Debbaut Charlotte, Vierendeels Jan, Casteleyn Christophe, Cornillie Pieter, Van Loo Denis, Simoens Paul, Van Hoorebeke Luc, Monbaliu Diethard, Segers Patrick
Biofluid, Tissue and Solid Mechanics for Medical Applications Institute Biomedical Technology, Ghent University De Pintelaan 185, Block B, B-9000 Gent, Belgium.
J Biomech Eng. 2012 Jan;134(1):011003. doi: 10.1115/1.4005545.
The perfusion of the liver microcirculation is often analyzed in terms of idealized functional units (hexagonal liver lobules) based on a porous medium approach. More elaborate research is essential to assess the validity of this approach and to provide a more adequate and quantitative characterization of the liver microcirculation. To this end, we modeled the perfusion of the liver microcirculation using an image-based three-dimensional (3D) reconstruction of human liver sinusoids and computational fluid dynamics techniques. After vascular corrosion casting, a microvascular sample (±0.134 mm(3)) representing three liver lobules, was dissected from a human liver vascular replica and scanned using a high resolution (2.6 μm) micro-CT scanner. Following image processing, a cube (0.15 × 0.15 × 0.15 mm(3)) representing a sample of intertwined and interconnected sinusoids, was isolated from the 3D reconstructed dataset to define the fluid domain. Three models were studied to simulate flow along three orthogonal directions (i.e., parallel to the central vein and in the radial and circumferential directions of the lobule). Inflow and outflow guidances were added to facilitate solution convergence, and good quality volume meshes were obtained using approximately 9 × 10(6) tetrahedral cells. Subsequently, three computational fluid dynamics models were generated and solved assuming Newtonian liquid properties (viscosity 3.5 mPa s). Post-processing allowed to visualize and quantify the microvascular flow characteristics, to calculate the permeability tensor and corresponding principal permeability axes, as well as the 3D porosity. The computational fluid dynamics simulations provided data on pressure differences, preferential flow pathways and wall shear stresses. Notably, the pressure difference resulting from the flow simulation parallel to the central vein (0-100 Pa) was clearly smaller than the difference from the radial (0-170 Pa) and circumferential (0-180 Pa) flow directions. This resulted in a higher permeability along the central vein direction (k(d,33) = 3.64 × 10(-14) m(2)) in comparison with the radial (k(d,11) = 1.56 × 10(-14) m(2)) and circumferential (k(d,22) = 1.75 × 10(-14) m(2)) permeabilities which were approximately equal. The mean 3D porosity was 14.3. Our data indicate that the human hepatic microcirculation is characterized by a higher permeability along the central vein direction, and an about two times lower permeability along the radial and circumferential directions of a lobule. Since the permeability coefficients depend on the flow direction, (porous medium) liver microcirculation models should take into account sinusoidal anisotropy.
肝脏微循环灌注通常基于多孔介质方法，根据理想化功能单元（六边形肝小叶）进行分析。开展更详尽的研究对于评估该方法的有效性以及更充分、定量地表征肝脏微循环至关重要。为此，我们利用人肝脏窦状隙的基于图像的三维（3D）重建和计算流体动力学技术，对肝脏微循环灌注进行建模。在血管铸型腐蚀后，从人肝脏血管复制品中解剖出一个代表三个肝小叶的微血管样本（±0.134 mm³），并使用高分辨率（2.6 μm）微型CT扫描仪进行扫描。经过图像处理后，从3D重建数据集中分离出一个代表相互交织和互连的窦状隙样本的立方体（0.15×0.15×0.15 mm³）来定义流体域。研究了三种模型以模拟沿三个正交方向（即平行于中央静脉以及在小叶的径向和圆周方向）的流动。添加了流入和流出引导以促进解的收敛，并使用大约9×10⁶个四面体单元获得了高质量的体网格。随后，生成并求解了三种计算流体动力学模型，假设液体具有牛顿流体性质（粘度3.5 mPa·s）。后处理能够可视化和量化微血管流动特性，计算渗透率张量和相应的主渗透率轴以及3D孔隙率。计算流体动力学模拟提供了关于压力差、优先流动路径和壁面剪应力的数据。值得注意的是，平行于中央静脉的流动模拟产生的压力差（0 - 100 Pa）明显小于径向（0 - 170 Pa）和圆周方向（0 - 180 Pa）的压力差。这导致沿中央静脉方向的渗透率更高（k(d,33) = 3.64×10⁻¹⁴ m²），相比之下，径向（k(d,11) = 1.56×10⁻¹⁴ m²）和圆周方向（k(d,22) = 1.75×10⁻¹⁴ m²）的渗透率大致相等。平均3D孔隙率为14.3。我们的数据表明，人肝脏微循环的特征是沿中央静脉方向具有较高的渗透率，而沿小叶的径向和圆周方向的渗透率约低两倍。由于渗透系数取决于流动方向，（多孔介质）肝脏微循环模型应考虑窦状隙各向异性。
