Characterization of a microprocessor-controlled tubular multiple metered dose inhaler aerosol generator for inhalation exposures of pharmaceuticals

A microprocessor-controlled tubular multiple metered dose inhaler (MDI) aer osol generator was constructed for the delivery of pharmaceutical aerosols to inhalation chambers. The MDIs were mounted in four cassettes containing one to four MDIs on a stepped end plate. The MDIs in each cassette were pne umatically activated at intervals that were controlled by the microprocesso r. The cassettes permitted easy replacement of each set of MDIs with a fres h set of MDIs whenever necessary. Aerosol concentration was controlled by v arying the number of active MDIs in each cassette and the frequency of acti vations per minute of each row. Aerosol from the MDIs flowed along the long axis of the tube, which provided a path length sufficient to diminish impa ction losses. Using a light-scattering device to monitor the aerosol concen tration, the pulsatile output from the MDIs in the cassettes was demonstrat ed to be adequately damped out provided that the dilution/mixing/aging cham ber exceeded 3 ft in length. The tube diameter selected was the minimum com patible with mounting the required number of MDIs so that the linear veloci ty of the aerosol was adequate to efficiently transport the aerosol out of the dilution chamber. Aerosol concentration and particle size data were rec orded for a nose-only rodent exposure chamber. Reproducible aerosol concent rations ranging from 0.03 to 0.6 mg/L were generated. Particle sizes ranged from 2- to 3-mum mass median aerodynamic diameter. Thus, the aerosol gener ated was within the size range suitable for inhalation exposures.