Reductions in Microvascular Function can be Detected by Near-infrared Spectroscopy (NIRS) following Ischemia-Reperfusion in Early Postmenopausal Women

The onset of menopause and accompanying changes to ovarian hormones often precedes endothelial dysfunction in women. In particular, accelerated impairments in microvascular function coincides with the loss of estrogen, as does impaired endothelial resilience to ischemia-reperfusion (IR) injury. In early postmenopausal women (4 ± 1 years since menopause), we tested the hypothesis that the NIRS-derived measurement of vascular responsiveness (reoxygenation slope, %.s−1) in the forearm could detect reductions in microvascular function following whole-arm IR injury. In conjunction, brachial artery flow-mediated dilation (FMD) and shear rate (area under curve; AUCpeak) were measured. Thirteen healthy, normotensive (116 ± 11/72 ± 9 mmHg) postmenopausal women (57 ± 3 years) were tested before (PreIR), after (PostIR), and 15 minutes following IR (Post15). The IR injury was achieved by inflating a cuff around the upper-arm to 250 mmHg for 20 min followed by 15 min of reperfusion. The NIRS-derived reoxygenation slope was lower PostIR (1.02 ± 0.56%.s−1 vs. 1.23 ± 0.64%.s−1 PreIR; p =0.04), but not at Post15 (1.17 ± 0.51%.s−1; p =0.08). Brachial artery FMD was lower PostIR (3.57 ± 0.52% vs. 8.14 ± 2.44% PreIR; p < 0.001), but not at Post15 (7.61 ± 1.89%; p = 0.54). Shear AUCpeak were similar across tests (p >0.05). Our findings suggest that the NIRS-derived reoxygenation slope is a non-invasive method that may detect transient impairments in forearm microvascular function, and may also be used to assess efficacy of therapeutic interventions in improving both vascular function and resilience in this population.