Follow-up respiratory measurements in Quebec chrysotile asbestos miners and millers

In 1974 changes in dyspnea, lung function, and pneumoconiotic radiographic abnormalities were recorded among the 1,015 Quebec chrysotile miners and millers surveyed in 1967-1968. The aim was to relate these changes to dust exposure--age, smoking, and earlier health status being taken into account. Dyspnea and lung function were assessed in 722 men, and for 277 recent radiographs were read separately by three experts for changes in the parenchyma and pleura. Each measure was analyzed independently for men without any abnormality when first seen (eligible for "attack") and for others (eligible for progression/regression). Age significantly influenced the rate of attack of pleural abnormality and the rates of attack and progression of dyspnea and lung function decline. Smoking had comparatively minor effects. The only associations with exposure were for progression of parenchymal change (one reader), and for progression of dyspnea. These essentially negative findings are similar to those obtained in a previous longitudinal survey of radiographs from the same workforce.