AEROSOL DEPOSITION IN THE HUMAN LUNG FOLLOWING ADMINISTRATION FROM A MICROPROCESSOR-CONTROLLED PRESSURIZED METERED-DOSE INHALER

Background - Gamma scintigraphy was employed to assess the deposition of aerosols emitted from a pressurised metered dose inhaler (MDI) cont ained in a microprocessor controlled device (SmartMist), a system whic h analyses an inspiratory flow profile and automatically actuates the MDI when predefined conditions of flow rate and cumulative inspired vo lume coincide. Methods - Micronised salbutamol particles contained ire a commercial MDI (Ventolin) were labelled with 99m-technetium using a method validated by the determination of (1) aerosol size characteris tics of the drug and radiotracer following actuation into an eight sta ge cascade impactor and (2) shot potencies of these non-volatile compo nents as a function of actuation number. Using nine healthy volunteers in a randomised factorial interaction design the effect of inspirator y flow rate (slow, 30 1/min; medium, 90 1/min; fast, 270 1/min) combin ed with cumulative inspired volume (early, 300 ml; late, 3000 ml) was determined on total and regional aerosol lung deposition using the tec hnique of gamma scintigraphy. Results - The SmartMist firing at the me dium/early setting (medium flow and early in the cumulative inspired v olume) resulted in the highest lung deposition at 18.6 (1.42)%. The sl ow/early setting gave the second highest deposition at 14.1 (2.06)% wi th the fast/late setting resulting in the lowest (7.6 (1.15)%). Periph eral lung deposition obtained for the medium/early (9.1 (0.9)%) and sl ow/early (7.5 (1.06)%) settings were equivalent but higher than those obtained with the other treatments. This reflected the lower total lun g deposition at these other settings as no difference in regional depo sition, expressed as a volume corrected central zone:peripheral zone r atio, was apparent for all modes of inhalation studied. Conclusions - The SmartMist device allowed reproducible actuation of an MDI at a pre programmed point during inspiration. The extent of aerosol deposition in the lung is affected by a change in firing point and is promoted by an inhaled flow rate of up to 90 1/min - that is, the slow and medium setting used in these studies.