On the shape of the common carotid artery with implications for blood velocity profiles

Abstract

Clinical and engineering studies typically assume that the common carotid artery (CCA) is straight enough to assume fully developed flow, yet recent studies have demonstrated the presence of skewed velocity profiles. Toward elucidating the influence of mild vascular curvatures on blood flow patterns and atherosclerosis, this study aimed to characterize the three-dimensional shape of the human CCA. The left and right carotid arteries of 28 participants (63 ± 12 years) in the VALIDATE (Vascular Aging--The Link that Bridges Age to Atherosclerosis) study were digitally segmented from 3D contrast-enhanced magnetic resonance angiograms, from the aortic arch to the carotid bifurcation. Each CCA was divided into nominal cervical and thoracic segments, for which curvatures were estimated by least-squares fitting of the respective centerlines to planar arcs. The cervical CCA had a mean radius of curvature of 127 mm, corresponding to a mean lumen:curvature radius ratio of 1:50. The thoracic CCA was significantly more curved at 1:16, with the plane of curvature tilted by a mean angle of 25° and rotated close to 90° with respect to that of the cervical CCA. The left CCA was significantly longer and slightly more curved than the right CCA, and there was a weak but significant increase in CCA curvature with age. Computational fluid dynamic simulations carried out for idealized CCA geometries derived from these and other measured geometric parameters demonstrated that mild cervical curvature is sufficient to prevent flow from fully-developing to axisymmetry, independent of the degree of thoracic curvature. These findings reinforce the idea that fully developed flow may be the exception rather than the rule for the CCA, and perhaps other nominally long and straight vessels.

Figure 1

(a) Maximum intensity projection of a representative 3D CEMRA. (b) Segmented right CCA viewed normal to best-fit cervical (left) and thoracic (right) planes. Note centerlines, pivot (P) and cervical (C) and thoracic (T) end points. (c) Best fit cervical and thoracic circular arcs (solid lines) compared to original centerline (dottedline). (d) Parametric CCA model derived from a spline fit of the indicated circular arc and pivot points, showing good agreement with the original CCA segmented surface.

Figure 2

Scatter plots of (a) curvature and (b) angle measurements from left (closed circles) and right (open circles) CCAs of 28 individuals. Horizontal lines indicate mean values.

Figure 3

Parametric CCA models with 1:60 cervical curvature and 1:10, 1:15 and 1:45 thoracic curvatures, along with a model with no thoracic segment. (a) Time-averaged wall shear stress (TAWSS), viewed normal to the cervical plane of curvature. TAWSS is normalized to its inlet value, with levels indicated by the contour legend. Shown also are the feature points and spline-fit centerlines used to construct the models; the no-thoracic model is superimposed on the 1:45 thoracic case to demonstrate that cervical feature points are the same in all cases. (b) The same parametric models, rotated 90° and then tilted 25° so as to be viewed normal to the thoracic plane of curvature, showing CFD-computed time-averaged velocity magnitudes on axial (Y) planes spaced one radius apart. Velocities are normalized to the mean inlet velocity, with levels indicated by the contour legend. (c) Time-averaged through-plane (axial) velocity contours and in-plane (secondary) velocity vectors from planes at the outlet and pivot points, with respective legends indicated.