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TECHNICAL BRIEFS

That Hemodynamics and Not Material Mismatch is of Primary Concern in Bypass Graft Failure: An Experimental Argument

[+] Author and Article Information
Thomas O'Brien

Center for Applied Biomedical Engineering Research and Materials and Surface Science Institute, Department of Mechanical and Aeronautical Engineering,  University of Limerick, Limerick, Irelandthomas.obrien@ul.ie

Liam Morris, Michael Walsh, Tim McGloughlin

Center for Applied Biomedical Engineering Research and Materials and Surface Science Institute, Department of Mechanical and Aeronautical Engineering,  University of Limerick, Limerick, Ireland

J Biomech Eng 127(5), 881-886 (Apr 28, 2005) (6 pages) doi:10.1115/1.1992532 History: Received September 07, 2004; Revised April 28, 2005

The long term patency of end-to-side peripheral artery bypasses are low due to failure of the graft generally at the distal end of the bypass. Both material mismatch between the graft and the host artery and junction hemodynamics are cited as being major factors in disease formation at the junction. This study uses experimental methods to investigate the major differences in fluid dynamics and wall mechanics at the proximal and distal ends for rigid and compliant bypass grafts. Injection moulding was used to produce idealized transparent and compliant models of the graft/artery junction configuration. An ePTFE graft was then used to stiffen one of the models. These models were then investigated using two-dimensional video extensometry and one-dimensional laser Doppler anemometry to determine the junction deformations and fluid velocity profiles for the rigid and complaint graft anastomotic junctions. Junction strains were evaluated and generally found to be under 5% with a peak stain measured in the stiff graft model junction of 8.3% at 100mmHg applied pressure. Hemodynamic results were found to yield up to 40% difference in fluid velocities for the stiff/compliant comparison but up to 80% for the proximal/distal end comparisons. Similar strain conditions were assumed for the proximal and distal models while significant differences were noted in their associated hemodynamic changes. In contrasting the fluid dynamics and wall mechanics for the proximal and distal anastomoses, it is evident from the results of this study, that junction hemodynamics are the more variable factor.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

The experimental setup used in the study. The sideview of the stiff graft model is shown together with the measurement locations. A schematic diagram of the flow circuit is also shown for the proximal model test. The graft pipe is connected to the head reservoir while the artery pipe is connected to the return reservoir. For the proximal model test, the connection of the graft and artery pipes to the reservoirs is reversed.

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Figure 2

Topview of junction illustrating bulging from 0mmHgto140mmHg (top) with graphical results of the top view deformations for the compliant graft model (Artery/Artery) and the stiff graft model (Graft/Artery) at the toe and 4.65mm from the toe (within the junction) which corresponds to the location of maximum displacement.

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Figure 3

Sideview illustrating constrained expansion of artery bed from 0mmHgto140mmHg (top). The graph shows the percentage less the deformations of the ESA models are when compared to the straight artery model (Healthy Artery). Sideview measurements were taken for various axial locations along the host artery of the ESA. The stiff graft (G/A) has a constraining effect on the host artery when compared to the compliant graft (A/A).

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Figure 4

Quantitative LDA results for the center-plane measurements in the proximal (top) and distal junctions (bottom). More significant fluid dynamic disturbance is evident in the distal junction when compared to normal fully developed flow. The comparisons between the stiff (bold line) graft model profiles and the compliant (dotted line) graft model profiles are less significant.

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Figure 5

Percentage difference plots of results of hemodynamic investigations for data across the artery. The proximal end results (top) show the magnitude of the velocity decrease in the compliant model when compared to the stiff model. The distal end results (bottom) show the magnitude of the velocity decrease in the compliant model when compared to the stiff model. It is seen that the differences between the profiles generally lie within 40% with notable exceptions at the distal end. The toe −4.65mm position corresponds to the position of the maximum bulge.

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Figure 6

Percentage difference plots of results of hemodynamic investigations for data across the artery. The compliant graft results (top) show the contrast in velocities between the proximal and distal end for the compliant model. The stiff graft results (bottom) show the contrast in velocities between the proximal and distal end for the stiff model. It is seen that the differences between the flows at the proximal and distal ends vary up to 80%. The toe −4.65mm position corresponds to the position of the maximum bulge.

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