Centre for Applied Biomedical Engineering Research, Health Research Institute, School of Engineering, Bernal Institute, University of Limerick, Limerick, Ireland.
Department of Vascular Surgery, University Hospital Limerick, Limerick, Ireland.
J Vasc Surg. 2018 Apr;67(4):1234-1246.e2. doi: 10.1016/j.jvs.2017.05.086. Epub 2017 Sep 9.
Parameters other than maximum diameter that predict rupture of abdominal aortic aneurysms (AAAs) may be helpful for risk-benefit analysis in individual patients. The aim of this study was to characterize the biomechanical-structural characteristics associated with AAA walls to better identify the related mechanistic variables required for an accurate prediction of rupture risk.
Anterior AAA wall (n = 40) and intraluminal thrombus (ILT; n = 114) samples were acquired from 18 patients undergoing open surgical repair. Biomechanical characterization was performed using controlled circumferential stretching tests combined with a speckle-strain tracking technique to quantify the spatial heterogeneity in deformation and localized strains in the AAA walls containing calcification. After mechanical testing, the accompanying microstructural characteristics of the AAA wall and ILT types were examined using electron microscopy.
No significant correlation was found between the AAA diameter and the wall mechanical properties in terms of Cauchy stress (r = -0.139; P = .596) or stiffness (r = -0.451; P = .069). Quantification of significant localized peak strains, which were concentrated in the tissue regions surrounding calcification, reveals that peak strains increased by a mean of 174% as a result of calcification and corresponding peak stresses by 18.2%. Four ILT types characteristic of diverse stages in the evolving tissue microstructure were directly associated with distinct mechanical stiffness properties of the ILT and underlying AAA wall. ILT types were independent of geometric factors, including ILT volume and AAA diameter measures (ILT stiffness and AAA diameter [r = -0.511; P = .074]; ILT stiffness and ILT volume [r = -0.245; P = .467]).
AAA wall stiffness properties are controlled by the load-bearing capacity of the noncalcified tissue portion, and low stiffness properties represent a highly degraded vulnerable wall. The presence of calcification that is contiguous with the inner wall causes severe tissue overstretching in surrounding tissue areas. The results highlight the use of additional biomechanical measures, detailing the biomechanical-structural characteristics of AAA tissue, that may be a helpful adjunct to improve the accuracy of rupture prediction.
除最大直径以外的其他参数可能有助于对个体患者的腹主动脉瘤（AAA）破裂风险进行获益-风险分析。本研究旨在描述与 AAA 壁相关的生物力学-结构特征，以更好地确定与准确预测破裂风险相关的机械学变量。
从 18 例行开放手术修复的患者中获取了前 AAA 壁（n=40）和管腔内血栓（ILT；n=114）样本。通过控制周向拉伸测试并结合散斑应变跟踪技术对生物力学进行了表征，以量化包含钙化的 AAA 壁的变形空间异质性和局部应变。力学测试后，使用电子显微镜检查 AAA 壁和 ILT 类型的伴随微观结构特征。
AAA 直径与壁力学性能（以 Cauchy 应力表示：r=-0.139；P=0.596）或刚度（r=-0.451；P=0.069）之间无显著相关性。在组织中钙化周围区域集中的显著局部峰值应变的定量分析表明，由于钙化，峰值应变平均增加了 174%，相应的峰值应力增加了 18.2%。4 种 ILT 类型代表了组织微观结构中不同阶段的演变，它们与 ILT 和下方 AAA 壁的不同力学刚度特性直接相关。ILT 类型与包括 ILT 体积和 AAA 直径测量在内的几何因素无关（ILT 刚度和 AAA 直径 [r=-0.511；P=0.074]；ILT 刚度和 ILT 体积 [r=-0.245；P=0.467]）。
AAA 壁的刚度特性受无钙化组织部分的承载能力控制，低刚度特性代表高度退化的脆弱壁。与内表面连续的钙化的存在会导致周围组织区域的严重组织过度拉伸。研究结果强调了使用额外的生物力学测量方法，详细描述 AAA 组织的生物力学-结构特征，这可能有助于提高破裂预测的准确性。
