Determinants of exercise capacity in cystic fibrosis patients with mild-to-moderate lung disease

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 (FEV(1) < 50%, group 1) and 54 had mild-to-moderate lung disease (FEV(1) ≥ 50%, group 2). VO(2) peak was measured and correlated with clinical, biological, and functional parameters. RESULTS: VO(2) 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). VO(2) peak was correlated with body mass index, C-reactive protein, FEV(1), FVC, RV, DLCO, V(E)/VCO(2) peak, V(D)/V(T), PaO(2), PaCO(2), P(A-a)O(2), and breathing reserve. In multivariate analysis, FEV(1) and overall hyperventilation during exercise were independent determinants of exercise capacity (R(2) = 0.67). FEV(1) was the major significant predictor of VO(2) peak impairment in group 1, accounting for 31% of VO(2) peak alteration, whereas excessive overall hyperventilation (reduced or absent breathing reserve and V(E)/VCO(2)) accounted for 41% of VO(2) alteration in group 2. CONCLUSION: Exercise limitation in adult patients with CF is largely dependent on FEV(1) in patients with severe lung disease and on the magnitude of the ventilatory response to exercise in patients with mild-to-moderate lung disease.