Comparative Study on the Size Distributions, Respiratory Deposition, and Transport of Particles Generated from Commonly Used Medical Nebulizers

Background: Medical nebulizers are widely and conveniently used to deliver medication to the lungs as an inhalable mist; however, the deposition of nebulized particles in the human respiratory system and the transport of the nebulized particles in the environment have not been studied in detail. Methods: Five medical nebulizers of three different types (constant output, breath enhanced, and dosimetric) were evaluated. The size distribution functions (SDFs) and respiratory deposition of the particles generated from the nebulizers were characterized. The SDFs were obtained with an aerodynamic particle sizer (APS; TSI, Inc., St. Paul) after data correction, and the respiratory deposition was calculated according to the model developed by the International Commission on Radiological Protection. The evaporation, Brownian diffusion, and convective movement are further calculated based on aerosol properties. Results and Conclusions: The SDFs measured by the APS indicated that most of the generated particles were in the size range of 1-8 μm. The operating pressure and flow rate affected the number-based SDF of the nebulized particles. Although different values of mean aerodynamic diameter (MAD) were obtained for the nebulizers, the mass median aerodynamic diameter did not differ significantly from each other (between 4 and 5 μm). According to calculation, the deposition of particles in the head airways region accounted for the most of the particle mass collected by the respiratory system. Convective movement was the dominant mechanism for the transport of particles in the size ranges investigated. Relative humidity-dependent evaporation can significantly decrease the size of the emitted particles, resulting in a different respiratory deposition pattern such that the amount of particles deposited in the alveolar region is greatly enhanced. Appropriate protection from these particles should be considered for those persons for whom the medication is not intended (e.g., healthcare workers, family members).