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A retrospective study of 561 patients with silicosis and 234 with asbestosis was performed to assess whether lung function decline in five years is related to the type (restrictive or obstructive) and/or to the degree of initial damage. Based on lung function tests, three groups of patients were identified: NC with normal lung function tests, CR with restrictive impairment and CO with airway obstruction. The degree of impairment was classified as mild, moderate and severe. Patients were considered worse if five years later they presented a higher degree of impairment. The prevalence of CR was significantly higher in asbestosis, that of NC and CO in silicosis (p less than 0.01). Among subjects with normal starting lung function, 9% only developed CR or CO 5 years later. The prevalence of subjects with worsened lung function in the CR groups was significantly higher (p less than 0.001) in asbestotics (36%) than in silicotics (14%) and was closely related to starting functional impairment. In the CO group the prevalence of worsened subjects was significantly higher than in CR (p less than 0.001), similar in the two diseases and independent of starting lung impairment.

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.