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 (ΔTWD-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.
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