Divergent prognostic roles of air trapping and reduced inspiratory reserve in COPD: Exacerbations versus functional decline

Abstract

Background: Lung hyperinflation is a key feature of COPD, yet it remains unclear if its primary components—reduced inspiratory reserve (IC/TLC) and air trapping (RV/TLC)—predict distinct clinical trajectories. We investigated the independent prognostic roles of these indices regarding acute exacerbations and functional decline. Methods: We analyzed 1214 COPD patients from the prospective KOCOSS cohort. Patients were stratified into four phenotypes using IC/TLC (<25%) and RV/TLC (>40%). Outcomes included 1-year acute exacerbation (AE) risk and 3-year longitudinal changes in health status (SGRQ) and exercise capacity (6MWD). Results: IC/TLC and RV/TLC predicted divergent outcomes. Lower IC/TLC was an independent predictor of acute instability, including 1-year AE risk (OR 0.97; p = 0.020) and health status deterioration. Conversely, higher RV/TLC specifically predicted a steeper 3-year decline in 6MWD (β −0.34 m/year; p = 0.030). The "Combined" phenotype (low IC/TLC + high RV/TLC) exhibited the greatest vulnerability, with a two-fold higher AE risk (OR 2.06; p = 0.015) and accelerated SGRQ worsening. Notably, these associations were independent of airflow limitation, as annual FEV1 decline did not differ across phenotypes. Conclusions: IC/TLC and RV/TLC provide complementary prognostic information. Reduced inspiratory reserve identifies patients at risk for acute events, while air trapping marks those prone to long-term functional loss. Lung volume-based phenotyping allows for refined risk stratification beyond standard spirometry. © 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.