Pulsatile Flow in Fusiform Models of Abdominal Aortic Aneurysms: Flow Fields, Velocity Patterns and Flow-Induced Wall Stresses

Abstract

As one important step in the investigation of the mechanical factors that lead to rupture of abdominal aortic aneurysms, flow fields and flow-induced wall stress distributions have been investigated in model aneurysms under pulsatile flow conditions simulating the in vivo aorta at rest. Vortex pattern emergence and evolution were evaluated, and conditions for flow stability were delineated. Systolic flow was found to be forward-directed throughout the bulge in all the models, regardless of size. Vortices appeared in the bulge initially during deceleration from systole, then expanded during the retrograde flow phase. The complexity of the vortex field depended strongly on bulge diameter In every model, the maximum shear stress occurred at peak systole at the distal bulge end, with the greatest shear stress developing in a model corresponding to a 4.3 cm AAA in vivo. Although the smallest models exhibited stable flow throughout the cycle, flow in the larger models became increasingly unstable as bulge size increased, with strong amplification of instability in the distal half of the bulge. These data suggest that larger aneurysms in vivo may be subject to more frequent and intense turbulence than smaller aneurysms. Concomitantly, increased turbulence may contribute significantly to wall stress magnitude and thereby to risk of rupture.

Intracranial and Abdominal Aortic Aneurysms: Similarities, Differences, and Need for a New Class of Computational Models

“…Unfortunately, this statement also characterizes the state-of-the art in aneurysm hemodynamics. As a result, many complex features observed in experimental studies of aneurysm flow (152,153) have not been replicated in computational simulations. Muller et al (154) and Sahni et al (155) recently described anisotropic adaptive finite element methods that are well suited for resolving complex, 3-D pulsatile flow dynamics as occur in aneurysms.…”

Biomechanical factors in Finite Element Analysis of abdominal aortic aneurysms

“…It is intuitive to assume that blood flow affects the AAA wall in such manner. Nevertheless, it has been argued that shear stress may be omitted in computer simulations as it does not affect the wall directly, since most of aneurysms have ILT deposits as an obstacle between wall and blood flow, and the value of possible shear stress is several orders of magnitude lower than pressure induced wall stress [60].…”

Multiphase non‐Newtonian effects on pulsatile hemodynamics in a coronary artery

“…Although a large number of investigations have led to a better understanding of the flow disturbances induced by an aneurysm or atherosclerosis, most theoretical and experimental studies have been performed under simplified assumptions. In several reports on arterial flow, blood is modeled as a Newtonian fluid [4][5][6]. The viscoelasticity of blood is ignored because shear rates in arteries whose diameters are larger than 0.5 mm [7] are predominantly high.…”