Functional variables associated with the clinical grade of dyspnoea in coal miners with pneumoconiosis and mild bronchial obstruction

Objectives-Dyspnoea is a common symptom in coal miners with pneumoconiosis. Among others, gas exchange disturbances due to airway obstruction or mismatch between ventilation and perfusion may be underlying mechanisms. The validation of dyspnoea by the degree of airway obstruction is controversial, because the extent of airway obstruction often does not correlate with the clinical grade of breathlessness. Methods-The association was investigated between breathlessness (self reported, on a six point scale) and indices of submaximal spiroergometry in 66 coal workers with radiographically confirmed pneumoconiosis (International Labour Organisation (ILO) grade of profusion greater than or equal to 1/0, mean (SD) age 64 (5.5) years, mean (SD) forced expired volume in 1 second (FEV) 77.5 (22.9) % predicted). Results-The clinical degree of breathlessness was independently associated with minute ventilation/oxygen consumption ((V)over dotE/(V)over dotO(2)) ratio (beta 0.423, 95% confidence interval (95% CI) 0.18 to 0.67, p=0.001) and smoking (beta 0.318, 95% CI 0.21 to 1.79, p=0.014) in a multiple linear regression analysis. The (V)over dotE/(V)over dotO(2) ratio (beta 0.556, 95% CI 0.20 to 0.90, p=0.003) was also the best predictor of breathlessness when only coal miners with airway obstruction (FEV1 < 80% predicted) were analyzed. Conclusion-The (V)over dot/(V)over dotO(2) ratio as a measurement of mismatch between ventilation and perfusion predicted the clinical grade of breathlessness better than measurements of bronchial obstruction at rest in coal workers with pneumoconiosis.