Novel Noninvasive Assessment of Pulmonary Arterial Stiffness Using Velocity Transfer Function

Abstract

BackgroundPulmonary 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 ResultsIn 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 (ρ=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 (ρ=−0.73; P<0.001) and a significant positive correlation with right ventricular mass index (ρ=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.

Cardiac Magnetic Resonance Imaging in Pulmonary Arterial Hypertension: Ready for Clinical Practice and Guidelines?

“…A novel measure reflecting PA stiffness is PA velocity transfer function, which describes the influence of vessel geometry and compliance/stiffness causing frequency-dependent changes in the input velocity profile (in the proximal part of the PA) as it travels through the artery and thus produces an output velocity profile (in the distal part of the PA) [ 102 •]. PA velocity transfer function is strongly associated with invasive measures of PA impedance, stiffness, and vascular resistance.…”

<p>Systemic Arterial Stiffness in New Diagnosed Idiopathic Pulmonary Arterial Hypertension Patients</p>

“…In the literature we were able to find some observations devoted to evaluation of the pulmonary artery resistance, 11,12,[29][30][31][32] but only a few of them studied the systemic arterial stiffness. [33][34][35] Before planning this study we hypothesized the following: 1) patients with IPAH have active factors in circulation which could damage not only the pulmonary but systemic arteries too as in arterial hypertensive patients; 2) if these changes are present, they might correlate with other parameters influencing on the prognosis.…”

<p>Velocity Transfer Function In The Right Pulmonary Artery And Impaired Cardiopulmonary Reserve In COPD</p>

“…Therefore, there is a growing interest in the use of CMR for the diagnosis and management of PH, including patients with lung diseases. Recently, we have validated a novel non-invasive CMR-derived parameter that, similar to impedance, reflects pulsatile and resistive properties of the PA 3. This approach relies on the principle that compliant PA vessel walls cause changes in the velocity profile as it travels through the PA over the cardiac cycle.…”

“…The frequency-dependent relationship between the input and output velocity profiles is described by a velocity transfer function (VTF), which is the relationship between the frequency spectra of input and output velocity 3. In suspected PH patients who underwent right heart catheterization, we found that VTF correlates with invasive PA impedance and the mean high-frequency modulus (MHFM) of VTF correlates with the pulmonary vascular resistance (PVR) and RV remodeling 3. Moreover, MHFM >1 accurately predicted an increased PVR 3.…”

“…In suspected PH patients who underwent right heart catheterization, we found that VTF correlates with invasive PA impedance and the mean high-frequency modulus (MHFM) of VTF correlates with the pulmonary vascular resistance (PVR) and RV remodeling 3. Moreover, MHFM >1 accurately predicted an increased PVR 3. We hypothesized that elevated MHFM of VTF, reflecting increased PVR and pulmonary vascular disease, would be associated with reduced exercise capacity measured by 6-mins walk distance (6MWD) in a COPD cohort.…”