Age- And Sex-related Differences In Skeletal Muscle Oxygen Consumption Rate And Microvascular Reactivity

Abstract

PURPOSE: To examine the influence of age and sex on non-invasive measurements of oxygen consumption rate and microvascular reactivity. METHODS: Seven young females (YF; mean ± SD, age = 20.9±2 y), 6 older females (OF; 57.5±10 y), 14 younger males (YM; 22.2±2 y), and 8 older males (OM; 59.5±5 y) visited the laboratory on one occasion during which skeletal muscle oxygen utilization and microvascular function were assessed following a 10-h fast using the near-infrared spectroscopy with vascular occlusion test (NIRS-VOT). During the NIRS-VOT, tissue saturation (StO2) was monitored, and the rate of decrease in StO2 (Slope 1) during cuff inflation (i.e., ischemia) was quantified, as were the reperfusion magnitude (RepMAG), rate of increase in StO2 (Slope 2), and the reperfusion area under the curve (StO2AUC) following cuff deflation. Two-way (age × sex) ANOVAs were used to examine the differences in Slope 1, RepMAG, Slope 2, and StO2AUC among the YW, OW, YM, and OM. Means ± 95% CIs are reported. RESULTS: There were significant age and sex effects for Slope 1 (p = 0.01 and 0.02, respectively), which was more negative (i.e., steeper) in males versus females (-0.132±0.12 vs. -0.108±0.15 %1s-1) and in the young versus older adults (-0.133±0.13 vs. -0.107±0.14 %1s-1). There was an age effect for RepMAG (p < 0.001), which was greater in the younger than older adults (50.7±4.0 vs. 38.5±4.6%). While there was no effect of age on Slope 2, Slope 2 was steeper (p = 0.002) in males than females (1.71±0.24 vs. 1.06±0.34 %1s-1). Finally, there were age (p = 0.02) and sex (p = 0.03) main effects for StO2AUC, which was greater in males versus females (1228.5±148.8 vs. 960.1±178.9 %1s) and in the young versus older adults (1240.7±148.8 vs. 947.9±178.9 %1s). CONCLUSIONS: Overall, our results suggest that there are age and sex-related differences in skeletal muscle oxygen consumption rate and microvascular reactivity, as assessed using the NIRS-VOT technique. However, because the degree of tissue desaturation is the stimulus for subsequent reperfusion responses and the rate of desaturation was greater in the younger than older adults and in males than females, it is not clear if the differences in Slope 2 and StO2AUC reflect differences in microvascular reactivity, per se. Additional studies are needed to more fully explore this interplay.