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Research Papers

A Quantitative Comparison of Mechanical Blood Damage Parameters in Rotary Ventricular Assist Devices: Shear Stress, Exposure Time and Hemolysis Index

[+] Author and Article Information
Katharine H. Fraser, Tao Zhang, M. Ertan Taskin, Bartley P. Griffith

Artificial Organs Laboratory,  University of Maryland School of Medicine, MSTF rm 436, 10 S. Pine Street, Baltimore, MD 21201

Zhongjun J. Wu

Artificial Organs Laboratory,  University of Maryland School of Medicine, MSTF rm 436, 10 S. Pine Street, Baltimore, MD 21201zwu@smail.umaryland.edu

J Biomech Eng 134(8), 081002 (Aug 06, 2012) (11 pages) doi:10.1115/1.4007092 History: Received October 24, 2011; Revised June 18, 2012; Posted July 06, 2012; Published August 06, 2012; Online August 06, 2012

Ventricular assist devices (VADs) have already helped many patients with heart failure but have the potential to assist more patients if current problems with blood damage (hemolysis, platelet activation, thrombosis and emboli, and destruction of the von Willebrand factor (vWf)) can be eliminated. A step towards this goal is better understanding of the relationships between shear stress, exposure time, and blood damage and, from there, the development of numerical models for the different types of blood damage to enable the design of improved VADs. In this study, computational fluid dynamics (CFD) was used to calculate the hemodynamics in three clinical VADs and two investigational VADs and the shear stress, residence time, and hemolysis were investigated. A new scalar transport model for hemolysis was developed. The results were compared with in vitro measurements of the pressure head in each VAD and the hemolysis index in two VADs. A comparative analysis of the blood damage related fluid dynamic parameters and hemolysis index was performed among the VADs. Compared to the centrifugal VADs, the axial VADs had: higher mean scalar shear stress (sss); a wider range of sss, with larger maxima and larger percentage volumes at both low and high sss; and longer residence times at very high sss. The hemolysis predictions were in agreement with the experiments and showed that the axial VADs had a higher hemolysis index. The increased hemolysis in axial VADs compared to centrifugal VADs is a direct result of their higher shear stresses and longer residence times. Since platelet activation and destruction of the vWf also require high shear stresses, the flow conditions inside axial VADs are likely to result in more of these types of blood damage compared with centrifugal VADs.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 3

Comparison of the experimental and numerical pressure head in each VAD

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Figure 4

Flow field in each VAD at the optimal operating condition represented as path lines and contours of velocity magnitude

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Figure 5

Contours of the sss and volumetric sss histogram for each VAD at the optimal operating condition

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Figure 6

Plots of sss parameters with a flow rate = 3 l/min. Low sss volume = volume with sss < 1 Pa. High sss volume = volume with sss > 9 Pa. Higher sss volume = volume with sss > 50 Pa. Very high sss volume = volume with sss > 150 Pa.

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Figure 7

Plots of residence time parameters at pressure = 100 mmHg. Low sss volume = volume with sss < 1 Pa. Higher sss volume = volume with sss > 50 Pa. Very high sss volume = volume with sss > 150 Pa.

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Figure 8

Left: contour plots of HI normalized to the outlet value to show the special variation in each VAD. Right: variation in the HI with the operating condition in each VAD and a comparison with the experimental data in the CentVAD1 and AxVAD1.

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Figure 9

Comparison of the HI between VADs with each VAD operating at a flow = 3 l/min and pressure = 100 mmHg. The speeds required to produce those conditions are also shown.

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Figure 2

Meshes used for the VAD calculations

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Figure 1

Hellums’ shear stress-exposure time threshold required to activate platelets, with some additional data

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