Association of Exercise Tolerance with Respiratory Health Outcomes in Mild-to-Moderate Chronic Obstructive Pulmonary Disease

Abstract Rationale Previous studies have identified exercise intolerance in patients with mild-to-moderate chronic obstructive pulmonary disease (COPD). The association of exercise tolerance with lung function decline and acute exacerbation risk in mild-to-moderate COPD is unclear, especially in the community population. Objectives We evaluated exercise tolerance in patients with mild-to-moderate COPD and analyzed its associations with respiratory health outcomes. Methods We analyzed data from the community-based ECOPD (Early Chronic Obstructive Pulmonary Disease) study of patients with mild-to-moderate COPD (postbronchodilator forced expiratory volume in 1 second (FEV1):forced vital capacity < 0.70 and FEV1 ≥ 50% predicted). Patients who completed questionnaires, spirometry, and cardiopulmonary exercise testing at baseline were included. Annual exacerbation assessment and spirometry were conducted for 2 years consecutively. Exercise tolerance was defined as the percentage of predicted peak oxygen uptake (V˙o2peak% predicted). We analyzed the association between exercise tolerance, annual lung function decline, and acute exacerbation risk. Results Overall, 338 patients were included in the baseline analysis, and 319 completed the 2-year follow up. The mean ± standard deviation of V˙o2peak% predicted was 79.8 ± 13.7%. Low V˙o2peak% predicted was associated with more chronic respiratory symptoms, worse lung function, severer emphysema, and air trapping at baseline. During the 2-year follow up, a decrease of 13.7% (1 standard deviation) in V˙o2peak% predicted was associated with a decline in prebronchodilator FEV1:forced vital capacity (difference, 0.4% [95% confidence interval, 0.1–0.7%]; P = 0.003) and higher total exacerbation risk (relative risk, 1.25 [95% confidence interval, 1.08–1.46]; P = 0.004) after adjustment. Conclusions Patients with mild-to-moderate COPD and exercise intolerance have worse respiratory health outcomes, for which low exercise tolerance is a prognostic marker. Clinical trial registered with www.chictr.org.cn (ChiCTR1900024643).