Effects of pressure and volume of the receiving chamber on the spatial distribution of regurgitant jets as imaged by color doppler flow mapping: An in vitro study

Regurgitant jet dimensions imaged by color Doppler flow mapping have been used to evaluate the severity of valvular insufficiency in clinical studies. To study the effect of pressure and volume within the receiving chamber on the magnitude of spatial distribution of regurgitant jets assessed by color Doppler techniques, we designed a simple constant-flow model in which a jet was driven through a known orifice (1.5 mm²) into a compliant receiving chamber by a steady-flow pump. A distal tube at the outflow closed the system and maintained the volume of the chamber constant during pump operation. We varied flow rate from 60 to 270 ml/min into elastic balloons with different static compliances of 1, 2, 4.5, and 9 ml/mm Hg (pressures of 57, 28, 18, and 8 mm Hg, respectively); the balloons served as receiving chambers at the constant volume of 150 ml. We also evaluated the effect of different volumes of a receiving chamber (110, 130, and 150 ml and pressures of 5, 15, and 24 mm Hg) with a static compliance of 2 ml/mm Hg over the same range of flow rates. For each of the different balloons, jet area correlated linearly with the jet velocity across the orifice (r=0.98, 0.99, 0.98, and 0.97) and also with flow rate (r=0.97, 0.99, 0.98, and 0.99). At the same flow rate and volume of receiving chamber, however, the jet area imaged by color Doppler decreased as the pressure in the receiving chamber increased, although receiving-chamber volume was constant. In the balloon with static compliance of 2 ml/mm Hg and constant flow rate, the absolute color Doppler jet area decreased as both volume and pressure of the receiving chamber increased. Our results suggest that in a pulsatile system the pressure-volume relationship inside the receiving chamber may be a major determinant of regurgitant jet area as imaged by color Doppler. Even in a chamber with constant static compliance, changes in volume and pressure within the receiving chamber can result in significant changes in jet area independent of changes in driving pressure and regurgitant volume.