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Analysis of Influence of Blood Flow and Arterial Geometry on Pathological Processes in Arteries
Jagoš, Jiří ; Rudolf, Pavel (oponent) ; Jonášová,, Alena (oponent) ; Burša, Jiří (vedoucí práce)
An occurrence of cardiovascular diseases is rising together with increasing average life expectancy as well as to an unhealthy lifestyle. Since the most of these diseases are asymptomatic, a great effort has been devoted to early detection of these diseases because if they are detected in early phase, a conservative treatment can be an option. If not, a highly invasive and risky surgery is usually the only option. We can still observe a very large portion of patients in the risk group to whom the disease does not develop, and, on the contrary, in many patients who are not in the risk group, it does. Computational modelling of cardiovascular system is one of the options, which can help with stratification of the patients that are at risk of developing cardiovascular diseases. Firstly, a successful validation of the numerical model of pulsatile flow in the rigid and compliant tubes via velocity profiles was performed. Experiment circuit was arranged to correspond conditions in the human aorta. Next part is devoted to proper treatment of boundary conditions (BCs) for numerical model of pulsatile flow in human arteries. The first approach works with pulse wave velocity which needs to be computed first. Then, a shift between input and outputs BCs can be determined easily. Nevertheless, we have to prescribe also flow or pressure waveforms for each inlet and outlet. Thus, the predictive capabilities of this approach are significantly limited. Its next disadvantage is applicability only for simulations considering compliance of the vessel wall. We used this approach in fluid-structure interaction simulations to check the potential risk factor of the aorto-iliac angle on development of an aneurysm in the abdominal aorta (AAA). It has been shown that the pressure increases due to a large (but still physiological) span of the aorto-iliac angles is negligible. We also investigated the influence of the area ratio on pressure in the abdominal aorta. The results of this computational study show a substantial increase in pressure as the ratio decreases and confirms clinical observations showing significantly elevated risk of AAA in patients with lower limp amputation or those with iliac artery stenosis. In the final part we have investigated the effect of a flow waveform shape in the human carotid artery on the risk of atherosclerosis. The five geometrically different geometries of the carotid bifurcation from “healthy” old individuals were reconstructed. The representative input flow BCs in the common carotid artery for the young and old individual were adopted from a literature. The outputs BCs for the internal and external carotid artery were represented by three-element Windkessel model. The parameters of the Windkessel model were iteratively tuned to reach flow waveform shape in internal carotid artery according to literature. These BCs represent the behaviour of the periphery very reliably. Moreover, the predictive capabilities and numerical stability of this approach are much better than the first approach. The results show that the time average wall shear stress decreases significantly in case of healthy elderly subjects in comparison to young ones which indicates elevated risk of atherosclerosis. The results are in agreement with clinical observations and further extend the existing knowledge with a much deeper analysis of this trend. The final discussion is devoted to a potential benefits of an antihypertensives and regular physical activity.
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