The effect of hypoxia on electrical activity of the visual system in cats.

Abstract

During the progressive induction of hypoxia in cats, there occurred small but variable increases in latency of evoked potentials from the retina (ERG), the optic chiasm, the superior colliculus (stratum intermedium) and the visual cerebral cortex. Large and quite variable decreases in the amplitude of these potentials and a simplification of originally complex waveforms occurred along with associated loss of secondary potentials.Spontaneous electrical activity first was enhanced, then fell off precipitously as the blood oxygen saturation dropped to 30%. After 10 to 15 minutes on reduced inspired oxygen tension, high amplitude spindle-burst activity was observed until the activity became isoelectric. Loss of the slow activity occurred of ter about 10 minutes under hypoxia. During recovery from hypoxia, the slow activity reappeared for a brief time as well as the spindle-burst activity. As the fast spontaneous activity approached the pre-hypoxia amplitude levels, both spindling and slow activity disappeared.When these results were compared to previous data collected under hypothermic conditions, the effects were quite different. In the case of hypoxia there is a lack of available oxygen at the neural tissue level ; in the case of hypothermia, the neuronal metabolism is reduced by the gradual blocking of intracellular enzyme systems by cold even though adequate oxygen in the blood is available.