[Flow and inspiratory pressure characteristics of In-Check(tm) and training whistles].

Background: The optimal inhalation effort using dry powder inhalers (DPI's) varies with the specific inhaler. Accordingly, the device used for instruction in the proper use of the specific DPI should have physical characteristics similar to the actual DPI. However, the precision with which these devices mimic the actual DPI's has not been established.

Methods: We measured mouthpiece pressure (PI) and flow through the In-Check with an added flow resistance (for DiskusTM, DiskhalerTM, PulmicortTM, HandihalerTM, and ClickhalerTM) and the training whistles (for Diskus, Pulmicort, SymbicortTM, TwisthalerTM) at different inhalation pressures.

Results: Both the In-Check with an added flow resistance for individual DPI and the training whistles for each DPI had parabolic PI-flow relationships similar to the actual DPI. When a curve was drawn from direct readings of the In-Check scale, it fell consistently below that based on the pneumotachometer values. PI-flow curves of the actual DPI fell below both of the above curves. Among the same type of DPI, PI-flow relationships resembled each other, but one of 13 in the Diskus group demonstrated curves above and one of 6 in Pulmicort demonstrated curves below the others. The flows at which sounds were generated from the whistle were between 25-50 L/min.

Conclusions: Both In-Check and training whistles had suitable PI-flow relationships. Flow readings taken directly from In-Check tended to be lower than the measured value. A few training whistles might generate sounds with efforts below the optimal one.