Advances in microcirculation network evaluation: an update.

Many methods are available today for clinical evaluation of the blood supply to an extremity or part of an extremity, some of which are excellent for determining the presence and severity of arterial and venous disorders. These methods, however, do not give any information on the microvascular status of the diseased areas. This is particularly true for the skin circulation, which has a rather complex vascular network with nutritional and thermoregulatory vessels, arteriovenous shunts, etc. The most useful method for clinical evaluation of the skin capillary circulation is vital capillary microscopy. The skin capillaries in an area with a reduced microcirculation change in structure, and it is possible to evaluate the viability of the skin by microscopic studies of these capillary changes. Both morphology and blood flow can be investigated. By using different intravital fluorescent dyes, e.g. sodium fluorescein and indocyanine green, the microvascular dynamics, flow distribution and microvascular permeability can also be studied. The total skin microcirculation can be evaluated by Laser Doppler fluxmetry, which measures primarily the blood flow in the thermoregulatory vascular bed, i.e. the subpapillary arterial and venous plexa. It is easy to use in clinical practice, but interpretation of the results can sometimes be difficult. Measuring transcutaneous oxygen tension has for many years been used in clinical routine to evaluate the viability of skin in patients with vascular disorders. It has recently been shown that inhalation of oxygen may induce vasoconstriction in healthy subjects and in patients with moderate arterial insufficiency, but an increase of the skin microcirculation in areas of severe ischaemia. By using different combinations of the above mentioned microcirculatory techniques, valuable information can be gained regarding pathophysiological phenomena of the microcirculation in many diseases, e.g. vascular disorders, collagenosis. Raynaud's phenomenon, diabetes and hypertension. Using techniques for both macro- and microcirculation is also of great importance for evaluating the effect of therapeutic procedures in several of these disorders.