Microcirculatory dynamics in human skin

Dynamic studies of human skin microcirculation by intravital videomicroscopy became possible using four different methods: Measurement of capillary red cell speed, continuous capillary pressure measurements, visualization of diffusion and pericapillary distribution of Na- fluorescein and fluorescence microlymphography. The latter two techniques are presented in some detail. In normals, Na- fluorescein which is given intravenously as a bolus (1ml of a 20 % -solution) leaves the capillary lumen showing a uniform and symmetrical pattern of pericapillary dye distribution (evaluation of fluorescent light intensities by videodensitometer, single frames of TV- recordings). Increased leakage and pathological dye distribution in the interstitial space is observed in microangiopathy due to scleroderma. In white atrophy, a common feature in chronic venous insuffiency, Na- fluorescein diffuses into the avascular field (mean diameter 1 mm) and reaches its peak concentration at the centre only after 30–40 min (around normal capillaries in the ankle region: 10 min). The long times needed for the exchange of small molecules explains that white atrophy is a predilection site of venous ulcer formation. For fluorescence microlymphography a 25 % solution of fluorescent dextran with a molecular weight of 150’000 (0,01ml) is injected into the subepidermal layer by a steel microneedle with an outer diameter of 0,2 mm. The superficial lymphatic capillaries are filled from the deposit of the dye. In lymphedema, the fluorescent dextran visualizes an extensive network, whereas in normals the extension of the dye remains limited. In some patients pathological microvessels appear.