Pulmonary input impedance or pulmonary vascular resistance?

Pulmonary artery input impedance (PAII) expresses the opposition of pulmonary vessels to pulsatile blood flow, in the same way that vascular resistance expresses opposition to steady flow. PAII spectrum includes information concerning not only the mean blood flow, pressure and resistance, but also proximal vessels stiffness, pulse wave velocity and arterial wave reflection. It is an adequate expression of the right ventricular afterload, and it is quite suitable for the description of the right-ventricular-pulmonary arterial interaction. Pulsatile properties must be taken into account, for instance, to understand the effects of pulmonary vasodilation on cardiac output. Characteristic PAII is increased in pulmonary hypertension due to stenosis, pulmonary thromboembolic disease, and in unexplained pulmonary hypertension.