Update on an exposure system for particles in the diagnosis of occupational asthma.

We have previously designed a system for exposure to particles and described the preliminary results in 20 subjects exposed to occupational sensitizers in powder form (Cloutier Y, et al. - Eur Respir J, 1989; 2: 769). Modifications have been made to the particles generator, exposure chamber and sampling ports. Furthermore, in order to improve the stability of concentrations in the exposure chamber and to make the system easy to operate by a technician, it has been completely automated using closed-loop feedback regulated by a computer program.