Flow rate-rise time profiles from model dry powder inhaler (DPI) testing of abbreviated impactor systems compared with their full resolution counterparts: Initial experimental data

We report the outcome of a European Pharmaceutical Aerosol Group study evaluating flow rate-rise times for reduced Next Generation Impactor (rNGI), Fast-Screening Impactor (FSI) and Fast-Screening Andersen impactor (FSA) with surrogate low-, medium- and high-resistance DPIs. Time for the flow rate to reach 90% of target (t₉₀) and flow acceleration rate (slope_t20/t80) defined the profiles. Volumes of the abbreviated impactors were estimated (±10mL) and compared to published values for their counterpart parent impactors (rNGI and FSI to NGI; FSA to Andersen Cascade Impactor (ACI)). t₉₀ (n=3 replicates; mean±S.D.) for rNGI (system volume 1990 mL, participant D) for target flow rates of 30 and 60 L/min were 387±5 and 218±8 ms respectively, close to corresponding values of 400±7 and 219±6 ms for the NGI (2000 mL). The slope_t20/t80) values were 0.09±0.00 and 0.31±0.00 L/min/ms at 30 and 60 L/min for the rNGI, also similar to the NGI value. Values of t₉₀ (170±5; 76±2 ms) and slope_t20/t80 (0.22±0.01; 0.96±0.01 L/min/ms) with the smaller FSI (1150 mL), were significantly different at 30 and 60 L/min respectively than those of the NGI. Participant G found similar divergences including tests at 90 L/min (t90 60±3 ms (FSI); 185±6 ms (NGI). When testing two FSAs (volume of 630 mL) at 60 L/min, Participant J found almost identical t₉₀ values (70±3; 71±2 ms), shorter than 60-L/min values (151±3; 162±6 ms) for their two ACIs (larger volume, 1180 ml). Apparatus internal volume is an important determinant of flow rate-rise time.