Hemodynamics of Diseased Coronary Arteries
| dc.contributor.advisor | Arjomandi, Maziar | |
| dc.contributor.advisor | Zander, Anthony | |
| dc.contributor.advisor | Chin, Ray | |
| dc.contributor.author | Freidoonimehr, Navid | |
| dc.contributor.school | School of Mechanical Engineering | en |
| dc.date.issued | 2021 | |
| dc.description.abstract | Cardiovascular diseases are one of the main causes of death worldwide. A common cardiovascular disease is atherosclerosis, caused by plaque deposition on the arterial wall which leads to the obstruction of the blood ow, known as stenosis. Atherosclerosis can form in any part of the arterial system but it may have serious consequences when located in one of the coronary arteries which supply blood to the heart. Plaque formation inside a coronary artery influences the flow behaviour and leads to the development of turbulence structures with physiological consequences, such as pressure drop. Percutaneous coronary intervention (PCI) is one of the most common treatments for coronary artery diseases (CADs). There are several benefits of PCI over other alternative methods for treatment of CADs including lower risks of complications and much shorter recovery period. However, it can result in thrombosis and in-stent restenosis, which are the major drawbacks of coronary stent placement in patients with CADs. It was shown that the likelihood of occurrence of restenosis and thrombosis is a function of the wall shear stress (WSS) distribution. The motivation for the research presented in this thesis is to develop an understanding of the hemodynamics of stenosed and stented coronary arteries with an ultimate goal of improving patient outcomes. This can only be achieved if the effect of stenoses and stents on the flow behaviour in arteries is well-characterised. Hence, in this thesis the relationship between the shape of stenosis, stent pattern, the downstream transitional ow behaviour, and the hemodynamic parameters is investigated. The research presented in this thesis is focused on the development of an in-depth understanding of the hemodynamics of diseased coronary arteries. Extensive pressure drop measurements, visualisation of the flow using particle image velocimetry (PIV), and computational modelling of the flow were conducted. Attention was mainly given to the stenosed and stented coronary arteries by investigating their influence on the flow behaviour, including velocity profile, pressure drop, time-averaged and -dependent WSS, and turbulent kinetic energy. The need for modelling the temporal geometric variations of the coronary arteries during a cardiac cycle for the investigation of the hemodynamics is discussed. Temporal geometric variations of the coronary arteries during a cardiac cycle are classified as a superposition of the changes in the position, curvature and torsion of the coronary artery and the variations in lumen cross-sectional shape due to distensible wall motion induced by the pulse pressure and/or contraction of the myocardium in a cardiac cycle. A sensitivity analysis was conducted to evaluate the effects of temporal geometric variations of the coronary arteries on the pressure drop and WSS. The results show that neglecting the effects of temporal geometric variations results in less than 5% deviation of the time-averaged pressure drop and WSS values. However, they lead to an approximately 20% deviation in the temporal geometric variations of hemodynamic parameters, such as time-dependent WSS. Based on the presented discussion, the temporal geometric variations of coronary arteries were not modelled in this thesis and the focus was on modelling the flow dynamics to develop an in-depth understanding of the ow features inside the stenosed and stented coronary arteries. In the next stage of the research, a model incorporating the plaque geometry, the pulsatile inlet ow and the induced turbulence in a stenosed coronary artery was developed and validated against numerical and experimental data. The transitional ow behaviour was quantified by investigation of the changes in the turbulent kinetic energy. The results suggest that there is a high risk of the formation of a secondary stenosis at a downstream distance of equal to 10 times the artery diameter in the regions to the side and downstream of the initial stenosis due to existence of the recirculation zones and low shear stresses. The applicability of the obtained results was tested with a patient-specific stenosed coronary artery model. Furthermore, for the non-invasive determination of the pressure drop in a stenosed artery model a mathematical model incorporating different physical parameters such as blood viscosity, artery length and diameter, ow rate and ow profile, and shape and degrees of stenosis, was developed. Extensive experimental pressure measurements were conducted for a wide range of degrees and shapes of stenosis to form a database in the process of the development of this equation. The validity of the developed relationship was also tested for the stenosed coronary artery models with the physiological flow profile of the left and right coronary arteries by comparing the pressure drop obtained from the developed equation and those from the experimental measurements. Moreover, the effect of artery curvature on the pressure drop and fractional ow reserve (FFR) wa investigated. The results show that neglecting the effect of artery curvature results in under-estimation of pressure drop by about 25{35%. The developed equation can determine the pressure drop inside a stenosed coronary artery using the measurement of the flow profle inside the artery as well as the images of the stenosed coronary artery. In order to develop an understanding of the hemodynamic performance of coronary stents, the effect of stent design on the hemodynamics of stented arteries was investigated experimentally and numerically. An innovative PIV technique was implemented for the visualisation of the entire ow and the investigation of WSS within the stent struts without covering the region of interest inside a stented coronary artery model. This novel technique was based on the construction of a transparent stented artery using silicone cast in one piece, instead of inserting a metal or non-metallic stent inside a cast artery model, which are translucent and distort the field of view. The results show that WSS is strongly dependent on the design of the stent. It was also shown that the likelihood of occurrence of restenosis is strongly dependent on strut depth and thickness, the distance between two consecutive struts, and the shape of the connector between the struts. This thesis provides an improved understanding of the hemodynamics of diseased coronary arteries with an ultimate goal of improving patient outcomes. The findings will provide a basis for improvement of the most common CAD diagnostic and treatment methods. Based on the results of this research, the susceptible regions for the formation of a new stenosis downstream of the initial stenosis can be determined. Identification of these locations, which are a function of different physical and geometrical parameters, such as shape, degree and eccentricity of the initial stenosis, can provide the necessary information for prevention of the distal propagation of stenoses. Furthermore, the equation developed to evaluate FFR non-invasively in this research can be used as a gatekeeper to prevent unnecessary FFR procedures for all patients. This will result in better patient outcomes and reduce costs related to unnecessary invasive FFR which will benefit the health system. In addition, the results of this study provide a better understanding of the effect of stents on the flow which can be used to improve stent designs. | |
| dc.description.dissertation | Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2021 | en |
| dc.identifier.uri | https://hdl.handle.net/2440/132621 | |
| dc.language.iso | en | en |
| dc.provenance | This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legals | en |
| dc.subject | Hemodynamics | en |
| dc.subject | coronary artery | en |
| dc.subject | stenosis | en |
| dc.subject | stent | en |
| dc.subject | computational fluid dynamics | en |
| dc.subject | particle image velocimetry | en |
| dc.title | Hemodynamics of Diseased Coronary Arteries | en |
| dc.type | Thesis | en |
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