Miners with Clinically Important Declines in FEV₁: Analysis of Data from the U.S. National Coal Study

Abstract

Several previous studies, including the U.S. National Study of Coal Workers' Pneumoconiosis (NSCWP), have demonstrated a loss of FEV₁ over time that is related to occupational dust exposure in miners. However, much of the variation in loss of FEV₁ in the mining cohorts studied remains unexplained. This study sought to identify individual miners with clinically important FEV₁ declines and investigate risk factors for the declines. Subjects were chosen from NSCWP longitudinal cohorts. All miners with at least 6 years follow up (N = 5900) were grouped into strata based on age, height, smoking status, gender, and initial FEV₁. Within these strata, pairs of miners were selected whose annual rate of FEV₁ decline differed by more than 60 ml/y, and 344 pairs were entered into the analysis. Miners with high rates of decline were assigned to the study group; those with low rates of decline served as referents. On the initial questionnaire, study miners had more cough and phlegm than referents (p < 0.01). At follow-up, prevalences of reported cough, phlegm, dyspnea, wheezing, bronchitis, asthma, and emphysema were all significantly higher in the study group than in the referent group; whereas prevalence of radiographic coal worker's pneumoconiosis (CWP) was not different. The distribution of case and referent miners by geographic mining region was different (p = 0.052). Weight gain in the study group was significantly greater than in the referent group. Study and referent groups were similar for age at entering mining and coal mining tenure. However, when mining region effects were reduced by only including pairs whose case and referent were from same region (N = 94 pairs), cases had significantly more mining tenure than referents. A group of coal miners with clinically important longitudinal lung function declines was identified. Mining tenure was a predictor of serious functional decline, when the effect of mining region was taken into account. Additional studies are underway in this group to define other potential risk factors, disease processes, and mechanisms for these changes.