Fractional Exhaled Nitric Oxide and Exacerbations of COPD

This is a pragmatic, prospective, longitudinal observational cohort study conducted in patients with COPD who are initiated on triple inhaler therapy as part of routine clinical care. No investigational drugs, devices, or protocol-mandated interventions are administered. Biomarker measurements, including fractional exhaled nitric oxide (FeNO), are performed for research purposes only and do not influence clinical decision-making. Participants will be followed for up to 12 months after enrollment with scheduled assessments of exacerbation events, lung function, symptom burden, and biomarkers. The total study duration is approximately 24 months, accounting for a 12-month enrollment period and completion of follow-up for the last enrolled participant. Environmental air pollution exposure will be estimated using a validated hybrid kriging/land-use regression model based on residential address.