Does expiratory flow limitation predict chronic dyspnoea in adults with cystic fibrosis?

Tidal expiratory flow limitation (EFL) may promote dynamic hyperinflation and contribute to chronic dyspnoea. The purpose of this study was to assess the contribution of EFL to chronic dyspnoea in adults with cystic fibrosis (CF). The presence of EFL was determined in 102 adults with stable CF (forced expiratory volume in one second (FEV1) 17.3-91.5% predicted) and 20 age-matched control subjects using the negative expiratory pressure technique. Measurements of inspiratory capacity (IC) and spirometry were performed, and chronic dyspnoea was evaluated using the modified Medical Research Council scale. EFL was present in 34 subjects (33%), with 18 subjects flow limited in the sitting position and 16 subjects flow limited only in the supine position. Flow limitation in the sitting position was associated with older age and lower FEV1 compared with flow-limited supine position and non-flow-limited subjects. A significant reduction in IC accompanied EFL in both the sitting and supine positions. Flow limitation in the sitting position was associated with significantly higher levels of chronic dyspnoea. Ordinal regression analysis indicated that EFL was the best predictor of chronic dyspnoea in a model that included FEV1 % pred. Expiratory flow limitation in cystic fibrosis is associated with reduced forced expiratory volume in one second, older age and dynamic hyperinflation. Expiratory flow limitation significantly contributes to chronic dyspnoea in cystic fibrosis.