Impairment of oxygen transfer in dyspneic, nonsmoking soft coal miners

Early radiographic pneumoconiosis is associated with impaired exercise gas exchange among coal miners with normal resting spirometry

RATIONALE

We sought to determine if radiographic pneumoconiosis predicts abnormal gas exchange during exercise in coal mine workers with preserved resting lung function.

METHODS

We analyzed data from former coal miners seen between 2006 and 2014 in a single clinic specializing in black lung evaluations. We limited the analysis to those with normal resting spirometry and an A-a gradient at peak exercise ≥10 mmHg. We used multivariable logistic regression to estimate predictors of A-a gradient widened to >150% of the reference value. We focused on chest radiographs consistent with pneumoconiosis, taking into account higher silica exposure mining activities and years underground, and adjusting for cigarette smoking, obesity, and coronary artery disease.

RESULTS

Of 5507 miners, we analyzed data for 742 subjects with normal spirometry and all key clinical variables available, of whom 372 (50.1%) had radiographic evidence of pneumoconiosis. All but 21 had small opacity profusion of less than 2/1. The median A-a gradient at peak exercise was 108% of reference value (interquartile range, 81%-141%). In the multivariable analysis, radiographic pneumoconiosis was associated with increased odds of widened A-a gradient (odds ratio [OR], 2.47; 95% confidence interval [CI], 1.7-3.7). Limited to 660 subjects with normal diffusing capacity for carbon monoxide, the odds were similarly increased (OR, 3.20; 95% CI, 1.5-3.6).

DISCUSSION

Among coal miners with preserved resting lung function, radiographic evidence of early pneumoconiosis more than doubled the odds of abnormal exercise physiology. Impairment in pneumoconiosis occurs in early disease and may only be evident on exercise testing.

Small Airway Dysfunction and Abnormal Exercise Responses. A Study in Coal Miners

RATIONALE

Coal mine dust exposure can cause symptoms and loss of lung function from multiple mechanisms, but the roles of each disease process are not fully understood.

OBJECTIVES

We investigated the implications of small airway dysfunction for exercise physiology among a group of workers exposed to coal mine dust.

METHODS

Twenty coal miners performed spirometry, first breathing air and then helium-oxygen, single-breath diffusing capacity, and computerized chest tomography, and then completed cardiopulmonary exercise testing.

MEASUREMENTS AND MAIN RESULTS

Six participants meeting criteria for small airway dysfunction were compared with 14 coal miners who did not. At submaximal workload, miners with small airway dysfunction used a higher proportion of their maximum voluntary ventilation and had higher ventilatory equivalents for both O2 and CO2. Regression modeling indicated that inefficient ventilation was significantly related to small airway dysfunction but not to FEV1 or diffusing capacity. At the end of exercise, miners with small airway dysfunction had 27% lower O2 consumption.

CONCLUSIONS

Small airway abnormalities may be associated with important inefficiency of exercise ventilation. In dust-exposed individuals with only mild abnormalities on resting lung function tests or chest radiographs, cardiopulmonary exercise testing may be important in defining causes of exercise intolerance.

Update on respiratory disease from coal mine and silica dust

Coal mine and silica dust cause significant respiratory disease in spite of modern dust control regulations. Susceptible individuals in exposed populations may develop fibrosing lung disease, obstructive airways disease, including chronic bronchitis and emphysema, or lung cancer. A careful occupational history that elicits exposure to respiratory hazards is the cornerstone of an accurate diagnosis. Treatment involves removal from exposure, supportive care, pulmonary rehabilitation, and when disabling disease is present, assistance obtaining compensation.

Compensation for occupational disease with multiple causes: the case of coal miners' respiratory diseases

Many diseases associated with occupational exposures are clinically indistinguishable from diseases with non-occupational causes. Given this, how are fair decisions made about eligibility for compensation? This problem is discussed in relation to the federal black lung program. Conflicting definitions of terms--coal workers' pneumoconiosis as defined by the medical profession, pneumoconiosis as defined by the United States Congress, and the popular term, black lung--are important considerations in this discussion. Each is embedded in different logical interpretations of the causes of occupational disease and of disability. Alternative views are presented and critically discussed.