Background: Aerosol drug delivery to the lungs is known to be very inefficient during all forms of noninvasive ventilation, especially when the aerosol is administered simultaneously with high-flow nasal cannula (HFNC) therapy. The objective of this study was to develop a new combination device based on vibrating mesh nebulizers that can provide continuously heated and humidified HFNC therapy as well as on-demand pharmaceutical aerosols with high efficiency. Methods: The combination device implemented separate mesh nebulizers for generating humidity (humidity nebulizer) and delivering the medical aerosol (drug nebulizer). Nebulizers were actuated in an alternating manner with the drug nebulizer delivering the medication during a portion of an adult inhalation cycle. Aerosol entered a small-volume mixing region where it was combined with ventilation gas flow and then entered a heating channel to produce small particles that are desirable for nose-to-lung administration and potentially excipient enhanced growth delivery. Three assessment methods (analytical calculations, computational fluid dynamics [CFD] simulations, and in vitro experiments in three-dimensional [3D] printed devices) were used to improve the mixer-heater design to minimize depositional drug losses, maintain a small device volume, ensure sufficient droplet evaporation, and control the outlet thermodynamic conditions. Results: For an initial configuration (Design 1), good agreement in performance metrics was found using the three assessment methods. Based on insights gained from the CFD simulations of Design 1, two new designs were developed and produced with 3D printing. Experimental analysis indicated that the new designs both achieved <5% depositional loss in the mixer-heater even with cyclic operation and sufficiently dried the aerosol from an initial size of 5.3 μm to an outlet size of ∼1.0 μm. A combination of the applied methods indicated that the desired thermodynamic conditions of HFNC therapy were also met. Conclusions: Multiple methodological approaches were used concurrently to develop a new combination device for administering HFNC therapy and simultaneous on-demand pharmaceutical aerosols to the lungs with high efficiency. The use of a small-volume mixer-heater (<100 mL), synchronization of the drug nebulizer with inhalation, and small outlet particle size should enable high efficiency lung delivery of the aerosol.
Keywords: high efficiency aerosol delivery; high-flow nasal cannula; high-flow therapy; noninvasive ventilation; pharmaceutical aerosols; respiratory drug delivery.