Abdominal aortic hemodynamics in young healthy adults at rest and during lower limb exercise: quantification using image-based computer modeling

Abstract

. Abdominal aortic hemodynamics in young healthy adults at rest and during lower limb exercise: quantification using image-based computer modeling. Am J Physiol Heart Circ Physiol 291: H668 -H676, 2006. First published April 7, 2006 doi:10.1152/ajpheart.01301.2005.-Localization of atherosclerotic lesions in the abdominal aorta has been previously correlated to areas of adverse hemodynamic conditions, such as flow recirculation, low mean wall shear stress, and high temporal oscillations in shear. Along with its many systemic benefits, exercise is also proposed to have local benefits in the vasculature via the alteration of these regional flow patterns. In this work, subject-specific models of the human abdominal aorta were constructed from magnetic resonance angiograms of five young, healthy subjects, and computer simulations were performed under resting and exercise (50% increase in resting heart rate) pulsatile flow conditions. Velocity fields and spatial variations in mean wall shear stress (WSS) and oscillatory shear index (OSI) are presented. When averaged over all subjects, WSS increased from 4.8 Ϯ 0.6 to 31.6 Ϯ 5.7 dyn/cm 2 and OSI decreased from 0.22 Ϯ 0.03 to 0.03 Ϯ 0.02 in the infrarenal aorta between rest and exercise. WSS significantly increased, whereas OSI decreased between rest and exercise at the supraceliac, infrarenal, and suprabifurcation levels, and significant differences in WSS were found between anterior and posterior sections. These results support the hypothesis that exercise provides localized benefits to the cardiovascular system through acute mechanical stimuli that trigger longer-term biological processes leading to protection against the development or progression of atherosclerosis. atherosclerosis; shear stress; magnetic resonance imaging; finite element analysis ADVERSE HEMODYNAMIC conditions, such as complex, recirculating flow, low mean wall shear stress, high spatial gradients in shear stress, and high particle residence times, are hypothesized to contribute to the localization of atherosclerotic plaque throughout the vasculature. In the abdominal aorta, a correlation between atherosclerosis and areas of low wall shear stress has been elucidated with prior autopsy (2,7,27,31,39) and experimental studies (5,16,19,20,22,32). Specifically, Cornhill et al. (2) observed a high probability of occurrence of sudanophilic lesions along the posterior and lateral walls of autopsy specimens obtained from young, healthy males, whereas Roberts et al. (27) and Glagov et al. (21), and in vitro cell culture work has shown that oscillating shear can induce an inflammatory response, including an increase in reactive oxygen species (3,9,29).Conversely, elevated blood flow associated with exercise has been hypothesized to result in hemodynamic conditions that inhibit atherosclerosis, such as unidirectional laminar flow, increased wall shear stress, and enhanced transport of cholesterol from the vessel wall (11,18,32,33). It has been shown in vitro that the vascular endothelium can sense and resp...

Altered hemodynamics, endothelial function, and protein expression occur with aortic coarctation and persist after repair

“…Time-averaged WSS (TAWSS) and the oscillatory shear index (OSI) were then calculated (39). Low TAWSS is thought to promote atherogenesis, as is elevated OSI, an index of directional changes in WSS (39,64). An OSI value of zero indicates that WSS is unidirectional, whereas a value of 0.5 is indicative of bidirectional WSS with a time-averaged value of zero.…”

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

“…Moreover, these studies do not include major branches immediately proximal to AAAs, such as the celiac, superior mesenteric, and renal arteries. These branches significantly influence conditions in the infrarenal aorta in normal subjects (119)(120)(121) and likely influence conditions in AAAs. In summary, while prior applications of CFD have increased our understanding of hemodynamics within AAAs, more realistic analyses will have to await more anatomically and physiologically accurate models and inclusion of wall properties.…”

Progress in the CFD Modeling of Flow Instabilities in Anatomical Total Cavopulmonary Connections

“…Meshes consisting of entirely tetrahedral elements are already being employed in complex anatomical domains with great success. 19,20,25 And for simpler anatomies, hexahedral unstructured grids can be readily implemented 14 as the boundary-layer mesh uniformity can be controlled with reasonable manual mesh generation effort. The algorithms for creating unstructured grids are also more amenable to automation.…”