Flow in the thoracic aorta.

Pulsed ultrasonic Doppler velocimetry and theoretical flow analysis have been combined to improve the knowledge and understanding of aortic velocity profiles and wall shear. From the theoretical point of view, particular aspects of the flow were developed, concerning the vorticity in the aorta, the interior velocity distribution, the boundary layer, the flow after separation and the effects of the branches. The experimental approach was performed on dogs, using pulsed ultrasonic Doppler velocimeter providing real-time acquisition of the instantaneous velocity distribution along vascular diameters and perivascular probes designed for bidimensional measurement of velocity distribution. The good agreement found between theory and the experimental velocity profiles has led to comparison of the assessments of axial shear. The peak of the measured shear agrees well with the calculated one; the largest observed shear, obtained at the level of the initial part of the descending thoracic aorta, varies from 4.5 Pa to 7.5 Pa depending on the cardiac output. Finally initial attempts have been made to correlate atheromatous wall lesion localisation with the flow and shear variation.