か電図測定に関する臨床的研究

Abstract

Electrocochleography (EcochG) is a useful method of investigating electrophysiological changes of the inner ear. In this study, we analyzed the reliability and clinical usefulness of electrocochleography.1) Extratympanic EcochG was performed in 239 ears, and transtympanic EcochG was performed in 224 ears. The recordings were repeated 2 times in each subject. The reliability of absolute changes in the SP/AP ratio was +/-0.19 in extratympanic recording and +/-0.12 in transtympanic recording. There was no significant difference in the reliability in the various diseases tested. The reliability of the SP/AP ratio was high when SP and AP amplitudes were high, or when the SP/AP ratio was low.2) Changes in the SP/AP ratio were investigated after endolymphatic decompression by glycerol dehydration or endolymphatic sac surgery.Pure tone audiometry and extra- and trans-tympanic EcochG were performed in 44 subjects before and after glycerol dehydration. In the group which showed reduction of the SP/AP ratio, there was a high incidence of audiometric improvement. Among 16 hydropic ears, only 2 ears showed significant reduction of the SP/AP ratio. Among the non-hydropic ears, 4 ears showed reduction of SP/AP ratio after glycerol dehydration.Intra-operative EcochG monitoring was performed during endolymphatic sac surgery and/or tympanoplastic surgery in order to investigate changes in the SP/AP ratio. Only 1 patient showed a significant reduction of the SP/AP ratio during sac surgery. It should be emphasized that changes in the SP/AP ratio after making an incision in the endolymphatic sac were not always due to a change in the condition of the membranous labyrinth.