出口边界条件和壁厚对冠状动脉壁面剪切力和冯米塞斯应力的影响

Effects of Outlet Boundary Condition and Wall Thickness on Wall Shear Stress and von Mises Stress in Coronary Artery

探讨基于个体化患者计算机断层血管造影(CTA)影像的冠状动脉流固耦合(FSI)数值分析中,不同出口边界条件和血管壁模型对时间平均壁面剪切力(TAWSS)和冯米塞斯应力(VMS)的影响。根据患者CTA影像重建右冠状动脉(RCA)管腔流域三维几何;将管腔流域表面向外扩张0.5 mm,形成均匀厚度血管壁;运用类似虚拟去除斑块的方法建立不均匀厚度血管壁模型。FSI分析时,分别给予zero和impedance两种出口边界条件;获得从舒张末期开始心动周期主要时间点TAWSS和VMS的分布,比较不同模型结果的差异。结果表明,两种出口边界条件下,TAWSS空间分布基本一致,且血管狭窄段均高于其他部位;zero条件下峰值VMS出现在压强最大时刻点0.42 s,而impedance条件下峰值VMS出现在入口血流速度最大时刻点0.64 s,并且达到前者的20倍。同是impedance出口边界条件时,TAWSS分布基本一致,没有显著性差异;两种血管壁模型中,VMS的分布一致,血管狭窄段比其他部位低,但是不均匀厚度血管壁模型中局部位置VMS绝对值高于均匀壁厚血管壁模型。医学影像技术的发展可以提供更高精度的冠脉结构以及出入口速度和压强边界条件,不但对研究血流动力学以及结构力学因素与心血管疾病的关系具有重要意义,也可以更好的服务于患者个体化诊断与治疗。

This study is aimed to investigate the effects of different outlet boundary conditions and vessel wall thickness on time-averaged wall shear stress（ TAWSS） and von Mises stress（ VMS） in the coronary artery fluid structure interaction（ FSI） analysis based on patient-specific computed tomography angiography（ CTA） images.Firstly,3D geometry of right coronary artery（ RCA） lumen was reconstructed from CTA images. Then,lumen surface was expanded outward by 0. 5 mm to establish uniform thickness vessel model. Finally,non-uniform thickness vessel was built by manually removing plaques. Zero and impedance boundary conditions were applied to the computational domains during FSI analysis. Distribution of TAWSS and VMS in a cardiac cycle from end diastolic phase were obtained and analyzed. TAWSS at stenosed sites were both significantly higher than other segments,and there was no significant difference with two outlet boundary conditions. Peak VMS appeared at0. 42 s（ maximum pressure） with zero condition,while it appeared at 0. 64 s（ maximum flow velocity） withimpedance condition and was 20 times higher. With impedance outlet boundary condition,the TAWSS in stenosed sites were both significantly higher than other segments, but had a similar distribution without statistical difference in different vessel models; the VMS distribution were both lower in stenosed sites and the absolute value of local VMS was higher in non-uniform thickness model than in uniform model. More accurate coronary structures and personalized flow and pressure boundary conditions were described based on the medical image,which is not only of great significance to studying relationship between hemodynamic,mechanical factors and cardiovascular disease,but also to serving patient-specific diagnosis and treatment.