Effect of exercise on hemodynamic conditions in the abdominal aorta

Purpose: The beneficial effect of exercise in the retardation of the progre ssion of cardiovascular disease is hypothesized to be caused, at least in p art, by the elimination of adverse hemodynamic conditions, including flow r ecirculation and low wall shear stress. In vitro and in vivo investigations have provided qualitative and limited quantitative information on flow pat terns in the abdominal aorta and on the effect of exercise on the eliminati on of adverse hemodynamic conditions. We used computational fluid mechanics methods to examine the effects of simulated exercise on hemodynamic condit ions in an idealized model of the human abdominal aorta. Methods: A three-dimensional computer model of a healthy human abdominal ao rta was created to simulate pulsatile aortic blood flow under conditions of rest and graded exercise. Plow velocity patterns and wall shear stress wer e computed in the lesion-prone infrarenal aorta, and the effects of exercis e were determined. Results: A recirculation zone was observed to form along the posterior wall of the aorta immediately distal to the renal vessels under resting conditi ons. Low time-averaged wall shear stress was present in this location, alon g the posterior wall opposite the superior mesenteric artery and along the anterior wall between the superior and inferior mesenteric arteries. Shear stress temporal oscillations, as measured with an oscillatory shear index, were elevated in these regions. Under simulated Light exercise conditions, a region of low wall shear stress and high oscillatory shear index remained along the posterior wall immediately distal to the renal arteries. Under s imulated moderate exercise conditions, all the regions of low wall shear st ress and high oscillatory shear index were eliminated. Conclusion: This numeric investigation provided detailed quantitative data on the effect of exercise on hemodynamic conditions in the abdominal aorta. Our results indicated that moderate levels of lower limb exercise are nece ssary to eliminate the flow reversal and regions of low wall shear stress i n the abdominal aorta that exist under resting conditions. The lack of flow reversal and increased wall shear stress during exercise suggest a mechani sm by which exercise may promote arterial health, namely with the eliminati on of adverse hemodynamic conditions.