Experimental Study of Spiriva Respimat Soft Mist Inhaler Spray Characterization: Size Distributions and Velocity

Background: Respiratory illnesses such as asthma, bronchitis, and chronic obstructive pulmonary disease (COPD) are considered to be debilitating diseases. A variety of inhalation devices have been used to deliver aerosol medication to patients in the treatment of those diseases. Soft Mist Inhalers (SMIs, for example, the Spiriva Respimat) are a new generation of propellant-free inhalers. In this type of inhalation device, inhalable droplets are generated from an aqueous solution. Droplet size and velocity are two of the most substantial factors that impact the deposition of SMI aerosol medication into the patient lungs. Methods: In this study, size and velocity of droplets generated from the Spiriva Respimat inhaler were measured using phase Doppler anemometry (PDA). Measurements were taken at four locations along the centerline of the Spiriva Respimat inhaler, in addition to three cross sections (free-spray configuration). In addition, measurements were also performed at a single cross section in confined spray configurations using two separate idealized mouth cavities. Results and Conclusions: Measurements along the centerline of the aerosol mist generated using the Spiriva Respimat inhaler (6.5, 25, 100, and 125 mm downstream of the inhaler nozzle' orifice) showed that droplets at the mouthpiece have the highest velocity of 10.95 m/s, decreasing to 1.33 m/s at the 125 mm location away from the nozzle. The mean diameter D10 values ranged from 3.97 to 3.67 μm at 6.5 and 125 mm locations, respectively. In addition, of the three probability density functions (PDFs) that were tested, the log-normal PDF showed better curve fitting for the empirical data (droplet size distributions) that were measured. The effect of spray confinement using two idealized mouth cavities shows that there was a drop in the particles' velocity for both models on each axes compared with the open-air environment (free-spray configuration).