外支架对移植静脉力学特性的影响

自体静脉移植是动脉粥样硬化等血管阻塞疾病的主要治疗手段之一,但移植静脉重建引起的再狭窄严重影响通畅率。研究表明,静脉和动脉之间几何尺寸与力学性质的不同以及力学环境的差异是吻合口再狭窄的主要原因。在动脉环境下,静脉桥路被严重扩张,桥路的内半径要比宿主动脉的大很多,这不仅大大提高了桥路管壁中的应力水平,而且也促使吻合口附近涡流的形成。管壁中增高的周向应力和由于涡流引起的紊乱的切应力是静脉桥路再狭窄的主要原因。为了提高静脉桥路的通畅率,外支架的技术日益引起人们的重视。外支架除了可以加强静脉桥路壁强度,降低管壁中的周向应力外,还可以消除吻合口附近的涡流,从而起到保护作用。本文将综述外支架保护静脉桥路的研究历史以及目前现状。

Effect of Exterhal Stent on Venous Graft Mechanical Property

The autogenous vein is widely used as a conduit in grafting surgical operation.Due to the mismatches of mechanical properties and geometry,the graft is over expanded by arterial blood pressure and forms step-depth where eddy flow develops.The overexpansion results dramatically increased circumferential stress in venous wall,which damages tissue in middle layer.At the same time the shear stress induced by eddy flow is harmful to the intima.Additionally other factors, such as surgical trauma,also damage venous tissues.All of them are involved in intimal hyperplasia and fibrosis wall,and finally lead to restenosis and cause re-operation in a few following years.For eliminating these negative factors,the engineering method(called external stent),using a sheath to cuff the graft and prevent it from distension and eliminate the step-depth,is suggested.Experimental studies and clinical applications have proved its efficiency and significant improvement of grafting patency.But up to now the external stent is not one of regular techniques in clinical service.Because many problems remain to by solved,such as how the strength and degradability of supporting material affect the growth of graft;the remodeling process of venous graft with external stent is unknown;lacks of standard procedure of grafting operation with external stent.So further quantitative research needs to carry out in order to allow the graft arterialize successfully.In this paper,the history and current state of external stent was reviewed.