The isotope clearance technique for measuring skin blood flow

The measurement of skin blood flow using the isotope clearance technique has been investigated in pig skin. The isotope used was technetium-99m; this was shown to be freely diffusible in skin. The volume injected (0.02 to 0.3 ml) did not affect the clearance parameters. Bi-exponential clearance curves were always obtained in normal pig skin. An analysis of what parameters of blood flow are indicated by the two exponents has been made by correlating changes in clearance parameters (animal age and depth of injection) with changes in vascular density and dermal thickness. It is suggested that the fast and slow clearance parameters are derived from clearance by capillaries in the papillary and reticular regions of the dermis respectively. Further evidence in support of this hypothesis was derived from the application of the clearance technique in skin traumatised by surgery (pedicle skin flaps) or x-irradiation. The value of the isotope clearance technique in the measurement of nutrient flow in the dermis is discussed.