Detection And Control Of Suction And Regurgitation In A RBP-assisted System

Heart failure is a pathological condition,which has already been a serious threat to human health due to its poor prognosis,high prevalence and mortality.In recent years,RBPs?Rotary Blood Pumps?have become an effective treatment for severe heart failure.In clinic,RBPs generally operate at a constant speed.This mode causes a decrease in pulsatility,which may lead to complications such as gastrointestinal bleeding,and aortic filling,and will result in left ventricular suction and regurgitation of a RBP.Therefore,both numerical simulation and in vitro experiments were performed to investigate suction and regurgitation,and a varying-speed control system was developed to assist the heart-failure patient.The main research contents are as follows:A cardiovascular-RBP model was established by coupling a cardiovascular model and a rotary blood pump model.Firstly,a left cardiovascular model was established combining a time-varying-resistance model of mitral valve and Suga model and was then validated.Then,the coupled model was developed by coupling the new RBP model and the left cardiovascular model.The results showed that the cardiovascular model was feasible to simulate different physiological states,and the cardiovascular-RBP model could generate physiological blood flow.The coupling model was applied to investigate and to detect suction and regurgitation.When the pump speed increased to a level which may cause a negative value of LVP?Left Ventricular Pressure?was observed,suction occurred.The characteristics of hemodynamic parameters during the suction process were analyzed,and the minimum envelope slope of pump flow dx₇/d_t was used to detect suction.RI?Regurgitation Index?was put forward to detect and classify regurgitation levels based on the theory of dynamic closed cavity.According to the value of RI and critical speed,regurgitation were classified into slight,mild and severe regurgitationA varying-speed control system using PI?Proportion Integral?was developed and simulations were conducted to evaluate its performance in improving pulsatility,and of prevention of suction and regurgitation.At the varying-speed control model,the assisted patient by a RBP could achieve,CO of 5.9L/min and AoP's pulsatility coefficient of 0.33 which is higher than that at the constant speed mode.In the varying-speed control system,pump speed was regulated in real time according to afterload so that suction and regurgitation could be prevented.The system elevated the pump speed to prevent regurgitation when AoP increased while decreased pump speed to eliminate suction when AoP decreased.An experimental platform of left cardiovascular system was developed and the open-loop control experiments of the coupled cardiovascular-RBP system were carried out to achieve the detection of suction and regurgitation.The results showed that CO and AoP of the pump-free assisted system conformed to the physiology,which proved that the system could mimic different physiological states,and the coupled system assisted by a RBP could produce physiological blood flow.Suction could be simulated in the open-loop experiments and could be detected by dx₇/d_t.Slight,mild and severe regurgitation were also mimicked and detected.The experimental data of open loop control is consistent with the numerical results,which proving the feasibility of detection methods of suction and regurgitation.A varying-speed control system of rotary blood pump were established and its performances were evaluated.Under varying-speed mode support,CO was 6.1L/min satisfying with the requirement of physiological perfusion.The pulsatility coefficient of aorta flow and AoP were 0.22 and 0.13 respectively,higher than those at the constant speed mode.By changing R_S to mimic the patient's motion states,the system could produce a physiological flow by adjusting the speed of the pump quickly.In accordance with the numerical data,the pump speed changes with the afterload and the system could improve pulsatility,and prevent suction and regurgitation,showing a good dynamic performance.