Experimental and Numerical Study of Inhaler Spray Characterization (Size Distributions and Velocity)

Particle size and velocity are two of the most significant factors that impact the deposition of pressurized metered-dose inhaler (pMDI) sprays in the mouth cavity. pMDIs are prominently used around the world in the treatment of patients suffering from a variety of lung diseases. Moreover, Soft Mist Inhalers (SMIs) are a new-generation of propellant-free Inhalers. The first delivery inhalation spray system of this kind is the Spiriva Respimat inhaler, which has its advantages, such as better medication delivering to the lungs. In the current study, particle velocity and size distribution are measured at three different locations along the centerline of the pMDI and the SMI spray using Phase Doppler Anemometry (PDA). pMDIs from four different pharmaceutical companies are tested, each pMDI using salbutamol sulfate as the medication, whereas the Spiriva Respimat inhaler using tiotropium bromide. Measurements along the pMDI centerline (at 0, 75, and 100 mm downstream of the inhaler mouthpiece) showed that the spray velocities were bimodal in time for all four pMDI brands. The first peak occurred as the spray was leaving the mouthpiece, while the second peak (at the same location, 0 mm) occurred at around 60, 95, 95, and 115 ms later, respectively, for the four tested inhalers, with a drop in the velocity between the two peaks. Three probability density functions (PDFs) were tested, and the Rosin-Rammler PDF best fit the empirical spray size distribution data. These results suggest that there is a difference in the mean particle velocities at the centerline for the tested pMDIs and the diameter of released particles varied statistically for each brand. Particle size distribution for the Spiriva Respimat inhaler using the Anderson Cascade Impactor (ACI) is also assessed. The results indicate that high percentage of inhaled medication was delivered to the lungs, which is still quite significant when compared to common pressurized metered dose inhalers. Computational fluid dynamics, implementing mean-flow and turbulent tracking of particles, is used to determine the ability of the software ANSYS CFX package, to emulate the Ventolin HFA spray behavior. The results exhibit very good agreement between both numerical and experimental results.