Three-dimensional cross-sectional velocity distribution in the ascending aorta in cardiac patients.

Knowledge of the distribution of velocities across the ascending aorta is important for measurements of cardiac output; for understanding the function of normal and diseased valves and for the evaluation of prosthetic valves. The aim of this study was to investigate, in detail, the spatial distribution of axial velocities in the human ascending aorta, covering a nearly complete cross-section of the lumen in a time continuous modus. During open-heart surgery, blood velocities in the ascending aorta were mapped in 10 patients. All patients had aortic valves with no significant clinical evidence of disease. Pulsed Doppler ultrasound technique was used to measure blood velocity using an intraluminal probe with a 1 mm, 10 MHz crystal connected to a position-sensitive device. The distribution of blood velocity in the aorta 6-8 cm above the valve was characterized by a skewed and irregular peak systolic flow, with maximum velocity posteriorly. There was a positive correlation (r=0.854, P<0.002) between the maximum skewness slope and the stroke volume. Significant retrograde flow was recorded in all patients in the left posterior part of aorta in late systole and early diastole. The rotation of the point of maximal velocity was anticlockwise in six patients, clockwise in three and alternating in one. The present study shows that there is a considerable individual variation in the velocity distribution in the ascending aorta, with no plane symmetric features, and that large sampling volumes are required for reliable estimates of mean velocity.