The Influences Of Internal Carotid Artery Stenosis And High Blood Pressure On The Circle Of Willis Based On Fluid-structure Couplied Finite Element Analysis

The circle of Willis (CoW) is one of the important structure of establishment of the cerebral collateral circulation. Two sides of the carotid artery system and the vertebrobasilar system are harmonically connected by anterior communicating artery (AcoA) and posterior communicating artery (PcoA). The occurrence and development of many cerebrovascular diseases has a close relationship with the haemodynamics of the CoW.In this paper, the CoW was reasonably simplified and assumed and the fluid-solid coupling finite element model was created. The haemodynamics and vascular stress were investigated considering effects of internal carotid stenosis and high blood pressure on CoW. At the same time, the openness degree of collateral circulation for CoW and the occurrence probability of the AcoA and PcoA aneurysms were conducted. The research results could provide some mechanical basis on the influenced factors of the brain collateral circulation openness for medical researches. Meanwhile, some references for clinical diagnosis and treatment for cerebrovascular diseases were presented.The main work of this thesis was outlined as follows:1. On the basis of the MRI of the blood vessels of brain, the centerline model of the blood vessels in the CoW was obtained. According to the radius and thickness data of the normal CoW in the literature,3D geometric model of the normal CoW was reconstructed by CAD software.2.3D geometric model of the normal CoW was modified and an axisymmetric model of stenosis was artificially constructed at the beginning of the left internal carotid artery (L-ICA). Thus the geometric models of CoW with different rate of internal carotid artery stenosis were founded.3. The3D finite element modes in different conditions were constructed by ANSYS and the meshing of the vessels and the blood was done by using this software. In the models of CoW, incompressible viscous Newtonian blood flow and elastic vessels were assumed.4. The fluid-structure finite element simulations of the CoW in different conditions were completed in the ANSYS-CFX software. Blood flow dynamics and force analysis of the CoW were discussed mainly from two aspects, which were the internal carotid artery stenosis degree and high blood pressure.Some conclusions were as follows:1.The conclusions of the CoW with different stenosis rate in the condition of one sided internal carotid artery stenosis were drawn.(1) AcoA and PcoA in the stenosis side both played important roles in the CoW in the condition of one sided internal carotid artery stenosis.(2) When the internal carotid artery stenosis rate is50%, the collateral pathways of the CoW would be opened; when stenosis rate is70%, the blood flow would significantly change in the opening of the collateral blood vessels, and the flow velocity and mass flow increased rapidly; when stenosis rate is 75%, the blood flow of the anterior cerebral arteries Al part would be reversed.(3) Under the condition of the internal carotid artery stenosis, the risk of the AcoA and PcoA aneurysms would increase. Moreover, the aneurysms would easily emerge in the part of the blood vessels where the stress was concentrated. The occurrence had a close relationship with the hemodynamics changes.2.The conclusions with different blood pressure were presented.(1) With the blood pressure increased, the imbalance hemodynamics of the CoW intensified due to internal carotid artery stenosis. Furthermore, the imbalance would promote the opening of the AcoA and PcoA. The larger the stenosis rate was, the greater the promoting role became.(2) In the condition of high blood pressure, the risk of occurrence the AcoA aneurysms and PcoA aneurysms would increase. Moreover, the aneurysms would easily emerge in the part of the blood vessels where the stress was concentrated.