A Novel High-Speed Imaging Technique to Predict the Macroscopic Spray Characteristics of Solution Based Pressurised Metered Dose Inhalers.

Abstract - Purpose: Non-volatile agents such as glycerol are being introduced into solution-based pMDI formulations in order to control mean precipitant droplet size. To assess their biopharmaceutical efficacy, both microscopic and macroscopic characteristics of the plume must be known, including the effects of external factors such as the flow generated by the patient’s inhalation. We test the hypothesis that the macroscopic properties (e.g. spray geometry) of a pMDI spray can be predicted using a self-similarity model, avoiding the need for repeated testing.
Methods: Glycerol-containing and glycerol-free pMDI formulations with matched mass median aerodynamic diameters are investigated. High-speed schlieren imag- ing is used to extract time-resolved velocity, penetration and spreading angle mea- surements of the pMDI spray plume. The experimental data are used to validate the analytical model.
Results: The pMDI spray develops in a manner characteristic of a fully- developed steady turbulent jet, supporting the hypothesis. Equivalent glycerol- containing and non glycerol-containing formulations exhibit similar non-dimensional growth rates and follow a self-similar scaling behaviour over a range of physiolog- ically relevant co-flow rates.