City Research Online

Abstract

Atherosclerosis is a problem that affects millions of people worldwide. The causative factors that contribute to the formation of atherosclerotic lesions have been studied extensively. Haemodynamic factors are known to be important determinants. However, the precise role played by haemodynamics in the development and progression of vascular disease is incompletely understood and findings have sometimes been contradictory. At the same time much solid mechanics oriented work has been done with a specific focus on stress concentrations in the arterial wall in order to examine other possible factors. While great progress has been made in studies of both haemodynamics and vessel wall mechanics separately, it is apparent that the problem of blood flow in arteries is one of fluid-wall interaction, and this necessitates the incorporation of the wall mechanics into fluid dynamics. The combination of fluid/solid mechanics may lead to further insight into the mechanisms underlying the formation of atherosclerotic lesions by taking the dynamic interaction between the blood and vessel wall into account.

In this study, a novel numerical algorithm for coupled solid/fluid problems was developed and applied to arterial flows. The coupled model involves the use of two commercial codes, CFX and ABAQUS. The hybrid nature (finite volume method for the fluid and finite element method for the solid) makes itself a highly efficient tool for modelling fluid/solid interactions. The method is able to predict the full, time-dependent wall behaviour, as well as the details of the flow field. Computer programs, originally developed to process clinically obtained MRI images, have been modified in order to provide geometrical data of in vivo human carotid bifurcations and to generate computational grids. New program routines were developed for the incorporation of wall movement required by the computer simulation, and integration of the fluid and solid mechanics codes for the coupled model. A comprehensive range of code validation exercises have been carried out to determine the reliability of the computer codes.

Finally, the coupled model has been applied to the modelling of pulsatile flow in anatomically realistic compliant human carotid bifurcations. In vivo pressure and mass flow waveforms in the carotid arteries were obtained from the individual subjects using non-invasive techniques. The geometry of the computational models was reconstructed from magnetic resonance angiograms. Results have been validated against the in vivo MRI measurements obtained from the individuals scanned. High wall stress and low shear stress was found in those areas most prone to atherosclerosis. It is demonstrated that the presented coupled modelling scheme can be used as an efficient and reliable tool for detailed analysis of blood flow and vessel mechanics. In future, application of the coupled model in a large number of individual cases together with disease patterns may further elucidate the roles of haemodynamics and vessel wall mechanics in atherosclerosis.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QA Mathematics > QA75 Electronic computers. Computer science Q Science > QH Natural history > QH301 Biology R Medicine
Departments:	School of Science & Technology > Engineering > Mechanical Engineering & Aeronautics School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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