LONGITUDINAL CHANGES IN LUNG-FUNCTION AMONG ASBESTOS-EXPOSED WORKERS

To prospectively identify the determinants of persistent or accelerated loss of lung function among workers occupationally exposed to asbestos and assess the relative contribution of cigarette smoking, asbestos-induced pleural fibrosis, and specific findings from bronchoalveolar lavage and high resolution CT scans, we examined the determinants of lung function changes in 117 subjects occupationally exposed to asbestos for at least 1 yr in a high exposure setting. A minimum of 20 yr was required between the first exposure to asbestos and entry into the study. Baseline studies included an independent assessment of dyspnea, lung volumes, diffusing capacity of carbon monoxide (DL(CO)), a chest radiograph, a high resolution CT (HRCT) scan, and bronchoalveolar lavage (BAL). Subjects were observed for an average of 2 yr (range, 0.5 to 4.0 yr), and lung function was measured on at least two separate occasions (mean, 4.1 separate tests). During the period of observation, there was an average 1.5% decrease in the TLC and 2.5% decrease in the DL(CO). In this longitudinal data set, after controlling for age, height, pack-years of cigarette smoking, and follow-up time, persistently lower measures of TLC were independently related to moderate to severe dyspnea (p = 0.005), diffuse pleural thickening (p = 0.007), and higher concentrations of fibronectin in BAL fluid (p = 0.01). Interstitial lung disease either on the chest radiograph or HRCT scan was not independently associated with persistently lower measures of TLC during the period of observation. However, none of the clinical variables we examined were associated with an accelerated decline in TLC. After controlling for age, height, and follow-up time persistently lower measures of DL(CO) were independently related to moderate to severe dyspnea (p = 0.006), increased pack-years of cigarette smoking (p = 0.00001), honeycombing on HRCT scan (p = 0.0009), and higher concentrations of lymphocytes (p = 0.0008), neutrophils (p = 0.0005), eosinophils (p = 0.03), and fibronectin (p = 0.02) in the BAL fluid. Importantly, higher concentrations of neutrophils and eosinophils in the BAL fluid were significantly associated with an accelerated decline in gas exchange during the period of observation. These results indicate that among asbestos-exposed subjects, prognostically important risk factors include symptoms of dyspnea, cigarette smoking, diffuse pleural thickening, honeycombing on HRCT scan, and higher concentrations of inflammatory cells and fibronectin in the BAL fluid.