Background: Dry powder inhalers (DPIs) are inspiratory flow driven and hence flow dependent. Most patients with chronic obstructive pulmonary disease (COPD) are elderly and have poor lung function. The factors affecting their inspiratory flows through inhalers are unclear.
Objective: To study peak inspiratory flows (PIFs) and their determinants through a DPI in COPD patients of varying age and severity.
Methods: Flow-volume spirometry was performed in 93 COPD patients. Maximum PIF rates were recorded through an empty Easyhaler (PIF(EH); Orion Corporation, Espoo, Finland), a DPI that provides consistent dose delivery at inhalation rates through the inhaler of 28 L/min or higher.
Results: The mean PIF(EH) was 54 L/min (range 26-95 L/min) with a coefficient of variation of 7%. All but two patients were able to generate a flow of > or = 28 L/min. In a general linear model, the independent determinants for PIF(EH) were age (P = 0.02) and gender (P = 0.01), and forced expiratory volume in 1 s (FEV(1)) expressed as percent predicted was not a significant factor. The regression model accounted only for 18% of the variation in PIF(EH).
Conclusion: In patients with COPD, age and gender are more important determinants of inspiratory flow through DPIs than the degree of expiratory airway obstruction. Most COPD patients with varying age and severity are able to generate inspiratory flows through the test inhaler that is sufficient for optimal drug delivery to the lower airways.
Keywords: COPD; forced expiratory volume; peak inspiratory flow.