BACKGROUND: Venous occlusion plethysmography (VOP) is the current gold standard for non-invasive measurements of forearm blood flow (FBF). Near-infrared spectroscopy (NIRS) has gained popularity for its ability to measure oxygenation parameters. However, mixed evidence exists concerning the ability of NIRS to serve as a surrogate to VOP, especially during reactive hyperemia (RH). Therefore, our purpose was to evaluate relationships between FBF and NIRS parameters as well as potential sex differences in young adults. METHODS: 32 adults (16 males and 16 females, age:21±3yrs, body mass:67.7±22.4kg, height:169.8±12.3cm) volunteered to participate. A mercury in-silastic strain gauge was used for VOP and placed 5cm distal to the antecubital fossa, and a NIRS device was also attached. FBF and oxygenation measures were collected during a series of venous occlusion intervals with 50mmHg (e.g., 4s inflated, 3s deflated) applied to the upper arm immediately after a 5min period of complete brachial occlusion (250mmHg). The rate of change (i.e., slope) in FBF and each NIRS parameter (oxygenated hemoglobin [O2Hb], deoxygenated hemoglobin [HHb], total hemoglobin [tHb], and hemoglobin difference [HbDiff]) were determined during the intervals of venous occlusion. Peak slope values were recorded within the first 30s immediately following the cuff deflation (i.e., reactive hyperemia). Pearson’s correlations (i.e., adjusts variables to equal units) were performed to assess associations between VOP and NIRS, and independent t-tests were used to evaluate sex differences. A p≤0.05 was considered significant. Cohen d (d) and 95% confidence intervals of mean differences (Δ) were reported as measures of effect. RESULTS: Peak FBF was significantly related to O2Hb (r=0.399; p=0.024) and HbDiff (r=0.469; p=0.007), whereas there was no association to either HHb (p=0.943) or tHb (p=0.175). There were mean sex differences such that peak FBF was significantly (p=0.006, d=1.05, Δ=1.82 to 9.93) greater for the men (22.9±6.2 ml ⋅ dl FAV-1 ⋅ min-1) than the women (17.0±4.9 ml ⋅ dl FAV-1 ⋅ min-1). O2Hb (p=0.001, d=1.25, Δ=0.19 to 1.46) and HbDiff (p=0.001, d=1.25, Δ=0.31 to 1.17) demonstrated a matching sex difference. CONCLUSIONS: Despite only observing moderate associations between VOP and NIRS measures, similar interpretations and effects were achieved. That is, VOP and NIRS both indicated men exhibited greater magnitudes of RH than women.

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