Current techniques for the clinical evaluation of the microcirculation.

Three main types of approaches are currently used for the exploration of th e microcirculation in man: Clinimetric measurements of the cutaneous temperature (thermometry). skin c olor (chromametry and tissue volume (leg or foot volumetry) allow a quantif ication of clinical indexes of skin blood flow. blood volume and edema that are useful in therapeutic trials. Global parameters evaluating the hemodynamic or nutritional efficacy of the microcirculation in a tissue sample (laser Doppler and TcPO2) are easy to perform in clinical routine. TcPO2 measurements through Clarke electrodes o r fluorescence lifetime imaging technology evaluate the nutritional efficac y of the microcirculation. Laser Doppler devices are producing a semi-quant itative index of superficial tissue perfusion, that can be split into a vol umic and a velocimetric components; its high sensitivity makes it a valuabl e tool for clinical research, mainly for dynamic measurements of reactivity of the superficial microcirculation to various stimuli. New instruments ar e able to use two different Frequencies in order to compare tissue perfusio n at different depths beneath the skin surface. The combination of a laser probe and a small automate can produce a two-dimensional image allowing the evaluation of spatial heterogeneity in tissue perfusion. Visualization of the skin capillary bed, i.e. capillaroscopy, was recently improved by the emergence of flexible videomicroscopes easily allowing the exploration of the whole body skin surface and not only the classical site of the nailfold. The use of the method was therefore broadened from vascula r acrosyndromes and connective tissue diseases to the whole spectrum of ski n trophic changes of the extremities. Combination with digital image analys is systems allows the quantification of the microvascular and microlymphati c structure (quantitative appraisal of microangiopathies) and function (cap illary hemodynamics and exchange). Laser-doppler and capillaroscopy can als o be combined for the measurement of red blood cell velocity in single capi llaries.