Date November 4, 2005
Speaker Seung E. Lee (MIT)
Topic: Transitional Flow in Stenosed Carotid Artery

Patients with severely stenotic arteries are at potential health risks such as ischemia, heart attack, and stroke. However, the study of hemodynamics within severe stenosis has been limited due to its complex flow nature. A number of studies employed numerical and experimental tools to study the transitional nature of the blood using simplifying assumptions (idealized geometries, turbulence model, or 2D model), and significant insights have been gained from them. Nevertheless, it is evidently clear from these reports that the use of the patient-specific flow conditions and geometries are essential in order to fully characterize the three-dimensional nature of the post-stenotic transitional flow, which can possibly help evaluate the patient-specific vulnerability from the determined flow pattern. In this paper, we report a direct numerical simulation result of the transitional flow in patient-specific-severely-stenosed carotid bifurcation using flow conditions obtained directly from the patient as the boundary conditions. The Spectral Element Method (SEM) software used for this study has been previously validated through comparison with experimental results of transitional flows.

Two sites of high frequency vortex shedding were observed during the deceleration phase of the systole. One vortex shedding was located downstream of the stenosis, and the other was located right in the stenosis, which broke off from the apex. The vortex shedding frequency was within the audible range, which the physicians listen for in search of stenosis-induced turbulence in their simple non-invasive diagnosis. The throat of the stenosis was subjected to very high shear stress, which was suggested to cause plaque rupture or platelet activation. Oscillatory flow reversal and low pressure were observed just distal of the stenosis, which may fatigue the calcified plaque or cause the formation of the thrombosis. This study provides a quantitative means of characterizing the post-stenotic flow field, and may help elucidate the mechanistic insights of plaque vulnerability.