The Effect Of Ventricular Unloading On Left Ventricular Blood Flow And Ventricular Wall Stress

The utility of ventricular assist device(VAD)is prevailing in clinical treating patients with end-stage heart failure due to the increasing case amount of VAD surgery,which is an effective clinical therapy method.Cardiac function recovery with VAD has been confirmed.However,the issues including low rate of cardiac function recovery and unstable therapeutic effect produce in clinical and are related to many factors.The key factor is the effect of ventricular unloading,especially in the change of cardiovascular hemodynamics,distribution of blood flow and wall stress,which attracted the attention of many scientists.This thesis combined with the numerical model of the cardiovascular system and LVAD and finite element model of left ventricular to clarify the change of cardiovascular hemodynamics,distribution of blood flow and wall stress.Moreover,the beginning study on hemodynamics on the VAD therapy with drug has been explored.Three parts have been researched.Firstly,the lumped parameters of unloading model of left ventricular have been reserached,which includes the multi-scale model of the cardiovascular system and the pump model of VAD.The multi-scale model built using the intracellular calcium icon and the theory of lump parameter and came from the fact that pressure inside a cardiac chamber derived from a model of the sarcomere behaviour.The pump model establishes by experiment.Based on these two models,the change of cardiovascular hemodynamics,distribution of blood flow and wall stress researched.The results show that the negative correlation of unloading level and parameters that include myocardial force,left ventricular pressure,left ventricular pressure-volume loop and external work.The unloading level,however,is positive correlation with right loading to explain clinical phenomenon,which increases the risk of right heart failure by support of VAD.0 degree phase differences between the BJUT-II VAD and native heart(call co-pulse support model)are the minimum left ventricular external work and maintain the pulsatility of arterial pressure and the minimum effect of right loading.Secondly,the fluid-structure interactions of the distribution of blood flow and wall stress have been studied.The 3-dementional geometrical model is extracted from a group of CT scan data from a patient suffered from the NYHA III heart failure.A time-dependent Young’s modulus of left ventricular wall is used to reflect the elastic property of the left ventricular wall.The change of blood distribution is researched in the cases that include heart failure case,unloading level(partial and full support modes)case and pulse support(co-pulse and counter-pulse)case.On this basis,a hyperelasticity constitutive and orthotropic finite element model established to explain the distribution of blood flow and wall stress.The results showed that the vortex corresponding formation time increased after VAD support(heart failure 0.1s vs.partial support 0.25s;heart failure 0.1s vs.co-pulse support 0.348s).Moreover,the area of high time-average wall shear stress and oscillatory shear changed(heart failure vs.constant speed vs.co-pulse mode,31.8 vs 37.3 vs 22.2 cm~2;9.9 vs.9.6 vs.9.2cm~2).In conclusion,partial support and co-pulse mode were benefited for the vortex of left ventricular and blood residence.In addition,high-stress region of ventricular wall decreased after the support.The minimum value of stress and the maximum changing of thickness generated under the co-pulse support.Finally,the VAD therapy with drug has been explorared.The drug of the angiotensin-converting enzyme inhibitor(ACEI)was chosen to study the effect of pharmacological therapy on the control strategy of VAD and the effect ofβ-adrenergic receptor antagonists with VAD on the hemodynamic characteristics was researched.The results demonstrate that the ACEI could decrease the loading of left ventricular and aortic pressure for heart rate control strategy.At the same time,ACEI changing the peripheral resistance and then affect the performance of VAD for blood assist index control strategy.Also,β-blocker was benefited for unloading the left ventricular.The co-pulse support withβ-blocker on the one hand has the significant unloading of left ventricular on the other hand has minimal impact to right ventricular.The thesis is to obtain the hemodynamic mechanism of left ventricular unloading to theoretically therapy the heart failure using the assist device.