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Research Papers

# Correlations Among Indicators of Disturbed Flow at the Normal Carotid Bifurcation

[+] Author and Article Information
Sang-Wook Lee

Biomedical Simulation Laboratory, University of Toronto, 5 King’s College Road Toronto, Toronto, ON M5S 3G8 Canada; School of Mechanical and Automotive Engineering, University of Ulsan, Ulsan 680-749, South Korea

Luca Antiga

Department of Bioengineering, Mario Negri Institute for Pharmacological Research, 24020 Ranica (BG), Italy

David A. Steinman1

Biomedical Simulation Laboratory, University of Toronto, 5 King’s College Road Toronto, Toronto, ON M5S 3G8 Canadasteinman@mie.utoronto.ca

1

Corresponding author.

J Biomech Eng 131(6), 061013 (May 11, 2009) (7 pages) doi:10.1115/1.3127252 History: Received August 12, 2008; Revised January 01, 2009; Published May 11, 2009

## Abstract

A variety of hemodynamic wall parameters (HWP) has been proposed over the years to quantify hemodynamic disturbances as potential predictors or indicators of vascular wall dysfunction. The aim of this study was to determine whether some of these might, for practical purposes, be considered redundant. Image-based computational fluid dynamics simulations were carried out for $N=50$ normal carotid bifurcations reconstructed from magnetic resonance imaging. Pairwise Spearman correlation analysis was performed for HWP quantifying wall shear stress magnitudes, spatial and temporal gradients, and harmonic contents. These were based on the spatial distributions of each HWP and, separately, the amount of the surface exposed to each HWP beyond an objectively-defined threshold. Strong and significant correlations were found among the related trio of time-averaged wall shear stress magnitude (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT). Wall shear stress spatial gradient (WSSG) was strongly and positively correlated with TAWSS. Correlations with Himburg and Friedman’s dominant harmonic (DH) parameter were found to depend on how the wall shear stress magnitude was defined in the presence of flow reversals. Many of the proposed HWP were found to provide essentially the same information about disturbed flow at the normal carotid bifurcation. RRT is recommended as a robust single metric of low and oscillating shear. On the other hand, gradient-based HWP may be of limited utility in light of possible redundancies with other HWP, and practical challenges in their measurement. Further investigations are encouraged before these findings should be extrapolated to other vascular territories.

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## Figures

Figure 1

HWP distributions for a representative case. Except for the ordinal DH, contour levels depicted in each frame’s legend correspond to the 80th, 85th, 90th, and 95th percentile values based on the HWP distribution pooled over all cases. Note identification of CCA3 and ICA5 clip planes in the upper left (TAWSS) panel.

Figure 2

Scatter plots for selected pairwise comparisons of HWP. Note that the local (patched) data are plotted using a log-log scale to better depict the full dynamic range of data.

Figure 3

Distributions of DH and HI based on the axial WSS component rather than WSS magnitude, shown for same case depicted in Fig. 1. The arrows indicate the site of the time-varying WSS waveforms and corresponding spectra shown to the right.

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