Pressure and inspiratory flow characteristics of dry powder inhalers.

This study compared inspiratory characteristics of the Novolizer and Turbuhaler. Sixty patients with obstructive lung disease (40 asthmatics, 20 patients with COPD) and without DPI experience were enrolled into this investigator initiated, randomized, cross-over study. Collected data of 56 patients were eligible for analysis. Inspiratory pressure and inspiratory flow through both devices were measured in every patient using a double-beam oscilloscope. Peak inspiratory flow (PIF), duration of inspiratory flow > 60 l/min and increase in inspiratory pressure were significantly higher in the Novolizer group. In addition, the inspiratory flow rate 0.1 s after beginning of inhalation was over two-times higher at inhalation through the Novolizer compared to inhalation through the Turbuhaler. The Turbuhaler data, but not the Novolizer data, showed a significant negative correlation between lung function and inspiratory flow. The dynamic resistance of the Turbuhaler was 5.5-times higher than that of the Novolizer. Patients using the Turbuhaler had to invest a significantly higher inspiratory effort compared to the use of the Novolizer in order to achieve the same inspiratory flow (e.g., 60 l/min). Indeed, more than 40% of the patients in the Turbuhaler group failed to reach an inspiratory flow of 60 l/min. Overall, patients inhaling through the Novolizer had a better inhalation performance than those inhaling through the Turbuhaler.