Nonuniform Deposition of Pressurized Metered-Dose Aerosol in Spacer Devices

Pressurized metered-dose inhalers (pMDIs) are commonly used to administer medication to patients suffering from chronic lower respiratory tract diseases such as asthma. Inhaling medication directly from a pMDI can prove difficult for some patients and, as a result, add-on devices (or spacers) have been designed to aid in the delivery of medication. Although spacers increase the percentage of medication that reaches the patient, medication will also nonsymmetrically deposit on the walls of the device and will be lost to the device itself.

The deposition of medication, salbutamol sulfate, within a large- and a small-volume spacer, has been studied through an experimental and numerical analysis. Experiments were conducted at inspiratory flow rates ranging from 30 to 60 L/min. The amount of deposition of the medication on the walls of the spacer was quantified through an application of spectrophotometry. Computational fluid dynamics was used to quantify the deposition numerically. Simulations were conducted by implementing mean flow and turbulent tracking of particles using unsteady Reynolds-averaged Navier-Stokes (URANS) equations with a shear stress transport turbulence model. Regions of deposition are of interest, as well as how the method of deposition varied for different inhalation flow rates.

The deposition of salbutamol sulfate in the Volumatic^® and OptiChamber^® spacers was found to be greater in the lower half as opposed to the upper half of the spacer due to a downward spray angle. With an increased flow rate, these spacers demonstrated a slight increase in medication delivered to the inline filter, which is analogous to that reaching the patient, and an increase in distal deposition. For the numerical analysis, the results indicated that inertial impaction is the most likely method of deposition for the Volumatic spacer, and turbulence is more likely to cause deposition in the OptiChamber spacer.