Comparison Of Two Methods For Analyzing Microvascular Reperfusion In Young, Middle-aged, And Older Adults

Near-infrared spectroscopy (NIRS) has become increasingly popular for non-invasively assessing microvascular reperfusion. Currently, two main methods for analyzing microvascular reperfusion following a vascular occlusion test exist in the literature, both demonstrating strong reproducibility. PURPOSE: Determine if NIRS analyses of microvascular reperfusion using a) rate of reperfusion and b) halftime to recovery will reveal similar results when comparing across young, middle-aged, and older adults. METHODS: Physically active young, (N = 22), middle-aged (N = 19), and older (N = 21) participants reported to the lab for a single visit. A NIRS device was placed on the belly of the tibialis anterior muscle and data were collected continuously. A vascular occlusion test was performed consisting of 2 min baseline, 5 min of arterial occlusion at a pressure of 300 mmHg, and 3 min of recovery. Analyses of NIRS data were performed using the halftime to peak reperfusion of the oxyhemoglobin (O2Hb) signal (T ½, reported in seconds) and the 10-second recovery slope of the tissue oxygen saturation (%StO2) signal immediately following cuff release (Slope 2, reported as % s-1). For both analyses, a one-way ANOVA and Bonferroni post-hoc analyses were performed to determine statistical differences. Results are reported as means ± SD. RESULTS: Across all individuals %StO2 Slope 2 and O2Hb T ½ were significantly correlated with one another (r = -0.692; p < 0.001). We observed a significant main effect of group when examining reperfusion using O2Hb T ½ (p = 0.007). Older (7.68 ± 2.46 seconds; p = 0.01) and middle-aged (8.03 ± 1.88 seconds; p = 0.04) adults exhibited significantly faster O2Hb T ½ compared with younger adults (9.82 ± 2.43 seconds). When examining reperfusion using Slope 2, we observed no group effect (1.52 ± 0.66, 1.85 ± 0.69, and 1.88 ± 0.67 % s-1 for younger, middle-aged, and older, respectively; p = 0.159). CONCLUSIONS: While both methods for assessing microvascular reperfusion using NIRS are significantly correlated, statistical significance between age groups was not consistently reported. Caution should be made when interpreting NIRS-based microvascular reperfusion results as the analysis method used may affect whether statistically significant differences are detected across groups. Supported by Towson University School of Emerging Technology, Towson University College of Health Professions, and the American Physiological Society John F. Perkins Research Enhancement Award