Association between sublingual microvascular structure and skeletal muscle microvascular reactivity: a combined sidestream dark field imaging and NIRS study

Objective: The structure of the microcirculation, particularly the endothelial glycocalyx and vessel density, plays a crucial role in regulating oxidative metabolism; however, their specific roles in modulating microvascular reactivity and deoxygenation are not fully understood. This study aimed to test the hypothesis that the sublingual microvascular structure would correlate with the functional microvascular reactivity of skeletal muscle. Methods: Eleven apparently healthy adults (age: 26 ± 6 yrs; 7 females) were recruited. Microvascular reactivity in the calf muscle was assessed using near-infrared spectroscopy (NIRS) combined with a vascular occlusion test (VOT). Microvascular structure, including perfused boundary region (PBR) and vessel density, was evaluated in the sublingual area using sidestream dark field imaging. Results: The occlusion slope during VOT correlated with the density of vessels in the 13-25 µm diameter range (r = -0.65, p = 0.03) and the PBR of capillaries in the 4-7 µm diameter range (r = -0.73, p = 0.01). The area above the curve of the occlusion slope correlated with overall vessel density, and specifically with density of vessels in the 8-12 µm diameter range and 13-25 µm diameter range (r = 0.79, 0.85, and 0.77, respectively, all p < 0.05) and PBR of capillaries in the 4-7 µm diameter range (r = 0.65, p = 0.03). Additionally, the reperfusion index, estimated by area under the curve after cuff release, showed a positive correlation with PBR of capillaries in the 4-7 µm diameter range (r = 0.59, p = 0.055). Conclusions: Our findings suggested that higher capillary density is associated with greater deoxygenation during vascular occlusion. Moreover, a more penetrable glycocalyx (higher PBR) may be associated with a greater deoxygenation and a greater hyperemic response, indicating the important role of the endothelial glycocalyx in modulating oxygen diffusion and the magnitude of microvascular reactivity. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.