Intraoperative measurement of cochlear microphonic (CM) caused by direct excitation of ossicles with transducer

Abstract

Cochlear microphonic (CM) is known to faithfully correspond to the frequency and level of sound pressure applied to the cochlea. If the CM is measured and compared before and after the treatment during an otologic surgery, the improvement of hearing of patients can be evaluated, and the risk of reoperation can be decreased. However, in some operations the sound transmission mechanism of the middle ear is temporarily disabled, and sound pressure cannot be applied to the cochlea with a speaker. In this study, a system for measuring the CM during surgery was constructed. The system consists of a vibration probe, electrodes, amplifier, and controller. The ossicles are vibrated by the vibration probe instead of sound from speaker, and the CM signals generated by the vibration are measured. The CM amplitude increased in proportion to the input voltage to the vibrator in the vibration probe as is the case with sound stimulation. This result suggests that the intraoperative assessment of improvement of hearing is possible by using the vibration probe.