Matthews Peter B, Jhun Choon-Sik, Yaung Stephanie, Azadani Ali N, Guccione Julius M, Ge Liang, Tseng Elaine E
Department of Surgery, University of California at San Francisco Medical Center, San Francisco, CA 94103-0118, USA.
J Heart Valve Dis. 2011 Jan;20(1):45-52.
Pulmonary autograft dilatation requiring reoperation is an Achilles' heel of the Ross procedure, as exposure to systemic pressure increases autograft wall stress, which may in turn lead to tissue remodeling and aneurysmal pathology. However, the magnitude of autograft wall stress with the Ross procedure is unknown. The study aim was to develop a realistic finite element (FE) model of the autograft, and to perform simulations at systemic pressure to determine wall stress distribution immediately after the Ross operation.
The porcine pulmonary root geometry was generated from high-resolution microcomputed tomography (microCT) images to create a mesh composed of hexahedral elements. Previously defined constitutive equations were used to describe the regional material properties of the native porcine pulmonary root. The anterior and posterior pulmonary arteries, and each of the pulmonary sinuses, were best described by non-linear, anisotropic Fung strain energy functions, and input individually into the model. Autograft dilatation and wall stress distribution during pulmonary and systemic loading prior to remodeling were determined using explicit FE analysis in LS-DYNA.
The autograft was highly compliant in the low-strain region, and the majority of dilation occurred with < 30 mmHg of pressurization. During pulmonic loading, a typical inflation/deflation was observed between systole and diastole, but the autograft remained almost completely dilated throughout the cardiac cycle at systemic pressure. Although the systolic blood pressure was 380% greater in the aortic than in the pulmonary position, the peak systolic diameter was increased by only 28%. The maximum principal wall stress increased approximately 10-fold during systole and 25-fold during diastole, and was greater in the sinus than the distal artery for all simulations.
Under systemic loading conditions, the pulmonary autograft remained fully dilated and experienced large wall stresses concentrated in the sinus. The future correlation of this model with explanted autografts may lead to an improved understanding of tissue remodeling following the Ross procedure.
需要再次手术的肺动脉自体移植扩张是Ross手术的致命弱点，因为暴露于体循环压力会增加自体移植血管壁应力，这进而可能导致组织重塑和动脉瘤病变。然而，Ross手术中自体移植血管壁应力的大小尚不清楚。本研究的目的是建立一个逼真的自体移植血管有限元（FE）模型，并在体循环压力下进行模拟，以确定Ross手术后即刻的血管壁应力分布。
从高分辨率微型计算机断层扫描（microCT）图像生成猪肺动脉根部几何形状，以创建由六面体单元组成的网格。使用先前定义的本构方程来描述天然猪肺动脉根部的区域材料特性。肺动脉前、后分支以及每个肺窦，最好用非线性、各向异性的冯氏应变能函数来描述，并分别输入模型。在重塑之前，使用LS-DYNA中的显式有限元分析确定肺循环和体循环加载期间自体移植血管的扩张和血管壁应力分布。
自体移植血管在低应变区域具有高度顺应性，大部分扩张发生在压力增加<30 mmHg时。在肺循环加载期间，在收缩期和舒张期之间观察到典型的充盈/排空，但在体循环压力下，自体移植血管在整个心动周期中几乎保持完全扩张。尽管主动脉位置的收缩压比肺动脉位置高380%，但收缩期峰值直径仅增加了28%。在所有模拟中，最大主壁应力在收缩期增加约10倍，在舒张期增加25倍，并且在窦部比远端动脉更大。
在体循环加载条件下，肺动脉自体移植血管保持完全扩张，并经历集中在窦部的大血管壁应力。该模型与取出的自体移植血管的未来相关性可能会增进对Ross手术后组织重塑的理解。
