Doppler color flow mapping of simulated in vitro regurgitant jets: Evaluation of the effects of orifice size and hemodynamic variables

The spatial distribution of simulated regurgitant jets imaged by Doppler color flow mapping was evaluated under constant flow and pulsatile flow conditions. Jets were simulated through latex tubings of 3.2, 4.8, 6.35 and 7.9 mm by varying flow rates from 137 to 1,260 cc/min. Color jet area was linearly related to flow rate at each orifice (r = 0.96, SEE = 3.0.4; r = 0.99, SEE = 1.6; r = 0.97, SEE =2.3; r = 0.97, SEE = 3.2, respectively), but significantly higher flow rates were required to maintain the same maximal spatial distribution of the jet at the larger regurgitant orifices. Constant flow jets were also simulated through needle orifices of 0.2, 0.5 and 1 mm, with a known total volume (5 cc) injected at varying flow rates and with differing absolute volumes injected at the same flow rate (0.2, 1.0 and 2.0 cc/s, respectively). Again, maximal color jet area was linearly related to flow rate at each orifice (r = 0.97, SEE = 2.3; r = 0.97, SEE = 2.4; r = 0.92, SEE = 3.9, respectively), but was not related to the absolute volume of regurgitation. Color encoding of regurgitant jets on Doppler color flow maps was demonstrated to be highly dependent on velocity and, hence, driving pressure, such that color encoding was obtained from a constant flow jet injected at a velocity of 4 m/s through an orifice of 0.04 mm diameter with flow rates as low as 0.008 cc/s. Mitral regurgitant jets were also simulated in a physiologic in vitro pulsatile flow model through three prosthetic valves with known regurgitant orifice sizes (0.2, 0.6 and 2.0 mm²). For each regurgitant orifice size, color jet area at each was linearly related to a regurgitant pressure drop (r = 0.98, SEE = 0.15; r = 0.97, SEE = 0.20; r = 0.97, SEE = 0.23, respectively), regurgitant stroke volume (r = 0.77, SEE = 0.55; r = 0.94, SEE = 0.30; r = 0.91, SEE = 0.41, respectively) and peak regurgitant flow rate (r = 0.98, SEE = 0.16; r = 0.97, SEE = 0.21; r = 0.93, SEE = 0.37, respectively), but the spatial distribution of the regurgitant jets was most highly dependent on the regurgitant pressure drop. Jet kinetic energy calculated from the summation of the individual pixel intensities integrated over the jet area was closely related to driving pressure (r = 0.84), but integration of the power mode area times pixel intensities provided the best estimation of regurgitant stroke volume (r = 0.80). The extreme velocity dependence of color encoding in velocity variance mode flow mapping may account for some of the difficulties in accurately assessing the volume of regurgitation, but the power mode algorithm has potential for the quantitative assessment of the volume of valvular regurgitation.