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

Departments of 1 Mechanical Engineering, 2 Surgery, 3 Medicine, 4 Radiology, and 5 Bioengineering, Stanford University, Stanford, California Submitted 8 December 2005 ; accepted in final form 8 March 2006 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 ± 0.6 to 31.6 ± 5.7 dyn/cm 2 and OSI decreased from 0.22 ± 0.03 to 0.03 ± 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 Address for reprint requests and other correspondence: C. A. Taylor, Clark Center, E350, 318 Campus Dr., Stanford, CA 94305-5431 (e-mail: taylorca{at}stanford.edu )