Airways obstruction from asbestos exposure. Effects of asbestosis and smoking.

OBJECTIVE: To define the apparent steps in developing airways obstruction vs restrictive lung disease in men exposed to asbestos for more than 20 years who had never smoked vs cigarette smokers.
DESIGN: Physiologic signs of asbestosis were studied in cross-sectional age-matched groups of never, current, and ex-cigarette smoking workers. SETTING AND PARTICIPANTS: The study included 8,720 asbestos-exposed construction and shipyard workers in the United States. MEASUREMENTS: FVC, FEV1, FEF25-75, and FEF75-85 were measured by spirometry and total lung capacity (TLC) by planimetry of standard chest radiographs and adjusted for height, age, and duration of cigarette smoking and expressed as percentage of predicted. TLC minus FVC yielded RV. We compared means and mean residuals (measurement minus group mean) expiratory flows and lung volumes in 1,146 men with pulmonary asbestosis age matched to 1,146 without asbestosis who had similar durations of asbestos exposure and to 370 men without asbestos exposure. Next, flows and volumes were regressed against the International Labour Office (ILO) profusion scale of irregular opacities on chest radiographs (PIO) and the duration of asbestos exposure for 1,777 never smokers (NS), 4,550 current smokers, and 2,393 ex-smokers.
RESULTS: Asbestos exposure in NS men decreased expiratory flows and increased TLCs compared with unexposed NS men. Further reductions in flows and FVC and increases RV/TLC with radiographic asbestosis were not statistically significant. As the PIO increased from 1/1 to 3/3, obstruction and air trapping increased significantly but TLC did not.
CONCLUSIONS: Asbestos exposure reduced flows and produced air trapping after 20 years in workers who never smoked. Smoking increased these abnormalities.