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Research Papers

Two-Dimensional FSI Simulation of Closing Dynamics of a Tilting Disk Mechanical Heart Valve

[+] Author and Article Information
V. Govindarajan

Department of Biomedical Engineering, University of Iowa, Iowa City, IA 52242

H. S. Udaykumar

Department of Mechanical and Industrial Engineering, University of Iowa, Iowa City, IA 52242; IIHR-Hydroscience and Engineering, University of Iowa, Iowa City, IA 52242

L. H. Herbertson, S. Deutsch

Department of Bioengineering, Pennsylvania State University, University Park, PA 16802

K. B. Manning1

Department of Bioengineering, Pennsylvania State University, University Park, PA 16802kbm10@psu.edu

K. B. Chandran

Department of Biomedical Engineering, University of Iowa, Iowa City, IA 52242; IIHR-Hydroscience and Engineering, University of Iowa, Iowa City, IA 52242

1

Corresponding author.

J. Med. Devices 4(1), 011001 (Feb 04, 2010) (11 pages) doi:10.1115/1.4000876 History: Received January 28, 2009; Revised December 03, 2009; Published February 04, 2010; Online February 04, 2010

The fluid dynamics during valve closure resulting in high shear flows and large residence times of particles has been implicated in platelet activation and thrombus formation in mechanical heart valves. Our previous studies with bileaflet valves have shown that large shear stresses induced in the gap between the leaflet edge and valve housing results in relatively high platelet activation levels, whereas flow between the leaflets results in shed vortices not conducive to platelet damage. In this study we compare the result of closing dynamics of a tilting disk valve with that of a bileaflet valve. The two-dimensional fluid-structure interaction analysis of a tilting disk valve closure mechanics is performed with a fixed grid Cartesian mesh flow solver with local mesh refinement, and a Lagrangian particle dynamic analysis for computation of potential for platelet activation. Throughout the simulation the flow remains in the laminar regime, and the flow through the gap width is marked by the development of a shear layer, which separates from the leaflet downstream of the valve. Zones of recirculation are observed in the gap between the leaflet edge and valve housing on the major orifice region of the tilting disk valve and are seen to be migrating toward the minor orifice region. Jet flow is observed at the minor orifice region and a vortex is formed, which sheds in the direction of fluid motion, as observed in experiments using PIV measurements. The activation parameter computed for the tilting disk valve at the time of closure was found to be 2.7 times greater than that of the bileaflet mechanical valve and was found to be in the vicinity of the minor orifice region, mainly due to the migration of vortical structures from the major to the minor orifice region during the leaflet rebound of the closing phase.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Schematic depiction of a 27 mm BSM valve in the closed position, (b) leaflet in the fully open position with disk at 20 deg to the vertical rotates 70 deg to reach the fully closed position; (c) schematic of the 2D computational domain with the leaflet shown in the fully open and closed positions with the disk pivoted at the position of the strut; and (d) applied inlet ventricular pressure boundary condition. The data points in the plot refer to the time during the leaflet closure phase at which the computational results are presented in Figs.  578.

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Figure 2

(a) Particle distribution in the flow regime at the beginning of the computational cycle with high particle concentration at the inlet (dark region) and no particles present in the rest of the flow regime; (b) example of a single particle being traced over time with the light dot indicating the starting point and the dark dot indicating the end point of the particle path during the closing phase. The activation parameter is calculated cumulatively for each particle within the flow domain.

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Figure 3

Comparison of the angular position of the leaflets during the closing phase and the first rebound from the experimental study with the simulation results

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Figure 4

Comparison of the leaflet closing dynamics for the tilting disk and the bileaflet valves: (a) angular position of the leaflet closure with time during the closing and rebound phases; (b) leaflet angular velocity; and (c) leaflet tip velocity

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Figure 5

Comparison of the vorticity plots between the tilting disk valve and the bileaflet valve during the closing phase. The top panel ((a)–(c)) shows the plots for the tilting disk valve and the bottom panel ((d)–(f)) shows the plots for the bileaflet valve

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Figure 6

Plots of the shear stress, platelet concentration, and platelet activation parameter for the tilting disk valve (top panel: (a)–(c)) and the bileaflet valve (bottom panel: (d)–(f)) at the instant of closure

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Figure 7

Plots of the vorticity (left column), shear stress (middle column), and the calculated platelet activation contours (right column): (a) first rebound phase; and (b) closure following the first rebound for the tilting disk valve; (c) first rebound phase; and (d) closure following the first rebound for the bileaflet valve

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Figure 8

Plots of vorticity (left column), shear stress (middle column), and the calculated platelet activation contours (right column): (a) second rebound phase; (b) closure following the second rebound for the tilting disk valve; and (c) during the final closure of the bileaflet valve

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