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

Biomedical Simulation Laboratory, Department of Mechanical & Industrial Engineering, University of Toronto, Toronto, ON, Canada.
Physiological Measurement (Impact Factor: 1.81). 12/2011; 32(12):1885-97. DOI: 10.1088/0967-3334/32/12/001
Source: PubMed


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.

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    • "Contrast-enhanced angiograms and phase contrast (PC) MRI sequences were acquired at 3.0 Tesla field strength using surface radiofrequency (RF) coils. Scan parameters have been reported by Manbachi et al. (2011) and Hoi et al. (2010). "
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    ABSTRACT: Given evidence that fully developed axisymmetric flow may be the exception rather than the rule, even in nominally straight arteries, maximum velocity (Vmax) can lie outside the Doppler sample volume (SV). The link between Vmax and derived quantities, such as volume flow (Q), may therefore be more complex than commonly thought. We performed idealized virtual Doppler ultrasound on data from image-based computational fluid dynamics (CFD) models of the normal human carotid artery and investigated how velocity profile skewing and choice of sample volume affected Vmax waveforms and derived Q variables, considering common assumptions about velocity profile shape (i.e., Poiseuille or Womersley). Severe velocity profile skewing caused substantial errors in Vmax waveforms when using a small, centered SV, although peak Vmax was reliably detected; errors with a long SV covering the vessel diameter were orientation dependent but lower overall. Cycle-averaged Q calculated from Vmax was typically within ±15%, although substantial skewing and use of a small SV caused 10%-25% underestimation. Peak Q derived from Womersley's theory was generally accurate to within ±10%. Vmax pulsatility and resistance indexes differed from Q-based values, although the Q-based resistance index could be predicted reliably. Skewing introduced significant error into Vmax-derived Q waveforms, particularly during mid-to-late systole. Our findings suggest that errors in the Vmax and Q waveforms related to velocity profile skewing and use of a small SV, or orientation-dependent errors for a long SV, could limit their use in wave analysis or for constructing characteristic or patient-specific flow boundary conditions for model studies.
    Ultrasound in medicine & biology 02/2013; 39(5). DOI:10.1016/j.ultrasmedbio.2012.11.006 · 2.21 Impact Factor
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    ABSTRACT: There is evidence that helical blood flow elicits atheroprotective fluid-wall interaction processes and regulates the transport of atherogenic particles at the luminal surface [1]. In particular, with reference to the carotid bifurcation it was also suggested that helical flow might play a key role in determining wall shear stress patterns [2]. Those findings suggest that a relationship could exist in the carotid bifurcation between exposure to disturbed shear and helical bulk flow patterns, an hypothesis that has been tested only in simplified models [3]. For this reason, in the present study we aim to gain further knowledge on the existence of a link between local risk factors in atherosclerosis and the amount of helicity in the bulk flow of carotid bifurcations. In particular, here we want to confirm if a high amount of helical flow is instrumental in suppressing flow disturbances.
    ASME 2012 Summer Bioengineering Conference; 06/2012
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    ABSTRACT: Objective: Wall shear stress (WSS) is an important parameter with links to vascular (dys)function. Difficult to measure directly, WSS is often inferred from maximum spectral Doppler velocity (Vmax) by assuming fully-developed flow, which is valid only if the vessel is long and straight. Motivated by evidence that even slight/local curvatures in the nominally straight common carotid artery (CCA) prevent flow from fully developing, we investigated the effects of velocity profile skewing on Vmax-derived WSS. Methods: Velocity profiles, representing different degrees of skewing, were extracted from the CCA of image-based computational fluid dynamics (CFD) simulations carried out as part of the VALIDATE study. Maximum velocities were calculated from idealised sample volumes and used to estimate WSS via fully-developed (Poiseuille or Womersley) velocity profiles, for comparison with the actual (i.e. CFD-derived) WSS. Results: For cycle-averaged WSS, mild velocity profile skewing caused ±25% errors by assuming Poiseuille or Womersley profiles, while severe skewing caused a median error of 30% (maximum 55%). Peak systolic WSS was underestimated by ~50% irrespective of skewing with Poiseuille; using a Womersley profile removed this bias, but ±30% errors remained. Errors were greatest in late systole, when skewing was most pronounced. Skewing also introduced large circumferential WSS variations: ±60%, and up to ±100%, of the circumferentially averaged value. Conclusion: Vmax-derived WSS may be prone to substantial variable errors related to velocity profile skewing, and cannot detect possibly large circumferential WSS variations. Caution should be exercised when making assumptions about velocity profile shape to calculate WSS, even in vessels usually considered long and straight.
    Atherosclerosis 01/2013; 227(2). DOI:10.1016/j.atherosclerosis.2013.01.026 · 3.99 Impact Factor
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