[Enlarged and prolongated cochlear microphonics and its clinical significance]

Bilateral cochlear microphonics (CM) were evoked by tone burst simultaneously. A speaker was put in head-foot axis 2m from the mid-point of a given line connecting the bilateral external meatus. Seven normal persons and 106 cases of unilateral sensory hearing loss and recruitment were examined. When recruitment was present, CM at corresponding frequencies were enlarged and prolongated. In 62 cases CM delayed slowly, while other 27 cases quickly. In addition to 2 cases of bilateral Ménière disease with sensory hearing loss and recruitment, CM were enlarged and prolongated at some frequencies in left ears and at other frequencies in right ears in accordance with predominant recruitment. Meanwhile CM of the opposite normal ear decreased obviously. CM could not be evoked from profound and totally deaf ears.