Chronic obstructive pulmonary disease (COPD) is the most common chronic lung disease worldwide, leading to significant morbidity, mortality, and high treatment costs. In 2020, the global prevalence of COPD was estimated to be 10.6%, affecting around 480 million people. The diagnosis of COPD in suspected patients is typically confirmed through routine spirometry, a simple noninvasive test that assesses the degree of airway obstruction. However, research has revealed that extensive small airway disease exists in COPD before it can be detected using traditional spirometric measures, such as forced expiratory volume in the first second (FEV1) and the ratio of FEV1 to forced expiratory capacity (FEV1/FVC). Efforts are underway to find new parameters to improve early detection of airway obstruction in patients with COPD. The expiratory time constant (RCexp) is a promising variable studied in critical care medicine and may also prove useful in pulmonology. Data from ventilated COPD patients demonstrate that prolonged RCexp was present in all patients with COPD. The FEV1/FVC ratio is currently the gold standard for diagnosing COPD, but it only yields a single calculated value. In contrast, RCexp may offer more precision as it reflects exhalation dynamics at multiple time points during exhalation. If there is a prolongation of subsequent RCexp towards the end of exhalation, it could indicate the presence of obstruction. We hypothesize that RCexp during tidal and forced exhalation implemented to the routine spirometer may detect airway obstruction earlier than conventional spirometric indices such as FEV1 and FEV1/FVC.
