Prospective electrophysiologic findings of round window stimulation in a model of experimentally induced stapes fixation.
OBJECTIVE
Mechanical stimulation of the round window (RW) with an active middle ear implant (AMEI) with and without experimentally induced stapes fixation (SF) results in equivalent electrophysiologic measures of cochlear microphonic (CM), compound action potential (CAP), and auditory brainstem response (ABR).


BACKGROUND
Where normal oval window functionality is mitigated, the RW provides a pathway to mechanically stimulate the inner ear.


METHODS
Measurements of the CM, CAP, and ABR were made in 5 ears of 4 chinchillas with acoustic stimulation and with application of the AMEI to the RW with and without experimentally induced SF using pure-tone stimuli (0.25-20 kHz) presented at differing intensities (-20 to 80 dB SPL vs. 0.01 mV to 3.16 V).


RESULTS
Morphologies of the CM, CAP, and ABR were similar between acoustic and RW stimulation with and without SF. Stapes fixation increased CM thresholds relative to RW stimulation without fixation by a frequency-dependent 4- to 13-dB mV (mean, 7.9 +/- 3.2 dB mV). Although the thresholds changed with SF, CM sensitivities and amplitude dynamic range were identical to normal. The CAP in all conditions demonstrated equivalent decreasing amplitudes and increasing latency with decreasing intensity (decibel sound pressure level versus decibel millivolt). Stapes fixation increased the CAP thresholds at all frequencies, ranging from 9 to 24 dB mV (mean, 17.7 +/- 4.9 dB mV). Auditory brainstem response waveforms were preserved across experimental conditions.


CONCLUSIONS
Mechanical stimulation of the RW in an animal model of SF generates functionally similar inputs to the cochlea as normal acoustic and RW mechanical inputs but with increased thresholds. With further study, AMEIs may provide a surgical option for correction of otosclerosis and ossicular chain disruption.
Department of Otolaryngology, University of Colorado Denver School of Medicine, Aurora, Colorado, USA. james.lupo@ucdenver.edu
J Eric
JE
Lupo
Kanthaiah
K
Koka
N Julian
NJ
Holland
Herman A
HA
Jenkins
Daniel J
DJ
Tollin
D000161:Acoustic Stimulation; D000818:Animals; D001300:Audiometry, Evoked Response; D001306:Auditory Pathways / Q000502:physiology; D002138:Calibration; D002682:Chinchilla; D003055:Cochlear Microphonic Potentials / Q000502:physiology; D007758:Ear, Inner / Q000502:physiology; D004594:Electrophysiology; D005071:Evoked Potentials / Q000502:physiology; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D005260:Female; D017078:Laser-Doppler Flowmetry; D008297:Male; D008954:Models, Biological; D009998:Ossicular Prosthesis; D011817:Rabbits; D012405:Round Window, Ear / Q000502:physiology*; D013136:Spiral Ganglion / Q000503:physiopathology; D013199:Stapes / Q000502:physiology*; D013201:Stapes Surgery