Relation of lung function to silicosis, emphysema and respiratory symptoms in workers exposed to silica dust

Objective. The study was designed to estimate the relationships between lung function and radiographic silicosis, emphysema, and also respiratory symptoms. Subjects and Methods. The subjects consisted of 220 workers from a refractory plant of China, who were exposed to silica dust for at least 3 years. Radiographic findings of silicosis and emphysema were evaluated and recorded using the criteria of China. A survey including questions on respiratory symptoms (dyspnea, chronic cough and phlegm) and occupational history was conducted. Lung function tests were performed. Results. Emphysema was found to be more common in the higher silicosis category, as were respiratory symptoms: it was strongly associated with declines in FEV1 and FEV1/FVC even after being controlled for other relevant covariants. Dyspnea was strongly associated with declines in FVC, FEV1, and DLco; and cough was associated with reduced FEV1/FVC. Although mean values of lung function tended to decrease in the high-silicosis category, only a poor relationship was found between lung function and silicosis after controlling for the effects of emphysema, respiratory symptoms and smoking, in multiple linear models. Silicosis category correlated with dyspnea, cough and emphysema as well as with age and silica exposure. Conclusion. Impaired lung function occurring in silica-exposed workers is more strongly related to radiographic emphysema, rather than to silicosis. Dyspnea is a significant predictor of impaired luna function.