Quantifying microvascular responses to local heating using optical coherence tomography: Comparison between skin sites and sex differences.

Due to a lack of technical capacity to directly visualise and quantify microvessels in the skin, little is known regarding regional and/or sex differences. We compared diameter, velocity, flow and density at four regional sites using a novel optical coherence tomography (OCT) approach. OCT and laser Doppler flowmetry (LDF) were performed on the back, forearm, foot and thigh in 30 healthy adults (15♂ 15♀; 31 ± 6years) at rest (33°C) and after 30 min of local heating (LH; 44°C). At baseline, larger diameter, speed, flow, density and LDF flux were recorded on the back than other sites (P < 0.017). In response to LH, the smallest changes in OCT-derived diameter were observed on the back (Δ12 ± 6 µm) and foot (Δ13 ± 6 µm vs. forearm 17 ± 5 µm; thigh Δ18 ± 5 µm, all P < 0.005 vs. foot, back). The back exhibited the smallest change in density (back Δ19 ± 7%, forearm Δ24 ± 5%, thigh Δ26 ± 6%, foot Δ26 ± 8%, P < 0.02 vs. back) whilst the foot exhibited the smallest changes in speed (foot Δ27 ± 14, back Δ58 ± 22, forearm Δ47 ± 17, thigh Δ48 ± 11 µm/s, P < 0.001 vs. foot) and flow (Δ135 ± 60, back Δ204 ± 76, forearm Δ212 ± 60, thigh Δ247 ± 51 µL/s, P < 0.001 vs. foot). When sites were grouped, males had larger baseline diameters (♂ 45 ± 3 vs. ♀ 42 ± 3 µm, P = 0.019) and flows (♂ 109 ± 20 vs. ♀ 93 ± 17 µL/s, P = 0.025) whilst females exhibited larger LH-induced changes in speed in the thigh (♀ Δ53 ± 10 vs. ♂ Δ43 ± 10 µm/s, P = 0.014) and density in the forearm (♀ Δ26 ± 4 vs. ♂ Δ21% ± 6%, P = 0.006). Regional differences exist in OCT-derived cutaneous microvascular diameter, speed, flow and density at baseline and in response to LH. Males showed larger cutaneous diameter and flow at baseline, while females exhibited larger changes in the speed and density outcomes in response to local heating.