Development of A Noninvasive Ultrasound Color M-Mode Means of Estimating Pulmonary Vascular Resistance in Pediatric Pulmonary Hypertension

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Abstract
Background — Accurate determination of pulmonary vascular resistance (PVR) is an important component in the evaluation and treatment of pediatric patients with pulmonary hypertension. We developed a novel technique, based on the concept of flow propagation, to estimate PVR noninvasively. The hypothesis is that changes in PVR cause changes in the velocity propagation (Vel prop ) within the main pulmonary artery and that Vel prop can be quantified using color M-mode imaging. Methods and Results — We tested the hypothesis using mathematical modeling, in vitro experiments, and preliminary clinical studies. The mathematical model showed that pressure and velocity tracings are closely correlated in time and that 6 to 18 ms time resolution was needed to resolve propagation times within typical main pulmonary artery lengths (2 to 5 cm). The in vitro experiments demonstrated that it was feasible to use color M-mode to measure Vel prop and that Vel prop correlated well with downstream resistance [y=(−1.01x)+22.77; R =0.96]. The method was then evaluated on patients undergoing acute pulmonary reactivity testing (n=22 measurements). Good correlation between Vel prop and PVR was found [y=(−1.71x)+26.0; R =0.90; SEE=2.41]. Conclusion — This newly developed method promises to be useful in the noninvasive evaluation of adults and children with pulmonary hypertension.

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