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Research Papers

Comparison of Near-Wall Hemodynamic Parameters in Stented Artery Models

[+] Author and Article Information
Nandini Duraiswamy

Department of Biomedical Engineering, Florida International University, EAS 2610, Miami, FL 33174ndura002@fiu.edu

Richard T. Schoephoerster

College of Engineering, University of Texas at El Paso, 500 West University Avenue, Engineering Building M-305, El Paso, TX 79968schoephoerster@utep.edu

James E. Moore1

Department of Biomedical Engineering, Texas A&M University, 336D Zachry Engineering Center, 3120 TAMU, College Station, TX 77843jmoorejr@tamu.edu

1

Corresponding author. Present address: 336D Zachry Engineering Center, Department of Biomedical Engineering, 3120 TAMU, College Station, TX 77843-3120.

J Biomech Eng 131(6), 061006 (Apr 27, 2009) (9 pages) doi:10.1115/1.3118764 History: Received January 28, 2008; Revised November 11, 2008; Published April 27, 2009

Four commercially available stent designs (two balloon expandable—Bx Velocity and NIR, and two self-expanding—Wallstent and Aurora) were modeled to compare the near-wall flow characteristics of stented arteries using computational fluid dynamics simulations under pulsatile flow conditions. A flat rectangular stented vessel model was constructed and simulations were carried out using rigid walls and sinusoidal velocity input (nominal wall shear stress of 10±5dyn/cm2). Mesh independence was determined from convergence (<10%) of the axial wall shear stress (WSS) along the length of the stented model. The flow disturbance was characterized and quantified by the distributions of axial and transverse WSS, WSS gradients, and flow separation parameters. Normalized time-averaged effective WSS during the flow cycle was the smallest for the Wallstent (2.9dyn/cm2) compared with the others (5.8dyn/cm2 for the Bx Velocity stent, 5.0dyn/cm2 for the Aurora stent, and 5.3dyn/cm2 for the NIR stent). Regions of low mean WSS (<5dyn/cm2) and elevated WSS gradients (>20dyn/cm3) were also the largest for the Wallstent compared with the others. WSS gradients were the largest near the struts and remained distinctly nonzero for most of the region between the struts for all stent designs. Fully recirculating regions (as determined by separation parameter) were the largest for the Bx Velocity stent compared with the others. The most hemodynamically favorable stents from our computational analysis were the Bx Velocity and NIR stents, which were slotted-tube balloon-expandable designs. Since clinical data indicate lower restenosis rates for the Bx Velocity and NIR stents compared with the Wallstent, our data suggest that near-wall hemodynamics may predict some aspects of in vivo performance. Further consideration of biomechanics, including solid mechanics, in stent design is warranted.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

3D model of a Bx Velocity stent that would represent the near-strut flow characteristics

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Figure 2

Four different stent designs—Wallstent, Bx Velocity, Aurora, and NIR stents—were used. The strut thickness of the Bx Velocity and NIR stents were 0.132 mm, the Aurora stent was 0.12 mm, and the Wallstent was 0.09 mm. The areas represented by the boxes indicate regions modeled in CFD.

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Figure 3

Mesh design underlying the connector between the struts of the Bx Velocity stent

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Figure 4

Axial WSS (dynes/cm2) taken at the mean flow rate for (a) the Wallstent, (b) the Bx Velocity stent, (c) the Aurora stent, and (d) the NIR stent during the accelerating phase of the flow cycle

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Figure 5

Transverse WSS (dynes/cm2) taken at the mean flow rate for (a) the Wallstent, (b) the Bx Velocity stent, (c) the Aurora stent, and (d) the NIR stent during the accelerating phase of the flow cycle

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Figure 6

WSS gradients (dynes/cm3) taken at the mean flow rate for (a) the Wallstent, (b) the Bx Velocity stent, (c) the Aurora stent, and (d) the NIR stent during the accelerating phase of the flow cycle. Dark pink regions near struts show WSSG ⪢20 dynes/cm3.

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Figure 7

Flow stagnation areas taken at the mean flow rate for (a) the Wallstent, (b) the Bx Velocity stent, (c) the Aurora stent, and (d) the NIR stent during the accelerating phase of the flow cycle; 0 indicates no flow separation and 1 indicates flow stagnation

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Figure 8

(a) Normalized effective WSS, (b) normalized average axial WSS, (c) normalized average transverse WSS, and (d) ratio of normalized axial WSS to transverse WSS plotted for the different stent design types

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Figure 9

Percentage area of the region between struts, with averaged low WSS ((a) <5 dynes/cm2 and (b ) <2.5 dynes/cm2) for >50% of the flow cycle in the different stent design types

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Figure 10

Comparison of percentage area of the region between struts for (a) totally recirculating regions and (b) partially recirculating regions (with separation parameter ϕ) for the different stent designs

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Figure 11

Percentage area of the region between struts with the averaged WSSG >20 dynes/cm3 for >50% of the flow cycle in different stent design types.

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