Small airway involvement in cystic fibrosis lung disease: routine spirometry as an early and sensitive marker

Background: In young children with cystic fibrosis (CF) the forced expiratory volume in 1 second (FEV1 ) is often normal and a more sensitive measure to detect early obstructive lung disease is needed.

Aim: To evaluate the progression of selected spirometry parameters with age in a cohort of CF patients and healthy children aged 6 to 20 years.

Methods: Retrospective comparison of longitudinal spirometry data from CF patients with data from two cohort studies in healthy subjects. Quantile regression was used to calculate the longitudinal 10th percentile (P10 ), 50th percentile (P50 ), and 90th percentile (P90 ) of forced vital capacity (FVC), FEV1 , and the forced expiratory flow at 75% of FVC (FEF75 ). Sample size estimates were calculated using these three parameters as clinical trial endpoints.

Results: FVC, FEV1 , and FEF75 were all significantly lower in CF patients than healthy children. Abnormalities in FEF75 occurred at younger ages and remained substantially larger than abnormalities in FEV1 or FVC throughout childhood. Therefore, fewer patients would be required to detect a similar treatment effect if FEF75 is used as a primary endpoint compared with FEV1 or FVC.

Conclusions: Our data support the use of FEF75 as a more sensitive marker of early CF lung disease than FEV1 and FVC, because abnormalities in FEF75 occur at younger age and FEF75 is diminished more than other parameters.