基于4D-PCMR的主动脉夹层流固耦合分析

After the presentation of aortic dissection, several severe complications such as aortic rupture, visceral ischemia, retrograde type A dissection, and aneurysmal formation threaten the lives of the patient, compromising the therapeutic effect and long-term results. There is a general consensus that the significant causes of such consequences are related with hemodynamic interactions with aortic wall. The interactions often determine the progression of the disease: dilation and rupture. In order to assess such risks, we conducted our previous biomechanical and stent-graft developing research. The current study focuses on the following aspects: 1, the measurement of aortic hemodynamic data such as major entry pressure and velocity using 4D-PCMR and pressure catheter; 2, establishing the constitutive equation through the evaluation of aortic wall properties via ex vivo experiments; 3, computational simulation of the fluid structure interaction through finite element method and computational fluid dynamics software.4, the calculation of flow velocity, pressure, wall sheer stress, wall surface tension, and wall shift of the entry tear, ture lumen and false lumen. After these experiments, we hope to explore the biomechanical mechanism of aortic dissection progression and rupture, provide theoretical basis of preoperative and rupture risk evaluation, and improve the safety and validity of both medical and endovascular therapies.

主动脉夹层治疗前后可出现破裂、内脏动脉缺血等高致死率并发症，其原因与血流对动脉壁的相互有关。血液的主动脉相互作用的研究可用于对主动脉夹层扩张趋势及破裂风险的评估，但是目前国内缺乏对主动脉夹层流固耦合的相关研究。在前期生物力学研究和支架研发基础上，本项目拟①通过压力导管、4D-PCMRI等临床数据测量，获得主动脉夹层主要出入口的压力和血流速度等信息；②通过离体实验、管壁力学分析，建立表征主动脉壁力学性质的本构方程；③利用有限元分析软件结合计算流体力学软件，对主动脉夹层的脉动血液和血管壁的流固耦合作用进行数值模拟；④得出夹层模型中各个部位，如破裂口、真假腔中的血流速度、压力、壁面切应力、血管张力、管壁位移等信息。本研究将探索主动脉夹层进展和破裂的血流和主动脉相互作用的生物力学机制，为主动脉夹层术前扩张趋势与破裂风险评估提供理论依据，为提高主动脉夹层治疗的安全性提供科学性的实验依据和研究思路。

腔内支架修复(TEVAR)已成为治疗胸主动脉夹层(TAD)的首选术式，假腔内血栓化是评判术后疗效的关键因素。寻找血栓化的危险因素，阐明其机制，有助于改善预后。TAD假腔形态各异，血流分布复杂多变，单纯依赖CT影像评判具有较大局限性。我们前期通过动物建模探索B型主动脉夹层的进展和血流动力学特征，结果显示夹层撕裂层次影响夹层的进展，内膜片靠近外膜较靠近内膜时夹层更易进展，破裂风险更大。解剖因素和血流动力学变化共同影响夹层的进展和稳定。同时，本研究也通过Doppler导丝测量探索了人体B型主动脉夹层及腔内治疗后血流动力学的变化特征。我们成功获取了主动脉夹层4D PC-MRI数据采集的技术路线，并对图像数据进行后处理。结果提示该数据获取和后处理技术可行、有效。针对该结果的临床诠释提示假腔在心动周期内反复呈现涡流、螺旋流等复杂的血流形式；真、假腔内流速均与近、远端破口的位置和大小有关。本研究成果完成课题预期内容，但仍有许多问题需要深入研究。总之，本课题前期研究成果可为阐明TAD及TEVAR术后假腔血栓化的机制提供新思路，从而进一步推动TEVAR 治疗的精准化。