主动脉多层密网支架维持分支血流的理论与实验研究

The incidence of the aortic aneurysmal diseases(AAD) is increasing year by year, with high mortality and poor prognosis. Although the traditional endovascular aortic repair, which excludes the aneurysm with covered stents, has showed some benefit (such as less-invasiveness, better prognosis), not all aortic aneurysms are amenable to endovascular repair because of the anatomic features of the aortic branches. The multilayer stents(uncovered stents) provided an alternative approach to the treatment of AAD, which prevented the rupture of the aneurysms as well as maintained the patency of the aortic branches, therefore expanded the indication for endovascular repair. However, less clinical application and postoperative follow-up data of this new type of stent can be found overseas, while there is no domestic report. The critical technique of this type of stent was to control the diameter of the meshes, which reduced the shearing force on the wall of the aneurysm while preserved the patency of the branches, but its precise mechanism remained to be investigated. The aim of this study was to analysis the hemodynamic effects of the multilayer stent on the aneurysms and branches through hydrodynamic and animal experiments, to investigate the mechanism of this new type of stent, and to evaluate its efficacy and safety, in order to lay the theoretical and experimental basis for clinical application of this oncoming treatment method and achieve better outcomes.

主动脉扩张性疾病（AAD）发病率呈逐年上升趋势，且死亡率较高、预后较差。主动脉腔内修复术利用覆膜支架将瘤体隔绝，创伤小、疗效好，但其使用常受到主动脉分支的限制。多层密网支架既达到了传统覆膜支架防止主动脉瘤破裂的目的，同时保持了分支血流的通畅，扩大了腔内修复术的适应症。目前，国外该型支架的临床应用及术后随访资料较少，国内在此领域尚为空白。多层密网支架的关键技术在于通过控制网孔的大小，既降低了血流对瘤壁的剪切力，又维持了分支血流的通畅，但其机制尚有待深入研究。本研究拟通过流体力学实验，探讨分析多层密网支架对于瘤体及分支血管的血流动力学影响，之后再通过动物实验，直观定性分析多层密网支架对于动脉瘤瘤体以及分支血流的影响，对多层密网支架的治疗机理进行综合研究，并对其有效性和安全性进行评价，为临床应用奠定理论和实验基础，以期获得新的治疗方法以及更好的疗效。

主动脉扩张性疾病（AAD）发病率呈逐年上升趋势，且死亡率较高、预后较差。主动脉腔内修复术利用覆膜支架将瘤体隔绝，创伤小、疗效好，但其使用常受到主动脉分支的限制。多层密网支架既达到了传统覆膜支架防止主动脉瘤破裂的目的，同时保持了分支血流的通畅，扩大了腔内修复术的适应症。目前，国外该型支架的临床应用及术后随访资料较少，国内在此领域尚为空白。多层密网支架的关键技术在于通过控制网孔的大小，既降低了血流对瘤壁的剪切力，又维持了分支血流的通畅，但其机制尚有待深入研究。本研究先通过计算机流体力学数值模拟比较无支架和植入密网支架后腹主动脉瘤腔内血流动力学变化，发现与无支架相比，加入支架后血液进入瘤腔内的速度降低，在瘤腔内出现大范围的流动扰动且扰动程度增加，腔内壁面尤其瘤体中部和颈部等容易破裂的位置剪切力降低，瘤腔内压力有一定程度降低，从而保证了瘤体不会破裂。同时，植入多层密网支架后分支血管的血流保持通畅，有利于保证相应器官供血。进而通过体外流体力学试验，采用PIV粒子图像测速法比较植入多层裸支架前后玻璃动脉瘤腔内流场的变化，发现多层裸支架可以将瘤腔内大涡减小为小涡，且随裸支架层叠数量的增多，分叉管处瘤腔内的漩涡甚至消失，同时分叉管处瘤腔内的流动变为稳定、规则的层流。此外，植入多层裸支架后流体通过多层裸支架进入瘤腔内的速度明显减小，且随支架层叠数量增多，流速减小更多。最后通过动物实验，直观定性观察多层密网支架对于动脉瘤瘤体以及分支血流的影响，证实多层密网支架既可促进瘤腔缓慢血栓化，又可保持起自瘤体的分支血管通畅； 分支血流通路的形成不仅是血液动力学和血栓堆积相互作用的结果，还有血管内皮细胞的参与。但多层密网支架能否达到经典覆膜支架的治疗功效尚需进一步实验观察。