Background: Adult patients with cystic fibrosis (CF) frequently have reduced exercise tolerance, which is multifactorial but mainly due to bronchial obstruction. The aim of this retrospective analysis was to determine the mechanisms responsible for exercise intolerance in patients with mild-to-moderate or severe disease.
Methods: Cardiopulmonary exercise testing with blood gas analysis at peak exercise was performed in 102 patients aged 28 ± 11 years: 48 patients had severe lung disease (FEV1 < 50%, group 1) and 54 had mild-to-moderate lung disease (FEV1 ≥ 50%, group 2). VO2 peak was measured and correlated with clinical, biological, and functional parameters.
Results: VO2 peak for all patients was 25 ± 9 mL/kg/min (65 ± 21% of the predicted value) and was < 84% of predicted in 82% of patients (100% of group 1, 65% of group 2). VO2 peak was correlated with body mass index, C-reactive protein, FEV1, FVC, RV, DLCO, VE/VCO2 peak, VD/VT, PaO2, PaCO2, P(A-a)O2, and breathing reserve. In multivariate analysis, FEV1 and overall hyperventilation during exercise were independent determinants of exercise capacity (R(2) = 0.67). FEV1 was the major significant predictor of VO2 peak impairment in group 1, accounting for 31% of VO2 peak alteration, whereas excessive overall hyperventilation (reduced or absent breathing reserve and VE/VCO2) accounted for 41% of VO2 alteration in group 2.
Conclusion: Exercise limitation in adult patients with CF is largely dependent on FEV1 in patients with severe lung disease and on the magnitude of the ventilatory response to exercise in patients with mild-to-moderate lung disease.