Resistances of dry powder inhalers and training whistles and their clinical significance

BACKGROUND: Flow resistance of dry powder inhaler (DPI) is important information when physician choose a suitable DPI to individual patient. We previously reported flow resistances of several DPIs and training devices. In the present in vitro study, we measured resistances of new DPIs and new trainers. METHOD: Flow resistances were obtained from driving pressure and flow through the devices. RESULTS: All devices had parabolic relationships between the driving pressure and flow. Resistances were: 8.44 ± 0.45×10-2(mean±SD) for Elipta®, 5.53±0.13×10-2 for Breezhaler®, 7.27 ± 0.40×10-2 for new Diskhaler®, 12.15 ± 0.40×10-2 for Swinghaler®, 7.07 ± 0.24×10-2 for new Diskus trainer, 8.72 ± 0.4.5×10-2(√cmH2O/L/min) for Elipta trainer. Sounding threshold of Diskus trainer was 38.1 ± 5.1 and that of Elipta trainer was 39.9 (meidan) L/min. INTERPRETATIONS: In change from Diskus® to Elipta®, flow instruction is not necessary. Breezhaler® is a suitable DPI for patients with low pulmonary function but patients should be alert to avoid excessively high inhalational flow. In flow instruction, a flow higher than trainer sounding should be advised.