Analysis of the haemodynamics and biomechanics of endografts for complex aortic arch repair

主动脉起源于左心室，向上（升主动脉），然后弯曲并开始向下（降主动脉），将血液运送到身体的不同部位。主动脉的这个弯曲区域，称为主动脉弓，由将血液输送到上肢，最重要的是大脑的分支组成。弓部的畸形可以包括血管壁的撕裂，即主动脉夹层，或者更常见的是当壁变弱和扩张时，引起动脉瘤。主动脉瘤的发生可能是由于血管的动脉粥样硬化改变、血压不规则或马凡氏综合征或巨主动脉综合征等疾病。动脉瘤的大小随着时间的推移而发展，当破裂或达到一定大小时需要手术。主动脉弓手术是一项复杂的手术，自1964年首次报道以来，多年来外科手术已经发生了一些变化和发展。多年来，该程序的几种变化带来了不同程度的风险和回报。关于开放和/或混合手术方法的有效性以及决定患者是否适合任何一种修复方法的因素存在很多争议。最近的方法，如冷冻象鼻技术（涉及覆膜支架的顺行植入）和TEVAR（胸主动脉腔内修复术）已被证明成功地结合了不同的先前手术方法和治疗复杂的弓异常。这些方法包括在血管弓中插入一个覆膜支架，为血液提供一种通过的方式，而不会推动弱化的血管衬里。TEVAR中使用的覆膜支架可能会根据部署方法和放置区域而有所不同。覆膜支架对主动脉血液动力学和生物力学条件的影响非常重要，因为它们与手术的长期结局相关。本研究旨在使用计算方法研究覆膜支架及其对主动脉血流和生物力学的影响。计算流体动力学（CFD）是研究生物流动的常用工具，通常用于模拟和研究无法在体内测量的现象。它允许获得诸如流体速度、流动模式、壁面剪切应力和位移力等参数，所有这些参数在评价覆膜支架性能时都很重要。计算手段还允许进行流体-结构相互作用（FSI）研究。这有助于理解流经移植区域的血液如何与覆膜支架的组分以及血管衬里相互作用。之前已经进行了计算研究，以研究主动脉（主要是胸部和腹部区域）中支架和移植物的流量。然而，主动脉弓是一个在修复方法方面正在经历重大发展的区域，因此提供了一个新的平台来进行研究。通过不同设计和几何形状的覆膜支架的血液流动模式的研究将允许人们预测手术或特定覆膜支架设计的临床结局，从而提供优化和改进覆膜支架设计和特征的机会。

The aorta originates from the left ventricle, directed upwards (ascending aorta), before it curves and begins to travel downwards (descending aorta), carrying blood to different parts of the body. This curved region of the aorta, referred to as the aortic arch, consists of branches that carry blood to the upper limbs and most importantly, the brain. Deformities in the arch can include tears in the vessel wall, i.e. aortic dissection, or more commonly when the walls weaken and expand, giving rise to an aneurysm. Aortic aneurysms can occur due to atherosclerotic changes in the vessel, irregularities in blood pressure, or as a result of conditions such as Marfan's Syndrome or Mega-Aorta Syndrome.Aneurysms develop in size over time and require surgery when they rupture or have reached a certain size. Surgery in the aortic arch is a complex procedure and there have been several changes made and developments to the surgical procedure over the years, ever since it was first reportedly carried out back in 1964. Over the years, several variations to the procedure have presented with varying degrees of risk and reward. There has been much debate over the efficacy of open and/or hybrid surgical methods and what determines the suitability of patients for either repair method. Recent methods such as the Frozen Elephant Trunk Technique (involving the antegrade implantation of a stent graft) and TEVAR (Thoracic endovascular aortic repair) have proven successful in combining different previous surgical methods and treating complex arch abnormalities. These involve inserting an endograft in the arch, providing a means for blood to pass through without pushing on the weakened vessel lining.Endografts used in the TEVAR could vary according to the method of deployment, and the region where they are placed. The effects of endografts on haemodynamic and biomechanical conditions of the aorta are of significant importance, as they are related to the long-term outcomes of the procedure. This study aims to investigate endografts and their impact on aortic flow and biomechanics using computational means. Computational Fluid Dynamics (CFD) is a common tool for investigating biological flows and is often used to simulate and study phenomena that cannot be measured in vivo. It allows one to obtain parameters such as fluid velocity, flow patterns, wall shear stress and displacement forces, all of which would be important in evaluating the performance of endografts. Computational means also allow one to carry out fluid-structure interaction (FSI) studies. This is useful in understanding how the blood flowing through grafted regions interact with the components of the endograft as well as the vessel lining. Computational studies have been previously carried out to investigate flow across stents and grafts in the aorta, primarily the thoracic and abdominal regions. The aortic arch however, is a region undergoing significant developments in terms of methods of repair, and thus provides a novel platform to carry out investigations. The study of flow patterns of blood through endografts of different designs and geometries would allow one to predict clinical outcomes of a procedure or specific grafts designs, thereby providing opportunities to optimise and improve upon endograft designs and characteristics.