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Research Papers

The Quantification of Hemodynamic Parameters Downstream of a Gianturco Zenith Stent Wire Using Newtonian and Non-Newtonian Analog Fluids in a Pulsatile Flow Environment

[+] Author and Article Information
Andrew M. Walker1

Department of Mechanical and Manufacturing Engineering,  University of Calgary, 2500 University Drive N.W., Calgary, AB, T2N 1N4, Canadawalkeram@ucalgary.ca

Clifton R. Johnston

Department of Industrial Engineering,  Dalhousie University, 5269 Morris Street, P.O. Box 1000, Halifax, NS, B3H 4R2, Canadaclifton.johnston@dal.ca

David E. Rival

Department of Mechanical and Manufacturing Engineering,  University of Calgary, 2500 University Dr. N.W., Calgary, AB, T2N 1N4, Canadaderival@ucalgary.ca

1

Corresponding author.

J Biomech Eng 134(11), 111001 (Oct 12, 2012) (10 pages) doi:10.1115/1.4007746 History: Received June 14, 2012; Revised September 07, 2012; Posted September 29, 2012; Published October 12, 2012; Online October 12, 2012

Although deployed in the vasculature to expand vessel diameter and improve blood flow, protruding stent struts can create complex flow environments associated with flow separation and oscillating shear gradients. Given the association between magnitude and direction of wall shear stress (WSS) and endothelial phenotype expression, accurate representation of stent-induced flow patterns is critical if we are to predict sites susceptible to intimal hyperplasia. Despite the number of stents approved for clinical use, quantification on the alteration of hemodynamic flow parameters associated with the Gianturco Z-stent is limited in the literature. In using experimental and computational models to quantify strut-induced flow, the majority of past work has assumed blood or representative analogs to behave as Newtonian fluids. However, recent studies have challenged the validity of this assumption. We present here the experimental quantification of flow through a Gianturco Z-stent wire in representative Newtonian and non-Newtonian blood analog environments using particle image velocimetry (PIV). Fluid analogs were circulated through a closed flow loop at physiologically appropriate flow rates whereupon PIV snapshots were acquired downstream of the wire housed in an acrylic tube with a diameter characteristic of the carotid artery. Hemodynamic parameters including WSS, oscillatory shear index (OSI), and Reynolds shear stresses (RSS) were measured. Our findings show that the introduction of the stent wire altered downstream hemodynamic parameters through a reduction in WSS and increases in OSI and RSS from nonstented flow. The Newtonian analog solution of glycerol and water underestimated WSS while increasing the spatial coverage of flow reversal and oscillatory shear compared to a non-Newtonian fluid of glycerol, water, and xanthan gum. Peak RSS were increased with the Newtonian fluid, although peak values were similar upon a doubling of flow rate. The introduction of the stent wire promoted the development of flow patterns that are susceptible to intimal hyperplasia using both Newtonian and non-Newtonian analogs, although the magnitude of sites affected downstream was appreciably related to the rheological behavior of the analog. While the assumption of linear viscous behavior is often appropriate in quantifying flow in the largest arteries of the vasculature, the results presented here suggest this assumption overestimates sites susceptible to hyperplasia and restenosis in flow characterized by low and oscillatory shear.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic representation (a) and oblique angle view (b) of experimental closed flow loop setup to simulate pulsatile arterial blood flow conditions (flow direction indicated by arrows)

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Figure 2

Viscous behavior characterization of Newtonian and non-Newtonian blood analog fluids through steady pipe flow across a range of shear strain rates

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Figure 3

Representative 1 Hz pulsatile flow waveform as measured by the ultrasonic flow sensor (similar to Buchmann and Jermy [28] and Geoghegan [29])

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Figure 4

Gianturco Z-stent wire housed in a 0.635 cm diameter acrylic tube. Approximate laser beam plane and thickness of 0.15 cm is shown for reference.

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Figure 5

Measured PIV centerline velocities in nonstented and Gianturco stented flow at measured pulse cycle locations in comparison to the Womersley estimation using a Newtonian analog fluid at x/R = 0.4 from stent outlet. Error bars represent normalized standard deviation of velocity measurements.

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Figure 6

Measured PIV velocities in nonstented and Gianturco stented flow from the near wall to centerline in comparison to the Womersley estimation at peak pulsatile flow using a Newtonian analog fluid at x/R = 0.4 from stent outlet. Error bars represent normalized standard deviation of velocity measurements.

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Figure 7

Negative axial velocity contour plots (cm/s) of fluid flow downstream of the Gianturco Z-stent wire from the near wall to r/R = 0.5 at peak pulsatile flow (Re ≅ 384 (a), (b) and Re ≅ 768 (c), (d)) for Newtonian (a), (c) and non-Newtonian analog fluids (b), (d)

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Figure 8

Measured PIV WSS in nonstented and Gianturco stented flows at measured pulse cycle locations in comparison to the Womersley estimation using a Newtonian analog fluid at x/R = 0.4 from stent outlet

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Figure 9

OSI in Gianturco stented flow for Newtonian and non-Newtonian analog fluids

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Figure 10

Cycle averaged WSS (Pa) in Gianturco stented flow for Newtonian and non-Newtonian analog fluids. Critical WSS values of −0.4 Pa and 0.4 Pa are shown with the dashed line for reference.

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Figure 11

Measured RSS (Pa) downstream of the Gianturco stent wire at peak pulsatile flow (Re ≅ 384 (a), (b) and Re ≅ 768 (c), (d)) for Newtonian (a), (c) and non-Newtonian analog fluids (b), (d)

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Figure 12

Measured velocity profiles with Gianturco and Palmaz GenesisTM Transhepatic Biliary stents and for nonstented flow from the near wall to centerline in comparison to the Womersley estimation using a Newtonian analog fluid at x/R = 0.4 from stent outlet. Error bars represent normalized standard deviation of velocity measurements.

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Figure 13

Cycle averaged WSS for Newtonian and non-Newtonian analog fluids for a Palmaz GenesisTM Transhepatic Biliary stent. Critical values of WSS of −0.4 Pa and 0.4 Pa have been presented with dashed lines.

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