Simulation Study On Cardiovascular And Cerebovascular Diseases Based On Bond Graph Model Of Circulatory System

Cardiovascular and cerebrovascular diseases are global problems in public healthdue to their high morbidity and high risk. The goal of this study is to propose anextendable mathematical model for circulatory system and to investigate the hot spots inthe research of cardiovascular and cerebrovascular diseases by model simulation. Themain tasks and results are summarized as follows,1. For the simulation of various diseases, autonomic nervous regulation model wasestablished and the tone of venous unstressed volumes by efferent pathway ofbaroreceptor reflex was added. The adjustment of blood volume by the kidney wasconsidered and expressed by mathematical model. Model of the circle of Willis wasconstructed according to its anatomy, including internal carotid artery, basilar artery,vertebral artery, anterior cerebral artery, middle cerebral artery, posterior cerebral artery,posterior communicating artery and anterior communicating artery. The efficiency of themodels was verified by simulation results under normal conditions.2. The influence of carotid baroreflex resetting on hypertension was analyzed by thecirculatory system model including nervous regulation mechanism. Simulation resultsreveal that the regulation of autonomic nervous system still works and the blood pressureis controlled at prehypertension level even the baroreceptor reflex is damaged slightly, e.g.the set point of carotid baroreflex is 97mmHg. With the development of lesion inautonomic nervous system, i.e. the elevation of baroreflex set point, blood pressureincreases to stage 1 hypertension and worsens. Furthermore, the role of the effectors,including PVR, ventricular end-systolic elastance, venous unstressed volumes and heartrate, in the regulation of hypertension was analyzed. The results exhibit that the ANSregulation on hypertension works mainly by the reduction of PVR and the increase ofvenous unstressed volume.3. Chronic heart failure and the effects of commonly used drugs were simulated bythe circulatory system model with embeded autonomic nervous regulation and theadjustment mechanism of blood volume by kidney. Results demonstrate that based on the assumption that the drugsaffect the model parameters in the same extent,angiotensin-converting enzyme inhibitor (ACEI) induces more cardiac output changewhile angiotensin receptor blocker (ARB) causes more change in end diastolic volume ofleft ventricle and digitalis contributes less to the decrease of end systolic volume of leftventricle and end diastolic volume of left ventricle. Thus, the results show the necessity ofcombination therapy for chronic heart failure.4. Ischemic stroke and morphologic variation of circle of Willis were investigated bythe circulatory system model including detailed description of the circle of Willis.Simulation results reveal the hemodynamic characteristics in the circle of Willis whencerebral infarction and the left carotid artery stenosis occur and elucidate the changes ofcerebral hemodynamics in patients with hypertention. Meanwhile, results show that if themiddle cerebral artery stenosis is less than 50% in diameter, the flow in the circle ofWillis has no obvious difference from normal status. Results also demonstrate that notonly brain vascular diseases but morphologic variation in circle of Willis are responsiblefor the abnormality in the flow of circle of Willis, although morphologic variation incircle of Willis have slight influence on the overall hemodynamics. Furthermore, resultsindicate that in the case of morphologic variation of circle of Willis, the lack ofcompensatory pathways aggravates the burden of the remaining pathways and causes theelevation of cerebrovascular diseases occurrence.5. User-friendly interface for simulation model was established. Thus it is convenientfor the simulation of the physiological and pathological status.In conclusion, the models in the present study are efficient and flexible to beextended. To meet the needs in different research, they are able to be further developed,and thus provide a valid tool for the cardiovascular and cerebrovascular diseases study.