Comparison of noninvasive pulsed Doppler and Fick measurements of stroke volume in cardiac patients

We compared simultaneous measurements of stroke volume by direct Fick (SV_F) and noninvasive pulsed Doppler (SV_D) techniques in 15 resting, supine cardiac patients. Doppler measurements of ascending aorta blood velocity were obtained from the suprasternal notch with a single crystal transducer. The systolic velocity integral of the spatial-average velocity waveform was multiplied by cross-sectional area from the systolic aortic diameter, obtained independently by M-mode echocardiography, to determine absolute values for SV_D. The resulting linear regression equation was SV_D = ?1.14 + 0.95SV_F, r = +0.91, p < 0.0001. The mean SV_D and SV_F values were 68 and 73 cm³, respectively. These results in consecutive patients serve to validate empirically the pulsed Doppler method at rest. It is a convenient, safe, and painless procedure which appears appropriate for clinical diagnostic screening where serial measurements would be useful. However, this noninvasive technique does require technical experience and an understanding of anatomy and flow waveforms by the operator to obtain valid measurements.