Two-dimensional velocity measurements in a pulsatile flow model of the normal abdominal aorta simulating different hemodynamic conditions.

The infrarenal abdominal aorta and aortic bifurcation are frequent sites of atherosclerosis. The local hemodynamics are considered to be an atherogenetic factor, and a detailed description of the flow fields in this region of the arterial tree is therefore essential. The aim of this study was to provide quantitative two-dimensional data on the velocity fields in the abdominal aorta, using a realistic flow model of the abdominal aorta and its main branches, under various physiologic flow conditions (i.e. rest and exercise). Velocities in the suprarenal abdominal aorta were antegrade, with very little retrograde and radial velocity components present. In the infrarenal abdominal aorta, velocity profiles were not fully developed, and large-scale retrograde flow was present during part of diastole for the rest condition. For the exercise conditions small-scale retrograde velocities were present during diastole, especially at the distal posterior vessel wall, but not at the distal anterior vessel wall. For the rest and medium exercise conditions, secondary flows were created in the distal abdominal aorta during diastole, most prominent near the posterior wall. Calculated wall shear stress directions revealed the presence of both oscillatory and multidirectional wall shear stresses mainly in parts of the infrarenal abdominal aorta, and were found to correlate well with the published data on the distribution of early atherosclerotic lesions. This quantitative study demonstrates the necessity of carefully modeling both the anatomy and the physiology in order to understand the complex hemodynamics present in the abdominal aorta.