Optimal Maximal Forced Inspiratory Flow for Dry Powder Inhalers in Reducing Exacerbations in COPD

<b><i>Background:</i></b> The optimal management of chronic obstructive pulmonary disease (COPD) requires effective drug delivery through dry powder inhalers (DPIs). Maximum forced inspiratory flow (FIFmax), easily obtained from routine spirometry, can reflect inspiratory capacity and serve as a physiological marker associated with exacerbation risk. However, its clinical implications have not been fully established. <b><i>Methods:</i></b> This retrospective cohort study analyzed COPD patients treated with DPIs over a 5-year observational period. Baseline and follow-up FIFmax values were measured through repeated spirometric evaluations. The primary outcome was the incidence of moderate-to-severe exacerbations. The optimal cutoff of FIFmax for minimizing the risk of moderate-to-severe exacerbations was calculated, and the clinical factors associated with maintaining FIFmax above this optimal cutoff were explored. <b><i>Results:</i></b> A FIFmax threshold of 220 L/min was identified as the most optimal cutoff for lowering the risk of moderate-to-severe exacerbations. Patients who maintained FIFmax above this threshold over 5 years showed a significantly reduced risk of moderate-to-severe exacerbation (adjusted hazard ratio = 0.722 [95% confidence interval = 0.546-0.953], <i>p</i> = 0.022). Factors such as younger age, lower comorbidity burden, and better baseline lung function were linked to a higher FIFmax. In contrast, advanced age, severe comorbidities, and poor inhaler technique were associated with a rapid decline in FIFmax. <b><i>Conclusion:</i></b> FIFmax can be a promising physiological marker that reflects inspiratory capacity and stratifies exacerbation risk in COPD patients using DPIs. Regular assessment and patient education to maintain adequate inspiratory flow could support more effective disease management and stable long-term outcomes in this population.