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. 2014 Feb;30(2):280-95.
doi: 10.1002/cnm.2601. Epub 2013 Oct 28.

Effect of exercise on patient specific abdominal aortic aneurysm flow topology and mixing

Amirhossein Arzani  1 , Andrea S Les, Ronald L Dalman, Shawn C Shadden
Affiliations

Effect of exercise on patient specific abdominal aortic aneurysm flow topology and mixing

Amirhossein Arzani et al. Int J Numer Method Biomed Eng. 2014 Feb.

Abstract

Computational fluid dynamics modeling was used to investigate changes in blood transport topology between rest and exercise conditions in five patient-specific abdominal aortic aneurysm models. MRI was used to provide the vascular anatomy and necessary boundary conditions for simulating blood velocity and pressure fields inside each model. Finite-time Lyapunov exponent fields and associated Lagrangian coherent structures were computed from blood velocity data and were used to compare features of the transport topology between rest and exercise both mechanistically and qualitatively. A mix-norm and mix-variance measure based on fresh blood distribution throughout the aneurysm over time were implemented to quantitatively compare mixing between rest and exercise. Exercise conditions resulted in higher and more uniform mixing and reduced the overall residence time in all aneurysms. Separated regions of recirculating flow were commonly observed in rest, and these regions were either reduced or removed by attached and unidirectional flow during exercise, or replaced with regional chaotic and transiently turbulent mixing, or persisted and even extended during exercise. The main factor that dictated the change in flow topology from rest to exercise was the behavior of the jet of blood penetrating into the aneurysm during systole.

Keywords: Lagrangian coherent structures; computational fluid dynamics; hemodynamics; transport.

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Figures

Figure 1
Figure 1
Volumetric flow rates for rest and exercise used as inlet boundary condition.
Figure 2
Figure 2
AAA computer models, and the cross sections used for showing results.
Figure 3
Figure 3
Cross section view of FTLE (sagittal plane), at rest and exercise for Patient 1 at different phases of the cardiac cycle.
Figure 4
Figure 4
Cross section view of FTLE (sagittal plane), at rest and exercise for Patient 2 at different phases of the cardiac cycle.
Figure 5
Figure 5
Cross section view of FTLE (sagittal plane), at rest and exercise for Patient 3 at different phases of the cardiac cycle.
Figure 6
Figure 6
Cross section view of FTLE (sagittal plane), at rest and exercise for Patient 4 at different phases of the cardiac cycle.
Figure 7
Figure 7
Cross section view of FTLE (sagittal plane), at rest and exercise for Patient 5 at different phases of the cardiac cycle.
Figure 8
Figure 8
Effect of integration time on forward FTLE for different choices of τ in terms of the cardiac length T, during peak systole.
Figure 9
Figure 9
Mix-norm plots for the patients during rest (r) and exercise (e). Computations are done for 5 cardiac cycles.
Figure 10
Figure 10
Mix-variance plots for the patients during rest (r) and exercise (e). Computations are done for 5 cardiac cycles.
Figure 11
Figure 11
Residence time mix-norm plots for the patients during rest (r) and exercise (e). Computations are done for 5 cardiac cycles.
Figure 12
Figure 12
Comparison of measured PCMRI velocity fields versus computed velocity fields in the mid-aneurysm of Patient 2.
See this image and copyright information in PMC

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