Variation in the Color Doppler Area of a Regurgitant Jet with Changes in the Absolute Chamber Pressure: An In Vitro Study

The color Doppler appearance of a regurgitant jet depends on jet momentum, determined in part by the pressure difference between the two chambers. However, it is not clear if absolute chamber pressure has an independent effect on jet area. To test this question, an in vitro experiment was performed in which dynamically decaying jets were created with identical initial pressure gradients but five different levels of absolute chamber pressures. At every level of chamber pressure, color Doppler images were recorded with two different transducers (3.5 and 5.0 MHz) and jet areas were measured at four different flow rates (0 to 9.9 cm³/sec). A multilinear regression model was created with jet area as the dependent variable and jet flow rate, transducer frequency, and absolute chamber pressure as independent parameters. Jet area was most strongly predicted by flow rate (univariate r = 0.90) and transducer frequency (r = 9.32). Even after adjusting for these effects, however, a small but significant (p < 0.0001) effect of absolute chamber pressure on jet area was seen with jet area rising by 0.89 cm² for each 10 mm Hg increase in absolute chamber pressure (multivariate r = 0.96, p < 0.0001). We conclude that the color Doppler area of a regurgitant jet is dependent not only on the relative pressure and flow between the two chambers but also on the absolute chamber pressure.