Background: The use of a single sample volume in Doppler measurements of the velocity time integral (VTI) in the aortic annulus may introduce errors in calculations of stroke volumes, shunts, regurgitant fractions, and aortic valve area. To study the blood flow velocity distribution and assess this potential error, we used a dynamic 3-dimensional color flow Doppler imaging method.
Methods and results: Seventeen healthy volunteers were studied. The ultrasound data were captured from 10 to 20 heartbeats at a high frame rate (mean 57 frames per second) while freely tilting the transducer in the apical position. A magnetic position-sensor system recorded the spatial position and orientation of the probe. The raw digital ultrasound data were analyzed off-line with no loss of temporal resolution. Blood flow velocities were integrated across a spherical surface that tracked the aortic annulus during systole. The ratios of the systolic maximum to the systolic mean VTI ranged from 1.2 to 1.5 (mean 1.4). At the time of systolic peak flow, the ratios of the maximum to the mean velocity ranged from 1.1 to 2.0 (mean 1.5). The location of the maximum velocities and VTI showed individual variation.
Conclusion: The blood flow velocity profile was nonuniform. By using a single sample volume in Doppler measurements of the VTI in the aortic annulus, errors ranging from 20% to 50% may be introduced in calculations of stroke volumes.