Temporary Arterial Obstruction: Effect on Perilymph Oxygen and Microphonics

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.

Control mechanisms of inner ear microcirculation

Some disease processes, drugs, and noise are said to produce vascular disorders of the inner ear, and in some instances changes in the capillaries have been observed during histologic examination of the temporal bones. Consequently the ability to control the circulation is important because of its therapeutic implications. This brief review points out the areas of conflicting experimental evidence and some of the factors that may be responsible for the variations.

Oxygen reserve and autoregulation in the cochlea

Endolymphatic O2-concentration was measured in the guinea pig cochlea with a microelectrode inserted through the zona pectinata of the basilar membrane and the cells of Claudius, so as not to interfere with the blood supply to the organ of Corti. The O2-level and the amplitude of the cochlear potentials were followed during hypoxia produced by lowering the pO2 of the inspired air. Persistence of a normal endolymphatic O2-level following the fall in arterial pO2 indicated an O2-reserve and au autoregulation of the cochlear circulation.