Abstract

Background: We have previously shown that workers with occupational asthma caused by low molecular weight agents can be divided into those with raised and normal levels of sputum eosinophils, (>2.2%) measured during symptomatic exposure to the causative agent. Workers with continuing exposure to the causative agent have accelerated FEV1 decline.

Aims: To investigate the relationship between FEV1 decline (dFEV1) and sputum eosinophilia in workers with occupational asthma and continuing exposure to causative agents (both low molecular and high molecular agents) from two centres: Occupational Lung Disease Unit, Birmingham and Dipartimento Cardio Toracico, Università di Pisa, Pisa.

Methods: 63 consecutive workers with occupational asthma from 2 centres were investigated during symptomatic exposure to the causative agents at work with: (1) Sputum induction studies (2) bronchial hyper reactivity measurement and (3) serial FEV1 measurements for a minimum period of 12 months (mean period 4.69 years; SD 2.96).

dFEV1 during exposure was calculated by linear regression utilising all individual measurements in the eosinophilic and non-eosinophilic groups.

Results: 42.5% of the studied workers were atopic; 33.3% were current smokers and, 84.6% exhibited bronchial hyper reactivity (methacholine).

The majority of the patients were on treatment with inhaled corticosteroids (87.6%). Low molecular weight agents were the cause in 52.6% of workers; isocyanates were the single largest group.

The mean annual dFEV1 in the studied workers was -14.8 mL/year.

Conclusions: The eosinophilic group as a whole had greater FEV1 decline compared to the non-eosinophilic group; this group also had a higher number of individuals with a mean annual FEV1 decline of >60 mL/year. The variance was large however and the mean differences between the groups statistically non-significant. This may suggest that an additional variable, perhaps interacting with eosinophil phenotype, could be affecting the dFEV1.

Longitudinal FEV1 studies in workers with occupational asthma who tolerate continuing exposure to the causative agent are likely to be biased as a survivor population; those with rapid FEV1 decline are often unable to continue work due to disability. Larger studies are required to further define the phenotypes.

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