Repeatability of vascular responsiveness measures derived from near-infrared spectroscopy.

Near-infrared spectroscopy ( NIRS)-derived measures of tissue oxygen saturation (StO₂) have been recently shown to significantly correlate with the widely used method for noninvasively assessing vascular endothelial function, flow-mediated dilation ( FMD). The purpose of this study was to examine the intraday and interday reliability of the reperfusion slope of StO₂ (slope 2 StO₂) and compare it to FMD. Ultrasound-derived FMD was quantified following 5 min of distal cuff occlusion of the popliteal artery in nine healthy young men (26 ± 3 years). An FMD test was performed each of 4 days, with a fifth involving three tests. FMD was calculated as the greatest percent change in diameter from baseline (% FMD). StO₂ was measured using NIRS throughout each test, with slope 2 StO₂ being calculated as the upslope of 10-sec following cuff release. Reliability was determined using repeatability, intraclass correlation coefficients ( ICC), and coefficient of variation ( CV). Repeatability of slope 2 StO₂ was better than % FMD for both intraday (0.43 and 5.65, respectively) and interday (0.48 and 4.82, respectively) comparisons; approximately 30% of mean values for slope 2 StO₂ could be attributed to measurement error, whereas 100% of mean FMD could be for both intraday and interday comparisons. Similarly, ICC and CV values indicated stronger reliability of slope 2 StO₂ compared to % FMD for both intraday ( ICC 0.92 and 0.36, respectively; CV 9 ± 4% and 44 ± 24%, respectively) and interday ( ICC 0.94 and 0.25, respectively; CV 14 ± 5% and 40 ± 22%, respectively) comparisons. In conclusion, NIRS-derived slope 2 StO₂ can be used as a reliable measure of vascular reactivity. [ABSTRACT FROM AUTHOR]