Background: Previous studies have demonstrated the delivery of pharmaceutical aerosols through nasal cannula and the feasibility of enhanced condensational growth (ECG) with a nasal interface. The objectives of this study were to develop a device for generating submicrometer aerosols with minimal depositional loss in the formation process and to improve aerosol delivery efficiencies through nasal cannulas.
Methods: A combination of in vitro experiments and computational fluid dynamics (CFD) simulations that used the strengths of each method was applied. Aerosols were formed using a conventional mesh nebulizer, mixed with ventilation gas, and heated to produce submicrometer sizes. An improved version of the mixer and heater unit was developed based on CFD simulations, and performance was verified with experiments. Aerosol delivery was considered through a commercial large-bore adult cannula, a divided (D) design for use with ECG, and a divided and streamlined (DS) design.
Results: The improved mixer design reduced the total deposition fraction (DF) of drug within the mixer by a factor of 3 compared with an initial version, had a total DF of approximately 10%, and produced submicrometer aerosols at flow rates of 10 and 15 L/min. Compared with the commercial and D designs for submicrometer aerosols, the DS cannula reduced depositional losses by a factor of 2-3 and retained only approximately 5% or less of the nebulized dose at all flow rates considered. For conventional-sized aerosols (3.9 and 4.7 μm), the DS device provided delivery efficiencies of approximately 80% and above at flow rates of 2-15 L/min.
Conclusions: Submicrometer aerosols can be formed using a conventional mesh nebulizer and delivered through a nasal cannula with total delivery efficiencies of 80-90%. Streamlining the nasal cannula significantly improved the delivery efficiency of both submicrometer and micrometer aerosols; however, use of submicrometer particles with ECG delivery resulted in overall lower depositional losses.