Nonspecific bronchial reactivity in occupational asthma

Abstract

The provocative concentration (PC20 mg/ml) of methacholine required to produce a fall in the baseline FEV1 [baseline forced expiratory volume] by 20% was determined in 86 patients with occupational asthma due to exposure to western red cedar, California redwood, grain dust or isocyanates. Fifty-seven patients were assessed at the time of diagnosis when they were symptomatic. Twenty-nine patients were studied after they had been removed from exposure for a period from 2 mo. to 4 yr and were asymptomatic. Of the 57 patients with symptomatic asthma, 9 had repeat methacholine inhalation tests after removal from exposure. The results were compared with 33 normal healthy subjects, 30 patients with nonoccupational asthma, and 17 patients with nonindustrial chronic bronchitis. Patients with symptomatic occupational asthma had marked increase in bronchial reactivity similar to those with nonoccupational asthma. The degree of hyperreactivity decreased after removal from exposure and increased following re-exposure to the offending agents. There was little overlap in the range of PC20 in the asthmatic compared with the nonasthmatic groups. Nonspecific bronchial hyperreactivity may be the consequence rather than the predisposing factor in occupational asthma. The methacholine inhalation test is a simple, safe and useful procedure in the initial assessment of of patients suspected to have occupational asthma before institution of the time-consuming specific bronchial provocation test.