Blood velocity distribution in the human ascending aorta.

Mapping of blood velocities across the lumen of the ascending aorta was performed in eight patients during open-heart surgery. A Doppler ultrasound probe was constructed to measure velocities in 2 mm steps from the maximum convexity to the maximum concavity of aorta, 6 to 7 cm above the aortic valve. In five patients with angina and normal aortic valves, velocity profiles were very similar and showed the following main features: a skewed peak systolic velocity profile with the highest velocity along the left posterior wall, a bidirectional velocity profile in late systole and early diastole with retrograde velocities along the left posterior wall, and a sustained antegrade flow along the convexity well into diastole. The resultant mean velocity profile had the highest velocity at the convex side and a central minimum velocity. In patients with Medtronic-Hall tilting disc prostheses, where the larger opening was oriented backwards and to the right, mean flow velocity profile was skewed in the opposite direction of normal. Moreover, instant systolic velocity profiles were much more irregular and dependent on the exact orientation of the prosthesis. In one patient with aortic valvular disease, very irregular and different velocity profiles were found. Based on a symmetry assumption, overall mean velocity for the total cross section was computed, and the magnitude of error in estimation of total flow from measurement of velocities at different depths was calculated. To measure total flow in the aorta, i.e., cardiac output, by single-gated Doppler technique, the most representative sampling site was about one-third of the diameter from the convex wall.