A Simulation Study On The Responses Of Cardiovascular System To The Weightlessness

Microgravity is an extreme environment inducing relevant adaptive changes in the human body, especially after prolonged periods of exposure. Numerous studies on the effects of microgravity, during manned space fights, have produced an increasing amount of information concerning its physiological effects, globally defined "deconditioning". The most important effect of cardiovascular deconditioning is an inability to assume the standing position (orthostatic intolerance). The mechanism of cardiovascular deconditioning is complex. It is mainly caused by: the depression of cardio function, reduced cardiac output by 10%²0%. In addition, microgravity causes the shift of body fluids toward the head and thorax. Nearly 2000 ml blood shift from low body to the upper part of the body, which can notably affect the cerebral blood flow, cause the change of velocity of cerebral blood and baroreflex function. These can induce the change of blood pressure and volume of blood, so we can understand the mechanism of cardiovascular deconditioning in weightlessness by studying the change of blood pressure and volume of blood.The former researches are mainly on the human and animal's resDonses of cardiovascular svstem to simulated weightlessness, thevwere limited by the experimental conditions, many indices were difficult to get. Furthermore, the experiments may be harmful to human body and the results of the animal model are not completely suitable to human.Consideration of the defects of simulated weightlessness, thesimulation of the responses of cardiovascular system to weightlessness by computer is springed up. According to the basic principle of hydrodynamics, we established an improved multiple nonlinear body model by Pspice language. This model had 4 subparts: model of heart, model of artery, model of vein, model of peripheral blood vessel. For testing the validation of the model, the data of cardiovascular system simulated by the model on 1G was compared with the experimental data. The model was then employed to stimuate the changes in the human blood pressure and the cerebral blood volume, and the effects of the reduced blood volume on the cardiovascular system. The main results of our study are as follows:1. Study the physiological parameter on 1G The results of simulation were: arterial blood pressure (ABP) changed from 78 to 118 mmHg, left ventricular pressure (LVP) changed from 4 to 116 mmHg, left atria pressure (LAP) changed from 75 to 117 mmHg. The standard body's experimental data were: ABP changed from 75 to 117 mmHg, LVP changed from 2 to 118 mmHg, LAP changed from 2 to 12 mmHg.The curves of these two conditions were resemble.2. Simulation results of arterial blood pressure on 1G and 0GThe simulation results were: Systaltic blood pressures (SBP) were 118 mmHg on 1G and 115 mmHg on 0G, respectively. There was no remarkable difference in SBP between these two conditions. Diastolic blood pressure (DBP) were 75 mmHg on 1G and 58 mmHg on 0G, respectively. There is a degressive trend in DBP from 1G to 0G The curves of ABP, LVP and LAP on 1G resembled those on 0G3. Simulation results of central venous pressure on 1G, 0G andu g The results of simulation were: Central venous pressure (CVP) changed from 5.821 to 5.873 cmH₂O on 1G, the mean value was 5.847 cmH₂O. CVP changed from 9.053 to 9.137 cmH₂O on u g (G=0.001G), the mean value was 9.095 cmH₂O. CVP changed from 9.055 to 9.145cmH₂O on 0G, the mean value was 9.1 cmH₂O. Compared with the data of 1G, CVP significantly increased on 0G and u g conditions, but there was no remarkable difference in CVP between 0G and u g conditions.4. Simulation the change of cardiac output along with the decreasing change of blood volume on 0G The cardiac volume (CV) decreased 2.4% when blood volume (BV) has decreased 5%. CV decreased 5.2% when BV has decrease 10%. No significant changes of CV were found when the loss of BV was within 10%. CV decreased 8.3% when BV has decreased 15%. CV decreased 13.2% when BV has decreased 25%. CV decreased 16.2% when BV has decreased 30%. It is obvious that CV decreased drastically when BV has decreased over 20%.5. Simulation the change of blood along with the decreasing change of blood volume on 1G SBP decreased from 120 mmHg to 115 mmHg when BV has decreased less than 10%. When BV has decreased to 17%, SBP decreased to 100 mmHg. When BV has decreased to 23%, SBP decreased to 90 mmHg, which was the minimum value of the standard. The change of DBP was similar to SBP. DBP decreased from 70 mmHg to 75 mmHg when BV has decreased less than 10%. When BV has decreased to 20%, SBP decreased to 60 mmHg, which was the minimum value of the standard. SBP and DBP would decrease drastically if B V decreased constantly, and the model ofcardiovascular system would loss its stability simultaneity.6. Simulation the changes of cerebral blood volume on 1G and0G The simulation results showed that the curves of cerebral blood volume on 0G and 1G were similar, the values on 0G were higher than those on 1G The peak of the curve changed from 9.4 ml/s on 1G to 10.5...