Minimal Inspiratory Flow from Dry Powder Inhalers According to a Biphasic Model of Pressure vs. Flow Relationship

Inhalation therapy using the dry powder inhaler (DPI) is now the first choice for obstructive pulmonary diseases. We previously measured relationships between inspiratory pressure (PI) and flow rate of almost all of the DPIs available in Japan, and described an importance of inspiratory efforts. In the present study, we further analyzed the data obtained in the previous study. Although there were linear relationships between PI and flow2, the slope became steeper when PI was less than a certain value (critical PI, existed between 15-20 cmH2O). When PI was less than critical PI, linear rather than parabolic regression between PI and flow yielded better fits (r>0.90, p