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Research Papers

High-Resolution Measurements of Velocity and Shear Stress in Leakage Jets From Bileaflet Mechanical Heart Valve Hinge Models

[+] Author and Article Information
Ewa Klusak

Mechanical Engineering and
Biomechanics Research Centre,
National University of Ireland Galway,
Galway, Ireland
e-mail: e.klusak1@nuigalway.ie

Alessandro Bellofiore

Biomedical, Chemical and Materials Engineering,
San Jose State University,
College of Engineering,
San Jose, CA 95192

Sarah Loughnane

Mechanical Engineering and
Biomechanics Research Centre,
National University of Ireland Galway,
Galway, Ireland

Nathan J. Quinlan

Mechanical Engineering and
Biomechanics Research Centre,
National University of Ireland Galway,
Galway, Ireland
e-mail: nathan.quinlan@nuigalway.ie

Manuscript received April 2, 2015; final manuscript received July 29, 2015; published online August 31, 2015. Assoc. Editor: Tim David.

J Biomech Eng 137(11), 111008 (Oct 01, 2015) (11 pages) Paper No: BIO-15-1145; doi: 10.1115/1.4031350 History: Received April 02, 2015; Revised July 29, 2015

In flow through cardiovascular implants, hemolysis, and thrombosis may be initiated by nonphysiological shear stress on blood elements. To enhance understanding of the small-scale flow structures that stimulate cellular responses, and ultimately to design devices for reduced blood damage, it is necessary to study the flow-field at high spatial and temporal resolution. In this work, we investigate flow in the reverse leakage jet from the hinge of a bileaflet mechanical heart valve (BMHV). Scaled-up model hinges are employed, enabling measurement of the flow-field at effective spatial resolution of 167 μm and temporal resolution of 594 μs using two-component particle image velocimetry (PIV). High-velocity jets were observed at the hinge outflow, with time-average velocity up to 5.7 m/s, higher than reported in previous literature. Mean viscous shear stress is up to 60 Pa. For the first time, strongly unsteady flow has been observed in the leakage jet. Peak instantaneous shear stress is up to 120 Pa, twice as high as the average value. These high-resolution measurements identify the hinge leakage jet as a region of very high fluctuating shear stress which is likely to be thrombogenic and should be an important target for future design improvement.

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

Overall design of BMHV model. All dimensions in mm, given in physiological scale. (a) BMHV. (b) Section A-A. Leakage flow. (c) Section B-B. Hinge gap.

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Fig. 3

Scaled-up heart valve flow simulator rig with hinge model in the test section: (a) flow simulator and (b) test section

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Fig. 2

Schematic diagram of the experimental hinges model and computational fluid dynamics (CFD) model of the valve, halved on a symmetry plane normal to the leaflet axes of rotation: (a) test section with model enclosed in the transparent tube, (b) front view of two hinge models with different gap widths, and (c) CFD valve model

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Fig. 10

Distribution of time-average viscous shear stress at z1 = 86 μm with typical particle trajectories. Trajectories oriented in +y direction denote particles entering the domain in the direction of leakage flow, and trajectories oriented in −y direction represent particles entering the domain at the downstream boundary and flowing in the reverse direction. Results are presented in physiological scale. (a) Regular gap and (b) large gap.

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Fig. 11

rms velocity fluctuation, expressed as a percentage of global maximum velocity at plane z1 = 86 μm. Results are presented in physiological scale. (a) Regular hinge and (b) large hinge.

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Fig. 6

Measurement locations at the outflow from the two hinge models: (a) measurement locations in the x–y plane and (b) five measurement planes in the x–z plane

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Fig. 7

Measured pressure drop across the hinge model as a function of applied flow rate, expressed in equivalent physiological scale points show mean ± standard deviation and the curve is a quadratic fit

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Fig. 8

Time-average velocity contours downstream of the hinge with regular gap, measured at five elevations. Results are presented in physiological scale.

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Fig. 9

Time-average velocity contours downstream of the hinge with large gap, measured at five elevations. Results are presented in physiological scale.

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Fig. 12

Shear stress time history for particles released at various x0 locations at z1 = 86 μm, averaged over many particle release times. Solid curves denote particles entering the domain in the direction of leakage flow, and dashed curves represent particles entering the domain at the downstream boundary and flowing in the reverse direction. Results are presented in physiological scale. (a) Regular gap and (b) large gap.

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Fig. 13

Instantaneous flow-fields downstream from the regular hinge, measured at z = 86 μm. Results are presented in physiological scale.

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Fig. 14

Instantaneous flow-fields downstream from the regular hinge, measured at z = 86 μm. Results are presented in physiological scale.

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Fig. 15

Schematic diagram of measurement regions in the present study and previous in vitro and computational investigations of the leakage flow inside and downstream of the BMHV hinge: (a) measurement region in x–y plane and (b) measurement region in z–x plane

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Fig. 5

Velocity distribution on a x–y plane at z = 172 μm above the flat level: (a) experimental hinge model and (b) full-valve model

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Fig. 4

Velocity distribution on a y–z plane at x = 2.5 mm from the valve center plane: (a) experimental hinge model and (b) full-valve model

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