[Electrically evoked otoacoustic emissions and their distortion products in guinea pigs]

The objective of this study was to investigate micromechanical properties and electromotility of cochlear outer hair cells in vivo. Extracochlear electrically stimulation with sinusoid alternating current was delivered to cochlea of guinea pigs. Sound pressure level was recorded from ear canal by microphone and the electrically evoked otoacoustic emissions (EEOE) and their distortion products (DPEEOE) were analyzed with FFT spectrum analyzer. The EEOE in 3 kHz to 33 kHz were recorded from 15 guinea-pigs in 18 guinea-pigs, the transfer function was more smooth in 8 kHz to 31 kHz. The DP EEOE were very clear when F1 = 6 kHz, F2 = 7.2 kHz, and the current intensity higher than 100 microA. While the intensity increased to 300 microA, two distortion products, F2-F1 and 2(2F1-F2)-F1, could be seen in addition to 2F1-F2. The input-output function showed that EEOE and DP EEOE I/O function were linear when lower electric intensity stimulation was given, but they displayed compress non-linear features when higher intensity current was delivered. The authors conclude that EEOE and DP EEOE are expression of electrophonic hearing characteriged by wide frequency bandpass appearance, wide dynamic range and non-linear features, so they are good tools for studying the mechanical properties of outer hair cells and the integrate function of Corti's organ.