Pulmonary arterial input impedance reflects the mechanical properties of pulmonary arterial remodeling in rats with pulmonary hypertension

Aims: Although pulmonary arterial remolding in pulmonary hypertension (PH) changes the mechanical properties of the pulmonary artery, most clinical studies have focused on static mechanical properties (resistance), and dynamic mechanical properties (compliance) have not attracted much attention. As arterial compliance plays a significant role in determining afterload of the right ventricle, we evaluated how PH changes the dynamic mechanical properties of the pulmonary artery using high-resolution, wideband input impedance (Z_PA). We then examined how changes in Z_PA account for arterial remodeling. Clarification of the relationship between arterial remodeling and Z_PA could help evaluate arterial remodeling according to hemodynamics. Main methods: PH was induced in Sprague–Dawley rats with an injection of Sugen5416 (20 mg/kg) and 3-week exposure to hypoxia (10% oxygen) (SuHx). Z_PA was evaluated from pulmonary artery pressure and flow under irregular pacing. Pulmonary histology was examined at baseline and 1, 3, and 8 weeks (n = 7, each) after Sugen5416 injection. Key findings: SuHx progressively increased pulmonary arterial pressure. Z_PA findings indicated that SuHx progressively increased resistance (baseline: 9.3 ± 3.6, SuHx1W: 20.7 ± 7.9, SuHx3W: 48.8 ± 6.9, SuHx8W: 62.9 ± 17.8 mm Hg/mL/s, p < 0.01) and decreased compliance (baseline: 11.9 ± 2.1, SuHx1W: 5.3 ± 1.7, SuHx3W: 2.1 ± 0.7, SuHx8W: 1.9 ± 0.6 × 10⁻³ mL/mm Hg, p < 0.01). The time constant did not significantly change. The progressive reduction in compliance was closely associated with wall thickening of small pulmonary arteries. Significance: The finding that changes in resistance were reciprocally associated with those in compliance indicates that resistant and compliant vessels are anatomically inseparable. The analysis of Z_PA might help evaluate arterial remodeling in PH according to hemodynamics.