The Effect of Asymmetry in Abdominal Aortic Aneurysms Under Physiologically Realistic Pulsatile Flow Conditions

Abstract

In the abdominal segment of the human aorta under a patient's average resting conditions, pulsatile blood flow exhibits complex laminar patterns with secondary flows induced by adjacent branches and irregular vessel geometries. The flow dynamics becomes more complex when there is a pathological condition that causes changes in the normal structural composition of the vessel wall, for example, in the presence of an aneurysm. This work examines the hemodynamics of pulsatile blood flow in hypothetical three-dimensional models of abdominal aortic aneurysms (AAAs). Numerical predictions of blood flow patterns and hemodynamic stresses in AAAs are performed in single-aneurysm, asymmetric, rigid wall models using the finite element method. We characterize pulsatile flow dynamics in AAAs for average resting conditions by means of identifying regions of disturbed flow and quantifying the disturbance by evaluating flow-induced stresses at the aneurysm wall, specifically wall pressure and wall shear stress. Physiologically realistic abdominal aortic blood flow is simulated under pulsatile conditions for the range of time-average Reynolds numbers 50 < or = Rem < or = 300, corresponding to a range of peak Reynolds numbers 262.5 < or = Repeak < or = 1575. The vortex dynamics induced by pulsatile flow in AAAs is depicted by a sequence of four different flow phases in one period of the cardiac pulse. Peak wall shear stress and peak wall pressure are reported as a function of the time-average Reynolds number and aneurysm asymmetry. The effect of asymmetry in hypothetically shaped AAAs is to increase the maximum wall shear stress at peak flow and to induce the appearance of secondary flows in late diastole.

An analysis of blood flow dynamics in AAA

“…These waveforms are triphasic pulses appropriate for normal hemodynamics conditions in the infrarenal segment of the human abdominal aorta first reported by Mills (Mills et al, 1970). The use of an input transient velocity based on normal physiology is justified by the fact that the inlet boundary condition is applied in the section of undilated segment of the abdominal aorta anterior the proximal neck of the aneurysm (Finol et al, 2003). In order to prevent overestimating the wall shear stress, a zero pressure state AAA has been used in present numerical simulations (Marra et al, 2005).…”

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

“…Hemodynamics-Many investigators have similarly used CFD to study blood flow in AAAs (e.g., [113][114][115][116][117]. In many cases, regions of high pressure or high wall shear stress are singled out as potentially important to pathogenesis, though with little direct reference to the underlying mechanobiology.…”

Dynamics of pulsatile flow through model abdominal aortic aneurysms

“…This paper presents a study of pulsatile (physiological) flow through an axisymmetric model aneurysm with a wall that is described by a Gaussian function. In doing so, we follow, to a certain extent, the 'simplified approach' of the work by Taylor & Yamaguchi (1994), Finol, Keyhani & Amon (2002), Yip & Yu (2002), Salsac, Sparks & Lasheras (2004), Deplano et al (2007) and Sheard (2009). Regarding the assumption of an axisymmetric geometry, it may be added that it has been observed that aneurysms tend to be symmetric during the early stages of the disease, only becoming non-axisymmetric during the later stages, as reported in Salsac (2005).…”