Is flow-mediated dilatation associated with near-infrared spectroscopy-derived magnitude of muscle O2 desaturation in healthy young and individuals at risk for cardiovascular disease?

Vascular occlusion test (VOT)-induced reactive hyperemia in brachial artery is crucial to flow-mediated dilation (FMD). Emerging studies have suggested that reactive hyperemia depends on the magnitude of the O2 desaturation (ischemia) in downstream microvessels. Although near-infrared spectroscopy-derived tissue O2 saturation index (TSI) has been used to assess the magnitude of ischemia, the association between FMD and the magnitude of O2 desaturation has not been addressed. Therefore, the aim of the present study was to evaluate whether FMD correlates with the magnitude of muscle O2 desaturation in healthy young individuals and older adults at risk for cardiovascular disease (CVD). Twenty healthy young individuals and 20 others at risk for CVD participated in the study. The magnitude of ischemic stimulus was determined by calculating the area under curve of TSI signal over 5 min of cuff occlusion period. Oxygen resaturation rate was calculated as the upslope of the TSI signal over 10 s following cuff deflation. There was no significant correlation between FMD and the magnitude of ischemic stimulus in both groups assessed (young: R = 0.327; P = 0.159 and older: R = -0.184; P = 0.436). However, a significant correlation between the magnitude of O2 desaturation and O2 resaturation rate in young (R = 0.555; P = 0.011) and older individuals at risk for CVD (R = 0.539; P = 0.014). In conclusion, FMD response did not correlate with the magnitude of muscle O2 desaturation, although it seems to be partially associated with O2 resaturation rate.