It has been demonstrated that individuals exposed to actual or simulated microgravity often experience cardiovascular dysfunctions when returning to Earth. The underlying mechanisms of orthostatic intolerance and countermeasure treatment are still poorly understood. In this paper, the progress in the mechanism of cardiovascular deconditioning from the view of vascular remodeling, increased venous compliance in the lower limbs, cellular proliferation and differentiation, and cell signaling pathway was reviewed. Meanwhile, an overview of the countermeasures including exercise, lower body negative pressure, thigh cuffs, traditional Chinese herb medicine and artificial gravity was presented.
Cardiovascular Deconditioning ; physiology ; Cell Communication ; Cell Differentiation ; Cell Proliferation ; Gravity, Altered ; Humans ; Vascular Remodeling ; Weightlessness ; Weightlessness Simulation

PURPOSE: This study aimed to estimate the effects of a regular walking exercise program on metabolic syndrome, cardiovascular risk factors, and depressive symptoms among the elderly with diabetic mellitus (DM) based on the Theory of Reasoned Action (TRA). METHODS: This study has randomized and stratified experimental design with experimental and control groups. We developed a regular walking exercise program suitable for the elderly with DM based on the guidance of AAHPERD. The experimental group participated in the regular walking exercise program, which contains walking exercise 3 times a week and 50 minutes each time for 3 months and education on controlling diet and preventing complications once a week and 20 minutes each time for 4 weeks. Post-test was conducted after 3 months to estimate metabolic syndrome, cardiovascular risk factors, and depressive symptoms. RESULTS: The regular walking exercise program was effective for decreasing the waist size, the level of fasting blood glucose (FBG) and triglyceride (TG), cardiovascular risk factors and the severity of depressive symptoms among the elderly with DM. CONCLUSION: The incidence of complications would be decreased by applying a regular walking exercise program.
Aged* ; Blood Glucose ; Cardiovascular Deconditioning ; Depression* ; Diabetes Mellitus ; Diet ; Education ; Fasting ; Humans ; Incidence ; Metabolic Syndrome X ; Research Design ; Risk Factors* ; Triglycerides ; Walking*

We introduced the method of computer simulation in the studies of gravitational physiology. Based on work of Melchior (1994), we developed a mathematical model that can be used to stimulate cardiovascular responses to orthostatic stress (lower body negative pressure, LBNP). The model includes 7 sub-models: the redistribution of blood, the filling of left ventricle, left ventricle working, peripheral circulation, control of heart rate (HR), control of peripheral resistance and control of venous tone. Then we simulated the changes of blood pressure (BP) and heart rate during lower body negative pressure, and the results agreed well with the results of our human experiment. By using the developed model, we also simulated the effects of hypovolemia on the BP, HR and shock index during orthostatic stress. The simulation results indicate that the cardiovascular responses to orthostatic stress change significantly when the decrease of blood volume is more than 15% of the total blood volume. However, if the amount of the decrease of blood volume is less than 5% of the total blood volume, HR and BP could be maintained in normal range by the regulation of baroreflex during LBNP. Our simulation results suggest that hypovolemia may be the main cause of orthostatic intolerance induced by weightlessness.
Adult ; Blood Pressure ; physiology ; Cardiovascular Deconditioning ; physiology ; Computer Simulation ; Heart Rate ; physiology ; Humans ; Hypotension, Orthostatic ; etiology ; physiopathology ; Hypovolemia ; etiology ; physiopathology ; Lower Body Negative Pressure ; adverse effects ; Male ; Models, Cardiovascular ; Ventricular Function, Left ; physiology ; Weightlessness Simulation ; adverse effects

BACKGROUND: The hindlimb unweighting (HLU) rat model mimics cardiovascular deconditioning following microgravity or human bed rest, particularly for the development of orthostatic intolerance. We have examined vascular responses to alpha1 adrenergic and non-alpha1 adrenergic agonists in vitro. We have also explored the reversibility of the contractile abnormalities observed. METHODS: Dose-response curves were generated to phenylephrine (PE) and norepinephrine (NE) (10(-9) to 10(-4) M), U46619 (U4) (10(-10) to 10(-6) M) at one-half log order intervals in controls (n = 6), HLU (n = 6), or recovered rats (n = 6). EC(50)s and maximal responses (E(max)) were calculated by nonlinear logistic regression analysis with PRIZM software (Graphpad, Mountain View, CA). RESULTS: Simulated microgravity results in attenuated contractile responses to both alpha1 adrenergic and non-alpha1 adrenergic agonists, but the impaired contractile phenomenon reverses with time. CONCLUSIONS: The decreased vascular reactivity after microgravity and prolonged bed rest could cause attenuated baroreflex function and produce orthostatic intolerance, but that problem resolved with time.
15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid ; Adrenergic Agonists ; Animals ; Baroreflex ; Bed Rest ; Cardiovascular Deconditioning ; Hindlimb ; Humans ; Logistic Models ; Norepinephrine ; Orthostatic Intolerance ; Phenylephrine ; Rats ; Weightlessness

BACKGROUND: The hindlimb unweighting (HLU) rat model mimics cardiovascular deconditioning following microgravity or human bed rest, particularly for the development of orthostatic intolerance. We have examined vascular responses to alpha1 adrenergic and non-alpha1 adrenergic agonists in vitro. We have also explored the reversibility of the contractile abnormalities observed. METHODS: Dose-response curves were generated to phenylephrine (PE) and norepinephrine (NE) (10(-9) to 10(-4) M), U46619 (U4) (10(-10) to 10(-6) M) at one-half log order intervals in controls (n = 6), HLU (n = 6), or recovered rats (n = 6). EC(50)s and maximal responses (E(max)) were calculated by nonlinear logistic regression analysis with PRIZM software (Graphpad, Mountain View, CA). RESULTS: Simulated microgravity results in attenuated contractile responses to both alpha1 adrenergic and non-alpha1 adrenergic agonists, but the impaired contractile phenomenon reverses with time. CONCLUSIONS: The decreased vascular reactivity after microgravity and prolonged bed rest could cause attenuated baroreflex function and produce orthostatic intolerance, but that problem resolved with time.
15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid ; Adrenergic Agonists ; Animals ; Baroreflex ; Bed Rest ; Cardiovascular Deconditioning ; Hindlimb ; Humans ; Logistic Models ; Norepinephrine ; Orthostatic Intolerance ; Phenylephrine ; Rats ; Weightlessness