Recently, a new method for conducting specific inhalation challenges with occupational allergens in particulate form has been described. The particle size of the allergen is first reduced in a cyclone sample mill. The allergen is then placed in a vibrating reservoir, which feeds the allergen onto a rotating disk. The speed with which the allergen is delivered and the speed of the rotating disk control the amount of allergen released into the delivery system.
Compressed air creating a Venturi effect leads to aerosol delivery from the disk to the subject via a horizontal cylinder. A hole in the side of the cylinder connected to a face mask enables the subject to breathe the aerosol. The concentration and particle size of the allergen are continuously measured using a photometer and a cascade impactor connected to the cylinder. The system allows the delivery of allergen to the subject in well-controlled concentrations. This method appears to be an important development in particulate inhalation challenge testing: it is safer, the pulmonary responses are more reproducible, and the technique avoids excessive exposures that might cause irritant responses in individuals with hyperreactive airways.
A further important factor influencing the outcome of allergen inhalation testing is medication taken by the subject. As far as is possible, all respiratory drugs should be withdrawn during the period of testing, since these may inhibit both immediate and late bronchial responses.