Development of a filter that mimics tracheobronchial deposition of respirable aerosols in humans

This article describes the development of a filter that mimics average tracheobronchial deposition in the human respiratory tract for particle diameters and inhalation flow rates relevant for inhaled pharmaceutical aerosols. To design the filter, a combination of classical filter theory, computational fluid dynamics, and experimental filtration measurements was used. From these results, a predictive model was developed and used to determine optimal filter parameter values prior to building the filter. Experiments were then performed with nebulized jojoba oil aerosols, using an Electrical Low Pressure Impactor (ELPI) to measure filtration efficiency versus particle diameter in the range of 0.5–5.5 µm. Experiments were conducted for both constant flow rates and tidal inhalation profiles with average flow rates over the range of 15–90 L/min. When compared with various existing empirical models of tracheobronchial deposition, the purpose-built filter was observed to closely mimic tracheobronchial deposition and its dependence on particle diameter and flow rate for the range explored. As intended by design, instantaneous filter performance was found to be unaffected by time dependence of the inhalation flow profile. When placed downstream of a mouth-throat replica, the present filter may be useful for bench-top estimation of regional lung delivery with inhalers, particularly when tested during breath simulation.

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