TECHNICAL PAPERS: Fluids/Heat/Transport

Effects of Wall Motion and Compliance on Flow Patterns in the Ascending Aorta

[+] Author and Article Information
Suo Jin

Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University School of Medicine, Atlanta, GA 30332

John Oshinski

Department of Radiology, Emory University School of Medicine, Atlanta, GA 30322

Don P. Giddens

Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University School of Medicine, Atlanta, GA 30332 e-mail: don.giddens@bme.gatech.edu

J Biomech Eng 125(3), 347-354 (Jun 10, 2003) (8 pages) doi:10.1115/1.1574332 History: Received June 01, 2002; Revised January 01, 2003; Online June 10, 2003
Copyright © 2003 by ASME
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Through-plane image of region of interest and location of slices for velocity measurements. Phase velocity MR data were recorded at three cross-sections. A slice located just distal to the aortic valve provided CFD inlet boundary conditions for velocity, and boundary conditions for outflow were obtained from a section in the descending aorta. The “middle” section provided velocity information that was used to validate the CFD results.
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The CFD model reconstructed from MRI data. MR images provided the geometry for the CFD model and included wall motion at the inlet and middle sections. Interpolation was employed to prescribe wall motion between the inlet and middle sections and between the middle section and a section located just proximal to the first arch vessel. Beyond this, the aorta was assumed to be rigid.
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Flow waveforms as determined from MR phase velocity data. Measured velocity profiles were integrated to construct instantaneous flow waveforms at the inflow, middle and outflow sections.
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Measured motion of the aorta at the inlet section. a, The lumen expands and contracts during the pulsatile cycle as well as experiences translational motion due to aortic attachment. The numbers represent times (in seconds) as referenced to the flow waveforms in Figure 3. b, The centroid of the lumen can be determined at each time and the location tracked as an indication of translational motion of the section. These motion data were prescribed in the CFD model.
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Comparison of velocities calculated from CFD with those measured by phase velocity MR at the middle section. a, An MR image illustrates the orientation of the aortic lumen. The points P1, P2, P3 and P4 where WSS data were calculated are shown in the enlarged MR image in the right of the figure. b, A series of columns for comparison of velocity data, with the time during the cycle denoted. The left column represents phase contrast velocity (axial component) results from the MR studies at the middle section, with the velocity color-coded according to magnitude. The next column presents results from the full motion CFD model. The remaining columns present data from CFD results for models incorporating radial motion only (third column) and for a completely rigid wall (right column). Color-code scales are indicated by each figure and are not normalized to a uniform scale.
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Instantaneous streamlines computed from the CFD model that includes full motion. Instantaneous streamlines can be computed from the CFD results to help visualize flow patterns. The individual red lines originate from twelve dispersed locations at the inlet section. Each line follows an instantaneous tangent to the local velocity vector (these do not represent particle trajectories). During early systole, streamlines are generally directed downstream, but strong secondary patterns occur as flow decelerates. This behavior is qualitatively similar to previous observations using MRI 5.
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Comparison of WSS calculations at locations P1-P4 (see Figure 5a) under the assumption of a rigid wall (dashed line) and accounting for full wall motion (solid line).




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