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Assessment of the Pulmonary Volume Pulse in Idiopathic Pulmonary Arterial Hypertension by Means of Electrical Impedance Tomography

Background: Electrical impedance tomography (EIT) is a non-invasive imaging technique which can be used to measure the blood volume changes in the pulmonary vascular bed during the cardiac cycle. Study Objectives: This study was performed to evaluate the differences in the EIT signal of the pulmonary vascular bed between healthy subjects and patients with idiopathic pulmonary arterial hypertension (IPAH), who are known to have a remodelled pulmonary vascular bed. Patients and Methods: Twenty-one patients (17 females, 4 males) with IPAH and 30 healthy controls (5 females, 25 males) were measured. EIT measurements were performed in duplicate, on the same day as right heart catheterization to obtain haemodynamic data. The maximal impedance change during systole (Δ Zsys) was used as a measure of the pulmonary volume pulse and expressed in arbitrary units (AU). Total lung capacity, spirometric values and diffusion capacity for carbon monoxide were measured as well. Results: Mean Δ Zsys was 215 ± 58 × 10–2 AU (95% CI 193 × 10–2 to 236 × 10–2) in the healthy subjects and 78 ± 27 × 10–2 AU (95% CI 66 × 10–2 to 91 × 10–2) in the IPAH patient group (p < 0.0001). No significant correlation was found between Δ Zsys and any of the haemodynamic or lung function data. Conclusion: The impedance pulsation of the pulmonary vascular bed is reduced in IPAH in comparison with controls, indicating a reduced volume pulse. This might represent the reduced cross section area, as well as the reduced compliance and number of the pulmonary vessels in these patients.