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Computational fluid dynamic modelling for arterial diseases assessment
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One of the leading causes of death is cardiovascular disease, being 30% of all deaths worldwide and 40% of those in New Zealand. In other words, every 90 minutes a New Zealander dies due to cardiovascular disease. Cardiovascular mortality is higher in New Zealand than Australia, but the reasons for this are not clear. Although Australia and New Zealand are similar politically, culturally, and socioeconomically, mortality from cardiovascular disease is about 25% higher in New Zealand than in Australia. In recent years, engineers and scientists have collaborated with the medical community to find new methods and approaches for assessing and investigating the development of cardiovascular diseases such as abdominal aortic aneurysm and atherosclerosis. In this thesis, atherosclerosis and aneurysm diseases are investigated and analysed using computational fluid dynamic/finite element (CFD/FE) methods. These models are validated against the in vivo and in vitro experiments performed on animals. The experimental models are also investigated; the assessment of arterial blockages using blood pressure waveforms obtained invasively at the right femoral artery. The animal experiments are performed following appropriate ethical protocols (R915) on Wistar rats weighing between 250-350g. An arterial blockage is created surgically within the abdominal aorta of healthy animals to create an unhealthy condition. Blood pressure waveforms are measured by injecting catheter into the right femoral artery of the rat. These measurements are taken at the baseline (healthy condition) and at four different severities of arterial blockage of the abdominal aorta for the same specimen. In vivo and in vitro measurements of the arterial diameter and wall thickness are also taken using Magnetic Resonance Imaging (MRI) and microscopic techniques, respectively. These data are then input onto CFD/FE models in order to develop a new, non-invasive method of assessing arterial blockage. The experimental and computational results indicate that arterial blockages occurring within the abdominal aorta could be assessed, and the development of the disease diagnosed, very clearly and non-invasively at the right femoral artery. The findings of the animal model are then implemented in the human model for screening atherosclerosis and aneurysm at the brachial artery. These diseases are modelled and simulated in a 3D CFD/FE aorta geometry using the fluid–structure interaction (FSI) approach on the commercial software ANSYS®14.0. Literature blood flow waveform datum is assumed at the inlet and invasive catheter pulsatile pressure waveforms data is imposed at the four outlets of the aorta (provided by Green Lane Hospital under ethic approval number NTX/09/11/109). Correlations between the stress phase angle (SPA), augmentation index (AI), lumen diameter and blood pressure waveforms for various scenarios of diseased models are made and compared to the control model. The results show that CFD/FE models with different radii and thicknesses at the abdominal aorta significantly influence blood pressure waveforms, high negative SPA values, and high AI detected at the brachial artery.