Hirohide Osawa

Electrocochleographic Study of Low-Tone Hearing Loss without Vertigo

Auditory nerve action potential (AP), cochlear microphonics (CM) and summating potential (SP) were recorded from 6 patients with low-tone hearing loss without vertigo. All these cases showed high AP and -SP amplitude and satisfactory CM response. These findings resembled the electrocochleographic findings of type 1, which is an early stage of Ménières disease. Hearing returned to normal range in half of the cases but remained hardly changed in the other half. The difference between these two groups could not be clarified electrocochleographically. On the other hand, low-tone hearing loss due to retrolabyrinthine lesion and due to familial sensorineural deafness was shown to have a low AP amplitude.

Electrocochleographic Studies of Recruitment Phenomenon

Electrocochleography by the tympanic electrode technique was performed on 37 ears of positive recruitment phenomenon and 10 ears of negative recuitment, totalling 47 ears, and the following results were obtained. The positive recruitment phenomenon was understood to be observed in cases wherein the auditory nerve action potential (AP) shows a steep increment, and where the AP output potnetial at intensive sound stimulation is equal to or higher than normal level. The recruitment phenomenon was positive in cases of dominant negative summating potential (dominant — SP) even if the AP output potential was low. The negative recruitment phenomenon was observed mostly in cases wherein the AP output potential was much lower than normal level even at stimulation of intensive sound pressure, and where the —SP was lower than normal level. Even though clinical EcoG is recorded from the promontory, the —SP seems to play an important role in increasing the AP output potential, in other words, causing recruitment phenomena.