Individual cell motion in healthy human skin microvasculature by reflectance confocal video microscopy.

OBJECTIVE: To describe upper dermal microvasculature of healthy human skin in terms of density and size of cutaneous blood vessels, leukocyte velocity, and leukocyte interactions with the endothelium. METHODS: We used a reflectance confocal microscope, the VivaScope 1500, to acquire videos of individual cell motion. RESULTS: We found no rolling leukocytes in the upper microvasculature of ten healthy subjects. We observed "paused" leukocytes, that is, leukocytes that temporarily stop, coinciding with the simultaneous stopping of the rest of the blood flow. We imaged more paused (median: 1.0 per subject) and adherent (1.5) leukocytes in the forearm than in the chest (median 0 paused and 0 adherent per subject) per 5 minutes of videos per body site. Leukocytes were paused for a median of 7 seconds in the forearm and 3 seconds in the chest, and we found no correlation between this parameter and the blood vessel or leukocyte size. We visualized blood flow change direction. Flowing leukocyte velocities followed a lognormal distribution and were on average higher in the chest (117 µm/s) than in the forearm (66 µm/s). CONCLUSION: The proposed method and reported values in healthy skin provide new insights into intact human skin microcirculation.