Dynamics of pulsatile flow through model abdominal aortic aneurysms

Abstract

To contribute to the understanding of flow phenomena in abdominal aortic aneurysms, numerical computations of pulsatile flows through aneurysm models and a stability analysis of these flows were carried out. The volume flow rate waveforms into the aneurysms were based on measurements of these waveforms, under rest and exercise conditions, of patients suffering abdominal aortic aneurysms. The Reynolds number and Womersley number, the dimensionless quantities that characterize the flow, were varied within the physiologically relevant range, and the two geometric quantities that characterize the model aneurysm were varied to assess the influence of the length and maximal diameter of an aneurysm on the details of the flow. The computed flow phenomena and the induced wall shear stress distributions agree well with what was found in PIV measurements by Salsac et al. (J. Fluid Mech., vol. 560, 2006, pp. 19-51). The results suggest that long aneurysms are less pathological than short ones, and that patients with an abdominal aortic aneurysm are better to avoid physical exercise. The pulsatile flows were found to be unstable to three-dimensional disturbances if the aneurysm was sufficiently localized or had a sufficiently large maximal diameter, even for flow conditions during rest. The abdominal aortic aneurysm can be viewed as acting like a 'wavemaker' that induces disturbed flow conditions in healthy segments of the arterial system far downstream of the aneurysm; this may be related to the fact that one-fifth of the larger abdominal aortic aneurysms are found to extend into the common iliac arteries. Finally, we report a remarkable sensitivity of the wall shear stress distribution and the growth rate of three-dimensional disturbances to small details of the aneurysm geometry near the proximal end. These findings suggest that a sensitivity analysis is appropriate when a patient-specific computational study is carried out to obtain a quantitative description of the wall shear stress distribution.

Lagrangian wall shear stress structures and near-wall transport in high-Schmidt-number aneurysmal flows

“…Indeed, Gopalakrishnan et al (2014) have shown that small changes in the AAA geometry can significantly affect the WSS distribution, and changes in the curvature of the vessel wall have also been shown to affect WSS (Siggers & Waters 2008). In the current study we demonstrated results in two patient geometries, however, we also performed similar simulations in a total of six patient geometries and observed similar WSS LCS structures influencing the observed near wall concentration fields.…”

Effects of Reynolds and Womersley Numbers on the Hemodynamics of Intracranial Aneurysms

“…A similar conclusion was made by Le et al [17] and Cebral et al [19] based on their CFD simulations of cerebral aneurysms in rabbits and humans, respectively. In contrast, Gopalakrishnan et al [18] stated that, by increasing Re, the strength of the main vortex structure increases.…”

“…In contrast, Le et al [17] stated that Womersley number does not affect the flow feature and structures based on their CFD simulations of an IA from a rabbit. Furthermore, Gopalakrishnan et al [18] stated that while Womersley number does not change the vortex mode, but high Womersley number is associated with weak vortex rings in their simulation on abdominal aortic aneurysms. Bouillot et al [10] concluded that Re has a negligible effect on the flow structures of an idealized sidewall intracranial aneurysm for a steady inflow according to their PIV measurements.…”

Flow complexity in open systems: interlacing complexity index based on mutual information

“…Aneurysms are pathologic dilations of the vessel wall, and their flow characteristics have been extensively investigated as mechanically and biologically related with the initiation, growth, and eventual rupture of aneurysms (Cebral et al 2011;Geers et al 2011;Schnell et al 2014;Gopalakrishnan et al 2014;Arzani et al 2016).…”