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Exaggerated bronchoconstriction due to inhalation challenges with occupational agents

¹ Dept of Chest Medicine, Sacré-Cur Hospital, and ² Institut de recherche Robert-Sauvé ensanté et sécurité du travail du Québec, Montreal, Canada

CORRESPONDENCE: J-L. Malo, Dept of Chest Medicine, Sacré-Cur Hospital, 5400 West Gouin Blvd, Montréal, H4J 1C5, Canada. Fax: 1 514 3383123. E-mail: malojl@meddir.umontreal.ca

Keywords: asthma, bronchial provocation tests, occupational asthma

Received: May 15, 2003
Accepted September 2, 2003

Inhalation challenges with occupational agents are used to confirm the aetiology of occupational asthma. It has been proposed that using closed-circuit equipment rather than the realistic challenge method would improve the methodology of these tests.

Changes in forced expiratory volume in one second (FEV₁) were examined in 496 subjects with "positive specific inhalation challenges", i.e. changes in FEV₁ of 20% after exposure to an occupational agent, including 357 subjects exposed by the realistic method, 108 using the closed-circuit method and 31 by both methods.

For immediate reactions, 18 of 95 (19%) showed changes in FEV₁ of 30% with the closed-circuit method, whereas a significantly larger proportion, i.e. 77 of 200 (38.5%), showed such changes using the realistic method. As regards nonimmediate reactions, changes in FEV₁ of 30% occurred in 16 of 43 (37%) cases with the closed-circuit method as compared to a larger proportion, i.e. 87 of 180 (48%) cases, using the realistic method. This favourable effect was significantly more pronounced in workers with higher levels of bronchial hyperresponsiveness to methacholine.

It is concluded that, for agents that can be generated using the closed-circuit method, use of such apparatus results in a smaller proportion of exaggerated bronchoconstriction than does the realistic method, this being particularly true for low-molecular weight agents.

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