Design And Investigation Of A Physiological Control System For Rotating Heart Pumps

For patients with severe heart failure,heart pumps have become an effective treatment or a transitional therapy for patients waiting for heart transplantation,and often used as left ventricular assist device(LVAD)in clinical practice and works in the constant speed mode(CSC).Although CSC has the merit of high robust,it cannot feed back the real-time hemodynamic parameters of the patient.Therefor the pump speed cannot be adjusted immediately to achieve the normal perfusion level according to the physiological states of the patient.In order to solve the above problems,this dissertation puts forward a physiological control system using Frank-Starling mechanism which mimics the pumping principle of a native heart and using a non-invasive measurement method.Simulation methods are used to investigate the control system and the main contents are as follows:Firstly,In this dissertation,a non-invasive physiological control system(NAC-FSL)of using Starling-Like mechanism is developed in this dissertation.The system includes three modules:the non-invasive detection module,the module of achieving average reference pump flow and the PI algorithm module.In the non-invasive detection module,the pump speed is combined with the cardiovascular coupled system to estimate the pump flow and the preload.The function between the measured average pump flow and the estimated average pump flow and the function between preload and rotational speed are fitted to prove the feasibility of the algorithm.The results show that the fitting coefficients R~2between the measured and the estimated pump flow are 0.9891 and 0.9953 at rest and exercise respectively.The fitting coefficients between preload and rotational speed are high than 0.9310 at different physiological states and high than 0.9632 with different heart failure degrees,respectively.The module for obtaining the average reference pump flow uses the control baseline in the Starling-Like mechanism to achieve the reference average pump flow.PI algorithm module is used to track the reference pump flow in real time to meet the physiological needs of patients.Secondly,using the cardiovascular coupled model,the effect of NAC-FSL system on hemodynamic parameters in cardiovascular system is investigated and compared with Starling-Like mechanism(SLC)and CSC system.Under the control of NAC-FSL or SLC,the results show that the aortic pressure,aortic flow and unloading ability to left ventricles all reach healthy physiological level,and are greater than the CSC mode.The estimated data in the NAC-FSL controller are approximate to the measured data with small errors at sleep,rest and exercise states.The average errors of the average pump flow of SLC and NAC-FSL controllers are 2.55%,2.95%and1.96%respectively,while the average error of preload are 4.46%,3.31%and 4.27%,which prove the feasibility of non-invasive measurement.Finally,considering the degree of heart failure and the type of LVADs,the effect of K value indicating the pump response sensibility to preload changes on the robust of NAC-FSL physiological system is explored.It is found that the NAC-FSL system cannot adjust the pump speed when the K value is lower than a certain threshold,and when another K value is higher than the threshold,cardiac output decreases and the waveform of pump flow and rotating speed oscillate greatly.After analyzing the parameters,the optimal K ranges have been determined according to the degree of heart failure and the type of LVADs to achieve the robustness of the system.