Influence of the orifice inlet angle on the velocity profile across a flowconvergence region by color Doppler in vitro

The converging flow field proximal to a leaking valve is determined among o ther things by the orifice inlet angle formed by the leaflets. Thus, the in let angle affects the determination of regurgitant flow rate by the flow co nvergence method. Based on the hypothesis of spheric isovelocity surfaces, others had postulated that a local velocity within the flow convergence sho uld change inversely proportional to changes in the three-dimensional inlet angle. This concept would allow correction of the determination, of regurg itant flow for nonplanar orifice inlet angles. We tested this concept in vi tro. In a flow model, the flow convergence region proximal to different ori fice plates was imaged by color Doppler: funnel-shaped, planar and tip-shap ed (inverted funnels) orifice plates, with circular orifices of 2- and 7-mm diameter. Velocity profiles across the flow convergence along the flow cen terline were read from the color maps. As predicted, the local velocities w ere inversely related to the inlet angle, but only at the 2-mm funnel orifi ces, this effect was inversely proportional to the three-dimensional inlet angle (i.e., in agreement with the mentioned concept). However, for any 7-m m orifice and/or inlet angle of > 180 degrees, the effect of the inlet angl e was considerably less than predicted by the aforementioned concept. With increasing orifice diameter and with decreasing distance to the orifice, th e effect of the orifice inlet angle was reduced. The effect of the orifice inlet angle on the flow convergence region is modulated by orifice size and the distance to the orifice. Therefore, correction of flow estimates in pr oportion to the three-dimensional inlet angle will lead to considerable err ors in most situations of clinical relevance, namely to massive overcorrect ion when analyzing velocities located close to wide orifices.