Prevalence and COPD Phenotype for a Suboptimal Peak Inspiratory Flow Rate against the Simulated Resistance of the Diskus ® Dry Powder Inhaler

BACKGROUND: Patients who exhibit a suboptimal peak inspiratory flow rate (PIFR) against the resistance (resist) of a dry powder inhaler (DPI) may not be able to effectively inhale the medication into their lower respiratory tract. PIFRresist was measured using the In-Check DIAL(®) to simulate the resistance of the Diskus(®) DPI in patients with chronic obstructive pulmonary disease (COPD) who were ≥ 60 years of age and had forced expiratory volume in 1 sec (FEV1) of ≤ 50% predicted. Our objectives were to: establish the prevalence of a suboptimal PIFRresist (< 60 L/min) in this population; identify a phenotype of patients with COPD who exhibit a suboptimal PIFRresist; and assess test-retest reliability of PIFRresist. METHODS: PIFRresist and inspiratory capacity (IC) were measured after spirometry was performed in patients with advanced COPD. Repeat measurement of PIFRresist was performed in a subset of patients who returned for scheduled follow-up appointments. RESULTS: The prevalence of a PIFRresist of <60 L/min was 19% among 213 patients. The clinical phenotype of these 41 patients included predominantly female gender (80%), shorter height, and lower values for forced vital capacity (FVC) and IC as percentage predicted compared with the 172 patients with PIFRresist of > 60 L/min. Multivariate regression analysis performed on all patients demonstrated that age, gender, height, FVC % predicted, and IC % predicted were independent predictors of PIFRresist (R(2)=36%). Repeat testing showed no difference between the PIFRresist values. CONCLUSIONS: Approximately one out of five patients with advanced COPD and ≥ 60 years of age exhibited a suboptimal PIFRresist against the Diskus. For the first time, a clinical phenotype of such patients with a suboptimal PIFRresist was identified. It is reasonable to measure a patient's PIFR against the simulated resistance of a specific DPI if there is concern about clinical benefit using the dry powder medication.