The association between near-infrared spectroscopy-derived and flow-mediated dilation assessment of vascular responsiveness in the arm

Introduction: Following a period of blood flow occlusion, the near-infrared spectroscopy (NIRS)-derived reperfusion slope of the oxygen saturation signal (StO ₂ ) is a measure of microvascular responsiveness that has been shown to be positively correlated with flow-mediated dilation (FMD) assessment of conduit artery function in the lower limb vasculature. Given that previously established differences in structure and function of the vessels in the upper compared to the lower limbs may change this relationship, investigating whether this correlation between the reperfusion slope of the StO ₂ and the FMD response is maintained in upper limbs is important. Accordingly, this study investigated the correlation between the reperfusion slope of the StO ₂ and FMD in the arm vasculature. Methods: 18 physically active individuals were submitted to a vascular occlusion test (VOT). Microvascular responsiveness was calculated as the NIRS-derived reperfusion slope assessed in a forearm muscle. Macrovascular responsiveness was assessed at the brachial artery and calculated as a percent of change in FMD (%FMD). Results: A statistically significant correlation (r = 0.66; P = 0.001) was found between the reperfusion slope and %FMD response. Conclusion: The significant correlation between the reperfusion slope in the forearm muscle and %FMD in the brachial artery, reinforces the relationship between downstream and upstream vascular reactivity in healthy human limbs.