Calf Muscle Oxygen Saturation during 6-Minute Walk Test and Its Relationship with Walking Impairment in Symptomatic Peripheral Artery Disease

Background: Impaired microcirculation is associated with poor walking capacity in symptomatic peripheral artery disease (PAD) patients during treadmill test; however, this test does not simulate the efforts of daily walking of these patients. Thus, the aim of the study was to describe the microcirculation responses during a 6-minute walk test (6MWT) and to analyze the relationship between microcirculation indicators and walking impairment in symptomatic PAD patients. Methods: Thirty-four patients were included (mean age = 67.6 +/- 11.2 years). Their clinical characteristics were collected, and they performed a 6MWT, in which the initial claudication distance (ICD) and total walking distance (TWD) were recorded. During and after the 6MWT, calf muscle oxygen saturation (StO(2)) parameters were monitored continuously to measure microcirculation behavior. The association between calf muscle StO(2) parameters and walking impairment were analyzed by Pearson or Spearman correlations. Results: Walking impairment was not associated with any StO(2) parameters during exercise. In contrast, after 6MWT, recovery time of StO(2) (r = -0.472, P = 0.008) and recovery time to maximal StO(2) (r = -0.402, P = 0.019) were negatively correlated with ICD. Furthermore, the distance walked under claudication symptoms (ATWD-ICD) was positively correlated with recovery time to maximal StO(2) (r = 0.347, P = 0.048). Conclusions: In symptomatic PAD patients, shorter ICD values during a 6MWT are associated with a delayed recovery in calf muscle StO(2) after exercise. Calf muscle StO(2) parameters decrease subtly during 6MWT, suggesting that the degree of ischemia in the calf muscle during ground walking, simulating efforts of the daily walking, is relatively low.