Clinical usefulness of end-tidal CO2 profiles during incremental exercise in patients with chronic thromboembolic pulmonary hypertension

- Patients with CTEPH have important gas exchange abnormalities during exercise.
- Desaturation is associated with disease severity of IPAH, but not of CTEPH.
- PetCO2 pattern abnormalities during exercise may be used to identify more clinically and hemodynamically severe patients.

IntroductionGreat 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 PetCO2 profiles during exercise may be more prominent in patients with CTEPH and could be helpful to indicate disease severity.MethodsSeventy patients with CTEPH and 34 with IPAH underwent right heart catheterization and cardiopulmonary exercise testing. According to PetCO2 pattern during exercise, patients were classified as having an increase or stabilization in PetCO2 up 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.ResultsMultivariate logistic regression analyses showed that progressive decreases in PetCO2 and SpO2 were better discriminative parameters than ΔV˙E/ΔV˙CO2 to distinguish CTEPH from IPAH. This pattern of PetCO2 was associated with worse functional impairment and greater reduction in PaCO2 during exercise.ConclusionCompared to patients with IPAH, patients with CTEPH present more impaired gas exchange during exercise, and PetCO2 abnormalities may be used to identify more clinically and hemodynamically severe cases.