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. Towards elucidating the influence of mild vascular curvatures on blood flow patterns and atherosclerosis, the present study aimed to characterize the three-dimensional shape of the human CCA. The left and right carotid arteries of 28 participants (62±13 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 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 degrees and rotated close to 90 degrees 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 (CFD) 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, 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.

An Insight into the Mechanistic Role of the Common Carotid Artery on the Hemodynamics at the Carotid Bifurcation

“…4,17,43 Previous studies on the geometric characterization of CCA compare favorably with our results reported in Table 3 and in Fig. 5, e.g., Tortoli et al 44 reported a curvature varying from 0.0025 to 0.01 mm 21 and Manbachi et al 23 reported an average thoracic CCA curvature of 0.007 ± 0.004 mm 21 . Furthermore, as described by Manbachi et al, 23 the CCA geometry can be divided into thoracic and cervical portions, the thoracic CCA segment being significantly more curved that the cervical segment.…”

“…5 Our quantitative findings enforce and widen recent evidences of complex non-axisymmetric flow fields in CCA. 9,14,23,35,44 With respect to full-length models, incorporating both the thoracic and the cervical CCA, the amount of helical flow in the carotid bifurcation can be reasonably captured if the CCA is extended until the CCA7 location. It is general practice, in computational hemodynamic studies of the carotid bifurcation, the assumption that CCA is nominally straight to justify the adoption of classical theories valid for long straight tubes (e.g., Womersley theory) for the prescription of (Dirichlet) conditions at the inflow boundaries of the fluid domain.…”

“…In this regard, a first in silico investigation focused on the role of vessel curvature in the generation of skewed velocity profiles and secondary flows in parametric, idealized CCA geometries has demonstrated that even a mild curvature is sufficient to produce velocity profile skewing. 23 Notwithstanding the evidence that complex fourdimensional fluid structures arise and develop in CCA, 6,8,21,44 their potential physiological significance has never been characterized in-depth. Here we investigate for the first time the mechanistic role of CCA in (1) generating such complex fluid structures and (2) influencing the distal hemodynamics at the bifurcation.…”

Cardiovascular morphometry with high-resolution 3D magnetic resonance: First application to left ventricle diastolic dysfunction

“…1 B). The relative orientation of two subsequent best-fit planes was expressed by a tilt ( α) and a twist ( θ ) angle, calculated as the arccosine of the internal product between the two tangent vectors and the two normal vectors, respectively [36] . Moreover, twist angle can be related to Euler's rotation theorem, stating that a rotation in the 3D space can be expressed as a single rotation around an axis, which is invariant to the rotation.…”

Simultaneous imaging of blood flow dynamics and vascular remodelling during development

“…Many studies on shear stress have relied on the assumption that increased flow rates result in increased shear stress (Milkiewicz et al, 2001;Ziada et al, 1989). Though this is a valid assumption for straight, unbranched blood vessels, shear stress levels cannot be calculated purely based on the flow rate for more complex geometries (Manbachi et al, 2011). In these more complicated situations, calculation of shear stress levels requires solving a set of partial differential equations, called the Navier-Stoke's equation, for each specific geometry.…”