Analysis of causes of velocity spread during initial deceleration in the ascending aorta in children and young adults.

Factors that predict the magnitude of instantaneous systolic velocities within the Doppler sample volume in the ascending aorta have not been elucidated in normal persons. This study determines whether the magnitude of instantaneous velocity spread in the ascending aorta is related to ascending aortic diameter, Reynolds number or other factors. Ascending aortic velocity tracings and diameters were recorded for 77 normal subjects using a 25 degrees off-axis transducer that permitted beam-flow alignment. Percent instantaneous velocity spread at peak modal velocity, which corresponds temporally to initial deceleration, was determined by dividing instantaneous velocity spread by peak modal velocity. Using standard formulations, values were computed in the ascending aorta of each subject for Reynolds number using peak and mean velocity, Womersley's alpha, and critical oscillatory Reynolds number. The highest correlation occurred for percent instantaneous velocity spread and ascending aortic diameter (r = 0.54) (p less than 0.001). The second highest correlation occurred for percent instantaneous velocity spread and critical oscillatory Reynolds number (r = -0.47) (p less than 0.001). A low but significant correlation (r = 0.30) (p less than 0.05) was found between alpha and percent instantaneous velocity spread. No significant correlation was found between percent instantaneous velocity spread and heart rate (r = 0.23), Reynolds number (r = -0.11) or maximal ascending aortic velocity (r = 0.14). This study demonstrates that percent instantaneous velocity spread in the human aorta is most closely related to ascending aortic diameter, an increase of which will cause a higher percent instantaneous velocity spread at initial deceleration.(ABSTRACT TRUNCATED AT 250 WORDS)