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Research Papers

Reduction of Procoagulant Potential of b-Datum Leakage Jet Flow in Bileaflet Mechanical Heart Valves via Application of Vortex Generator Arrays

[+] Author and Article Information
David W. Murphy, Jelena Vukasinovic, Ari Glezer

Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405

Lakshmi P. Dasi

Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80523-1374

Ajit P. Yoganathan1

The Wallace H. Coulter Distinguished Faculty Chair of Biomedical Engineering and Regents Professor Associate Chair of Research Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332-0535ajit.yoganathan@bme.gatech.edu

1

Corresponding author.

J Biomech Eng 132(7), 071011 (Jun 02, 2010) (10 pages) doi:10.1115/1.4001260 History: Received December 17, 2009; Revised January 27, 2010; Posted February 12, 2010; Published June 02, 2010; Online June 02, 2010

Current designs of bileaflet mechanical heart valves put patients at an increased risk of thromboembolism. In particular, regurgitant flow through the b-datum line is associated with nonphysiologic flow characteristics such as elevated shear stresses, regions of recirculation, and increased mixing, all of which may promote thrombus formation. We have previously shown that passive flow control in the form of vortex generators mounted on the downstream leaflet surfaces can effectively diminish turbulent stresses. The objective of the current work is thus to determine the effect of vortex generators on the thromboembolic potential of the b-datum line leakage jet and to correlate that effect with the vortex generator-induced changes to the flow structure. Flow experiments were performed using a steady model of the transient b-datum line jet. These experiments encompassed flow visualization to gain an overall picture of the flow system, particle image velocimetry to quantify the flow field in detail, and in vitro experiments with human blood to quantify thrombus formation in response to the applied passive flow control. Thrombus formation was quantified over time by an assay for thrombin-antithrombin III (TAT III). In comparing results with and without vortex generators, significantly lower mean TAT III levels were observed at one time point for the case with vortex generators. Also, the TAT III growth rate of the case with vortex generators was significantly lower. While no differences in jet spreading were found with and without vortex generators, lower peak turbulent stresses were observed for the case with vortex generators. The results thus demonstrate the potential of applying passive flow control to cardiovascular hardware in order to mitigate the hemodynamic factors leading to thrombus formation.

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Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Counter-rotating vortex generator design applied to BMHV leaflets

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Figure 2

Pictures of Saint Jude Medical valve encased in PDMS, with VGs applied to downstream leaflet surface

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Figure 3

Schematic of flow loop used in flow experiments

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Figure 4

Schematic of laser hitting flow chamber

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Figure 5

Example of an instantaneous jet velocity profile

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Figure 6

Histograms showing number of instantaneous velocity realizations within each possible jet position

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Figure 7

Example scatter plot of correlation coefficients showing the selected quadrant of instantaneous velocity field realizations, which most closely correlate with the mean velocity field

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Figure 8

Mean TAT levels over five experimental time points for the control and VG cases

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Figure 9

Variation of the TAT levels over five experimental time points for the Control (light) and VG (dark) cases. Individual data points as well as mean levels (large filled circles) are shown. Also included are the linear regression lines and their regression equations.

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Figure 10

Mean velocity magnitude and RSS magnitudes for the control and VG cases before the application of the phase-averaging analysis

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Figure 11

Normalized jet widths for the control and VG cases, both before and after the phase-averaging (binning) analysis

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Figure 12

Reynolds shear stress plots of all nine Bins for Control and VG cases

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Figure 13

Histogram plots showing the distribution of RSS values in each bin for both control (dark) and VG (light). The bin number is shown in the upper right hand corner of each histogram.

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