning characterized by orthostatic intolerance and reduced exercise capacity, which appear on returning to Earth after space flight. Therefore, effective countermeasures during spaceflight are needed to maintain the cardiovascular system, and will be essential for the health, well-being and safety of the crew members during space flight and upon return to Earth.Many different methods have been suggested to counteract orthostatic intolerance, including sessions of lower body negative pressure (LBNP), exercise, combined LBNP and exercise protocols, thigh cuffs, oral saline loading, and various pharmacological agents. These countermeasures have been evaluated in flight and on the ground; however, their efficacy is uncertain and their mechanism of action is sometimes unknown.In oriental society, herbs and herbal preparations are widely used as medicines by consumers with a long history. Recent studies demonstrated that traditional Chinese medicine is a unique promising candidate for preventing cardiovascular deconditioning during space flight. Taikong Yangxin Pill (TYP), a traditional Chinese herbal medicine, has been reported to be an effective countermeasure for improving cardiac pumping function of rats with tail-suspended. However, the effectiveness of TYP to prevent cardiovascular deconditioning remains unclear during long-term simulated microgravity.Another promising countermeasure is vibration training. As a special method for strength training, it has attracted attention for two decades. Previous studies have confirmed that vibration training is an effective training method in order to improve maximal strength and flexibility as well as various other factors if the training is properly designed, and bone loss during long term spaceflight is prevented by the application of a short term impulsive mechanical stimulation. The body reactions during vibration are not only biomechanical, but also physiological. Namely, all systems in the body, including cardiovascular system, neuromuscular system, etc., are reacting to the vibrations. However, the efficiency of vibration training on the cardiovascular system has not been identified during space flight or simulated microgravity.The purpose of this study was to assess the effects of Chinese herbal medicine and vibration training on the cardiac function and cerebral blood flow velocity during 60 days of head-down tilt (HDT) bed rest. The study here was a subset of a series of HDT studies in normal subjects to simulate the effects of weightlessness. We hypothesized that Chinese herbal medicine and vibration training would improve the cardiac function and meliorate cerebral blood flow. To test this hypothesis, we assessed cardiac pumping and systolic function using an impedance cardiography, and measured cerebral blood flow velocity by transcranial Doppler ultrasound during HDT.The main results and findings of this study are as follows:1. Effects of vibration and Chinese herbal medicine on cardiac function during 60d head-down tilt bed rest. We observed and compared effects of vibration and Chinese herbal medicine on cardiac systole function and cardiac pump function during 60 d HDT bed rest. Twenty-one healthy male subjects were randomly divided into control, vibration and Chinese herb groups, with 7 in each group. All of them were exposed to -6°HDT for 60 d. The control group took placebo, the vibration group received vibration training and the Chinese herb group took Taikong Yangxin Pill. The cardiac systolic and pump functions were measured before and during HDT. The main results showed that in the control group, stroke volume (SV) and cardiac output (CO) decreased significantly on day 30 of HDT (P<0.05), decreased further on day 60 of HDT (P<0.05), while total peripheral resistance (TPR) increased significantly on day 60 of HDT (P<0.05). In the vibration group, SV and CO decreased significantly on day 60 of HDT (P<0.05), TPR increased significantly on day 60 of HDT (P<0.05). In the Chinese herb group, the data above had no significant change during HDT. Pre-ejection period/ left ventricular ejection time (PEP/LVET) and isovolumetric contraction time/left ventricular ejection time (ICT/LVET) increased significantly on day 60 of HDT (P<0.05) in the three groups. On day 60 of HDT, PEP/LVET and ICT/LVET of Chinese herb group decreased significantly compared with the control and vibration groups (P<0.05). It suggests that 60d HDT induce a reduction of the cardiac pump and systolic function. Chinese herbal medicine is effective in preventing the effect of HDT on cardiac function. Vibration training partially improves cardiac functions.2. Effects of vibration and Chinese herbal medicine on cerebral blood flow during 60d head-down tilt bed rest. We observed and compared effects of vibration and Chinese herbal medicine on cerebral blood flow (CBF) during 60 d HDT bed rest by TCD. Twenty-one healthy male subjects were randomly divided into control, vibration and Chinese herb groups, with 7 in each group. All of them were exposed to -6°HDT for 60 d. The control group took placebo, the vibration group received vibration training and the Chinese herb group took Taikong Yangxin Pill. Cerebral blood flow velocity in the right middle cerebral artery was measured before and during HDT. The main results showed that in the control group, peak systolic flow velocity (Vs) decreased significantly on day 30 of HDT (P<0.05), and decreased further on day 60 of HDT (P<0.05), mean flow velocity (Vm) and end diastolic flow velocity (Vd) decreased significantly on day 60 of HDT (P<0.05). In the vibration group, Vs decreased significantly on day 30 of HDT (P<0.05), and decreased further on day 60 of HDT (P<0.05). It suggests that 60 d HDT induce a reduction of cerebral blood flow velocity. Chinese herb partially improves the cerebral blood flow during head-down tilt bed rest, but vibration exercise has no obvious effect on cerebral blood flow.In conclusion, our data show that 60 days HDT bed rest induced cardiovascular dysfunction and a reduction of cerebral blood flow. Chinese herbal medicine is effective in preventing the effect of HDT on cardiac function and cerebral blood flow. Vibration training partially improves cardiac functions. These results suggest that Chinese herbal medicine that we used seems to provide an optimal cardiovascular countermeasure, but vibration training seems to have only potential beneficial effects on cardiovascular function. The suitable countermeasure program of vibration and Chinese herbal medicine should be studied further during prolonged spaceflight, and the mechanisms responsible for these countermeasures require an integrative perspective for a more complete understanding.