Determination of pulmonary to systemic blood flow ratio in children by a simplified Doppler echocardiographic method

Department of Pediatrics, University of California, San Francisco 94143.

Doppler echocardiographic determination of the pulmonary to systemic blood flow (Qp/Qs) ratio requires calculation of pulmonary artery and aortic luminal areas and integrals of the Doppler systolic velocity curves. To simplify the Doppler calculation of the Qp/Qs ratio, the square of the ratio of pulmonary to aortic luminal diameters, substituted for the ratio of vessel areas, was multiplied by the ratio of pulmonary to aortic peak flow velocities, substituted for the ratio of velocity time integrals. The Qp/Qs ratios were calculated by both the conventional and the simplified Doppler method in 42 children, 1 month to 16 years of age. Fifteen children had no evidence of shunt and 27 had an intracardiac left to right shunt at the atrial or ventricular level, or both. In children with a shunt, the Qp/Qs ratio obtained at cardiac catheterization by oximetry ranged from 1.4:1 to 4.3:1. Both the conventional and the simplified Doppler Qp/Qs ratios correlated well with the oximetric Qp/Qs ratios (r = 0.94 and 0.93, respectively). Since the pulmonary to aortic luminal area ratio and velocity time integral ratio varied in each patient, neither measurement alone correlated well with the oximetric Qp/Qs ratio and, therefore, neither alone could be used as an estimate of the Qp/Qs ratio. The simplified Doppler calculation of the Qp/Qs ratio, which requires less time and no computer facilities, provides an excellent estimate of the Qp/Qs ratio in children.

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