Repeatability of vascular responsiveness measures derived from near-infrared spectroscopy

Abstract

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.

Vascular responsiveness measured by tissue oxygen saturation reperfusion slope is sensitive to different occlusion durations and training status

“…This is important because the FMD technique, which is widely employed for estimation of vascular responsiveness in humans, uses a single occlusion duration because the technique is associated with challenges such as the high cost of equipment, technical skill required and time for analysis. In opposition to this, NIRS measures have been shown to be repeatable (Gómez et al 2008;McLay et al 2016b), the equipment is easy to operate, and the subsequent data analysis is simple so that assessments of vascular responsiveness can be obtained rapidly. The present study reported that the AUC during the occlusion period increased with the lengthening of occlusion duration and that, although there was no significant difference between groups, there was a trend toward significance, such that the trained group may have a greater occlusion AUC.…”

Impaired Muscle Oxygenation and Elevated Exercise Blood Pressure in Hypertensive Patients

“…25,32 The TSI reperfusion slope and magnitude were used as indices of the vessels' ability to accommodate the blood flow increase (microvascular reactivity). 22,23 The peak hyperemic response was calculated as the difference between peak TSI during reperfusion and baseline TSI. 24,31 During exercise, peak and average TSI responses were used as indices of muscle oxygen extraction.…”

“…NIRS measurements have been shown to be valid and highly reproducible. 22,23,25 were averaged per testing period (ie, baseline, occlusion, exercise, and recovery) and analyzed using 2-way ANOVA with repeated measures, followed by Tukey post hoc (Statistica 7.0; StatSoft). A regression line (y=a+bx; b=slope and a=intercept) was applied to the occlusion/reperfusion data.…”

“…Using the arterial occlusion/reoxygenation maneuver, the NIRS technology provides information on skeletal muscle's oxidative capacity, microvascular function, and muscle oxygenation at rest and during exercise. [22][23][24][25] Our aims were to examine in vivo skeletal muscle oxygenation and microvascular function (as assessed by muscle microvascular reactivity), at rest and during submaximal handgrip exercise, and their associations with (1) arterial stiffness and other macrovascular function indices and (2) BP responses during handgrip exercise, in newly diagnosed, never-treated patients with hypertension (HYP) and age-, sex-, and BMI-matched normotensive individuals (NORMO). We hypothesized that (1) untreated individuals with hypertension will present compromised muscle oxygenation and impaired microvascular function versus normotensives and (2) these alterations could limit oxygen delivery to exercising muscles in hypertensive patients versus normotensives and contribute to further amplifications in BP responses during exercise in the former group.…”

“…25,32 The TSI reperfusion slope and magnitude were used as indices of the vessels' ability to accommodate the blood flow increase (microvascular reactivity). 22,23 The peak hyperemic response was calculated as the difference between peak TSI during reperfusion and baseline TSI.24,31 During exercise, peak and average TSI responses were used as indices of muscle oxygen extraction. 33 The BP response during the first minute of exercise (ΔBP=BP exercise −BP baseline ) was divided by the average TSI response during exercise and was used as an index of exercise BP rise per unit of muscle oxygenation (ie, ΔBP/ΔTSI).…”