Physical Activity, Muscle Oxidative Capacity, and Coronary Artery Calcium in Smokers with and without COPD

INTRODUCTION: Severe chronic obstructive pulmonary disease (COPD) is partly characterized by diminished skeletal muscle oxidative capacity and concurrent dyslipidemia. It is unknown whether such metabolic derangements increase the risk of cardiovascular disease. This study explored associations among physical activity (PA), muscle oxidative capacity, and coronary artery calcium (CAC) in COPDGene participants. METHODS: Data from current and former smokers with COPD (n = 75) and normal spirometry (n = 70) were retrospectively analyzed. Physical activity was measured for seven days using triaxial accelerometry (steps/day and vector magnitude units [VMU]) along with the aggregate of self-reported PA amount and PA difficulty using the PROactive D-PPAC instrument. Muscle oxidative capacity (k) was assessed via near-infrared spectroscopy, and CAC was assessed via chest computerized tomography. RESULTS: Relative to controls, COPD patients exhibited higher CAC (median [IQR], 31 [0–431] vs 264 [40–799] HU; p = 0.003), lower k (mean ± SD = 1.66 ± 0.48 vs 1.25 ± 0.37 min(−1); p < 0.001), and lower D-PPAC total score (65.2 ± 9.9 vs 58.8 ± 13.2; p = 0.003). Multivariate analysis—adjusting for age, sex, race, diabetes, disease severity, hyperlipidemia, smoking status, and hypertension—revealed a significant negative association between CAC and D-PPAC total score (β, −0.05; p = 0.013), driven primarily by D-PPAC difficulty score (β, −0.03; p = 0.026). A 1 unit increase in D-PPAC total score was associated with a 5% lower CAC (p = 0.013). There was no association between CAC and either k, steps/day, VMU, or D-PPAC amount. CONCLUSION: Patients with COPD and concomitantly elevated CAC exhibit greater perceptions of difficulty when performing daily activities. This may have implications for exercise adherence and risk of overall physical decline.