[Functional compromise of the small airways in subjects exposed to SiO2]

Aims of our study were: to evaluate small airway function of subjects with past or present silica dust exposure and normal spirometric values; to investigate whether small airway disease is related to radiographic signs of silicosis, to cumulative dust exposure (ES) and to cigarette smoking. Maximal expiratory flow at 50% (MEF50) and 25% (MEF25) of forced expired vital capacity were measured in 112 subjects, 69 with radiographic signs of silicosis, group I, and the remaining 43 with normal chest X-rays. Even if age and ES were significantly higher in group I, no significant difference in respiratory function tests and in prevalence of small airway disease was found between the two groups. In both groups small airway function was significantly negatively related to smoking habits, while it was independent of the other variables considered. Multiple regression analysis with MEF50 and MEF25 as dependent variables did not show any significant relationship. We conclude that small airway disease due to encroachment of bronchiolar walls by SiO2 deposition is masqued by the damage produced by cigarette smoking, even in the presence of radiographic signs of silicosis.