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Feasibility of Routine Pulmonary Arterial Impedance Measurements in Pulmonary Hypertension^*

^* From the Departments of Cardiology (Drs. Huez and Vachiéry), Intensive Care (Dr. Brimioulle), and Physiology (Dr. Naeije), the Erasme Hospital and the Faculty of Medicine of the Free University of Brussels, Belgium.

Correspondence to: Robert Naeije, MD, Laboratory of Physiology, Erasmus Campus, CP 604 Route de Lennik 808, B-1070 Brussels, Belgium; e-mail: rnaeije{at}ulb.ac.be

Objectives: Right ventricular (RV) afterload is best described by a pulmonary arterial impedance (PVZ) spectrum, which integrates pulmonary vascular resistance (PVR), elastance, and wave reflection. We evaluated the feasibility of PVZ determinations in patients with pulmonary arterial hypertension (PAH) during routine right heart catheterization and Doppler echocardiography.

Design: Prospective study.

Setting: Academic hospital.

Patients: Twenty-two patients with PAH.

Interventions: Right heart catheterization with a fluid-filled Swan-Ganz catheter, Doppler echocardiography, and administration of inhaled nitric oxide (NO) [10 to 20 ppm; 17 patients], maximum tolerated dose of IV epoprostenol (average, 8.5 ng/kg/min; 5 patients), and IV dobutamine (8 µg/kg/min; 8 patients).

Measurements and results: PVZ was calculated from the spectral analysis of synchronized pulmonary artery pressure (Ppa) and flow waves. The mean (± SE) Ppa was 63 ± 3 mm Hg, and the mean PVR was 16 ± 2 Wood units. The PVZ spectrum was markedly shifted to higher than normal pressures and frequencies, with a mean 0-Hz impedance (Z₀) of 1,506 ± 138 dyne · s · cm^–5, and a mean characteristic impedance (Zc) of 124 ± 11 dyne · s · cm^–5, which are in keeping with data from previous studies. Inhaled NO levels decreased Ppa, PVR, Z₀, and Zc without a change in cardiac output. Epoprostenol administration did not affect Ppa, increased cardiac output, and decreased Z₀ and Zc. Dobutamine administration increased cardiac output and Ppa, and decreased PVR and Z₀, without changing Zc.

Conclusions: The determination of PVZ to quantify RV afterload is feasible during routine right heart catheterization and Doppler echocardiography. The measurement is sensitive to pharmacologic interventions.

Key Words: characteristic impedance • dobutamine • echocardiography • epoprostenol • nitric oxide • pulmonary arterial hypertension • pulmonary vascular impedance • pulmonary vascular resistance

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