Vortex Shedding as a Mechanism for Free Emboli Formation in Mechanical Heart Valves

[+] Author and Article Information
Danny Bluestein

State University of New York at Stony Brook, Stony Brook, NY 11794-8181

Edmond Rambod, Morteza Gharib

California Institute of Technology, Pasadena, CA 91125

J Biomech Eng 122(2), 125-134 (Nov 03, 1999) (10 pages) doi:10.1115/1.429634 History: Received December 09, 1998; Revised November 03, 1999
Copyright © 2000 by ASME
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(a) Details of the numerical mesh in the valve area, (b) inlet velocity waveform
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Schematics of the Caltech pulse duplicator system. The system has been designed for investigating different features of aortic valve flows and consists of three major components: (1) test section, (2) pulsatile pump, (3) lumped compliance and peripheral resistance. A prototype bileaflet valve was constructed using a pair of 27 mm Pyrolitic Carbon leaflets mounted in a precisely machined transparent housing to allow Digital Particle Image Velocimetry. A typical aortic flow waveform is shown.
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Velocity vectors depicting the shed vortices in the wake of a St. Jude Medical bileaflet MHV during the deceleration phase (105 ms after peak systole). The leaflets (side view cross section) are shown in the fully open position.
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The development of axial velocity profiles past the valve and in the wake (105 ms after peak systole)
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Periodic vortex shedding coupled with vortex pairing during deceleration (85 ms to 142 ms after peak systole)
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Fundamental and subharmonic frequency peaks, characteristic of vortex coalescence, populating the velocity spectra in the leaflet’s wake
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Shear distribution around the valve’s leaflet (67 ms after peak systole). Note the two shear layers that are formed around the leaflet, extending downstream to surround the wake.
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Turbulent platelet paths through areas of highest stresses around the leaflet: above the leaflet (top) and below (bottom), leading to entrapment within the shed vortices in the leaflet’s wake. The corresponding velocity vectors are shown (paths are computed from 165 ms to 419 ms after peak systole).
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Comparison between the shear stress history (level of activation) of a platelet that flows near the leaflet and gets trapped in the wake’s vortices, and a platelet that flows in the core flow, where shear stress levels are relatively low. The two level of activation curves were computed along the corresponding platelet paths shown above.
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(a) DPIV measurements of the velocity vector field distal to the valve during peak systole. The tips of the leaflets are located at y=±0.3 cm. The trailing wakes, extending from the two leaflets downstream, induce visible fluctuations on the velocity vectors. (b) Vorticity field distal to the valve during peak systole. Dashed contours represent counterclockwise rotation, and solid lines represent clockwise rotation.
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Comparison between DPIV measurements and numerical results zooming in the wake of a single leaflet (105 ms after peak systole, from 0.05 cm to 1.2 cm distal to the tip of the leaflet)
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Vorticity distribution in the wake, along a straight line from the leaflet tip. The vorticity alternates between positive and negative values (clockwise and counterclockwise rotation), typical of the “Karman vortex street” dynamics.
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DPIV measurements of velocity profiles in the wake, distal to the valve




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