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 μm) in adult human oral-pharyngeallaryngeal (OPL) airway cast models at various inspiratory flow rates (30, 60, 90, and 120 L/min). Deposition efficiency of 2-μm particles was unaffected by changes in mouthpiece diameter at all flow rates. Deposition of 4-μm particles decreased significantly with the 2.0- and 2.7- cm mouthpieces compared to the 1.5 cm mouthpiece at 60, 90, and 120 L/min (p < 0.01). Deposition of 4-μm 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 μm 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-μm particles least affected. However, our findings may have important implications for improving the future design of mouthpieces of devices that deliver particles with 4-μm diameters and require inspiratory flow rates of ≥60 L/min (i.e., DPIs) for adequate drug delivery.