Soulis Johannes V, Giannoglou George D, Papaioannou Vassilios, Parcharidis George E, Louridas George E
Fluid Mechanics Division, School of Engineering, Democrition University of Thrace, Xanthi, Greece.
Biomed Eng Online. 2008 Oct 17;7:26. doi: 10.1186/1475-925X-7-26.
The blood flow and transportation of molecules in the cardiovascular system plays a crucial role in the genesis and progression of atherosclerosis. This computational study elucidates the Low Density Lipoprotein (LDL) site concentration in the entire normal human 3D tree of the LCA.
A 3D geometry model of the normal human LCA tree is constructed. Angiographic data used for geometry construction correspond to end-diastole. The resulted model includes the LMCA, LAD, LCxA and their main branches. The numerical simulation couples the flow equations with the transport equation applying realistic boundary conditions at the wall.
High concentration of LDL values appears at bifurcation opposite to the flow dividers in the proximal regions of the Left Coronary Artery (LCA) tree, where atherosclerosis frequently occurs. The area-averaged normalized luminal surface LDL concentrations over the entire LCA tree are, 1.0348, 1.054 and 1.23, for the low, median and high water infiltration velocities, respectively. For the high, median and low molecular diffusivities, the peak values of the normalized LDL luminal surface concentration at the LMCA bifurcation reach 1.065, 1.080 and 1.205, respectively. LCA tree walls are exposed to a cholesterolemic environment although the applied mass and flow conditions refer to normal human geometry and normal mass-flow conditions.
The relationship between WSS and luminal surface concentration of LDL indicates that LDL is elevated at locations where WSS is low. Concave sides of the LCA tree exhibit higher concentration of LDL than the convex sides. Decreased molecular diffusivity increases the LDL concentration. Increased water infiltration velocity increases the LDL concentration. The regional area of high luminal surface concentration is increased with increasing water infiltration velocity. Regions of high LDL luminal surface concentration do not necessarily co-locate to the sites of lowest WSS. The degree of elevation in luminal surface LDL concentration is mostly affected from the water infiltration velocity at the vessel wall. The paths of the velocities in proximity to the endothelium might be the most important factor for the elevated LDL concentration.
心血管系统中血液流动和分子运输在动脉粥样硬化的发生和发展中起着关键作用。这项计算研究阐明了正常人左冠状动脉（LCA）三维树状结构中低密度脂蛋白（LDL）的局部浓度。
构建正常人LCA树状结构的三维几何模型。用于几何结构构建的血管造影数据对应于心室舒张末期。所得模型包括左主干冠状动脉（LMCA）、左前降支（LAD）、左旋支（LCxA）及其主要分支。数值模拟将流动方程与传输方程耦合，并在血管壁处应用实际边界条件。
在左冠状动脉（LCA）树状结构近端与血流分流器相对的分叉处出现高浓度的LDL值，此处经常发生动脉粥样硬化。对于低、中、高水渗透速度，整个LCA树状结构上的面积平均归一化管腔表面LDL浓度分别为1.0348、1.054和1.23。对于高、中、低分子扩散率，LMCA分叉处归一化LDL管腔表面浓度的峰值分别达到1.065、1.080和1.205。尽管所应用的质量和流动条件参考了正常人体几何结构和正常质量流条件，但LCA树状结构的血管壁仍暴露于致胆固醇环境中。
壁面切应力（WSS）与LDL管腔表面浓度之间的关系表明，在WSS较低的位置LDL浓度升高。LCA树状结构的凹侧比凸侧表现出更高的LDL浓度。分子扩散率降低会增加LDL浓度。水渗透速度增加会增加LDL浓度。随着水渗透速度增加，高管腔表面浓度的区域面积会增大。高LDL管腔表面浓度区域不一定与最低WSS位置重合。管腔表面LDL浓度升高的程度主要受血管壁处水渗透速度的影响。靠近内皮的速度路径可能是LDL浓度升高的最重要因素。
