The difference of gas exchange pulmonary arterial capacitance with postural change between chronic thromboembolic pulmonary hypertension and pulmonary arterial hypertension

Background: Pulmonary artery compliance (PAC), which could be estimated with gas exchange pulmonary arterial capacitance (GXcap), reflects the elasticity of the pulmonary vessels, and it is known that PAC is changed by pulmonary perfusion. GXcap could be measured using ventilatory gas analysis and is calculated using O₂ pulse × peak end-tidal CO₂ pressure. Moreover, it is known that pulmonary perfusion by postural changes is different between chronic thromboembolic pulmonary hypertension (CTEPH) and pulmonary arterial hypertension (PAH). However, it was unclear whether GXcap could estimate PAC in CTEPH and PAH. Furthermore, it was unclear that change in GXcap with postural change (ΔGXcap) [Δ (Sitting - Supine)] was different between CTEPH and PAH. Methods: Patients with suspected pulmonary hypertension who underwent right heart catheterization (RHC) from May 2022 to February 2023 in our institution were prospectively enrolled. Ventilatory gas analysis was performed before RHC in both the supine and sitting positions and calculated. Moreover, PAC was calculated with RHC. The diagnosis of PAH and CTEPH was based on the European Society of Cardiology/European Respiratory Society 2022 guidelines. Results: Forty patients (CTEPH, n = 18; PAH, n = 22) were enrolled in this study. GXcap was positively related to PAC in these patients (R = 0.62, p < 0.001). Furthermore, PAC was significantly lower in CTEPH patients compared to PAH patients (median 1.63 mL/mmHg vs 2.05 mL/mmHg, p = 0.013). Moreover, GXcap was increased in CTEPH patients with postural change, while GXcap was decreased in PAH patients with postural change. Thus, ΔGXcap was significantly higher in CTEPH patients compared to PAH patients (median 5.8 mL × mmHg vs −2.6 mL × mmHg, p = 0.005). Conclusions: It was suggested that PAC could be moderately estimated using GXcap in PAH and CTEPH patients. Moreover, it was suggested that ΔGXcap was higher in CTEPH patients compared with PAH patients.