Mouthpiece diameter affects deposition efficiency in cast models of the human oral airways

We examined the effect of altering mouthpiece diameter to 1.5, 2.0, and 2.7-cm on the deposition efficiency of inertial size particles (2, 4, and 8 mum) in adult human oral-pharyngeal-laryngeal (OPL) airway cast models at various inspiratory flow rates (30, 60, 90, and 120 L/min). Deposition efficiency of 2-mum particles was unaffected by changes in mouthpiece diameter at all flow rates. Deposition of 4-mum particles decreased significantly with the 2.0- and 2.7cm mouthpieces compared to the 1.5 cm mouthpiece at 60, 90, and 120 L/min (p < 0.01). Deposition of 4-mum particles was significantly reduced with the 2.7-cm mouthpiece compared to the 2.0-cm mouthpiece at 90 and 120 L/min (p < 0.05). Deposition efficiency of 8 mum particles decreased significantly with the 2.0- and 2.7-cm mouthpieces compared to the 1.5-cm mouthpiece at 60 L/min (p < 0.05), and with the 2.7-cm mouthpiece compared to the 1.5-cm mouthpiece at 120 L/min (p < 0.05). These results suggest that the effect of mouthpiece diameter varies with particle size, with 2- and 8-mum particles least affected. However, our findings may have important implications for improving the future design of mouthpieces of devices that deliver particles with 4-mum diameters and require inspiratory flow rates of greater than or equal to 60 L/min (i.e., DPIs) for adequate drug delivery.