On the effect of perturbations on idealized flow in model stenotic arteries

Sean D Peterson, Purdue University

Abstract

Cardiovascular diseases, particularly atherosclerosis, are a significant threat to the long-term health of westernized societies. Diseases such as atherosclerosis are responsible for nearly half of all deaths in the United States. The aetiology of atherosclerosis is highly complex, involving risk factors (both environmental and genetic) such as high levels of circulating low-density lipoproteins (LDLs), injury and/or increased permeability of the intimal lining of the arteries to LDLs, and ultimately fatty streak and plaque initiation. Vessel homeostasis has been correlated to the various mechanical stimuli present in the vasculature. Of particular importance in the study of atherosclerosis is the wall shear stress, which has been shown to elicit an atherogenic response from the endothelial cells lining the arterial walls under certain conditions. The apparent connection between the fluid mechanical factors and a deleterious response of the vasculature has prompted researchers to investigate atherosclerosis from both a mechanical and biochemical perspective. Of particular interest are pathological stenotic flows, as the forces on an established plaque can result in rupture, which is often fatal. Additionally, the altered wall shear stress distal to the occlusion is harmful to the vessel. The present study is directed towards understanding the impact of various flow disturbance types encountered in the systemic circulation on idealized stenotic flows. An experimental investigation is conducted to determine the influence of three fundamental disturbances on stenotic flows: a geometric perturbation resulting in asymmetry of the stenosis; a skewed mean inlet velocity profile; and flow downstream of a bend (skewed mean inlet velocity profile plus secondary flow). The stenosis is modeled as an axisymmetric 75% area reduction occlusion with a length-to-diameter ratio of 2. Laser Doppler velocimetry and particle image velocimetry are used to characterize the spatial and temporal evolution of a baseline case (no disturbances) and the various disturbed flow cases. Of interest are key features such as reattachment and transition locations, as these are regions known to be injurious to the vessel wall. All disturbances studied are found to reduce the extent of the stenotic jet, forcing it's trajectory to deviate from the tube centerline. Curvature-induced secondary flow has a lesser role in the near-stenosis region. Vortex ring formation is significantly impacted by the geometric anomaly, but is relatively unaffected by the mean velocity gradient and secondary flow. Downstream of the transition zone, the flow fields become quite similar and redevelop slowly.

Degree

Ph.D.

Advisors

Plesniak, Purdue University.

Subject Area

Biomedical engineering|Mechanical engineering

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