An animal model to study microcirculatory changes associated with vascular delay.

Vascular delay is a surgical procedure that renders a flap partially ischaemic several days prior to its transfer in order to increase its viability after its transfer. Though much debate exists regarding the actual mechanism of vascular delay, most theories agree that changes in the microcirculation play a key role. In this paper, we describe four experiments that establish the ear of the homozygous (hr/hr) hairless mouse as an effective model for directly viewing and measuring delay-induced changes in microcirculation. In our first experiment, we compared mouse ears that were delayed (n = 18) with ones that were not (control) (n = 13) and showed that vascular delay significantly (P < 0.05) reduced ear flap necrosis. In a second experiment, we delayed mouse ears for 2 (n = 9), 4 (n = 14), 6 (n = 10), 8 (n = 10), 10 (n = 10), 20 (n = 18), 40 (n = 10) and 80 (n = 11) days and found that the reduction in necrosis becomes statistically significant (P < 0.05) over non-delayed controls (n = 12) after a minimum delay period of 6 days. In a third experiment, we delayed mouse ears by ligating only the vein (n = 14), only the artery (n = 11), only the nerve (sympathectomy) (n = 14), and vein, artery and nerve (n = 14) of the main neurovascular pedicle and found significant (P < 0.05) reductions in flap necrosis in all groups compared to nondelayed controls (n = 12). Finally, in a fourth experiment, we measured vessel directionality changes in mouse ears that were delayed for 6 (n = 4), 10 (n = 4), 20 (n = 4), 40 (n = 4) and 80 (n = 4) days, and found that directionality changes became significant (P < 0.05) at 6 days of delay and remained so for all the days studied when compared with non-delayed controls (n = 4).