A longitudinal study of symptoms and respiratory function tests in iron miners

A first survey has been conducted on 1179 iron-ore mine workers, 35-55 years old, who were randomly selected from 5900 at work with normal chest roentgenograms. Five years later, 871 of them were re-examined. Both surveys included a standard respiratory symptoms questionnaire (British MRC), a physical examination of the chest, and measurement of pulmonary function (vital capacity - VC; forced expiratory volume during 1 s - FEV1.0; residual volume - R.V. by helium dilution: carbon monoxide uptake - FuCO by the steady-state method). Both surveys were done by the same research team under identical conditions, using the same equipment. The mine technical services determined the dust and noxious gas concentrations at work places. No evidence of worsening of respiratory health status was observed overall. Symptoms of chronic bronchitis and asthma were recorded with a similar prevalence in both surveys; the decline in lung function was minimal for the total sample. However, our aim was to compare changes that were observed in groups differing by work place (surface or underground) or by activity (active or retired). Analysis showed that development of respiratory symptoms was more frequent and decline in lung function accelerated in the 5-year interval among underground workers who were still active as compared to those retired. In all subgroups (surface or underground workers, active or retired), decline of lung function values was more marked in smokers compared to non-smokers.