A Feedback Control Method To Increase Vascular Pulsatility For Rotary Blood Pumps

According to statistics,the number of deaths due to various cardiovascular diseases such as myocardial infarction,coronary heart disease,atherosclerosis and valve insufficiency ranks first in the world.Most of the various types of cardiovascular disease will lead to the occurrence of heart failure.Heart Failure results from the heart's declining capability in both relaxation and contraction,which limits the amount of blood returning from the veins to the aorta,and causes the blood stagnation in the venous system.It triggers a chain reaction that ultimately disorders the whole blood circulation system.For patients who suffer from end-stage heart failure,the traditional heart transplants are limited by the number of donor hearts and other issues and constraints,most of the heart failure patients died while waiting for a donor heart,therefore,researchers developed rotary blood pumps(RBP)to take place of donor hearts to sustain the life of the patients with heart failure.RBP will sustain patient's life while they are waiting for a donor heart or can be directly used throughout their lives.Therefore,researches of RBP have been carried out gradually.RBP is an important clinical method for the treatment of end-stage heart failure.RBP draws the blood flow from the left ventricle into the aorta,partially or even completely replacing the function of the sick heart.In current clinical practice,RBP is usually set at a constant blood pump speed to ensure sufficient blood flow from the left ventricle to the aorta.However,this method will significantly reduce the pulsatility of blood vessels,resulting in complications such as blood injury,incomplete aortic valve closure,and diastolic hypertension.This paper firstly uses the equivalent circuit model to simulate the circulatory system,and derive the corresponding equivalent circuit of the human circulatory system,then derive state space equations according to the kirchhoff's law,calculate various important hemodynamic and RBP parameters by solving the equations.Secondly,this paper developed a new feedback control method of RBPs to improve pulsatility.The method sets the the difference between the maximum and minimum values of the blood pump speed(?RPM)with high and low reference value(?RPM_H/?RPM_L),the gain scheduled PI c ontroller makes the actual?RPM value approximate to one reference value,then the reference value immediately switches to another one,making the actual?RPM approach to it,meaning that the two(high and low)reference values are switching each other once the actual?RPM approaches to one of them.Based on the actual requirements,this method simulates the heart failure patients'hemodynamic parameters following the RBP implementation under different physiological status.By changing the cardiac cycle and the blood flow resistance,the paper also simulates the condition of rest,exercise,transition from exercise to rest,and inadequate blood back to the heart through a rapid(20 s)five-fold increase in pulmonary vascular resistance(PVR).In addition,the feasibility and robustness of the closed-loop control algorithm will be evaluated through observing the related hemodynamic parameters.The simulation results show that:with this closed-loop feedback control,the heart failure patients with RBP implantation can ensure sufficient blood flow from the left ventricle to the aorta.Moreover,their vascular pulsatility can be significantly improved,suction and blood reflux can also be prevented.