Airway function and respiratory resistance in Taiwanese coal workers with simple pneumoconiosis

Occupational exposure to coalmine dust consisting of coal particles and free silica eventually results in massive lung fibrosis. However, clinical observations of patients with coal workers' pneumoconiosis (CWP) suggest that airway dysfunction may be a predominant feature in the initial development of the disease.

Forced expirogram, plethysmographic determination of lung volumes, and measurement of respiratory resistance (Rrs) by the forced oscillation technique at 3, 9, and 18 Hz were conducted in a sample of 71 coal miners with simple pneumoconiosis and 36 healthy subjects.

The forced vital capacity (FVC) was well-preserved even in miners with category 2 and 3 CWP. There were no differences in the mean forced expiratory volume in 1 second (FEV1) values between healthy subjects and miners with category 1 disease. However, the level of airflow limitation in these miners increased with the transition from category 1 to category 2 and 3. The FEV1/FVC ratio fell below 70% in miners with category 2 and 3 disease, in both smokers and non-smokers. A consistent increase in the ratio of the residual volume to total lung capacity (RV/TLC) in the miners compared with that of the control workers was found. An abnormally high Rrs at 3 Hz (Rrs3) and frequency dependence in the flow resistance were also demonstrated in these subjects. There was an upward trend in the values of Rrs3 in the higher radiological categories. The correlation between respiratory conductance at this frequency (Grs3) and the RV/TLC ratio was good (r = - 0.763, p< 0.001).

Simple CWP is not associated with a clinically apparent reduction in lung volume. The Rrs3 appears to be a sensitive parameter for detecting airway obstruction in patients with simple CWP associated or not with a reduced FEV1.