Maximal expiratory flow at 25% forced vital capacity (V25), V25 divided by height (V25/HT), and mean transit time (MTT) were calculated from the same forced expiratory maneuver performed in welding workers. The values were compared to determine variations between individuals and changes with age and chest X-ray findings. The results showed that MTT may be a less variable and equally sensitive measurement of the function of peripheral airways as compared with V25 and V25/HT. Its usefulness in the detection of the early changes of pneumoconiosis, however, must be further investigated in a prospective cohort study on workers exposed to various kinds of dust.

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Magnetic field at the chest in 93 male workers exposed to asbestos dust in an asbestos products factory in China was studied by local magnetization and flux-gate gradiometry. The average field intensity at 12 measurement points over the anterior chest wall was compared among workers with and without asbestosis and among workers of different working age. The field intensity in workers with asbestosis and those suspected to have asbestosis on the basis of X-ray findings was significantly higher than that in workers without asbestosis. It was also found that the field intensity increased with working age. It is suggested that dynamic measurement of magnetic field in the lung of workers exposed to dust containing ferrimagnetic particles would at least serve as a quantitative method for estimating lung dust loads and be valuable for pneumoconiosis prevention.

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