The Time Sequence of the Delay Phenomenon

We have shown previously that when a flap is delayed, the maximal anatomic effect on the arterial side of the circulation is focused at the level of the reduced-caliber choke vessels that link adjacent vascular territories. These anastomotic vessels were noted to increase in size to the dimension of true anastomoses. However, we did not define when this occurred. The present experiment therefore was designed to elucidate the chronologic sequence of events that occur in the “choke” vessels using a rabbit flank skin flap as the experimental model. A long two-territory osteocutaneous flank flap was designed on one side of each rabbit (n = 30), with the opposite unoperated side serving as a control. The flap was elevated and sutured back in place. At various times postoperatively, namely, 1 (n = 2), 2 (n = 2), 3 (n = 2), 4 (n = 2), 6 (n = 2), 8 (n = 2), 12 (n = 2), 24 (n = 2), 48 (n = 2), and 72 (n = 2) hours and 7 days (n = 10), the animals were sacrificed, and total-body arteriograms were obtained using a lead oxide mixture. The density and size of the choke arteries between the territories in the flap and their counterparts on the control side were assessed by histologic analysis (n = 3). We observed a sequential dilation of choke vessels during the delay period. In particular, we found that the vessels increased rapidly in size between the 48− and 72-hour studies. Histologic analysis revealed an increase in the diameter of the choke vessels and a decrease in vessel wall thickness compared with the contralateral control vessels. We conclude from these findings that the increase in viability and blood flow previously noted in delayed flaps is due primarily to the increase in the caliber of choke vessels between adjacent vascular territories, which has its maximal effect between 48 and 72 hours in the skin of the rabbit.