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TECHNICAL PAPERS: Fluids/Heat/Transport

Flow and Thrombosis at Orifices Simulating Mechanical Heart Valve Leakage Regions

[+] Author and Article Information
Anna M. Fallon, Nisha Shah

School of Chemical Engineering,  Georgia Institute of Technology, Atlanta, GA 30332

Ulla M. Marzec, Stephen R. Hanson

Department of Biomedical Engineering,  Oregon Health and Science University, Portland, OR 97006

James N. Warnock

Woodruff School of Mechanical Engineering,  Georgia Institute of Technology, Atlanta, GA 30332

Ajit P. Yoganathan1

Wallace H. Coulter School of Biomedical Engineering,  Georgia Institute of Technology and Emory University, Atlanta, GA 30332ajit.yoganathan@bme.gatech.edu

1

To whom correspondence should be addressed.

J Biomech Eng 128(1), 30-39 (Aug 22, 2005) (10 pages) doi:10.1115/1.2133768 History: Received June 28, 2004; Revised August 22, 2005

Background: While it is established that mechanical heart valves (MHVs) damage blood elements during leakage and forward flow, the role in thrombus formation of platelet activation by high shear flow geometries remains unclear. In this study, continuously recalcified blood was used to measure the effects of blood flow through orifices, which model MHVs, on the generation of procoagulant thrombin and the resulting formation of thrombus. The contribution of platelets to this process was also assessed. Method of Approach: 200, 400, 800, and 1200μm orifices simulated the hinge region of bileaflet MHVs, and 200, 400, and 800μm wide slits modeled the centerline where the two leaflets meet when the MHV is closed. To assess activation of coagulation during blood recirculation, samples were withdrawn over 047min and the plasmas assayed for thrombin-antithrombin-III (TAT) levels. Model geometries were also inspected visually. Results: The 200 and 400μm round orifices induced significant TAT generation and thrombosis over the study interval. In contrast, thrombin generation by the slit orifices, and by the 800 and 1200μm round orifices, was negligible. In additional experiments with nonrecalcified or platelet-depleted blood, TAT levels were markedly reduced versus the studies with fully anticoagulated whole blood (p<0.05). Conclusions: Using the present method, a significant increase in TAT concentration was found for 200 and 400μm orifices, but not 800 and 1200μm orifices, indicating that these flow geometries exhibit a critical threshold for activation of coagulation and resulting formation of thrombus. Markedly lower TAT levels were produced in studies with platelet-depleted blood, documenting a key role for platelets in the thrombotic process.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Hinge region of a SJM reagent valve. Inset on right shows the open SJM valve and the location of the b-datum line when the valve is closed.

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Figure 2

Diagram of orifice plate chamber and steady flow loop

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Figure 7

TAT concentration over time for the noncalcium infused runs (p*<0.05, N=6)

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Figure 8

Hemoglobin concentration over time for the round orifices. Statistical significance was determined vs the 200μm orifice only (p*<0.05, N=6). Base line hemoglobin concentration at t=0 is indicated by the dotted line.

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Figure 9

SEM pictures of the inlet clot under 1300× magnification (above pictures) and outlet clot under 1100× magnification (bottom left) and location away from the outlet clot under 1200× magnification (bottom right)

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Figure 10

Flow diagram detailing flow field through the round orifices

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Figure 3

TAT concentration over time for the round orifices (p*<0.05, N=6)

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Figure 4

TAT concentration over time for the slit orifices

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Figure 5

Photographs of clot resulting from flow through the 200μm orifice. Clot is occluding the orifice and covering the periphery of the orifice. Total clot diameter was approximately 1.5mm.

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Figure 6

TAT concentration over time for the platelet-depleted runs (p*<0.05, N=6). At all time points, significantly more TAT was produced in the normal experiments than in the platelet reduced experiments.

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