Pulmonary artery wave reflection: observations in pulmonary hypertension

Abstract

Introduction: PIMR is a novel index of pulmonary microvascular function calculated from PressureWirederived distal pressure and flow. While PIMR has been reported in a large animal model of pulmonary arterial hypertension (PAH), its utility in the clinical setting has not been explored. Methods: Patients referred for diagnostic right heart catheterisation underwent Swan Ganz catheter and PressureWire (placed in 3rd order PA branch) measurement of pulmonary haemodynamics both before and during adenosine infusion. PIMR was calculated as mean transit time× (distal PA pressure−PA wedge pressure). Results: Thirty-eight subjects (average age 61 years) were studied including five normal, eleven PAH, fifteen heart failure with normal ejection fraction (HFNEF), five mitral valve disease, and two interstitial lung disease patients. Adenosine infusion resulted in 28% fall in pulmonary vascular resistance (PVR) and a 29% fall in systemic vascular resistance driven mainly by an increase in cardiac output (5.9± 0.3 L/min vs. 8.6± 0.4 L/min, p< 0.001). PIMR was closely related to PVR during adenosine (r= 0.63, p< 0.001). PIMR was higher in patients with transpulmonary gradient greater than 12 (6.9± 1.3 vs. 3.6± 0.9, p< 0.018) and in patients with PAH compared to those with HFNEF (10.5± 1.7 vs. 3.2± 0.4, p< 0.001). Conclusions: PIMR is closely related to PVR, suggesting that resistance in the pulmonary circulation occurs mainly at the microvascular level. While adenosine is an effective pulmonary vasodilator, its substantial effect on systemic resistance may make alternative agents such as PDE-5 inhibitors more attractive for pulmonary vasodilator challenge.