[Noninvasive determination of the ratio of pulmonary to systemic blood flow with two-dimensional Doppler echocardiography: efficacy and limitation]

Abstract

Noninvasive determination of the ratio of the pulmonary to systemic blood flow (Qp/Qs) was attempted in 31 cases with intracardiac shunt using two-dimensional pulsed Doppler echocardiography. The Qp/Qs of these cases was ranged from 0.99 to 4.55 with an average of 2.63 by cardiac catheterization. Technical problems in the measurement were also studied. Seventeen cases with no shunt were served as controls. Systemic and pulmonary flow volumes, Qp and Qs (ml/min), were calculated by the following equation: Q (ml/min) = mean flow velocity (cm/sec) X cross sectional area of the semilunar valve ring (cm2) X 60 Here, the sample volume was set in the center of the valve ring at the phase when the flow velocity attained its peak in a pulse period. The mean velocity was obtained by dividing the integration of instantaneous mean frequency in the sample volume for a pulse period by RR interval. The ultrasonic incident angle was measured on the echocardiogram. The velocity profile at the valve ring was assumed to be a plane wave. The diameter (D) of the valve ring was measured on the echocardiograms of the long-axis view of the outflow tract. To make a correction referring to the value obtained by angiocardiography, 0.22 cm was added to the value obtained on the echocardiogram (D). The cross sectional area of the valve ring was calculated according to the following formula: Cross sectional area (cm2) = pi X [(D + 0.22/2)]2 The Qp/Qs ratio by the Doppler method in the cases with no intracardiac shunt was 1.11 (S.D. = 0.21) on an average and the Qp/Qs in the cases with an intracardiac shunt was well correlated with that by catheterization (r = 0.82). These results suggested the feasibility of the clinical application of the Doppler method for noninvasive determination of Qp/Qs. In 17 cases, pulmonary and systemic flow volumes measured by the direct Fick method were compared with those by the Doppler method, respectively. Considerable differences were observed between them. There was a tendency that both pulmonary and systemic flow volumes were under-estimated by the Doppler method in cases with a large shunt.(ABSTRACT TRUNCATED AT 400 WORDS)