Computerized equipment for the delivery of inhaled doses of solid particles in specific bronchial challenge

An apparatus to generate solid particles was tested for use in diagnosing o ccupational asthma. This equipment measures the inhaled dose of dry particl es during specific inhalation challenge. It includes an aerosol generator, a cyclone type particle size selector, and an inhalation chamber to which a patient breathing at tidal volume can be connected for the test. It is ful ly controlled by a standard personal computer in automatic mode, acting on the flow rate and the aerosol generator to maintain the concentration at a fixed value, usually 3 mg/m(3). The dose of aerosol delivered to the patien t was calculated from the aerosol concentration, and the inhaled volume was calculated by integration of the corresponding signals. The coefficient of variation for this measurement was estimated to be 12%. The mass median ae rodynamic diameter (MMAD) of aerosol inside the inhalation chamber was meas ured for three substances: lactose, wheat flour, and buckwheat flour. The M MAD of the aerosol inside the chamber was also estimated from the particle size distribution of the raw powder. The relative difference between the me asured MMAD and the calculated value was less than 15%. The corresponding r elative difference between the measured geometrical SD and the calculated v alue was found to be less than 26%.