Association of Exercise Tolerance with Respiratory Health Outcomes in Mild-to-Moderate COPD.

Abstract

Rationale: Previous studies have identified exercise intolerance in patients with mild-to-moderate chronic obstructive pulmonary disease (COPD). The associations 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 mild-to-moderate COPD and analyzed its associations with respiratory health outcomes. Methods: We analyzed data from the Early Chronic Obstructive Pulmonary Disease community-based study of patients with mild-to-moderate COPD (post- bronchodilator FEV₁/FVC <0.70 and FEV₁ ≥50% predicted). Patients who completed questionnaires, spirometry, and cardiopulmonary exercise testing at baseline were included. Annual exacerbation assessment and spirometry testing were conducted for 2 years consecutively. Exercise tolerance was defined as the percentage of predicted peak oxygen uptake (VO_2peak %predicted). We analyzed the association between exercise tolerance, annual lung function decline, and acute exacerbation risk. Measurements and Main Results: Overall, 338 patients were included in the baseline analysis, and 319 completed the 2-year follow-up. The mean and standard deviation (SD) of VO_2peak %predicted was 79.8±13.7. Low VO_2peak %predicted was associated with more chronic respiratory symptoms, worse lung function, severe emphysema, and air trapping at baseline. During the 2-year follow-up, a decrease of 13.7% (1-SD) in VO_2peak %predicted was associated with a decline in pre-bronchodilator FEV₁/FVC (difference=0.4%, 95% CI: 0.1%-0.7%, P= 0.003), and higher total exacerbation risk (relative risk [RR]=1.25, 95% CI: 1.08-1.46, P=0.004) after adjustment. Conclusions: Mild-to-moderate COPD patients with exercise intolerance have worse respiratory health outcomes, for which a low exercise tolerance as a prognostic marker.