Abdominal Aortic Flow Velocity at Rest and During Exercise
(From the Cardiovascular Dynamics DBP led by Charles A. Taylor, Ph.D. and Christopher K Zarins, M.D.)
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.
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) were computed. WSS significantly increased while 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.
Figure: Velocity magnitude plotted on a midplane slice of the abdominal aorta for one representative subject under resting (left) and simulated exercise (right) conditions. Three time points during the cardiac cycle, corresponding to peak systole (a), end systole (b), and mid-diastole (c), are shown. Note that regions of low flow velocities and recirculation zones that exist along the posterior wall under resting conditions were replaced by higher flow velocities and more laminar flow under simulated exercise conditions.