The relationship between skeletal muscle oxygenation and systemic oxygen uptake during exercise in subjects with COPD: a preliminary study.

BACKGROUND Muscle oxygenation correlates with systemic oxygen uptake (V(O₂)) in normal subjects; however, whether this relationship exists in COPD patients remains unclear. The purpose of this study was to investigate the influence of skeletal muscle oxygenation on V(O₂) during exercise in patients with COPD. METHODS Eight subjects performed an incremental cycle ergometer exercise test. We measured ventilation and pulmonary gas exchange with a metabolic measurement system. We also continuously monitored S(pO₂), and measured tissue oxygen saturation (S(tO₂)) in the vastus lateralis with continuous-wave near-infrared spectroscopy. We calculated the muscle oxygen extraction rate (MOER) based on S(pO₂) and S(tO₂). In addition, we calculated Pearson correlation coefficients to examine the relationships between the V(O₂) obtained during exercise testing and the mean values of S(pO₂), S(tO₂), heart rate (HR), and MOER for each 30-second interval of the tests. Finally, we analyzed the relationships between the peak V(O₂) and the slopes of HR/V(O₂), S(pO₂)/V(O₂), S(tO₂)/V(O₂), and MOER/V(O₂). RESULTS With the increasing exercise intensity, many subjects showed a gradual decrease in S(tO₂) and S(pO₂), but a gradual increase in HR and MOER. V(O₂) was negatively correlated with S(tO₂) and S(pO₂), and was positively correlated with HR and MOER. However, peak V(O₂) was not correlated with any of the slopes. CONCLUSIONS V(O₂) is highly influenced by oxygen utilization in exercising muscles, as well as by blood oxygenation levels and cardiac function. However, the impact of skeletal muscle utilization during exercise on peak V(O₂) varied greatly among the subjects.