Comparison of compound action potential audiograms with distortion product otoacoustic emissions in experimentally induced hydrops.

Endolymphatic hydrops was induced in a series of adult pigmented guinea pigs. Distortion product oto-acoustic emissions in general reflected the typical form of the hydropic compound action potential (CAP) audiogram, either with predominant low-frequency losses or a relatively flat audiogram. However, at certain two-tone combinations in some control ears the emissions could be smaller than expected from respective CAP audiograms, while in some hydropic ears the emissions could be larger than expected. The data presented here suggest that whilst the diagnostic value of distortion product emissions in the clinical situation might, at this time, be limited, the data from these emissions can give some insight into tonotopic hair cell function.