Pattern of hearing loss in a rat model of cochlear implantation trauma.
OBJECTIVE
Trauma caused by cochlear implant electrode insertion is attributable to the combination of direct physical trauma and the delayed cell death of oxidative stress-injured auditory sensory cells.


BACKGROUND
Histologic evaluation of cochlear implant electrode trauma has demonstrated that the extent of sensory cell losses is proportional to the degree of injury. However, the impact of delayed oxidative stress within injured cochlear tissues and the progressive loss of injured hair cells by way of apoptosis are at present unknown.


METHODS
Laboratory rats were evaluated for hearing acuity before and after electrode insertion, before and after round window membrane incision only. Hearing was measured before trauma or incision and over the next 7 days. Objective measurements of hearing function were distortion products of otoacoustic emissions (DPOAEs) in the frequency range of 2 to 32 kHz and tone-burst (i.e., 4-32 kHz) evoked auditory brain stem responses (ABRs).


RESULTS
For the experimental cochleae, there were progressive increases in ABR thresholds and decreases in ABR amplitudes. The amplitude of the DPOAEs in the experimental cochleae also showed progressive decreases. For the contralateral control and round window membrane surgical control ears, there were no significant changes in either DPOAE or ABR thresholds.


CONCLUSIONS
These results document a progressive loss of hearing acuity postimplantation and strongly suggest that electrode insertion trauma generated oxidative stress within injured cochlear tissues.
Eshraghi
Adrien A
AA
Department of Otolaryngology, University of Miami Leonard M. Miller School of Medicine, Miami, Florida, USA.
Polak
Marek
M
He
Jiao
J
Telischi
Fred F
FF
Balkany
Thomas J
TJ
Van De Water
Thomas R
TR
D000818:Animals; D001309:Auditory Threshold; D019929:Cochlear Implantation / Q000009:adverse effects*; D018450:Disease Progression; D007758:Ear, Inner / Q000293:injuries; D004567:Electrodes, Implanted / Q000009:adverse effects; D016057:Evoked Potentials, Auditory, Brain Stem; D006309:Hearing; D034381:Hearing Loss / Q000209:etiology* / Q000503:physiopathology; D017084:Otoacoustic Emissions, Spontaneous; D010469:Perceptual Distortion; D051381:Rats; D011916:Rats, Inbred F344; D014947:Wounds and Injuries / Q000209:etiology