Abstract
Atherosclerotic disease, and the subsequent complications of thrombosis and plaque rupture, has been associated with local shear stress. In the diseased carotid artery, local variations in shear stress are induced by various geometrical features of the stenotic plaque. Greater stenosis severity, plaque eccentricity (symmetry) and plaque ulceration have been associated with increased risk of cerebrovascular events based on clinical trial studies. Using particle image velocimetry, the levels and patterns of shear stress (derived from both laminar and turbulent phases) were studied for a family of eight matched-geometry models incorporating independently varied plaque features – i.e. stenosis severity up to 70%, one of two forms of plaque eccentricity, and the presence of plaque ulceration). The level of laminar (ensemble-averaged) shear stress increased with increasing stenosis severity resulting in 2–16 Pa for free shear stress (FSS) and approximately double (4–36 Pa) for wall shear stress (WSS). Independent of stenosis severity, marked differences were found in the distribution and extent of shear stress between the concentric and eccentric plaque formations. The maximum WSS, found at the apex of the stenosis, decayed significantly steeper along the outer wall of an eccentric model compared to the concentric counterpart, with a 70% eccentric stenosis having 249% steeper decay coinciding with the large outer-wall recirculation zone. The presence of ulceration (in a 50% eccentric plaque) resulted in both elevated FSS and WSS levels that were sustained longer (∼20 ms) through the systolic phase compared to the non-ulcerated counterpart model, among other notable differences. Reynolds (turbulent) shear stress, elevated around the point of distal jet detachment, became prominent during the systolic deceleration phase and was widely distributed over the large recirculation zone in the eccentric stenoses.
Highlights
The association between shear stress and atherosclerosis-related complications is well established [1,2]
We have provided a detailed analysis of shear-stress spatial distribution and time evolution for varying carotid plaque geometries
Two factors were observed that can potentially contribute to a higher level of thrombosis due to increasing stenosis severity: 1) increased shear-stress levels for each examined time point (Figs 5 and 7) and 2) a steeper slope of decay descending from the maximum shear stress at the stenosis apex (Fig. 8)
Summary
The association between shear stress and atherosclerosis-related complications is well established [1,2]. Once stenotic plaque has formed and matured, shear stress forces – altered due to the changed vessel geometry – play a role in plaque instability [3,4]. With regard to plaque rupture and flow-induced shear stress forces, conflicting results have been reported. Groen et al [5] reported that the site of plaque rupture coincided with the region of elevated WSS. Leach et al [6] showed that the region of plaque rupture is associated with a local minimum WSS. In addition to flow-induced WSS, several studies [7,8] have shown the possible association between plaque rupture and increased biomechanical structural stresses on the plaque. Teng et al [9] suggested that plaque maximum wall stress
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