Near-Infrared Spectroscopy Does Not Track Forearm Blood Flow during Venous Occlusion Plethysmography

Abstract

Featured Application: Near-infrared spectroscopy (NIRS) has gained popularity in biomedical and sport sciences to non-invasively assess the microvascular responses and health in men and women. Venous occlusion plethysmography (VOP) is also capable of assessing microvascular health. However, due to the ease of assessment and portability of a NIRS sensor, this method may be more favorable to some individuals. Currently, there are limited direct comparisons between each approach, and thus, the ability to interchange values is not clear. Here, it was reported that NIRS responses do not correlate well with strain-gauge VOP values. Background: Venous occlusion plethysmography (VOP) non-invasively measures forearm blood flow (FBF), whereas near-infrared spectroscopy (NIRS) assesses skeletal muscle oxygenation. Using these techniques has revealed sex differences in microvascular responses. However, it is not clear if NIRS and VOP results are interchangeable under various conditions like reactive hyperemia (RH). Our purpose was to evaluate sex-specific associations between FBF and NIRS-derived parameters: oxygenated hemoglobin, deoxygenated hemoglobin, total hemoglobin, and hemoglobin difference (O2Hb, HHb, tHb, and HbDiff). Methods: In total, 29 adults (15 men) participated, and a strain-gauge was placed on the forearm for VOP and a NIRS device was distally attached. Slopes for FBF and NIRS parameters were quantified during venous occlusion intervals at rest and during RH. Pearson’s correlations were assessed between VOP and NIRS slopes. Intraclass correlation coefficients (ICC2,1) examined the sex-specific consistency of the slopes at rest. p ≤ 0.05 was considered significant. Results: During RH, FBF was not correlated with O2Hb (r = −0.126), HHb (r = 0.228), tHb (r = 0.061), or HbDiff (r = 0.046). Seemingly, there were no sex differences. Resting FBF and NIRS-derived variables, except for HbDiff, displayed suitable consistency as suggested by the reliability results (ICC2,1 = 0.115–0.577). Conclusions: The NIRS values collected did not match the strain-gauge slopes. Individuals should practice caution when generating blood flow inferences from NIRS-based data during VOP.