Peak Inspiratory Flow Capability for Simulated Dry Powder Inhaler Resistances in Asthma Patients Prescribed Pressurized Metered-Dose Inhalers with Valved Holding Chambers: The USE-DPI Study

Background: Inhaled therapy is the mainstay of asthma management, yet many patients are prescribed pressurized metered-dose inhalers (pMDIs) with valved holding chambers (VHCs) based on a presumed low inspiratory capacity, often without objective measurement. The USE-DPI study aimed to determine how many of these patients can generate sufficient peak inspiratory flow (PIF) to use a dry powder inhaler (DPI). Methods: This multicenter, observational, cross-sectional study included 346 patients with asthma treated with pMDI and VHC. PIF was measured using the In-Check Dial at two resistance settings (R2 and R4). The primary outcome was the proportion of patients achieving PIF ≥ 30 L/min. Results: Almost all patients reached the 30 L/min threshold (99.4% at R2 and 98.7% at R4). Using a higher threshold of 60 L/min (R2), 76.1% met this criterion. Lower PIF (<60 L/min) was associated with older age, reduced lung function (FEV1 ≤ 80% predicted), and poorer asthma control. No significant variables were associated with failure to reach 30 L/min. Conclusions: Most patients using pMDI with VHC can generate sufficient inspiratory flow for medium- to high-resistance DPIs. Objective PIF assessment may help guide inhaler selection, although its clinical impact requires further study.