Pharmacologic manipulation of the microcirculation in cutaneous and myocutaneous flaps in pigs.

The vascular effects of isoxsuprine, diazoxide, and isoproterenol were studied in arterial buttock flaps and latissimus dorsi myocutaneous flaps in pigs. Capillary blood flow to the skin and muscle of these flaps was measured by the radioactive microsphere (15-mu diameter) technique 6 hours postoperatively under pentobarbital anesthesia. It was observed that isoproterenol, a beta-adrenergic receptor agonist, was not effective in augmentation of skin blood flow in the arterial buttock flaps. However, isoproterenol significantly increased capillary blood flow to the arterialized portion of latissimus dorsi myocutaneous flaps compared with controls. Isoxsuprine and diazoxide (vascular smooth muscle relaxants) significantly (p less than 0.05) increased total capillary blood flow to the skin of arterial buttock flaps and to the skin and muscle of the latissimus dorsi myocutaneous flaps. However, the increase in capillary blood flow occurred mainly in the arterialized portion of these flaps. The capillary blood flow, which was supplied by the small arteries in the distal portion of the arterial buttock and latissimus dorsi flaps, was not increased by treatment with isoxsuprine or diazoxide. Therefore, there was also no increase in the maximum distance of capillary blood flow from the pedicle to the distal end of the flaps. These observations led us to hypothesize that different sizes (diameters) of arteries in the skin and muscle have different reactivity (or sensitivity) to vasodilatory drugs. In the present experiment, the large dominant artery of the arterial buttock and latissimus dorsi flaps responded to isoxsuprine or diazoxide (vascular smooth-muscle relaxants), resulting in an increase in blood supply to the capillaries in the proximal portion of the flaps. On the other hand, the small arteries in the distal portion (random portion) of these flaps were not sensitive to isoxsuprine or diazoxide. Therefore vasodilation did not occur, and there was no increase in blood supply to the capillaries in the distal portion of arterial buttock and latissimus dorsi flaps. This explanation also lent support to our previous report that treatment with isoxsuprine did not augment skin viability in the distal portion of arterial buttock and latissimus dorsi flaps. It is suggested that research in pharmacologic manipulation of skin blood flow and viability in skin flap surgery should emphasize the sensitivity of small arteries to various drug actions.(ABSTRACT TRUNCATED AT 400 WORDS)