New methodology for specific inhalation challenges with occupational agents in powder form.

Numerous agents in powder form (wood dust, flour, antibiotics, drugs, etc.) can cause occupational asthma. The diagnosis is generally confirmed by specific inhalation challenges in a special challenge room. There are several pitfalls to the procedure: 1) subjects may be exposed to high concentrations of particles; the concentrations of particles may be higher than the threshold limit value-short term exposure level (TLV-STEL), possibly resulting in severe or irritant reactions; 2) the exposure is erratic. To overcome these problems, a new device for aerosolization of powders has been developed. This apparatus consists of three parts: a particles generator, an aerosol delivery system connected to an orofacial mask, and monitors - a photometer and a cascade impactor. Information on the concentration and size distribution of inhaled particles can therefore be obtained. We performed specific inhalation challenges with this apparatus on 20 subjects suspected of having occupational asthma. The concentration of particles was generally below or close to the TLV-STEL and information was obtained on the proportion of particles with a diameter less than 10 mu. Falls in forced expiratory volume in one second (FEV1) were progressive with each increase in the duration of exposure. The five subjects who had negative reactions to exposure were asked to tip the relevant product from one tray to another in the traditional realistic way. All had negative responses. We conclude that this new procedure offers advantages over the traditional method as it gives information on the concentration and size distribution of inhaled particles and makes the drawing of a dose-response curve possible, both of which may improve the safety and accuracy of the test.