Quantification of jet flow by momentum analysis: An in vitro color doppler flow study

Previous investigations have shown that the size of a regurgitant jet as assessed by color Doppler flow mapping is independently affected by the flow rate and velocity (or driving pressure) of the jet. Fluid dynamics theory predicts that jet momentum (given by the orifice flow rate multiplied by velocity) should best predict the appearance of the jet in the receiving chamber and also that this momentum should remain constant throughout the jet. To test this hypothesis, we measured jet area versus driving pressure, flow rate, velocity, orifice area, and momentum and showed that momentum is the optimal jet parameter: jet area=1.25 (momentum)^.28, r=0.989, p<0.0001. However, the very curvilinear nature of this function indicated that chamber constraint strongly affected jet area, which limited the ability to predict jet momentum from observed jet area. To circumvent this limitation, we analyzed the velocities per se within the Doppler flow map. For jets formed by 1-81-mm Hg driving pressure through 0.005-0.5-cm² orifices, the velocity distribution confirmed the fluid dynamic prediction: Gaussian (bell-shaped) profiles across the jet at each level with the centerline velocity decaying inversely with distance from the orifice. Furthermore, momentum was calculated directly from the flow maps, which was relatively constant within the jet and in good agreement with the known jet momentum at the orifice (r=0.99). Finally, the measured momentum was divided by orifice velocity to yield an accurate estimate of the orifice flow rate (r=0.99). Momentum was also divided by the square of velocity to yield effective orifice area (r=0.84). We conclude that momentum is the single jet parameter that best predicts the color area displayed by Doppler flow mapping. Momentum can be measured directly from the velocities within the flow map, and when combined with orifice velocity, momentum provides an accurate estimate of flow rate and orifice area.