Impaired Muscle Oxygenation During Incremental Cycle Exercise in COPD Patients Compared with Age-Matched Healthy Subjects

This study examined the dynamics of muscle oxygenation during exercise between chronic obstructive pulmonary disease (COPD) patients and age-matched healthy controls. Oxygen saturation of the vastus lateralis muscle (SmO2) was measured during incremental cycle exercise in 11 patients with exercise intolerance below the anaerobic threshold (AT) workload (COPD-AT(-)), 11 patients with exercise intolerance above the AT workload (COPD-AT(+)), and 8 controls by using near-infrared spectroscopy. Despite lower peak workload in COPD patients than in controls, trough SmO2 in COPD-AT(-) patients was significantly lower than SmO2 at the AT workload in controls, and was the same level as trough SmO2 in COPD-AT(+) patients and trough SmO2 in controls. The decrease of SmO2 was correlated with forced expiratory volume in one second % in COPD-AT(+) patients, and with exercise-induced hypoxemia in COPD-AT(-) patients. In conclusion, muscle oxygenation status deteriorates more steeply during exercise in COPD patients than in age-matched controls. Such severe impairment of muscle oxygenation in COPD patients may be affected by the impairment of lung function caused by COPD.