In cystic fibrosis, lung clearance index is sensitive to detecting abnormalities appearing at exercise in children with normal spirometry.

Symptom-limited incremental cardiopulmonary exercise test was performed in school-age children with clinically stable cystic fibrosis (CF), all with normal spirometry. Physiological parameters were compared between patients with normal lung clearance index (LCI; n=6) and patients with elevated LCI (n=6). Dyspnoea ratings during exercise were similar in both groups. Although no patient had significant dynamic hyperinflation, end-expiratory lung volumes were higher throughout exercise in patients with elevated LCI. In addition, alveolar-arterial oxygen gradient at peak exercise was higher, and SpO2 was lower in patients with elevated LCI. LCI can thus be regarded as a test performed at rest that predicts some abnormalities appearing at exercise in CF children with normal spirometry.