Experimental modelling of vascular haemodynamics

Dalton, M.W., 2002. Experimental modelling of vascular haemodynamics. PhD, Nottingham Trent University.

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Abstract

Cardiovascular disease is known to be one of the greatest causes of natural mortality in Western society. At this time there is a worldwide drive to reduce the effect of heart disease upon the population and its impact upon health centers and resources. A common and lethal form of heart disease is manifest in the human body through a weakening and subsequent bulging of arterial vessels. This is known as an aneurysm. Often found, but more so in the older\male demographic, abdominal aortic aneurysms are known to develop and rupture due to material failure in the integrity of the vessel wall due to excessive load applied by mechanical forces. Development of aneurysms as been linked to factors such as smoking, poor diet and hypertension. However, physical haemodynamic forces acting upon the vessel wall also have an integral part to play in the further growth and eventual rupture of these afflicted vessels. Specifically wall shear forces and areas of stagnation and low fluid shear have been linked to the growth of atherosclerotic lesions and atheroma. Through scientific study of the physical forces involved and the flow regimes observed in aneurysms 1 understanding of these mechanical forces is gained.

Haemodynamic study into aneurysms is conducted through clinical, numerical and experimental work. Due to the delicate nature of aneurysms and that of the human body clinical studies are limited in live patients. Numerical studies are commonplace and gain much knowledge of the fluid flow involved. However, research carried out through computational means requires validation to ensure confidence in the findings. As such experimental work has a part to play in these investigations, most especially in with regard to three-dimensional flows and those exhibiting turbulence. It is the pursuit of any in vitro haemodynamic research to construct increasingly more complex and physiologically appropriate models in which to study these forces. As yet, torsion in the aortic flow has been neglected with regard to its distal effects.

A haemodynamic flow rig has been designed to carry out studies into abdominal aortic aneurysms. Both steady and pulsatile flow regimes were implemented and inlet torsion induced by the presence of the aortic arch was studied. Detailed flow measurements were taken using laser Doppler velocimetry techniques to study the effect of torsion upon the flow field through a grid-based analysis. Also near wall measurements were taken in the distal sector of the aneurysm to measure wall shear stress gradients experienced by the aneurysm. Comparisons were made between the flow regimes and forces measured in order to assess the requirement of including torsional inlet parameters in further experimental and numerical studies of aneurysmal geometries in the aorta.

It was concluded from data analysis that inlet torsion is maintained in this model of aneurysmal flow. Steady flows are particularly prone to expressing torsion and as such distal flows and forces are greatly affected. In pulsatile flows the distal hill field flow remained almost symmetrical as the effects of torsion were diminished. However, broadening of the core velocity jet was seen which altered regions of recirculation and implied jet impingement. Furthermore, wall shear stress gradients were particularly susceptible to variations in inlet boundary conditions and patterns of bias were seen in their distribution. As such torsion should not be discounted in any detail flow analysis of the abdominal aortic aneurysms at high flow rates.

Item Type:	Thesis
Creators:	Dalton, M.W.
Date:	2002
ISBN:	9781369323078
Identifiers:	Number Type PQ10290058 Other
Rights:	This copy of the thesis has been supplied for the purpose of research or private study under the condition that anyone who consults it is understood to recognise that its copyright rests with The Nottingham Trent University and that no quotation from the thesis, and no information derived from it, may be published without proper acknowledgment.
Divisions:	Schools > School of Science and Technology
Record created by:	Linda Sullivan
Date Added:	30 Nov 2020 16:24
Last Modified:	21 Sep 2023 09:46
URI:	https://irep.ntu.ac.uk/id/eprint/41729

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