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Research Papers

A Study on the Compliance of a Right Coronary Artery and Its Impact on Wall Shear Stress

[+] Author and Article Information
Dehong Zeng, Evangelos Boutsianis, Marc Ammann, Kevin Boomsma

Laboratory of Thermodynamics in Emerging Technologies, Department of Mechanical and Process Engineering, ETH Zurich, ML J 36, CH-8092 Zurich, Switzerland

Simon Wildermuth

Institute of Diagnostic Radiology, University Hospital Zurich, CH-8092 Zurich, Switzerland

Dimos Poulikakos1

Laboratory of Thermodynamics in Emerging Technologies, Department of Mechanical and Process Engineering, ETH Zurich, ML J 36, CH-8092 Zurich, Switzerlanddimos.poulikakos@ethz.ch

1

Corresponding author.

J Biomech Eng 130(4), 041014 (Jun 11, 2008) (11 pages) doi:10.1115/1.2937744 History: Received May 14, 2007; Revised January 22, 2008; Published June 11, 2008

A computational model incorporating physiological motion and uniform transient wall deformation of a branchless right coronary artery (RCA) was developed to assess the influence of artery compliance on wall shear stress (WSS). Arterial geometry and deformation were derived from modern medical imaging techniques, whereas the blood flow was solved numerically employing a moving-grid approach using a well-validated in-house finite element code. The simulation results indicate that artery compliance affects the WSS in the RCA heterogeneously, with the distal region mostly experiencing these effects. Under physiological inflow conditions, coronary compliance contributed to phase changes in the WSS time history, without affecting the temporal gradient of the local WSS nor the bounds of the WSS magnitude. Compliance does not cause considerable changes to the topology of WSS vector patterns nor to the localization of WSS minima along the RCA. We conclude that compliance is not an important factor affecting local hemodynamics in the proximal region of the RCA while the influence of compliance in the distal region needs to be evaluated in conjunction with the outflow to the myocardium through the major branches of the RCA.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Dynamic mesh of the RCA lumen incorporating the global geometric variations. Panel (a): Meshes at time t∕T=0 and t∕T=0.6, where T is the cardiac period. Each point on the centerline traces out a closed curve over a complete cardiac cycle. The two closed curves in the plot are path lines of two points on the centerline. Panel (b): Magnified views of the centerline point trajectory near the proximal region. Locations of the centerline point at ten times in the cardiac cycle are shown. Panel (c): The RCA model at t∕T=0 is shown in the AP view. The curvature seen in the AP view is the primary curvature. Inner side of the primary curvature is designated as the inner wall, the outer side the outer wall. The actual RCA lumen is the section between Markers 1 and 126, while the rest are inlet and outlet extensions. These markers are distributed along the inner and outer walls in pairs.

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Figure 2

Panel (a): Average cross-sectional area of the RCA lumen within the cardiac cycle. Panel (b): Flow rate wave form imposed at the inlet for pulsatile simulations. The time is normalized by the cardiac period, T=0.8s, and the flow rate by the time-averaged flow rate. The average cross section area wave form is synchronized with the flow rate wave form by matching the ED and ES time points to those of the flow rate wave form, respectively.

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Figure 3

WSS distribution along the inner and outer walls at times t∕T=0.4 (panels (a) and (c)) when the artery contracts and t∕T=0.7 (panels (b) and (d)) when the artery dilates, from both Cases 1 and 2 simulations. The distance is normalized by the total length of the RCA lumen. The inlet and outlet extensions are excluded when calculating the WSS.

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Figure 4

WSS difference at Markers 1, 60, and 125 was checked during a cardiac cycle. We examined the WSS difference at both the inner (panel (a)) and outer (panel (b)) walls. In panel (a), cross-sectional area ratio is also shown to represent the RCA compliance. The locations of the markers are shown in panel (c) of Fig. 1.

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Figure 5

WSS time history at Marker 5 (panels (a) and (c)) and 87 (panels (b) and (d)). WSS on the inner wall is shown in the upper row, outer wall, the lower row. Note that the scales of y-axis are the same in all panels. Marker 5 is in the proximal region, and marker 87 is close to the distal region. Inlet flow rate wave form is plotted in panel (d).

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Figure 6

The compliance wave form was perturbed to reach a phase angle of almost 180deg versus the measured compliance wave form. This perturbed compliance wave form was applied in a second set of simulations to investigate the sensitivity of the obtained numerical results on the compliance wave form.

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Figure 7

WSS time history at Markers 5 (panels (a) and (c)) and 87 (panels (b) and (d)) with the perturbed compliance wave form as shown in Fig. 6. WSS on the inner wall is shown in the upper row, outer wall, the lower row. Note that the scales of y-axis are the same in all panels. Marker 5 is in the proximal region, and marker 87 is close to the distal region. Inlet flow rate wave form is plotted in panel (d).

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Figure 8

Contour plot of WSS magnitude in a proximal region at times t∕T=0 (left column) and t∕T=0.1 (right column) for Cases 1 (panels (a) and (b)) and 2 (panels (c) and (d)). The curves in panel (a)–(d) are the field lines of WSS vectors. The position of the region on the whole RCA domain is indicated by a square in panel (e).

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