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Background There is a spectrum of possibilities for analyzing muscle O2 resaturation parameters for measurement of reactive hyperemia in microvasculature. However, there is no consensus with respect to the responsiveness of these O2 resaturation parameters for assessing reactive hyperemia. Objectives This study investigates the responsiveness of the most utilized muscle O2 resaturation parameters to assess reactive hyperemia in the microvasculature of a clinical group known to exhibit impairments of tissue O2 saturation (StO2). Methods Twenty-three healthy young adults, twenty-nine healthy older adults, and thirty-five older adults at risk of cardiovascular disease (CVD) were recruited. Near-infrared spectroscopy (NIRS) was used to assess StO2 after a 5-min arterial occlusion challenge and the following parameters were analyzed: StO2slope_10s, StO2slope_30s, and StO2slope_until_baseline (upslope of StO2 over 10s and 30s and until StO2 reaches the baseline value); time to StO2baseline and time to StO2max (time taken for StO2 to reach baseline and peak values, respectively); ∆StO2reperfusion (the difference between minimum and maximum StO2 values); total area under the curve (StO2AUCt); and AUC above the baseline value (StO2AUC_above_base). Results Only StO2slope_10s was significantly slower in older adults at risk for CVD compared to healthy young individuals (p < 0.001) and to healthy older adults (p < 0.001). Conversely, time to StO2max was significantly longer in healthy young individuals than in older adult at CVD risk. Conclusions Our findings suggest that StO2slope_10s may be a measure of reactive hyperemia, which provides clinical insight into microvascular function assessment.

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Flow-mediated dilation (FMD) and muscle oxygen saturation (StO2) are measurements utilized to assess macro- and microvascular function, respectively. Macro- and microvascular dysfunction may occur differently depending on the clinical condition. Since microvascular responsiveness can influence upstream conduit artery hemodynamics, the present study aimed to investigate whether a correlation between FMD and muscle StO2 parameters exists. Sixteen healthy, young individuals were enrolled in this study. Femoral artery FMD and tibial anterior muscle StO2 were evaluated by ultrasound and near-infrared spectroscopy, respectively. The FMD and muscle StO2 parameters were assessed by employing a vascular occlusion test (VOT). The oxygen resaturation rate was determined by calculating the upslope of StO2 immediately after occlusion and the magnitude of reperfusion as the difference between the highest and lowest StO2 value achieved during the reperfusion phase. The oxygen desaturation rate and the magnitude of desaturation during the VOT were also evaluated. A significant correlation between the FMD and oxygen resaturation rate (r = 0.628; p = 0.009), magnitude of reperfusion (r = 0.568; p = 0.022), oxygen desaturation rate (r = −0.509; p = 0.044), and magnitude of desaturation (r = 0.644; p = 0.007) was observed. This study demonstrated a moderate association between the femoral artery FMD and tibial anterior StO2 parameters in young individuals.

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