• Jason Weatherald, Athénaïs Boucly, David Montani, Xavier Jaïs, Laurent Savale, Marc Humbert, Olivier Sitbon, Gilles Garcia, and Pierantonio Laveneziana.
• University of Calgary, Department of Medicine, Division of Respirology, Calgary, Alberta, Canada; Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada; Université Paris-Sud, Faculté de Médecine, Université Paris-Saclay, Le Kremlin-Bicêtre, France; Service de Pneumologie, Hôpital Bicêtre, AP-HP, Le Kremlin-Bicêtre, France; INSERM U999, LabEx LERMIT, Centre Chirurgical Marie Lannelongue, Le Plessis-Robinson, France.
• Arch. Bronconeumol. 2020 Sep 1; 56 (9): 578-585.

Background And ObjectiveVentilatory 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.MethodsPulmonary 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 ≤34mmHg) or normocapnic (PaCO2 35-45mmHg). The PaCO2 set-point was estimated by the maximal value of end-tidal PCO2 (maximal PETCO2) between the anaerobic threshold and respiratory compensation point.ResultsThe hypocapnic group (n=39) had lower resting cardiac index (3.1±0.8 vs. 3.7±0.7L/min/m2, p<0.01), lower peak V'O2 (15.8±3.5 vs. 20.7±4.3mL/kg/min, p<0.01), and higher V'E/V'CO2 slope (60.6±17.6 vs. 38.2±8.0, p<0.01). At peak exercise, hypocapic patients had lower PaO2, higher VD/VT and higher P(a-ET)CO2. Maximal PETCO2 (r=0.59) and VD/VT (r=-0.59) were more related to cardiac index than PaO2 or PaCO2 at rest or peak exercise. Maximal PETCO2 was the strongest correlate of V'E/V'CO2 slope (r=-0.86), peak V'O2 (r=0.64) and peak work rate (r=0.49).ConclusionsResting 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.Copyright © 2020. Publicado por Elsevier España, S.L.U.

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