Evoked otoacoustic emissions: A comparison between responses from humans and guinea pigs

Transiently evoked otoacoustic emissions (TEOAEs) from 16 normal human ears and 26 normal guinea pig ears were measured with the ILO 88 (ver 3.91). The following results were obtained: 1) In one animal ear, waveforms of TEOAEs were unchanged after administration of muscle relaxants, and showed reversible changes before and after asphyxia. 2) In 3 guinea pig and 2 human ears, the input-output functions showed a strong saturation at higher stimulus levels, when measurement of the highest peak-to-peak amplitude was used as the output energy. 3) Highest peak frequencies (HPFs) of TEOAEs were distributed at around 1 kHz in human ears but were concentrated around frequencies of 2 kHz to 3 kHz in almost all guinea pig ears. 4) Latencies of predominant TEOAEs in human and guinea pig ears were 9.26±1.89 msec and 2.37±0.47 msec, respectively. Endpoint times of TEOAEs were 16.37±1.79 msec and 5.74±1.10 msec, respectively. Both indicators in human ears were 3-4 times longer than those in guinea pig ears. From these results, we conclude that click-evoked TEOAEs can be detected even in guinea pigs. In addition, our measurements showed that HPFs of TEOAEs in guinea pig ears were higher than those in human ears, and that latencies and durations in guinea pig ears were much shorter than those in human ears. The higher HPFs of TEOAEs in guinea pig ears may be attributable to higher resonant frequencies in the middle ear than are found in human ears. The short latencies of TEOAEs in guinea pig ears may be related to travel time through the guinea pig basilar membranes.