Radionuclide methodology for the assessment of the microcirculation in island pedicle flaps in a sheep model

Island pedicle flaps with a proximal well-perfused part and a distal poorly-perfused part were raised in eight anaesthetized sheep. Autologous red blood cells were labelled in vitro with 99TcmO4 and plasma with 111In chloride. The labelled cells and plasma were injected intraarterially and both dynamic and static images of the time-course of radioactivity were obtained with a gamma camera. Time activity curves were generated for selected regions of interest of the flap. For both plasma and red cells there was a substantial decline in the amount of tracer reaching the distal part of the flap; the time to maximum counts increased and the time activity curves indicated a minor uptake and almost no clearance pattern. In general there were marked local differences in the flow of plasma and red cells. The flow of plasma was more rapid than that of the red cells in five of the eight sheep. The model provides a standardized pedicle flap having a proximal part with adequate circulation and a distal part with inadequate circulation. It is concluded that this sheep model is suitable for radionuclide studies examining those factors that influence the distribution of blood flow within this tissue.