970–6 In Vivo Studies of Aortic Stenosis: Role of Inertial and Viscous Forces in Doppler/Catheter Discrepancies

In previous studies in vitro we have used a Reynolds number approach to analyze second order effects on pressure recovery distal to stenosis. It was shown that two fundamentally different effects, viscous losses and turbulent dissipation, can control the basic overestimation due to pressure recovery at both ends of the Reynolds number scale. Having quantified this effect in vitro, this study attempted to reconcile Doppler and catheter gradients across aortic stenosis in vivo.MethodsIn 4 sheep with surgically created aortic stenosis, 30 hemodynamic states were studied (4–11 per sheep) using Millar transducers in the LV and Aorta (peak PG ranged 3–150mmHg). A Vingmed 775 interfaced to a computer was used to measure CVV velocities simultaneously with catheter recordings.ResultsInstantaneous Doppler peak gradient correlated with catheter instantaneous gradient throughout the range of baseline and stenotic conditions (r=0.973, SEE=8.7mmHg). but Doppler overestimated cath gradient (up to 70%) for all stenotic valve conditions by an average of 17%. Plotting overestimation versus Reynolds number revealed a second order profile of the shape derived in vitro. Correction of Doppler gradients using this parabolic factor reduced average overestimation from 17% to 1.5%.ConclusionsOverestimation due to pressure recovery is basic to aortic stenosis, but this overestimation can be partially canceled by two apparently unrelated effects: viscous effects and turbulent dissipation. The former is deleted from the simplified Bernoulli equation, but more importantly, the latter is not characterized by any form of the Bernoulli equation. A Reynolds number based approach characterizes the relative importance of these effects and could lead to reconciliation of Doppler and catheter gradients in the clinical setting

Clinical utility of two-dimensional Doppler echocardiographic techniques for estimating pulmonary to systemic blood flow ratios in children with left to right shunting atrial septal defect, ventricular septal defect or patent ductus arteriosus

Range gated two-dimensional Doppler echocardiographic methods were evaluated for quantifying pulmonary (QP) to systemic (QS) blood flow ratios. Twenty-one patients were studied, 4 with patent ductus arteriosus, 6 with atrial septal defect and 11 with ventricular septal defect. The Doppler pulmonary to systemic flow (QP:QS) estimation method involved calculating volume flow (liters/min) at a variety of intracardiac sites by using imaging information for flow area and Doppler outputs to calculate mean flow velocity as a function of time. Area volume flows were combined to yield QP:QS ratios. The sites sampled were main pulmonary artery, ascending aorta, mitral valve orifice and subpulmonary right ventricular outflow tract. The overall correlation between Doppler QP:QS estimates and those obtained at cardiac catheterization (n = 18) or radionuclide angiography (n = 3) was r = 0.85 (standard error of the estimate = 0.48:1). These preliminary results suggest that clinical application of this Doppler echocardiographic method should allow noninvasive estimation of the magnitude of cardiac shunts