RESUMO
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.
