Usefulness of ventilatory gas analysis for the non-invasive evaluation of the severity of chronic thromboembolic pulmonary hypertension

Background: Chronic thromboembolic pulmonary hypertension (CTEPH) is characterized by organic thrombotic obstructions in the pulmonary arteries with reduced pulmonary vascular reserve. This study aimed to examine whether postural changes in ventilatory gas analysis parameters are useful for assessing pulmonary hemodynamics in patients with CTEPH. Methods: A total of 44 patients with newly diagnosed CTEPH (CTEPH group), 33 patients with improved CTEPH (mean pulmonary arterial pressure [mPAP] <25 mm Hg), and 25 controls were enrolled. Patients with improved CTEPH referred to patients without residual PH who were previously diagnosed with CTEPH and already received optimal therapies. Various pulmonary function parameters were examined in supine and sitting positions, and postural changes were calculated (Δ[supine − sitting]). In 32 patients with CTEPH, we examined hemodynamic and ventilatory gas analysis parameters before the first balloon pulmonary angioplasty (BPA) and during follow-up. Results: Patients with CTEPH had significantly lower supine end-tidal carbon dioxide pressure (P_ETCO₂) and ΔP_ETCO₂ than controls (both P < 0.001), and these parameters were significantly correlated with mPAP (R² = 0.507, P < 0.0001 and R² = 0.470, P < 0.001, respectively). Supine P_ETCO₂ and ΔP_ETCO₂ were significantly lower in patients with improved CTEPH than in controls (both P < 0.001). Hemodynamic and echocardiographic parameters were comparable in both groups. Furthermore, significant correlation between the change in mPAP and change in supine P_ETCO₂ by BPA was noted (R² = 0.478, P < 0.001). Conclusion: These results indicate that postural changes in ventilatory gas analysis parameters are useful and non-invasive method for the evaluation of mPAP, which is one of the hemodynamic parameters of CTEPH severity.