Clinical usefulness of end-tidal CO2profiles during incremental exercise in patients with chronic thromboembolic pulmonary hypertension

Introduction Great ventilation to carbon dioxide output (ΔV...E/ΔV...CO2) and reduced end-tidal partial pressures for CO2(PetCO2) during incremental exercise are hallmarks of chronic thromboembolic pulmonary hypertension (CTEPH) and idiopathic pulmonary arterial hypertension (IPAH). However, CTEPH is more likely to involve proximal arteries, which may lead to poorer right ventricle-pulmonary vascular coupling and worse gas exchange abnormalities. Therefore, abnormal PetCO2profiles during exercise may be more prominent in patients with CTEPH and could be helpful to indicate disease severity. Methods Seventy patients with CTEPH and 34 with IPAH underwent right heart catheterization and cardiopulmonary exercise testing. According to PetCO2pattern during exercise, patients were classified as having an increase or stabilization in PetCO2up to the gas exchange threshold (GET), an abrupt decrease in the rest-exercise transition or a progressive and slow decrease throughout exercise. A subgroup of patients with CTEPH underwent a constant work rate exercise test to obtain arterial blood samples during steady-state exercise. Results Multivariate logistic regression analyses showed that progressive decreases in PetCO2and SpO2were better discriminative parameters than ΔV...E/ΔV...CO2to distinguish CTEPH from IPAH. This pattern of PetCO2was associated with worse functional impairment and greater reduction in PaCO2during exercise. Conclusion Compared to patients with IPAH, patients with CTEPH present more impaired gas exchange during exercise, and PetCO2abnormalities may be used to identify more clinically and hemodynamically severe cases.