Distortion-product otoacoustic emissions in experimentally induced hydropic ears

The postoperative changes of distortion-product otoacoustic emissions (DPOAEs) and cochlear potentials were examined using 15 albino guinea pigs in which endolymphatic hydrops was induced by obliterating the endolymphatic sac. DPOAEs (geometric mean: 4,6 and 8 kHz) were measured once before and every week after surgery. At the 2nd (n = 5), 4th (n = 5) and 12th (n = 5) postoperative weeks, endocochlear potential (EP) and compound action potential (CAP) were measured. Although the reduction in DPOAEs at 8 kHz was first detected at the 12th week, the amplitude of DPOAEs at 4 and 6 kHz was already reduced at the first week and decreased gradually thereafter. In contrast to these results, the CAP threshold was not elevated at the 2nd week and a slight increase was first detected at the 4th week. The results obtained in the present study suggest that DPOAEs are more sensitive than CAP in detecting the presence of hydrops.