Color-encoded maps of total shear stress for the time point of maximum TSS in each of the eight carotid models.

<p>For each model, a map demonstrating maximum TSS is shown, where the time point corresponding to the maximum value varied only slightly (20±10 ms beyond peak systole) for the eight models. Note the bottom right color bar (set to the maximum of 150 Pa) represents the seven stenosed models; the time and color bar associated with the normal model are shown in the enclosed box.</p

In Vitro Shear Stress Measurements Using Particle Image Velocimetry in a Family of Carotid Artery Models: Effect of Stenosis Severity, Plaque Eccentricity, and Ulceration

<div><p>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.</p></div

Ensemble-averaged wall shear stress shown for peak systole in the eight carotid models.

<p>For optimal display, the ICA is shown from two different perspectives as indicated by the orientation schematic in the bottom right corner. The color bar represents all the models including the normal geometry. For improved accommodation, the dynamic range of the color bar is reduced to a maximum of 30%-stenosed models.</p

In-plane RSS component () as a function of time for the three 50%-stenosed models.

<p>Maps are shown at three time points: 20 ms before peak systole (top row), 20 ms after peak systole (middle), and 20 ms before the dicrotic notch (bottom), as indicated by the respective flow-rate waveforms on the right. Three cross-sectional slices are shown alongside the ICA lumen at the locations indicated by the black lines at approximately 2, 2.5, and 3 CCA diameters downstream (i.e. ∼16, 20, 24 mm). Note the separate color bar used for the bottom row with the same zero-value color as for the upper rows.</p

Spatial and temporal distribution of the maximum free (i.e. non wall) shear stress in the eight models shown for a 180-ms window, incorporating peak systole (PS), as indicated on the reference flow-rate waveform at the bottom right.

<p>For each time point, maximum FSS values were extracted across the entire ICA lumen along 25(0 mm). Note the range-appropriate color bar associated with each row of models and the 1-Pa isocontour increments used for all maps.</p

Volumetric flow-rate waveforms, measured using electromagnetic flow meters, at the inlet of the CCA and outlets of the ICA and ECA.

<p>Volumetric flow-rate waveforms, measured using electromagnetic flow meters, at the inlet of the CCA and outlets of the ICA and ECA.</p

Spatial distribution of inner WSS (upper row) and outer WSS (lower row) associated with an interval during peak systole.

<p>Values are mean and standard deviation (whiskers) over five WSS values covering five time points straddling (±20 ms) peak systole.</p