Numerical Investigation of blood flow and structure interactions in aortic endovascular repair

Abstract

xx newlineABSTRACT newlineCardiovascular disease (CVD) is the major cause of death in the worldwide.Aortic newlineaneurysm (AA) is a life-threatening cardiovascular diseaseand it has high mortality newlinerate.An aortic aneurysmis a general term fordilationof a region of the aorta and it may newlinerupture if it is untreated.This disease can be treated by either conventional aneurysm newlinerepair or endovascular aneurysm repair (EVAR) when diagnosed timely.In both clinical newlinetreatments a stent-graft (SG) will be placed in the diseased region of the aorta which newlineshields the aneurysm from systemic pressure. These treatment procedures could cause newlinemany failures such as endoleakes, migration of stent-graft and stent-graft failure. It was newlinenoticed from in vivo and in vitro measurements that the aortic aneurysm growth is likely newlineto be related to the hemodynamics of blood flow in the aneurysmal aorta. The newlinehemodynamic parameters such as blood flow pattern, velocity distribution, aortic wall newlinepressure distribution, aortic wall shear stress distribution and aortic wall stress newlinedistribution are essential parameters to gain more understanding on the formation, newlineprogression and rupture of aortic aneurysms. The clinical treatment complications like newlinestent-graft migration, endoleakes are associated with the hemodynamics of blood flow in newlinethe stent-graft and aortic wall mechanics.These hemodynamic parameters are difficult to newlineobserve in vivo, but recent improvements in medical imaging and computer technology newlinehave enabled to evaluate these parameters using numerical simulations. Computational newlinesimulation of blood flow in arterial structure and arterial wall mechanics has been widely newlineemployed as a research tool to study the arterial diseases. newlineIn this study, the Computational Fluid Dynamic (CFD) technique was used to obtain newlinenumerical simulation of thesteady and transient flowin an idealized normal aorta, newlineaneurysmal aorta with different aneurysm diameters. The computational simulations of newlineNewtonian and non-Newtonian blood flow through an aorta model of normal subject newlinewere carried out to find the effect of non-Newtonian nature of blood on a pulsatileflow. newlineThe transient fluid dynamics study was carried out in an aorta model of normal subject newlinewith non-Newtonian fluid behaviorto find the effect of considering the branches of aorta newlinein the model. The numerical investigation on pulsatile blood flow through patient specific newlineaortic aneurysm models has been conducted to understand the severity of disease. The newlinexxi newlinepulsatile blood flow through patient specific aortic aneurysm models with stent-graft has newlinebeen simulated to compare the blood flow pattern of aneurysm model with the blood flow newlinepattern of aneurysm model with stent-graft and to calculate drag force acting on the stentgraft. In all these studies, the aortic wall was assumed as rigid wall. The Fluid-Structure newlineInteraction (FSI)technique was employed to simulate the blood flow through patientspecific aortic aneurysm models with and without stent-graft to compare stress newlinedistribution in the aneurysm model with stress distribution in the aneurysm model with newlinestent-graft. newlineResults were obtained for velocity fields, wall pressure, wall shear stress (WSS), wall newlinestress (WS) and drag force on the stent-graft. The flow in the smaller aneurysm models newlinebecame stable, but in the larger aneurysm models it became unstable with bigger newlinemagnitude of instability at the distal section of aneurysm. Results depicted similar blood newlineflow patterns for Newtonian and non-Newtonian fluid assumption, but the nonNewtonian nature of blood caused considerable increase in wall shear stress. The newlineinclusion of aortic branches in the aortic model reduced the wall pressure and wall shear newlinestress magnitudes. The results from computational fluid dynamics study demonstrated newlinethat the insertion of stent-graft in the aneurysm region prevents abnormal wall shear newlinestress distribution and recirculation of flow. The magnitude of drag force acting on the newlinestent-graft increased in high blood pressure situation. The results of Fluid-Structure newlineInteraction study has revealedthat the higher wall stress in the larger aneurysm model. newlineThe wall stress value increased inhigh blood pressure situation.From the results, it may newlinebe concluded that the peak wall stress on aneurysmal wall could be reduced when stentgraft is inserted. newlineThis Computational Fluid Dynamics and Fluid-Structure Interaction studies of patient newlinespecific aortic aneurysm, patient specific aortic aneurysm with stent-graft yield physical newlineinsight for measuring the blood hemodynamics, peak aortic aneurysm stress and drag newlineforce leading to migration of stent-graft. These measured parameters from this study newlinecould help the surgeons in assessing the severity of aortic aneurysms, finding the newlineeffectiveness of stent-graft and to suggest guidelines for post-operative care of newlineendovascular treatment. newline