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），将血液输送到身体的不同部位。主动脉的弯曲区域被称为主动脉弓，由分支组成，将血液输送到上肢，最重要的是输送到大脑。弓的畸形可能包括血管壁撕裂，即主动脉夹层，或者更常见的是当血管壁变弱和扩张时，产生动脉瘤。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，或者是马凡氏综合征或大主动脉综合征等疾病的结果。动脉瘤随着时间的推移而增大，当它们破裂或达到一定大小时需要手术。主动脉弓的手术是一项复杂的手术，自从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，该程序的几种变化呈现出不同程度的风险和回报。关于开放和/或混合手术方法的疗效以及决定患者是否适合这两种修复方法的因素一直存在很多争论。最近的方法，如冷冻象鼻技术（包括顺行植入支架）和TEVAR（胸椎血管内主动脉修复）已被证明成功地结合了不同的先前的手术方法和治疗复杂的弓异常。这包括在弓内插入一个内移植物，为血液通过提供一个途径，而不挤压脆弱的血管内膜。TEVAR中使用的内移植物可以根据部署方法和放置区域而变化。内移植物对主动脉血流动力学和生物力学条件的影响是非常重要的，因为它们关系到手术的长期结果。本研究旨在利用计算方法研究内移植物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，经常用于模拟和研究无法在体内测量的现象。它允许人们获得诸如流体速度、流动模式、壁剪切应力和位移力等参数，所有这些对于评估内移植物的性能都是重要的。计算手段也允许进行流固相互作用（FSI）的研究。这有助于理解流经移植物区域的血液是如何与移植物的成分以及血管内膜相互作用的。先前已经进行了计算研究，以调查主动脉内支架和移植物的流动，主要是胸部和腹部区域。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，因此为开展研究提供了一个新的平台。通过研究不同设计和几何形状的内移植物的血流模式，可以预测手术或特定移植物设计的临床结果，从而提供优化和改进内移植物设计和特性的机会。

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.