Dynamic characteristics of flow trainer for dpi and its clinical relevance

BACKGROUND: Trainer devices are widely employed for flow instruction in the use of dry powder inhalers (DPI). However, their aerodynamic characteristics in actual use have yet to be investigated. METHODS: We recorded inhalation flow signals and sounds produced from trainers for Diskus®, Symbicort®, Pulmicort® and Twisthaler® while five volunteers inhaled from the trainers with various inhalation patterns. RESULTS: Inhalation flow was classified into four patterns; the best, trapezoid, delayed peak and others. All the trainers exhibited flow-thresholds with appropriate precision for instruction. Sound intensity from the Diskus® trainer was almost proportional to inhaled flow rate, and it may be useful for flow pattern estimation. In other trainers, when flow exceeded some thresholds, sounds abruptly developed and continued with high intensity. Thus, they may be convenient for recognizing appropriate flow rates. In all trainers, when the subjects inhaled rapidly and forcefully, sound developed at 0.19-0.24 s after the onset of inhalation. Thus, with this flow pattern, trainers may indicate a flow rate approaching the peak of drug dispersion from the DPI. When the subject inhaled less rapidly, the threshold for sound development decreased by 10%. CONCLUSION: The instructor in DPI use should be aware of the aerodynamic characteristics of each individual trainer. Rapid inhalation should also be encouraged.