Number size distribution of particles dosed by MDI and DPI inhalers

Abstract

The purpose of this research was to determine the influence of inspiratory flow rate and relative humidity on particle size distributions (PSDs) generated by three MDI inhalers (Flutiform, Fullhale and Ventolin) and one DPI inhaler (Spiriva). Particle size distribution was measured by APS 3321 (TSI, USA) for three different inspiratory flow rates – 30, 60 and 90 l/min. Aerosol from individual inhalers was led through a stainless steel tubing simulating the geometry of the human respiratory tract. The hygroscopicity of the particles was determined by comparing data obtained at laboratory conditions and at relative humidity of 90%. During the measurements of number PSDs by using of APS spectrometer, we measured bimodal distributions for Flutiform and Fullhale and monomodal distributions for Ventolin and DPI Spiriva. The increasing inspiratory flow rate had a minimal effect on the position of the modes of the individual distributions. The differences in PSD, measured under ambient conditions and at RH of 90%, were minimal and did not significantly affect the assumed probability of drug deposition. The results showed that determination of the PSDs by online spectrometer is a suitable alternative to traditional methods of measuring the particle size distributions of inhalation aerosol by NGI impactor.