The Rotational Speed Change And The Internal Flow Field Analysis Of The Axial Flow Blood Pump Under Optimal Assistant State

As one of the main treatments for the patients with end-stage heart failure,the ventricular assist devices have been widely used in clinical application.When the ventricular assist devices are used to assist left heart,most of them adopt constant speed control to make the average aortic pressure and cardiac output reach normal physiological level.This control method reduces the pulsatility of the aortic pressure,causes the decrease of aortic systolic pressure and the increase of aortic diastolic pressure,which will affect the function and geometric structure of the blood vessels,thus leading to a series of clinical complications.In addition,the constant speed control mode may also cause suction and regurgitation phenomenon,and cannot achieve effective left-heart assistant purposes.Therefore,the formulation of varying speed control strategy of the ventricular assist device is an effective way to improve its left ventricular assistant effect,and it is a key technology to be solved urgently.The axial flow blood pump has gradually become one of the main development directions of the ventricular assist devices due to its compact size,easy implantation and small trauma.In this paper,the self-developed axial flow blood pump is taken as the research object.By establishing the coupling parameter model of the blood circulation system and the axial flow blood pump,the varying speed control method of the blood pump is proposed and the variation rule of the speed curve under the optimal assistant state is analyzed.The numerical results of the varying speed assistance under various heart failure conditions are obtained,and compared with that of the constant speed assistance.Finally,the characteristic time points are selected according to the speed change curve,and the internal flow field distribution of the axial flow blood pump at the instantaneous speed is analyzed by CFD numerical simulation,and compared with the internal flow field of the characteristic time point during constant speed control,which further proves the feasibility of the varying speed assistant research of the axial flow blood pump under the ideal optimal assistant state.The specific contents are as follows:First,a series coupling parameter model of blood circulation system-axial blood pump is established.Firstly,a lumped parameter model of the blood circulation system is established to determine the corresponding parameters and validate the model.Secondly,a three-dimensional model of the axial flow blood pump is established and its mathematical equation is determined.The pump is equivalent to a lumped parameter model,which is connected in series at the position of aortic valve to establish the coupling parameter model of the blood circulation system and the axial flow blood pump.Second,based on the coupled parameter model,the velocity control equation is obtained,and the numerical results of varying speed assistance under the optimal assistant state are analyzed,and compared with the results of constant speed assistance.Firstly,the centralized parameter model of blood circulation was used to adjust the corresponding parameters,and the cardiac physiological status of grade ?,?,? and ? heart failure models was obtained.Secondly,the velocity control equation is proposed to obtain the speed change curve of the optimal assistant state of varying speed assistance under different heart failure conditions.Then,according to the speed change curve,the numerical results of varying speed assistance are obtained and compared with that of constant speed assistance.Third,according to the numerical results of the optimal assistant state achieved by varying speed assistance,the internal flow field of the axial flow blood pump assisted by varying speed was analyzed by Fluent,and compared with that assisted by constant speed.According to the numerical results of varying speed assistance,the characteristic time points are selected in a cardiac cycle,and the boundary conditions of numerical simulation of the axial flow blood pump are set.The flow field velocity and shear stress distributions of the blood pump assisted by varying speed are analyzed and compared with those assisted by constant speed.It was found that with the increase of the degree of heart failure,the peak value of varying speed assistant speed curve increased,from grade ? heart failure to grade ? heart failure,with an increase of 1500 rpm.Because the varying speed assistance achieves the optimal assistant state,the flow rate and the rotational speed of the bloodpump assisted by varying speed are higher than those assisted by constant speed during ejection period.The internal flow field of the blood pump assisted by varying speed is stable,the shear stress is higher,and the hemolysis will occur locally,but the time of the state is very short,which will not cause large hemolysis.During isovolumic systole,isovolumic diastole and filling period,the flow rate and the rotational speed of the blood pump assisted by varying speed are lower than those assisted by constant speed.The internal flow field of blood pump assisted by varying speed is disordered.Turbulence will occur obviously at the position of inlet and outlet guide vanes,but its shear stress is lower and hemolysis is less.