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Research Papers

Study of the Velocity and Strain Fields in the Flow Through Prosthetic Heart Valves

[+] Author and Article Information
A. López-Zazueta, R. Ledesma-Alonso, J. E. V. Guzman

Instituto de Investigaciones en Materiales,  Universidad Nacional Autónoma de México, Coyoacan 04510, Mexico D.F., Mexico

R. Zenit1

Instituto de Investigaciones en Materiales,  Universidad Nacional Autónoma de México, Coyoacan 04510, Mexico D.F., Mexicozenit@servidor.unam.mx

1

Corresponding author.

J Biomech Eng 133(12), 121003 (Dec 21, 2011) (10 pages) doi:10.1115/1.4005475 History: Received May 24, 2011; Revised November 15, 2011; Published December 21, 2011; Online December 21, 2011

A comparative experimental study of the velocity field and the strain field produced down-stream of biological and mechanical artificial valves is presented. In order to determine the spatial and temporal distributions of these fields, a phase-locked stereoscopic particle image velocimetry (or 3D-PIV) technique was implemented. Emphasis was placed on the identification of the fundamental differences between the extensional and the shear components of the strain tensor. The analysis of the characteristic flows reveal that the strains in every direction may reach high values at different times during the cardiac cycle. It was found that elevated strain levels persist throughout the cardiac cycle as a result of all these contributions. Finally, it is suggested that the frequency with which the strain variations occur at particular instants and locations could be associated to the cumulative damage process of the blood constituents and should be taken into account in the overall assessment of existing valve types, as well as in future design efforts.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Components of the flow circuit: (a) pulsatile pump, (b) laminarization section, (c) test section, (d) compliance chamber, (e) needle valve, (f) valve, (g) upstream pressure transducer, (h) downstream pressure transducer.

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Figure 2

The positions of the measurement planes are indicated by red dotted lines. (left) For cases A1, A2, and B, the planes are perpendicular with respect to the direction of the flow. (right) For cases A3 and C the planes are parallel with respect to the direction of the flow. The separation between planes is given by di /2, with di taken from Table 1 for each valve.

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Figure 3

(a) Maximum velocities, (b) Maximum normalized strains, (c) Maximum normalized pressure drop. All quantities are phase-averaged.

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Figure 4

Velocity fields produced by the selected valves. The first, second and third rows correspond to the biological A3, the bileaflet, and the monoleaflet valves types, respectively. The images in any given row represent a time sequence for the valve within one period, T, of the operating cycle. The highest normalized velocities are shown in red and the lowest in blue according to the color scale at the bottom. Additionally, an insert at the upper right corner of each image shows the peak velocity, |v¯|max, measured at that particular instant of the cardiac cycle [actual values can be read from Fig. 3a]. The photo of the valve at the particular flow condition appear at the bottom of each image.

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Figure 5

Shear strain field produced by the selected valves. The first, second and third rows correspond to the biological A3, the bileaflet and the monoleaflet, respectively. The images in any given row represent a time sequence for the valve within one period, T, of the operating cycle. The highest normalized shears are shown in yellow and the lowest in red according to the color scale at the bottom (specific to each valve type). Additionally, an insert at the upper right corner of each image shows the peak velocity, |v|max , measured at that particular instant of the cardiac cycle [actual values can be read from Fig. 3a]. A photo of the valve at the particular flow condition appear at the bottom of each image.

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Figure 6

Components of the strain tensor measured 10 mm downstream of the tested valves. The ranges shown in figures (a) Biological A1, (b) Biological A2, (c) Biological A3, and (d) Bileaflet, is 0 ≤ Dii  /λ ≤ 3. (e) In the corresponding range, Monoleaflet is 0 ≤ Dii  /λ ≤ 6. It is also noted that the main flow is oriented in the z-direction.

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Figure 7

Frequency histograms for the Biological A2 (a), the Bileaflet (b), and the Monoleaflet (c) prostheses. The frequency f represents the number of times that a value of |D¯¯|/λ < 2 occurs on the measuring plane at time t/T. The color scale spans the full frequency range, with red indicating the highest values in each case.

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