Pulmonary dysfunction in silica-exposed workers: a relationship to radiographic signs of silicosis and emphysema.

BACKGROUND

It has been established that occupational exposure to silica dust may cause significant impairment of pulmonary function. To compare the contribution of silicosis and emphysema to pulmonary dysfunction, radiographic signs of silicosis and emphysema in silica exposed workers were analyzed.

METHODS

Two hundred and twenty workers exposed to silica working in a Chinese refractory plant were selected as study subjects. Their findings of silicosis and emphysematous changes on radiograph were classified and evaluated. A questionnaire on respiratory symptoms, smoking, and occupational history was administered. All the workers performed measurements of spirometry and CO single-breath diffusing capacity.

RESULTS

Radiographic hyperinflation was detected in 9% of the workers without silicosis and in 33% of the workers with silicosis. Silicosis was significantly associated with hyperinflation after adjusting for exposure duration, age, and smoking. Respiratory symptoms were more frequent in the more severe cases of silicosis. Regression analysis showed that silicosis was significantly associated with decreases in the parameters of pulmonary function, but the significance disappeared when the hyperinflation term was added to the models. Radiographic hyperinflation was strongly associated with decreases in FEV1 and FEV1/FVC while relevant factors were controlled. Comparison between workers with and without hyperinflation showed that the former had significantly lower pulmonary function values.

CONCLUSIONS

The results suggest that emphysema associated with silicosis is likely to be responsible for pulmonary obstruction and decreased diffusing capacity occurring in silica-exposed workers.