Cardiopulmonary and Oxygenation Impairment in Underground Versus Surface Coal Miners: A Comparative Cross-Sectional Assessment of Occupational Health

Abstract

Background: Underground coal mining combines respirable dust, diesel emissions, heat, noise and heavy physical work, yet ventilatory, oxygenation and cardiovascular function are rarely assessed together in the same miners. We compared these domains between male underground and surface coal miners. Methods: In this comparative cross-sectional study, 90 underground workers (UW) and 90 surface workers (SW) underwent anthropometry, blood pressure (BP), resting pulse, peripheral oxygen saturation (SpO2), peak expiratory flow (PEF) and spirometry (FVC, FEV1, FEV1/FVC, FEF25–75). Groups were compared with Welch’s t test (Hedges’ g with 95% CI), the Mann–Whitney U test, chi-square/Fisher’s exact tests with Holm correction, and multivariable linear regression adjusted for age and body mass index (BMI). Results: The groups were balanced for age (47.8 vs 48.1 years) and BMI (25.7 vs 26.3 kg/m2). Compared with SW, UW had higher systolic BP (+10.8 mmHg, 95% CI 7.0 to 14.5), diastolic BP (+7.1 mmHg, 5.2 to 9.1) and pulse (+13.7 beats/min, 10.6 to 16.7), and lower SpO2 (−3.3 percentage points, −3.7 to −2.9), FEV1 (−0.79 L, −0.90 to −0.68), FVC (−0.64 L), PEF (−101.9 L/min) and FEV1/FVC (−0.099) (all p < 0.001; |g| 0.84–2.43). Hypertensive-range BP (73.3% vs. 25.6%; odds ratio 8.0, 95% CI 4.1 to 15.6), SpO2 < 95% (60.0% vs. 0%), FEV1/FVC < 0.70 (38.9% vs. 1.1%), PEF < 300 L/min (20.0% vs. 0%) and tachycardia (16.7% vs. 3.3%) were more frequent in UW; overweight and obesity did not differ. Adjustment for age and BMI changed the estimates by < 1.5%. The pooled SpO2–FEV1 correlation (r = 0.647) largely reflected between-group separation; within UW it was weak (r = 0.09). Conclusions: Underground work was associated with a markedly poorer cardiopulmonary and oxygenation profile than surface work, independent of age and BMI. Because of the cross-sectional, non-random design and the absence of exposure, smoking and tenure data, causality cannot be inferred, and the unusually large effect sizes warrant confirmation in exposure-resolved, longitudinal studies