Study On Fluid-Structure Interaction Of Venous Valve Based On Immersed Boundary/Finite Element Method

Veins are important components of cardiovascular system,responsible for transporting blood from muscles and organs back to the heart.Veins contain paired semilunar valves that act as "one-way valves" to ensure that blood flows unidirectionally in veins,preventing backflow.Abnormalities in venous function may lead to venous diseases such as varicose veins and deep vein thrombosis.Studies on the hemodynamics of venous system help elucidate the pathophysiological mechanisms of venous diseases,providing effective supports for the clinical diagnosis and treatment of venous diseases,as well as the design of artificial valves.In this study,numerical simulation was constructed to explore the fluid-structure interaction between intravenous blood and valves.Firstly,based on the medical images of human lower extremity veins and the anatomical structure and geometric dimensions of bovine saphenous vein,three-dimensional geometric model of venous vessels and venous valves was carried out.Subsequently,a numerical framework was constructed based on the immersed boundary-finite element method.In the simulation,hyperelastic constitutive model was used to describe the incompressible,nonlinear and hyperelastic mechanical response of venous valves under physiological conditions,and boundary conditions in line with physiological reality were applied.Finally,by comparing the simulation results with in vivo and in vitro experimental results,the validity of the simulation results was illustrated.The main findings of this study are as follows:(1)The process of venous blood transportation and the mechanism of venous valve regurgitation prevention function were demonstrated via visualization,and the periodic characteristics of venous valve movement and intravenous blood flow were reproduced.In addition,important physiological data such as blood pressure,blood flow rate,venous valve geometry opening area,and venous valve surface stress and strain distribution were discussed and quantified throughout a dynamic cycle.The results indicated that the dynamic opening and closing processes of the venous valve was significantly related to the vortex present in the blood flow.Venous valves exhibited a significant antihypertensive effect,which could effectively reduce the pressure from the distal end.Blood flow in veins showed a layered pattern,with the numerical values of velocity and flow rate positively correlated with boundary pressure.During the movement of venous valves,the stress and strain were mostly concentrated in the free edge of venous valves.(2)Under different contributing factors,this study investigated and analyzed the changes in the mechanical characteristics of venous valves and the characteristics of blood flow within veins.Results showed that the increase of boundary pressure increased the flow rate and velocity of intravenous blood and the geometry opening area of venous valve,and the opening degree of venous valve was limited by the vortex in the sinus.The increase of hydrostatic pressure in the vein expanded the venous vessels,and the maximum shear stress was concentrated at the suture edge where the venous valve meets the venous vessel;Atrophied venous valves are prone to valve insufficiency,while fibrotic venous valves are prone to valve stenosis.(3)Model that included multiple pairs of venous valves analyzed and investigated the impact of fibre-reinforced tissue on the mechanical characteristics of venous valves,as well as the synergistic mechanism among multiple pairs of sequential venous valves.The simulation results revealed differences in the rhythmic motion patterns of adjacent venous valves and similarities in the distribution of surface stresses on venous valves.Additionally,the blood flow velocity between adjacent venous valves showed similar changes during a cardiac cycle.This study conducted an in-depth investigation on the hemodynamic mechanisms inside veins based on a three-dimensional fluid-structure interaction numerical model.The research results are expected to provide important references for understanding the formation mechanisms of venous diseases and to offer scientific evidence for the prevention,diagnosis,and treatment of such diseases.