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TECHNICAL PAPERS: Fluids/Heat/Transport

Blood Flow in Stented Arteries: A Parametric Comparison of Strut Design Patterns in Three Dimensions

[+] Author and Article Information
Yong He

Department of Bioengineering,  University of Pittsburgh, 768 Benedum Hall, Pittsburgh, PA 15261

Nandini Duraiswamy

Department of Biomedical Engineering,  Florida International University, Miami, FL 33199

Andreas O. Frank

 Applied Research Associates, Inc., 6320 Southwest Blvd., Suite 103, Fort Worth, TX 76109

James E. Moore1

Department of Biomedical Engineering,  Texas A&M University, College Station, TX 77843

1

Address correspondence to Dr. James E Moore. Current address: Department of Biomedical Engineering, Texas A&M University, Zachry Building 234E, College Station, TX 77843-3120. Telephone: 979-845-3299; fax: 979-845-4450

J Biomech Eng 127(4), 637-647 (Feb 10, 2005) (11 pages) doi:10.1115/1.1934122 History: Received May 03, 2004; Revised February 10, 2005

Background: Restenosis after stent implantation varies with stent design. Alterations in secondary flow patterns and wall shear stress (WSS) can modulate intimal hyperplasia via their effects on platelet and inflammatory cell transport toward the wall, as well as direct effects on the endothelium. Method of Approach: Detailed flow characteristics were compared by estimating the WSS in the near-strut region of realistic stent designs using three-dimensional computational fluid dynamics (CFD), under pulsatile high and low flow conditions. The stent geometry employed was characterized by three geometric parameters (axial strut pitch, strut amplitude, and radius of curvature), and by the presence or lack of the longitudinal connector. Results: Stagnation regions were localized around stent struts. The regions of low WSS are larger distal to the strut. Under low flow conditions, the percentage restoration of mean axial WSS between struts was lower than that for the high flow by 10–12%. The largest mean transverse shear stresses were 30–50% of the largest mean axial shear stresses. The percentage restoration in WSS in the models without the longitudinal connector was as much as 11% larger than with the connector. The mean axial WSS restoration between the struts was larger for the stent model with larger interstrut spacing. Conclusion: The results indicate that stent design is crucial in determining the fluid mechanical environment in an artery. The sensitivity of flow characteristics to strut configuration could be partially responsible for the dependence of restenosis on stent design. From a fluid dynamics point of view, interstrut spacing should be larger in order to restore the disturbed flow; struts should be oriented to the flow direction in order to reduce the area of flow recirculation. Longitudinal connectors should be used only as necessary, and should be parallel to the axis. These results could guide future stent designs toward reducing restenosis.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Computational domain and (b) computational mesh of one of the stent models used in XZ plane (see the text)

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Figure 2

Four parametric models of stent struts geometries. (a) h=1.8mm, f=0.9mm, r=0.45mm; (b) h=1.8mm, f=1.8mm, r=0.9mm; (c) h=3.6mm, f=1.8mm, r=0.9mm; and (d) h=3.6mm, f=3.6mm, r=0.9mm

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Figure 4

(a) Line-probe locations at 0.25H, 0.5H, 1H, 2H,…, 10H shown for stent model (b) with a connector; used for obtaining WSS information along the length of the line-probe at each location. Streamlines at the 30th time step for h=1.8mm, f=1.8mm, r=0.9mm model with a connector for (b) low flow and (c) high flow

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Figure 3

(a) The velocity profile curve [also shows time point t1 (30th time point)] and the corresponding WSS for the low flow condition and (b) the velocity profile curve [also shows time point t1 (30th time point)] and the corresponding WSS for a high flow condition

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Figure 5

Contour plot of (a) mean axial WSS, (b) mean transverse WSS, and (c) separation parameter, for the h=1.8mm, f=0.9mm, r=0.45mm model [stent model (a)] with a connector under high flow

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Figure 6

Contour plot of (a) mean axial WSS, (b) mean transverse WSS, and (c) separation parameter, for the h=1.8mm, f=0.9mm, r=0.45mm model [stent model (a)] without a connector under high flow

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Figure 7

Contour plot of (a) mean axial WSS, (b) mean transverse WSS, and (c) separation parameter, for the h=1.8mm, f=0.9mm, r=0.45mm model [stent model (a)] with a connector under low flow

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Figure 8

Contour plot of (a) mean axial WSS, (b) mean transverse WSS, and (c) separation parameter, for the h=1.8mm, f=1.8mm, r=0.9mm model [stent model (b)] with a connector under low flow

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Figure 9

Contour plot of (a) mean axial WSS, (b) mean transverse WSS, and (c) separation parameter, for the h=3.6mm, f=1.8mm, r=0.9mm model [stent model (c)] with a connector under high flow

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Figure 10

Contour plot of (a) mean axial WSS, (b) mean transverse WSS, and (c) separation parameter, for the h=3.6mm, f=3.6mm, r=0.9mm model [stent model (d)] with a connector under high flow

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Figure 11

Normalized mean axial WSS between struts in different strut geometries for high and low flow conditions. First two geometries correspond to h=1.8mm models; third and fourth geometries correspond to h=3.6mm models

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Figure 12

Mean transverse WSS between struts in different strut geometries for high and low flow conditions

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Figure 13

Percentage area between struts where the separation parameter >0.5 in different strut geometries for high and low flow conditions

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Figure 14

Percentage area between struts where the separation parameter ranged from 0.1–0.5 in different strut geometries for high and low flow conditions

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