Gas Exchange and Ventilatory Efficiency During Exercise in Pulmonary Vascular Diseases

Background and Objective Ventilatory inefficiency (high V′E/V′CO2) and resting hypocapnia are common in pulmonary vascular disease and are associated with poor prognosis. Low resting PaCO2 suggests increased chemosensitivity or an altered PaCO2 set-point. We aimed to determine the relationships between exercise gas exchange variables reflecting the PaCO2 set-point, exercise capacity, hemodynamics and V′E/V′CO2. Methods Pulmonary arterial hypertension (n = 34), chronic thromboembolic pulmonary hypertension (CTEPH, n = 19) and pulmonary veno-occlusive disease (PVOD, n = 6) patients underwent rest and peak exercise arterial blood gas measurements during cardiopulmonary exercise testing. Patients were grouped according to resting PaCO2: hypocapnic (PaCO2 ≤34 mmHg) or normocapnic (PaCO2 35–45 mmHg). The PaCO2 set-point was estimated by the maximal value of end-tidal PCO2 (maximal PETCO2) between the anaerobic threshold and respiratory compensation point. Results The hypocapnic group (n = 39) had lower resting cardiac index (3.1 ±0.8 vs. 3.7 ±0.7 L/min/m2, p Conclusions Resting hypocapnia is associated with worse cardiac function, more ventilatory inefficiency and reduced exercise capacity. This could be explained by elevated chemosensitivity and lower PaCO2 set-point. Maximal PETCO2 may be a useful non-invasive marker of PaCO2 setpoint and disease severity even with submaximal effort.