City Research Online

Abstract

Atherosclerosis is a chronic disease affecting millions worldwide by leading to heart attack and stroke. It usually develops in regions with disturbed flow like the carotid artery, aorta, and coronary arteries. The major cause of atherosclerosis development is the deposition of lipids under the endothelial layer of the artery leading to plaque build-up. Also, evidence that the plaque formation occurs mainly near the bifurcations or curvatures had led to the hypothesis that irregular flow conditions plays a major role in development and progression of atherosclerosis. In vivo and in vitro studies at the cellular level and macroscopic levels shows the importance of understanding the local haemodynamics in atherosclerosis prone regions. Although diagnostic techniques such as Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) provides detailed anatomic information non-invasively, local haemodynamics can be studied at patient specific models using computational techniques like Computational Fluid Dynamics (CFD) and Fluid Structure Interaction (FSI). Therefore, it is very important to reconstruct anatomical models using CT or MRI images to gain accurate results in CFD or FSI analysis. The flow behaviour in large arteries is complex and it is influenced by the elasticity of the artery. Apart from this, the blood pressure changes during day to day activities. This interesting phenomenon of variation of blood pressure is studied by numerical simulation of blood flow in the normal and stenosed carotid artery. In this work, a three-dimensional (3D) Fluid Structure Interaction (FSI) study was carried out for a normal and stenosed patient specific carotid artery models. By considering physiological conditions, first the normal and then with hypertension disease, haemodynamic parameters were evaluated to better understand the genesis and progression of atherosclerotic plaques in the carotid artery bifurcation. Two-way FSI was performed by applying a fully implicit second-order backward Euler differencing scheme using commercial software ANSYS and ANSYS CFX (version 19.0). Arbitrary Lagrangian–Eulerian (ALE) formulation was employed to calculate the arterial response by using the temporal blood response. Due to arterial bifurcation, obvious velocity reduction and backflow formation were observed which decreased shear stress and made it oscillatory at the starting point of the internal carotid artery near the carotid sinus, which resulted in low shear stress. Oscillatory shear index (OSI) signifies oscillatory behaviour of artery wall shear stress. Comparison of the results of this study with those in the published literature showed that the regions with low wall shear stress and with OSI value greater than 0.3 pose potential risk to the development of plaques. It was observed that haemodynamics of the carotid artery was very much affected by the geometry and flow conditions. Furthermore, regions of relatively low wall shear stress were observed post stenosis, which is a known cause of plaque development and progression. The results were compared between Newtonian and Carreau – Yasuda blood viscosity models. Critical haemodynamic parameters such as wall shear stress (WSS) and Oscillatory Shear Index (OSI) were examined. Simulated hemodynamic parameters were able to capture the disturbed flow conditions in a normal and a stenosed carotid artery bifurcation, which play an important role in the development of local atherosclerotic plaques. Computational simulations based on diagnostic tools such as Ultrasound might help improving diagnostic and treatment management of carotid atherosclerosis.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TJ Mechanical engineering and machinery
Departments:	Doctoral Theses School of Science & Technology > School of Science & Technology Doctoral Theses School of Science & Technology > Engineering > Mechanical Engineering & Aeronautics

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