Model Research Of Haemodynamics With The Cardiovascular System During Left Ventricular Assistance

Heart failure (HF) has increasingly become one of the fatal factors that threatenhuman health. Heart transplantation and left ventricular assistance are the maintreatments for end-stage HF. Left ventricular assist devices (LVADs) have beenattracting a great deal of clinical attention and technical research owing to theshortage of donor heart. LVADs are devices that partially or totally alternate the pumpfunction of nature heart and pump the blood throughout the whole body.Cardiovascular system is a complex system with strong coupling parameter, in whichthe physiological regulatory mechanisms reflect the interaction of physiologicalparameters by compensatory mechanisms of nervous system and humoral systems.Heart failure patients are in the decompensated state, their regulatory mechanisms ofthe cardiovascular system are changed; however, the study on the changes inregulatory mechanisms has not yet been clear. Moreover, the LVADs to improve organperfunsion and heart function recovery change the hemodynamic characteristics of thecirculatory system, whereas the hemodynamic effects by both different connectionsand control strategies are unclear.Aiming at the both issues on the regulatory mechanism of HF patients and thecardiovascular haemodynamic effect for heart failure patients with left ventricularassistance, in this work, physiological parameter models, including the myocardialcontractility, systemic vascular resistance (SVR) and vascular compliance, wereestablished to research the heart failure physiological adjustment mechanism, and acardiovascular-pump coupled model was established to study changes inhemodynamics of circulatory system with left ventricular assistance. Firstly, themodel of the myocardial contractility, systemic vascular resistance and vascularcompliance were established according to clinical data to study the physiologicalregulatory mechanism. Then based on the regulatory mechanism, the model ofcardiovascular system and the coupled model were designed by using lumpedparameter model theory. Secondly, in order to research the hemodynamic interactionbetween the cardiovascular system and the blood pump, a numerical study werecarried out using a cardiovascular model simulation system. Utilizing thecardiovascular model simulation system, the effects of cannulation locations,consisting of bypassing from cardiac apex to aorta and being series from aortic root toaortic arch, to the blood perfusion and cardiac recovery were studied. Moreover, theimpact of control strategies, including the continuous flow method, the constantrotational speed and the constant pressure head, for ventricular unloading and vesselresponse were researched. Finally, the animal experiments were applied to researchthe effect of LVADs on cardiovascular haemodynamics. The experimental system wasdesigned to sample the physiological parameters and to control the blood pump. Onthe one hand, using experimental data to establish an animal model during leftventricular assistance, and then comparing the simulated data with the actual data toverify the validity of the model. On the other hand, according to the experimental data,the hemodynamic charactristics, including the left ventricular unloading, blood perfusion and pulsatility of blood, were researched during left ventricular assistance.The results indicated that the left ventricular pressure derived from numericalstudy is consistent with that of animal experiments, which means that the model ofcardiovascular system can reflect the cardiovascular hemodynamic charactristics. Theconstant pressure head method had benefit for left ventricular unloading, vesselresponse and achieving the pulsatile blood flow synchronized with the cardiacejection. For bypass model, the constant rotational speed generates more bloodperfusion and the continuous flow achieves greater left ventricular unloading. Inaddition, pulsatility of blood flow is gradually reduced with the increase of the bloodassist index. The animal experiment demonstrated that along with the increase of thespeed, the left ventricular unloading and the blood perfusion increased, while thepulsatile index decreased, which was consistent with the results of numerical study. Inshort, the study on hemodynamic model of the cardiovascular system providestheoretical foundation for clinical treatment of heart failure; and the study onconnection and control strategies provides guides for long-term ventricular assistance.