Small airways function of silica-exposed workers.

Small airways obstruction may be present for many years before chronic airway obstruction becomes evident. Several spirometric indices, especially flow rates at low lung volumes, may reflect the status of small airways. Time domain indices, by using moments analysis of the volume time spirogram, have also been shown to be sensitive indicators of small airways obstruction. In this study, we have applied the various spirometric indices as well as time domain indices to a group of granite quarry workers without radiographic evidence of silicosis or physiological evidence of obstruction to the larger airways. The aim was to evaluate small airways function in relation to dust exposure in subjects with normal ratio of the forced expiratory volume in one second to the forced vital capacity (FEV1/FVC) and normal FVC. The volume-time spirograms of 140 quarry workers were digitized using an electronic digitizer connected to a microcomputer where flow and time domain indices were computed. The workers were divided into three exposure groups based on their occupational history. With adjustment for age, height, and smoking status, all the time domain indices showed significant small airways obstruction with increasing dust exposure. Smokers had greater degree of airways obstruction than the non-smokers, with a similar trend of increase in small airways obstruction in relation to higher exposure. Our present study suggests that small airways obstruction is present among silica exposed workers in the absence of radiological evidence of silicosis and large airways obstruction. There was also evidence of increasing small airways obstruction in higher dust exposure group. Our study also suggests that time domain indices are more sensitive to small airways obstruction.