Novel Noninvasive Assessment of Pulmonary Arterial Stiffness Using Velocity Transfer Function

Background-Pulmonary artery (PA) stiffness is associated with increased pulmonary vascular resistance (PVR). PA stiffness is accurately described by invasive PA impedance because it considers pulsatile blood flow through elastic PAs. We hypothesized that PA stiffness and impedance could be evaluated noninvasively by PA velocity transfer function (VTF), calculated as a ratio of the frequency spectra of output / input mean velocity profiles in PAs. Methods and Results-In 20 participants (55 +/- 19 years, 14 women) undergoing clinically indicated right-sided heart catheterization, comprehensive phase-contrast and cine-cardiac magnetic resonance imaging was performed to calculate PA VTF, along with right ventricular mass and function. PA impedance was measured as a ratio of frequency spectra of invasive PA pressure and echocardiographically derived PA flow waveforms. Mean PA pressure was 29.5 +/- 13.6 mm Hg, and PVR was 3.5 +/- 2.8 Wood units. A mixed-effects model showed VTF was significantly associated with PA impedance independent of elevation in pulmonary capillary wedge pressure (P=0.005). The mean of higher frequency moduli of VTF correlated with PVR (rho=0.63; P=0.003) and discriminated subjects with low (n=10) versus elevated PVR (>= 2.5 Wood units, n=10), with an area under the curve of 0.95, similar to discrimination by impedance (area under the curve=0.93). VTF had a strong inverse association with right ventricular ejection fraction (rho=-0.73; P<0.001) and a significant positive correlation with right ventricular mass index (rho=0.51; P=0.02). Conclusions-VTF, a novel right ventricular-PA axis coupling parameter, is a surrogate for PA impedance with the potential to assess PA stiffness and elevation in PVR noninvasively and reliably using cardiac magnetic resonance imaging.