The effect of artery ligation and asphyxia on auditory evoked brain stem response

Auditory evoked brain stem response (ABR) was recorded in two groups of cats during artery ligation. Group A underwent bilateral ligation of the vertebral artery (V.A.) for 180 min after which bilateral ligation of the carotid artery (C.A.) was done. In group B animals, initially V.A. was bilaterally ligated and right C.A. was also ligated, then after the same period, left C.A. was additionally ligated. ABR changes were also observed under asphyxia induced by turning off the respirator. Ligation of V.A. bilaterally resulted in a trend toward prolongation of the ABR latencies (group A). Ligation of V.A. bilaterally and right C.A. resulted not only in a trend toward prolongation of the latencies, but also in an increase in the amplitude in wave III and V (group B). Asphyxia caused more rapid and remarkable changes in ABR than artery ligation. After the onset of asphyxia, temporary increase in the amplitude was observed before the waves deteriorated. ABR is affected by changes of the blood flow and asphixic condition. ABR changes possibly depend on the development of the collateral vessels, vasodilation effect, or increase in blood pressure after artery obstruction or sustained asphyxia.