Electrocochleography in the presence and absence of perilymphatic fistula

The purpose of the present study was to evaluate the effect of an acute perilymphatic fistula on the amplitude ratio (SP/AP) of the summating potential (SP) and action potential (AP). The effect of the acute fistula on AP threshold was also addressed. Electrocochleographic recordings were obtained before and immediately after surgical laceration of the round window membrane in 19 guinea pigs. Stimuli comprised clicks and 2,000-Hz and 8,000-Hz tone bursts, presented initially at 100 dB peak equivalent sound pressure level and in descending 10-dB steps. After fistula induction the SP/AP significantly increased for the click and 8,000-Hz tone burst stimuli but not for the 2,000-Hz tone burst stimuli. No significant change in AP threshold occurred. These findings suggest that the SP/AP may be sensitive to perilymphatic fistula, at least in guinea pigs. The changes in the SP/AP do not appear to be related to changes in threshold.