Dependence of traumatic vasospasm on blood flow in the central artery of the ear in rabbits.

The effect of total obstruction of blood flow on traumatically induced vasospasm was studied in the central arteries of rabbits' ears. All side branches were ligated along a 7 cm segment of the artery. Obstruction of blood flow was achieved by ligation of the central artery distal to this segment. The inner diameter of the artery was measured microscopically after transillumination. A standardised injury was induced with a clip applying forceps. The duration, intensity (reduction of diameter) and severity (integrated change in diameter over time) of the resulting spasm were assessed. Spasm induced after cessation of blood flow lasted significantly less time (mean (SEM), 6.0 (2.0) minutes compared with 18.1 (2.5) min) and was less severe than spasm induced when the blood flow was intact (1.6 (0.6) mm/min compared with 6.2 (0.6) mm/min). The results may be explained by local accumulation of vasodilating substances in the injured segment of the vessel in the absence of blood flow.