Abstract Background Spirometry remains central to chronic obstructive pulmonary disease (COPD) assessment but insufficiently reflect the complexity of small airway dysfunction and fails to identify patients at risk before their first exacerbation. The time constant, a physiologic measure derived from expiratory flow characteristics, may serve as a complementary marker for early risk stratification. Methods This retrospective cohort study included 1,479 patients with COPD from two tertiary hospitals who underwent baseline chest computed tomography and post-bronchodilator spirometry between 2014 and 2023, with at least five years of follow-up. The time constant was computed from volume-time curves via standardized image analysis. The primary outcome was moderate-to-severe exacerbation. Subgroup analyses were conducted based on symptom severity, airflow limitation, emphysema extent, and airway wall thickness. Results A prolonged time constant was independently associated with an increased risk of moderate-to-severe exacerbations (adjusted hazard ratio, 1.188; 95% confidence interval, 1.028-1.373). This association was more evident in dyspneic patients with prior exacerbations. Although the interaction was not statistically significant, the predictive value of the time constant appeared to be more pronounced in individuals with airway-predominant features, characterized by reduced forced expiratory volume in 1 second (FEV1) and increased Pi10. A threshold of 1.14 seconds was identified, above which the risk of exacerbation was significantly elevated. Conclusions The time constant may improve individualized risk stratification by identifying patients with COPD who are at increased risk of exacerbations, even in the absence of prior exacerbation history or before the development of advanced parenchymal destruction. This abstract is funded by: None
Kwon et al. (Fri,) studied this question.