Microvascular transfer-related abrogation of capillary flow motion in critically reperfused composite flaps

Capillary flow motion is defined as rhythmic fluctuations of blood flow in the capillaries. Although critical perfusion has been demonstrated to induce capillary flow motion, little is known about the role of capillary flow motion in microvascular free flaps. The aim of this study was to elucidate the tissue-confined incidence and consequence of capillary flow motion in microvascularly transferred composite flaps, using intravital fluorescence microscopy. In Wistar rats, transferred osteomyocutaneous flaps (n = 7), which were exposed to 1 h of ischaemia during the anastomotic procedure followed by 1 h of reperfusion, were subjected to critical perfusion by stepwise reduction of the femoral-artery blood flow to 0.15 ml min(-1), 0.10 ml min(-1) and 0.05 ml min(-1). Pedicled osteomyocutaneous flaps that were not subjected to ischaemia (n=8) served as controls. In pedicled flaps critical perfusion induced capillary flow motion in the muscle, but not in the skin, subcutis and periosteum. In these flaps, the functional capillary density was preserved in all tissues analysed, including the skeletal muscle. Additional sympathetic denervation of the pedicled flaps did not change the incidence or pattern of capillary flow motion. In contrast, after flap transfer capillary flow motion in muscle tissue did not occur during critical perfusion. As a consequence, a shutdown of perfusion of individual capillaries was observed, resulting in a significant reduction (P<0.05) in functional capillary density, not only in the subcutis, skin and periosteum but also in the muscle itself. Thus, our data suggest that the microcirculatory control of pedicled osteomyocutaneous flaps is preserved during critical perfusion by skeletal-muscle capillary flow motion, whereas this protective regulatory mechanism is lost during the initial reperfusion period after flap transfer, probably not because of denervation but because of surgery- and/or ischaemia-reperfusion-associated injury.