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Blood flow dynamics and wall shear stress in the circle of Willis

Page, J.H.; (2009) Blood flow dynamics and wall shear stress in the circle of Willis. Doctoral thesis, UCL (University College London).

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Abstract

Local blood flow can cause wall shear stress (WSS) patterns which are linked to the formation of aneurysms[1]. A common location for intracranial aneurysms is the anterior communicating artery (ACoA) which connects the anterior cerebral arteries (ACAs) in the circle of Willis (CoW)[2]. The CoW is a ringlike four-to-six junction[3] with potentially highly complex flow patterns[3-5]. In this thesis, we develop a two-dimensional, rigid CoW model, with pulsatile inlet pressure conditions and resistance outlet conditions. The Navier-Stokes equations are solved using the latest finite volume method derivation[6] and some additional mathematics for the pressure condition. A code, based on that of the author's supervisor, is developed to carry out flow simulations. Three simulation set-ups cover a physiological range of flows: symmetric inlet conditions and configuration; internal carotid artery inlet pressure phase difference and symmetric configuration; symmetric inlet conditions and a narrow proximal (A1) section of the left ACA. In the first case, we find asymmetric, weak ACoA flow with vortex patches at each end due to stronger passing ACA streams. This causes areas of raised WSS in the ACA, narrow WSS peaks at the ACoA ends, and low magnitude, oscillating WSS along the ACoA. In the second case, we find that small phase differences lead to significant ACoA flow, oscillating in direction. This results in (potentially low magnitude) oscillating ACoA WSS. Compared with the first case, we see increases in the raised ACA WSS on the upstream ACoA side and considerable increases in the narrow peaks leading to high magnitude WSS and high WSS gradient. In the third case, a one-half normal width left A1 causes a significant right-to-left ACoA flow. Striking consequences include increases in both narrow peaks, from the first case, causing high magnitude WSS and high WSS gradients, and separation inducing disturbances and low magnitude, oscillating WSS.

Type:Thesis (Doctoral)
Title:Blood flow dynamics and wall shear stress in the circle of Willis
Language:English
Additional information:Authorisation for digitisation not received
UCL classification:UCL > School of BEAMS > Faculty of Engineering Science > Mechanical Engineering

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