LONGITUDINAL AND CROSS-SECTIONAL ANALYSES OF EXPOSURE TO COAL-MINE DUST AND PULMONARY-FUNCTION IN NEW MINERS

The association between exposure to dust and pulmonary function was st udied by longitudinal and cross sectional analyses in a group of Unite d States underground coal miners beginning work in or after 1970. Quan titative estimates of exposure to respirable coal mine dust were deriv ed from air samples taken periodically over the entire study period. T he cohort included 977 miners examined both in round 2 (R2) (1972-5) a nd round 4 (R4) (1985-8) of the National Study of Coal Workers' Pneumo coniosis. Multiple linear regression models were developed for both cr oss sectional (pulmonary function at R2 and R4) and longitudinal (chan ge in pulmonary function between R2 and R4) analyses with exposure par titioned into pre-R2 and post-R2 periods and controlled for covariates including smoking history. The results indicate a rapid initial (at R 2) loss of FVC and FEV1 in association with cumulative exposure of the order of 30 ml per mg/m3-years. Between R2 and R4 (about 13 years) no additional loss of function related to dust exposure was detected alt hough the percentage of predicted FVC and FEV1 did decline over the pe riod. After some 15 years since first exposure (at R4), a statisticall y significant association of cumulative exposure with FEV1 of about -5 .9 ml per mg/m3-years was found. These results indicate a significant non-linear effect of exposure to dust on pulmonary function at dust co ncentrations present after regulations took effect. The initial respon ses in both the FVC and FEV1 are consistent with inflammation of the s mall airways in response to exposure to dust.