In Vitro testing of Mdi Spacers: A Technique for Measuring Respirable Dose Output with Actuation In-Phase Or Out-Of-Phase with Inhalation

Abstract

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 µm 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 retained until the following inhalation.

Results

For all 4 devices the respirable dose was significantly less in the out-of-phase case than in the in-phase case. At the same time, the devices varied widely in the percentage of the usable aerosol plume that was retained in the out-of-phase case. The percentages retained until the following inhalation (as compared with the amount of drug delivered in the in-phase case) are as follows: MediSpacer 67%, ACE 23%, OptiHaler 9%, and AeroChamber 46%.

Conclusions

Timing greatly affects the amount of drug delivered by an MDI device, even one equipped with a valve. Also, device design has a large influence on the amount of drug delivered and the percentage of the drug plume retained when inhalation is delayed. The variable flow rate technique made this study possible, and this technique may also have applications in studying the effects of unusual breathing patterns.