Impaired muscle oxygenation recovery kinetics during the 6‐min walk test in COPD and smokers: A near‐infrared spectroscopy study

Abstract Objectives Chronic obstructive pulmonary disease (COPD) is associated with impaired peripheral muscle oxygenation and reduced exercise tolerance. In our study, we planned to use near‐infrared spectroscopy (NIRS) to measure muscle oxygenation dynamics during exercise in patients with COPD, active smokers and healthy individuals. Methods This prospective study included 50 stable COPD patients, 30 current smokers without COPD and 20 healthy controls. Clinical measures and pulmonary function were assessed, while muscle oxygenation was continuously monitored by NIRS during the 6‐min walk test (6MWT) to derive T½ recovery time, reoxygenation rate and functional exercise performance. Results COPD patients had significantly lower muscle oxygen saturation (SmO 2 ) at baseline, end‐6MWT and 5 min post‐test than controls ( p < 0.001). COPD patients had the longest T½ recovery time ( p = 0.03), and their reoxygenation rate was similar to that of active smokers but shorter than that of the healthy control group ( p < 0.001). Active smokers had lower SmO 2 and reoxygenation rates before and after exercise than the control group ( p < 0.05). In COPD patients, the greater the difference in oxygen saturation (SpO 2 ) levels before and after 6MWT, and the lower the haemoglobin level, the longer the T½ recovery time ( p < 0.05). The 6MWT interval was longer in those with high SpO 2 and SmO 2 levels before and after 6MWT, shorter T½ recovery times and high haemoglobin levels ( p < 0.05). Conclusion COPD and smoking significantly impair post‐exercise muscle oxygenation recovery, suggesting that peripheral microvascular dysfunction contributes to reduced functional exercise performance beyond pulmonary limitation.