We have studied the recovery of microvascular function in ischemic epigastric skin flaps by characterizing the regional hemodynamics in the axial and random portions of double- and single-pedicle island skin flaps in the rat. Blood flows were measured with radiolabeled microspheres 1 day after bipedicle flaps were elevated and at 4 hr, 72 hr, and 1 week after ligation of one of the pedicles. These hemodynamic measurements were correlated with assessments of angiogenesis and skin necrosis performed by lectin histochemistry and histopathology. Twenty-four hours after the skin flap elevation, the mean blood flow was 0.26 ml·min-1·g-1. After the ligation of one pedicle, the blood flow in the axial portion of the skin flap was unchanged at 4 hr (0.22 ml·min-1·g-1), declined insignificantly at 72 hr (0.15 ml·min-1·g-1), and remained normal at 1 week. In the random portion of the skin flap very little collateral blood flow was present at 4 hr (0.06 ml·min-1·g-1) and 72 hr (0.09 ml·min-1·g-1). Blood flow in the random skin flap returned to normal by 1 week (0.27 ml·min-1·g-1). Reelevation of the skin flap at 1 week caused an insignificant decline (10%) in total blood flow to the skin flap. Skin necrosis was detected histologically at 72 hr only in the lateral portion of the random skin flap, where blood flow was less than 0.03 ml·min-1·g-1. Increased areas of lectin binding to vascular endothelium were seen in the subdermal layers of the skin flap by 1 week, presumably due to angiogenesis. We conclude that (1) the critical level of blood flow necessary to maintain skin viability is 0.03-0.05 ml·min-1·g-1 (2) angiogenesis beneath the panniculus carnosus at the random tip is able to maintain blood flow at a level equal to the rest of the flap, even though the overlying skin and muscle is necrotic at 1 week postoperatively, (3) neovascularization from the flap edge and wound bed contributes little to overall blood flow in these flaps at 1 week postoperatively.
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