vitro testing of MDI spacers: A technique for measuring respirable dose output with actuation in-phase or out-of-phase with inhalation

BACKGROUND: Many studies have reported that users of metered dose inhalers (MDIs) have difficulty in coordinating inhalation with actuation of the MDI canister. The purpose of this study was to determine how a lack of coordination affects the respirable dose delivered to the patient’s lungs when an MDI spacer or chamber is used. Measuring respirable dose (the dose in the 1–5 mm particle size range) requires the use of a cascade impactor or other particle sizer. However, a cascade impactor requires a constant flow rate. This would appear to be incompatible with a study of coordination, which requires a variable flow rate to simulate the patient’s breathing through the MDI device. METHODS: We describe herein a new variable flow rate technique for measuring particle sizes and dose output with a cascade impactor (with a constant flow rate), while simulta-neously using a breathing machine to regulate the flow of aerosol medication through an MDI device and throat model. Using this technique, we tested 4 hand-held MDI devices: the Airlife Hand-Held MediSpacer, the Aerosol Cloud Enhancer (ACE), the OptiHaler, and the AeroCham-ber. Each device was tested under two different conditions: (a) in-phase, in which the MDI drug canister (Ventolin) is actuated at the start of inhalation, and (b) out-of-phase, in which the MDI canister is actuated at the start of exhalation and some portion of the drug plume may be retaine