Lung Function and Exercise Intolerance in Coal Miners with Occupational COPD

Aim. To assess lung function in coal miners with occupational chronic obstructive pulmonary disease (COPD) of different severity and to evaluate the associations between spirometric parameters and six-minute walk distance (6MWD). Materials and methods. This single-center cross-sectional study included 83 male coal miners with occupational COPD (mean age 54.6 ± 7.4 years [mean ± SD]; mean occupational exposure duration 25.7 ± 7.8 years [mean ± SD]). COPD was confirmed by persistent post-bronchodilator airflow limitation (FEV1/FVC < 0.70), and its occupational origin was established by an occupational pathology commission. Post-bronchodilator spirometry included FVC, FEV1, FEV1/FVC, MEF25, MEF50, MEF75, and FEF25–75. Expiratory flow parameters were analyzed as continuous variables. Exercise capacity was assessed using the six-minute walk test (6MWT). Associations between lung function parameters and 6MWD were evaluated using Pearson correlation analysis. Results. Patients with GOLD III–IV had a shorter 6MWD than those with GOLD I–II (364.1 ± 58.2 vs. 462.4 ± 64.7 m; p = 2.17 × 10−10) and a greater decrease in SpO2 from baseline to the value recorded immediately after the test (−4.7 ± 1.8% vs. −1.9 ± 1.2%; p = 3.43 × 10−12). 6MWD was positively correlated with FEV1 (r = 0.44; p = 0.000032), FVC (r = 0.39; p = 0.000268), MEF25 (r = 0.41; p = 0.000118), MEF50 (r = 0.43; p = 0.000050), MEF75 (r = 0.48; p = 0.000004), and FEF25–75 (r = 0.46; p = 0.000012). Conclusions. In coal miners with occupational COPD, greater airflow limitation was associated with lower exercise capacity and a greater fall in SpO2 measured immediately after the 6MWT. Additional expiratory flow parameters were associated with 6MWD; however, this cross-sectional correlation analysis does not establish their independent or incremental value beyond FEV1. A comprehensive functional assessment combining conventional spirometry, additional expiratory flow parameters, and the 6MWT may therefore be useful for describing functional impairment in occupational COPD.