Relation of airway responsiveness to duration of work in a dusty environment

Health selection within a workforce has been found in several industries and appears to be more pronounced in dustier occupations. In this study of airway disease among workers exposed to asbestos and man made mineral fibres, 215 of 246 construction insulators 50 years old or less and currently working in the Montreal area were examined. Spirometry was completed successfully in 214 workers without known asbestosis and 207 underwent methacholine bronchoprovocation testing. Airway responsiveness was expressed as PC15, the concentration of methacholine causing a 15% fall in the forced expiratory volume in one second (FEV1). Exposure to asbestos and synthetic mineral fibre dust was estimated from the total hours of work in the trade since first employment. After the effect of age, height, and pack years of smoking had been taken into account, no relation was found between hours of work and any indices obtained from the forced expiratory manoeuvre (FEV1/FVC, MMF). After the effect of airway calibre (FEV1/FVC), age, and pack years of cigarette consumption had been taken into account, airway responsiveness decreased as the total hours of work in the trade increased. These findings suggest that workers with greater levels of airway responsiveness are more sensitive to exposure in a dusty workplace and in consequence are less likely to continue. In studies of workforces a survivor effect of this nature will tend to weaken the relation between lung function abnormality and occupational exposure.