Prevalence and factors associated with suboptimal peak inspiratory flow rates in COPD

Adequate peak inspiratory flow rate (PIFR) is required for drug dispersion with dry powder inhalers (DPIs). Prevalence of PIFR discordance (suboptimal PIFR with prescribed inhalers) and factors influencing device-specific PIFR are unclear in COPD. The objective of this study was to determine the prevalence of PIFR discordance and associated clinical factors in a stable COPD population.

An observational, single-center, cohort study was conducted including 66 outpatients with COPD. PIFR was measured using the In-Check™ Dial with applied resistance of prescribed inhalers. Participants were defined as discordant if measured PIFR was <30 L/min and <60 L/min for high and low-medium resistance devices, respectively, using an inspiratory effort the participant normally used with their prescribed DPI.

The median age of the COPD participants was 69.4 years, 92% were white and 47% were female. A total of 48% were using low-medium resistance DPIs (Diskus^®/Ellipta^®) and 76% used high-resistance DPI (Handihaler^®). A total of 40% of COPD participants were discordant to prescribed inhalers. Female gender was the only factor consistently associated with lower PIFR. Shorter height was associated with reduced PIFR for low-medium resistance (r=0.44; P=0.01), but not high resistance (r=0.20; P=0.16). There was no correlation between PIFR by In-Check™ dial and PIFR measured by standard spirometer.

PIFR is reduced in stable COPD patients, with female gender being the only factor consistently associated with reduced PIFR. Discordance with prescribed inhalers was seen in 40% of COPD patients, suggesting that many COPD patients do not generate adequate inspiratory force to overcome prescribed DPIs resistance in the course of normal use.