Research On The Blood Circulatory System Using A Left Ventricular Assist Device

Heart failure is a typical clinical symptom of cardiac insufficiency due to heart diseases,which affects the life quality of human beings and even can cause death.At present,left ventricular assist devices(LVADS)have become an effective treatment for severe heart failure.The circulatory system was a complex dynamic system,and the interaction between the LVAD and blood circulatory system would make the hemodynamics of the system more complex when the patient was treated with a LVAD.To reveal the impact of LVAD on the human hemodynamics contributes to developing LVADS and putting forward a physiological control strategy.In this paper,both numerical method and experimental method were used to investigate the blood circulation system coupled with a LVAD.The main contents were as follows.Firstly,an improved model of blood circulatory system was built.Based on the physiological structures and functions of the mains components in the circulatory system,the model of each component was established and the time-varying resistance model was used to simulate mitral valve.Thus,an improved six-order lumped parameter model for blood circulatory system was completed.This model was used to mimic healthy physiological status and dilated cardiomyopathy status.Results showed that the hemodynamics of the two statuses matched the physiological characteristics,proving that the improved model could be used to simulate various physiological states and could be used to construct a blood circulatory system model using a LVAD.Secondly,based on the hydraulic characteristic and the similarity principle of the rotary pump,a new mathematical model of the LVAD was put forward.After coupling the new LVAD model with the circulatory system model,the circulatory system model using a LVAD was established.Then the model was used to study the impact of the LVAD on hemodynamics and suction due to excessive assistance of the LVAD.The numerical results showed that LVAD could assist the heart with failure and improved its characteristics.When the LVAD rotated at the speed of 9000 rpm,the aortic flow reached 5.90L/min,while aortic pressure was increased among 77 mmHg and 100 mmHg.For the unloading of LVAD,the left ventricle systolic pressure was decreased to 78 mmHg.Suction was found at the rotating speed of 12800 rpm.But after adopting the speed feedback control of the LVAD,the rotating speed was controlled and remained blow the suction speed and thus the circulatory system could provide physiological perfusion and prevent suction.Finally,an in-vitro experimental platform of the blood circulatory system using a LVAD was designed and built to investigate the impact of the LVAD on the hemodynamics.The experimental results revealed that,this platform could mimic healthy physiological status and dilated cardiomyopathy status.The LVAD could improve the hemodynamics of the patients with dilated cardiomyopathy.The increase of the rotating speed elevated the assisting level of LVAD and decreased the load for left ventricle.When the rotating speed of LVAD increased from 5000 rpm to 8000 rpm,mean aortic pressure increased from 106 mmHg to 109.5mmHg,and aortic flow reached 3.7L/min while ventricle systolic pressure decreased from 101 mmHg to 87 mmHg.At the rotating speed of 8200 rpm,negative transient pressure appeared in the ventricle and suction was found.These experiments proved the feasibility of this platform and reveal that the effect of LVAD on hemodynamics which was similar to numerical data.Both numerical date and experimental results provided technological support for developing LVADs and control strategies.