Measuring lung diffusing capacity: an opportunity for improved medical surveillance and disability evaluation of coal miners.

Objectives: Spirometry is the primary lung function test utilised for medical surveillance and disability examination for coal mine dust lung disease. However, spirometry likely underestimates physiologic impairment. We sought to characterise abnormalities of single-breath diffusing capacity for carbon monoxide (D_LCO) among a population of former coal miners.

Methods: Data from 3115 former coal miners evaluated at a West Virginia black lung clinic between 2006 and 2015 were retrospectively analysed to study the association between diffusion impairment (abnormally low D_LCO), resting spirometry and the presence and severity of coal workers' pneumoconiosis on chest radiography. We developed ordinary least squares linear regression models to evaluate factors associated with per cent predicted D_LCO (D_LCOpp).

Results: Diffusion impairment was identified in 20.2% of subjects. Ten per cent of all miners with normal spirometry had diffusion impairment including 7.4% of never smokers. The prevalence of diffusion impairment increased with worsening radiographic category of pneumoconiosis. Mean D_LCOpp decreased with increasing small opacity profusion subcategory in miners without progressive massive fibrosis. Linear regression analysis also showed significant decreases in D_LCOpp with increasing small opacity profusion and presence of large opacities.

Conclusions: Diffusion impairment is common among former coal miners, including among never smokers, miners without radiographic pneumoconiosis and miners with normal spirometry. These findings demonstrate the value of including D_LCO testing in disability examinations of former coal miners and an important role for its use in medical surveillance of working miners to detect early chronic lung disease.