Assessment of Pulmonary Vascular Impedance in Patients With Severe Pulmonary Arterial Hypertension
Keeley Shea Ravellette, Saad Kubba, Frank Servin, Michael Insel, Joe G. N. Garcia, Tushar Acharya, Franz P. Rischard, Rebecca R. VanderpoolABSTRACT
Introduction
Pulmonary arterial hypertension (PAH) is characterized by progressive pulmonary vascular remodeling. Pulmonary vascular impedance (PVZ) provides a comprehensive view of pulmonary arterial function. We hypothesized that functional vascular remodeling significantly alters pulsatile pulmonary hemodynamics and PVZ in severe PAH.
Methods
Participants with a right heart catheterization (RHC) and an echocardiogram including right ventricular outflow tract (RVOT) images (delay: 24 [5–76] days) were identified from the University of Arizona PH registry. Participants were split using the World Symposium PH classifications and PVR (mild: < 3.9WU, Moderate: 3.9–8.5WU and Severe: > 8.5WU). PVZ was calculated in the frequency domain using pulmonary artery (PA) pressure and RVOT‐PA flow profiles. Impedance measures of resistance ( Z 0 ), global stiffness ( Z 1 ) and proximal stiffness ( Z C , average Z 2‐4Hz ) were derived. To evaluate proximal arterial mechanics, we used the Z c‐mPAP relationship to distinguish pressure‐dependent from stiffness‐related changes on Z C . Data were presented as median [interquartile range].
Results
Forty‐eight subjects were identified (Control (mPAP < 25 mmHg): n = 8 and WSPH1: n = 40). Z 0 and Z C were significantly increased in WSPH1 compared to Control ( p < 0.05). Z 0 , Z 1 , and Z C were increased in WSPH1‐severe compared WSPH1‐mild and WSPH1‐moderate ( p < 0.05). All impedance parameters correlated with end‐systolic elastance (Ees) and arterial elastance (Ea, p < 0.05) but only Z 0 correlated with Ees/Ea ( p < 0.05). Z C ‐mPAP relationships were modeled for Control and WSPH groups using estimated unstressed diameters (16.7–27.0 mm) and wall thickness/elastic modulus pairs.
Conclusion
PVZ analysis demonstrates increased resistance ( Z 0 ), global stiffness ( Z 1 ), and proximal stiffness ( Z C ) in severe PAH. The Z C ‐mPAP relationship suggests proximal vascular stiffening.