Influence Of The Anatomical Structure On The Hemodynamics Of Iliac Vein Stenosis

Iliac-vein compression or abnormal intra-luminal adhesion causes lower limb and pelvic venous return obstruction diseases,namely iliac vein compression syndrome.With the rapid development of intravascular therapy,vascular stent implantation has become an effective and reliable method for treating iliac vein compression syndrome.Stent implantation can increase the risk of blood vessel damage and lead to intimal hyperplasia at the implantation segment,which is the main cause of restenosis in the stent after implantation.In this paper,the changes in the internal flow field of the iliac vein blood vessels are simulated through finite element analysis to study the influence of the anatomical structure of the iliac vein blood vessels and the stent implantation location on hemodynamics and judge the risk of clot formation in the blood vessels and restenosis in the stent,which is of great significance for the prevention,diagnosis and treatment of vascular diseases of the lower extremities.In this paper,theoretical analysis,numerical simulation and in vitro experimental research are carried out to analyze the influence of the left branch pendulum angle,stenosis rate,vascular taper and stent implantation of the iliac location of vein blood vessels on the blood flow field.The analysis covers hemodynamic indicators such as blood flow velocity,wall shear stress,and oscillating shear coefficient,which reveals the law of influence on hemodynamics.1)Based on human medical imaging data,a blood vessel model of the iliac vein was reconstructed,followed by establishment of watershed models of different stenosis rates,taper,and left branch pendulum angles.Hemodynamic analysis was conducted using the calculation method in fluid mechanics.It was found that stenosis causes a significant increase in the shear stress of the blood vessel wall at the stenosis site,as well as eddy currents at the remote blood vessels;tapered blood vessel causes the increased proportion of low-wall shear stress areas,resulting in increased risk of thrombosis;excessively small pendulum angle exacerbates the effect of stenosis on blood flow and blood vessel walls.2)Blood vessel models of different stent implantation locations were established.The three implementation locations are the location somewhere from the front end of the stent to the outlet of the left branch,the position of the contralateral turbulent flow,and the position of the main iliac vein.It was found that stent implantation causes the decreased maximum blood flow rate of the iliac vein;the OSI and RRT indexes of the Venastent stent at the three positions are smaller than those of the Zilver vena stent;the corolla design of the Venastent stent is conducive to reducing the effect of stent implantation on the blood flow of contralateral blood vessel.Among the three locations,the impact on the blood flow of the iliac vein is the smallest at the position of the contralateral turbulent flow.3)A model of the iliac vein blood vessel with stenosis and taper was established.The change of shear stress of the blood vessel wall with stenosis and taper was derived through the theory of fluid mechanics.Then,the blood flow characteristics of the iliac vein with stenosis and taper was analyzed theoretically.It was found that when the stenosis rate increases,the wall shear stress increases significantly;and that when the taper of blood vessel increases,the wall shear stress also increases.4)Three in vitro iliac vein models with different degrees of stenosis were established through advanced reverse engineering and 3D printing rapid prototyping.Next,an experimental platform for extracorporeal circulation of the iliac vein was built.The blood flow field in the blood vessels was tested through Particle image velocimetry(PIV),so as to analyze the blood flow field characteristics of the models with different stenosis and stent implantation locations.It was found that the result is basically the same as the simulation result.