| In recent years,the incidence of cardiovascular diseases is increasing annually,almost all types of cardiovascular diseases will cause left ventricular dysfunction and eventually lead to heart failure.Globally,the total number of heart failure patients has exceeded 20 million,and on average the annual rate of increase is about 2 million patients.In the clinical treatment of patients with end-stage heart failure,heart transplantation can provide the possibility for long-term survival of patients.But at present,due to the limited number of donor hearts,patients who need heart transplantation need one year on average to wait for suitable donors.However,the average survival time of patients with end-stage heart failure is only about 6 months.Heart transplantation was performed for only 5000 cases during the past 10 years.While waiting for the donor hearts,traditional drug therapy has obvious limitations.In comparison,implantation of rotary blood pump(RBP)can partly or completely replace the function of pumping blood for the natural heart,reduce the workload of hearts,help hearts provide sufficient physiological perfusion while the patients are waiting for heart transplantation,and even serve as the permanent auxiliary support device for patients' hearts.RBP is a mechanical circulatory support device,which can be implanted into human's body for long-term use.It can provide circulatory support for patients with heart failure by assisting ventricle to pump blood.However,if the pump speed cannot be adjusted in real time according to the changes of patients' physiological conditions after implantation,it will be difficult to provide sufficient physiological perfusion for patients at all times,and even it can induce ventricular suction.Insufficient physiological perfusion can lead to a large reduction of blood supply at the end of organs,ventricular volume overload,pulmonary edema and tissue hypoxia.Ventricular suction can cause ventricular collapse,sudden stop of pump flow,and easily lead to myocardial injury or ventricular arrhythmia,even cause death.Previously proposed algorithms for suction detection and physiological control always have obvious disadvantages,including the use of unreliable pressure and flow sensor,which can easily cause sensor drift and failure,and pump thrombus,inaccurate model-based parameters estimation that would be susceptible to pump inertia,friction forces,and blood viscosity changes,and constant pump speed control strategy that cannot generate adequate cardiac output,etc.Therefore,in this thesis,a sensorless control algorithm based on proportional integral(PI)controller is proposed by using the suction index(SI)as the control objective,which is calculated from an inherent RBP parameter-pump speed signal.The essence of the algorithm is to use the feedback controller to automatically adjust the RBP current(the control input),so that the actual value of SI is gradually stabilized near to the reference SI value,in order to maintain the patient's physiological perfusion,while effectively prevent suction phenomenon.This control method combines the human circulatory system with RBP as a non-linear dynamic model,and is compared with other four control methods,to evaluate the performance of the proposed control algorithm at different levels of activities with 2% noisy pump speed measurements,including(1)rest and exercise conditions,(2)rest and exercise conditions with rapid several-fold increase in pulmonary vascular resistance(PVR),(3)fast transition from exercise to rest condition.In-silico results show that the proposed SI-based control algorithm effectively prevented suction and provided sufficient physiologic perfusion.In the meantime,generally its performance was clearly superior to the other four control algorithms. |
PDF Full Text Request