THE TIME SEQUENCE OF THE DELAY PHENOMENON - WHEN IS A SURGICAL DELAY EFFECTIVE - AN EXPERIMENTAL-STUDY

We have shown previously that when a flap is delayed, the maximal anat omic 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 eluci date the chronologic sequence of events that occur in the ''choke'' ve ssels using a rabbit flank skin flap as the experimental model. A long two-territory osteocutaneous flank flap was designed on one side of e ach rabbit (n = 30), with the opposite unoperated side serving as a co ntrol. The flap was elevated and sutured back in place. At various tim es 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 densi ty and size of the choke arteries between the territories in the nap a nd their counterparts on the control side were assessed by histologic analysis (n = 3). We observed a sequential dilation of choke vessels d uring the delay period. In particular, we found that the vessels incre ased rapidly in size between the 48- and 72-hour studies. Histologic a nalysis revealed an increase in the diameter of the choke vessels and a decrease in vessel wall thickness compared with the contralateral co ntrol vessels. We conclude from these findings that the increase in vi ability and blood flow previously noted in delayed flaps is due primar ily to the increase in the caliber of choke vessels between adjacent v ascular territories, which has its maximal effect between 48 and 72 ho urs in the skin of the rabbit.