Follow-up study of pulmonary function and respiratory tract symptoms in workers in a Swedish iron ore mine.

In 1967, 240 workers in the Kiruna, Sweden, mine were examined with regard to lung function and respiratory symptoms. Seventeen years later, 167 of these workers were reexamined using a structured interview which covered respiratory symptoms, smoking habits, and workplace, and lung function tests, including dynamic spirometry and closing volume. The prevalence of chronic bronchitis in the present study was 9.6%. There was a strong relationship between chronic bronchitis and smoking but no relationship between chronic bronchitis and working underground in the mine. Only three persons had chronic obstructive lung disease. In the still active mine workers, dynamic spirometry results showed no difference between smokers or nonsmokers or between underground and surface workers. Thus, we found no excess of chronic obstructive lung disease or lung function disturbances in the mine workers studied. This probably reflects a self-selection process whereby the workers with airway obstruction due to smoking or underground exposure have left underground work and also the company. Underground workers with chronic mucous hypersecretion, on the other hand, have not felt motivated, because of this, to leave underground work. Some, however, may have stopped smoking but not necessarily because of the hypersecretion.