Structural changes to airway smooth muscle in cystic fibrosis.

BACKGROUND Chronic airway obstruction is characteristic of cystic fibrosis (CF) but there are few studies of airway smooth muscle remodelling in CF. METHODS Airway smooth muscle content and mean airway smooth muscle cell size were measured by applying design-based stereology to bronchoscopic biopsy specimens obtained from seven subjects with CF and 15 healthy controls. RESULTS The smooth muscle content increased by 63% in subjects with CF (mean (SD) 0.173 (0.08) v 0.106 (0.042) mm(3) smooth muscle/mm(3) submucosa, mean difference -0.067; 95% CI -0.12 to -0.013, p = 0.017) but there was no increase in mean cell size (2705 (351) v 2654 (757) microm(3), mean difference -51; 95% CI -687 to 585, p = 0.87). CONCLUSIONS These findings indicate hyperplasia of airway smooth muscle cells without hypertrophy and suggest that accumulation of airway smooth muscle cells may contribute to airway narrowing and bronchial hyperresponsiveness in CF.