Teng Zhong-zhao, Ji Guang-yu, Chu Hong-jun, Li Zhi-Yong, Zou Liang-jian, Xu Zhi-yun, Huang Sheng-dong
Aragon Institute of Engineering Research (I3A), University of Zaragoza, Spain.
Biomed Eng Online. 2007 Apr 16;6:12. doi: 10.1186/1475-925X-6-12.
Autogenous vein grafting is widely used in regular bypassing procedures. Due to its mismatch with the host artery in both mechanical property and geometry, the graft often over expands under high arterial blood pressure and forms a step-depth where eddy flow develops, thus causing restenosis, fibrous graft wall, etc. External stents, such as sheaths being used to cuff the graft, have been introduced to eliminate these mismatches and increase the patency. Although histological and immunochemical studies have shown some positive effects of the external stent, the mechanical mismatch under the protection of an external stent remains poorly analyzed.
In this study, the jugular veins taken from hypercholesterolemic rabbits were transplanted into the carotid arteries, and non-woven polyglycolic acid (PGA) fabric was used to fabricate the external stents to study the effect of the biodegradable external stent. Eight weeks after the operation, the grafts were harvested to perform mechanical tests and histological examinations. An arc tangent function was suggested to describe the relationship between pressure and cross-sectional area to analyse the compliance of the graft.
The results from the mechanical tests indicated that grafts either with or without external stents displayed large compliance in the low-pressure range and were almost inextensible in the high-pressure range. This was very different from the behavior of the arteries or veins in vivo. The data from histological tests showed that, with external stents, collagen fibers were more compact, whilst those in the graft without protection were looser and thicker. No elastic fiber was found in either kind of grafts. Furthermore, grafts without protection were over-expanded which resulted in much bigger cross-sectional areas.
The PGA external extent contributes little to the reduction of the mechanical mismatch between the graft and its host artery while remodeling develops. For the geometric mismatch, it reduces the cross-section area, therefore matching with the host artery much better. Although there are some positive effects, conclusively the PGA is not an ideal material for external stent.
自体静脉移植广泛应用于常规搭桥手术。由于其在力学性能和几何形状上与宿主动脉不匹配，移植血管在高动脉血压下常过度扩张，并形成涡流产生的阶跃深度，从而导致再狭窄、移植血管壁纤维化等问题。外部支架，如用于包裹移植血管的护套，已被引入以消除这些不匹配并提高通畅率。尽管组织学和免疫化学研究已显示外部支架有一些积极作用，但在外部支架保护下的力学不匹配仍未得到充分分析。
在本研究中，将取自高胆固醇血症兔的颈静脉移植到颈动脉中，并使用非织造聚乙醇酸（PGA）织物制作外部支架，以研究可生物降解外部支架的作用。术后8周，取出移植血管进行力学测试和组织学检查。建议使用反正切函数来描述压力与横截面积之间的关系，以分析移植血管的顺应性。
力学测试结果表明，有或没有外部支架的移植血管在低压范围内均表现出较大的顺应性，而在高压范围内几乎不可伸展。这与体内动脉或静脉的行为非常不同。组织学测试数据表明，有外部支架时，胶原纤维更致密，而无保护的移植血管中的胶原纤维更松散且更厚。两种移植血管中均未发现弹性纤维。此外，无保护的移植血管过度扩张，导致横截面积大得多。
在重塑过程中，PGA外部支架对减少移植血管与其宿主动脉之间的力学不匹配作用不大。对于几何不匹配，它减小了横截面积，因此与宿主动脉的匹配性更好。尽管有一些积极作用，但最终PGA不是外部支架的理想材料。
