[Experimental research on delayed responses in cochlear microphonics records in guinea pigs].
Clinical application of evoked otoacoustic emissions (EOAEs) is expected to serve as an objective indicator of inner ear function. Delayed extra waves (delayed responses) from human cochlear microphonics (CMs) have been observed and they appear to be electrical correlates of EOAEs. Delayed responses must be examined for their relation to EOAEs in animal experiments before clinical application. The present experiment was performed to elucidate the relationship between delayed responses and the EOAEs in guinea pigs. Delayed responses to weak sound stimuli were recorded from the round window and from the scala media. The second waves, which corresponded to CMs, were compared with the fourth or fifth waves. The input-output curves of the fifth waves saturated earlier and crossed the curves of the second waves. Both the second wave and the fifth wave decreased in anoxia, but their time course of amplitude changes in anoxia were different. EOAEs peaked between 2.5 kHz and 3.5 kHz in the frequency distribution. The EOAEs also were anoxia-sensitive, corresponding to changes in the CMs and the delayed responses in the time course of anoxia. The results of the present experiment demonstrate that the delayed responses were electrical correlates of the EOAEs. EOAEs are believed to represent energy leaks to the external and middle ear from intracochlear micromechanics linked to retrograde transduction mechanism of the outer hair cells. This was supported by the relationship between the delayed responses from the CMs and the EOAEs. The EOAEs and delayed responses may serve as tools for application in clinical testing as acoustical and electrical indicators of intracochlear micromechanical function.
Maseki
M
M
Department of Otolaryngology, Dokkyo University School of Medicine Koshigaya Hospital, Saitama.
D000818:Animals; D003051:Cochlea / Q000502:physiology; D003055:Cochlear Microphonic Potentials; D006168:Guinea Pigs; D006801:Humans; D017084:Otoacoustic Emissions, Spontaneous; D011930:Reaction Time / Q000502:physiology