Comparison of Analysis Strategies to Assess Sex Differences in Microvascular Reperfusion Using Near-Infrared Spectroscopy

The near-infrared spectroscopy (NIRS) vascular occlusion test (VOT) assesses microvascular reperfusion. Two strategies have been employed to quantify reperfusion following reactive hyperemia, but it is unclear if both yield similar results when comparing biological sex. Purpose: Determine if sex differences in NIRS-based microvascular reperfusion are similarly apparent using the 10-second reactive hyperemia slope of the StO2 signal (slope 2) and the halftime to maximal reperfusion (T 1/2). Methods: Healthy, recreationally active males (N = 31) and females (N = 31) between 18-82 years took part in this study. A NIRS VOT was performed on the tibialis anterior muscle and reperfusion was quantified using slope 2 (% s-1) and T 1/2 (seconds). Results: Adipose tissue thickness (ATT) was higher in females ( p = 0.009) which was associated with a lower StO2 ( p = 0.001) and O2Hb ( p = 0.05) signal range. The StO2 slope 2 was significantly steeper in males vs. females ( p = 0.001) but not after correcting for ATT ( p = 0.295). There were no sex differences in StO2 T 1/2 ( p = 0.067) or O2Hb T 1/2 ( p = 0.197). In a subset of males (N = 26) and females (N = 21) with similar ATT, there were no sex differences in StO2 slope 2 ( p = 0.068), StO2 T 1/2 ( p = 0.491), or O2Hb T 1/2 ( p = 0.899). Conclusion: An ATT-corrected StO2 slope 2 or the T 1/2 approach is recommended for analysis of NIRS-based microvascular reperfusion when differences in ATT are present between sexes.