Peak flow rate records in the diagnosis of occupational asthma due to isocyanates.

Peak expiratory flow rate (PEFR) has been recorded hourly or two-hourly from waking to sleeping in workers with respiratory symptoms who were exposed to isocyanate fumes at work. Twenty-three recordings averaging 33 days duration were recorded in 20 workers. Each worker was also admitted for bronchial provocation testing to toluene di-isocyanate (TDI) or diphenylmethane di-isocyanate (MDI) fumes or both. A final assessment of work-related asthma made from subsequent work exposure was compared with the results of bronchial provocation testing and a subjective assessment of the peak flow records. Both techniques were specific and sensitive. Physiological patterns of occupational asthma were defined from the records of PEFR. The most striking finding was the slow recovery from work-induced asthma. This commonly took several days to start and in one worker took 70 days to complete after leaving work. Several workers developed a pattern resembling fixed airways obstruction after repeated exposure at work. The consequences of these findings for the recording of symptoms of occupational asthma are discussed and recommendations are made for the recording of PEFR in workers in general.