BACKGROUND COPD primarily impairs expiratory flow due to progressive airflow obstruction and reduced lung elasticity. Increasing evidence underlines the importance of inspiratory flow as a biomarker for selecting inhaler devices and providing ancillary aerodynamic information.

RESEARCH QUESTION Do the longitudinal changes in maximum forced inspiratory flow (FIFmax) influence acute exacerbations and lung function decline in patients with COPD?

STUDY DESIGN AND METHODS This longitudinal study evaluated FIFmax in patients with COPD over a 7-year period from 2004 to 2020. Eligible patients were categorized into two groups based on FIFmax trajectory: the increased FIFmax group and the decreased FIFmax group. The study assessed the annual rate of acute exacerbations and the annual decline rate of FEV₁. Subgroup analyses were conducted based on treatment status, with a focus on inhaled therapy and inhaler device usage.

RESULTS Among the eligible 956 patients with COPD, 56.5% belonged to the increased FIFmax group. After propensity score matching, the increased FIFmax group experienced lower rates of severe exacerbations (0.16 per year vs 0.25 per year, P = .017) and a slower decline in FEV₁ (0 [interquartile range, -51 to 71] mL/y vs -43 [interquartile range, -119 to 6] mL/y; P < .001) compared with the decreased FIFmax group. These associations were particularly prominent in patients using specific inhaler therapies such as dry powder inhalers.

INTERPRETATION This study showed that the longitudinal changes in FIFmax are associated with clinical outcomes in patients with COPD. Patients with increased FIFmax experienced a lower rate of severe exacerbations and a slower decline in lung function. These findings suggest the potential benefits of optimizing inspiratory flow in COPD management, although further studies are needed to confirm these observations due to potential confounding factors.