A study of the pharmacologic control of blood flow to acute skin flaps using xenon washout. Part I

This study was undertaken to understand the control mechanisms differentiating circulation to normal skin and acute skin flaps. The approach was to compare the effects of systemic vasoactive drugs on skin blood flow in rats in acute skin flaps and identical areas of control skin. With this model it was felt that systemic changes would affect both areas equally and any difference in response would be due to vascular control mechanisms unique to the flap. Xenon washout by percutaneous injection was chosen to measure blood flow. The results of over 8000 observations in these studies were: 1. Vasodilation enhances blood flow and flap survival. 2. Vasoconstriction decreases blood flow. 3. Depletion of sympathetic nerve terminals enhances blood flow and flap survival. 4. The acute flap is less sensitive to systemic alpha-agonists than control skin. 5. The acute flap is less sensitive to vasodilators acting at the receptor-site level than control skin. 6. Total sympathetic denervation does not occur. 7. Biologic increases in area of flap survival did occur in drug dose ranges predicted by xenon washout measurements in this model. These findings indicate that the vessels in an acutely raised skin flap have a greater vasospastic tone than is optimal for maximum nutrient blood flow. One explanation consistent with these findings is offered in which the mechanism responsible for this tone is the release of catecholamines from the sympathetic nerve terminals after the flap has been raised.