Visualizing and quantifying the impact of reactive hyperemia on cutaneous microvessels in humans.

The mechanisms underlying reactive hyperemia (RH) responses in microvessels are poorly understood. Previous assessment tools have not been capable of directly visualizing microvessels during physiological stimulation in humans. Optical coherence tomography (OCT) is capable of imaging and quantifying subcutaneous microvessels as small as ~30 µm. In this study we use OCT to visualize and quantify skin microvascular changes in response to RH for the first time in humans. We also assessed the reproducibility of this technique. OCT and laser Doppler flowmetry (LDF) were used simultaneously to scan cutaneous microvessels in 10 young healthy subjects on 2 days. We applied a speckle decorrelation algorithm to assess OCT images and calculated flow rate, speed, diameter, and density parameters. Measures were obtained at rest (baseline) and 30-s following a 5-min cuff inflation (RH). All data were compared between days. The RH stimulus significantly increased (P < 0.0001) OCT-derived microvascular diameter (37.6 ± 3.4 vs. 44.5 ± 5.2 µm), flow rate (82.4 ± 23.4 vs. 240.1 ± 58.6 pl/s), speed (48 ± 5.7 vs. 101.5 ± 17.1 µm/s), density (5.1 ± 1.7 vs. 14.6 ± 2.6%), and also LDF-derived flux (12.3 ± 5.7 vs. 31.6 ± 9.1 perfusion units). At baseline, OCT-derived diameter (r = 0.55), flow rate (r = 0.64), speed (r = 0.55), and density (r = 0.75) showed significant between-day correlations (P < 0.05), as did LDF results (r = 0.74). In response to RH, OCT-derived diameter (r = 0.63) and density (r = 0.64) showed significant correlations (P < 0.05), whereas flow rate (r = 0.45), speed (r = 0.43), and LDF (r = 0.26) were less reproducible. Our study is novel in that it establishes the feasibility of using OCT to visualize and quantify microvascular structure and function responses to RH in humans.NEW & NOTEWORTHY This study describes the first evidence in humans that optical coherence tomography provides direct visualization and comprehensive quantification of cutaneous microvascular hemodynamics as a response to reactive hyperemia. This imaging technique will greatly improve human cutaneous microvascular assessment in physiological and clinical settings.