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Validity of cochlear microphonics at high sound pressure levels as an important clinical aspect
M Teschner1, T Lenarz, R-D Battmer
1Department of Otolaryngology, Medical University of Hannover, Carl Neuberg Strasse 1, Hannover, Germany. teschner.magnus@mh-hannover.de
Introduction:
Cochlear microphonics are electrical stimulus responses of the inner ear, generated by mechanical displacement of the hair cells caused by acoustic stimulation. As cochlear microphonics are often used in the diagnosis of hearing impairment and deafness, in preliminary investigations it was seen that obliteration or ossification have no effect on the extent to which cochlear microphonics can be recorded at high sound pressure levels. As artifacts at high sound pressure levels suggested, measurements were subsequently conducted using temporal bone specimens.
Methods:
In a test setup equivalent to that for electrocochleography, a needle electrode was placed on the cochlear promontory and used to record potentials following application of an acoustic stimulus.
Results:
Curves comparable to cochlear microphonics were registrable down to a threshold of 80 dB HL. Additional measurements conducted on damp cloths yielded comparable findings.
Conclusions:
Registration of cochlear microphonics at high sound pressure levels does not serve as an indicator of hair cell function, but should instead be regarded as artifacts. The possible sources are discussed.
Insights
Cochlear microphonics recorded at high sound pressure levels are not indicators of hair cell function but are artifacts. These findings suggest re-evaluating their diagnostic use in hearing impairment.
Area of Science:
- Otoacoustic Emissions
- Auditory Electrophysiology
Background:
- Cochlear microphonics (CM) are electrical responses from inner ear hair cells to acoustic stimuli.
- CM are utilized in diagnosing hearing impairment and deafness.
- Preliminary studies indicated ossification/obliteration did not affect CM recording at high sound pressure levels.
Purpose of the Study:
- To investigate the nature of cochlear microphonics recorded at high sound pressure levels.
- To determine if high-level CM recordings reflect hair cell function.
Main Methods:
- A needle electrode recorded potentials from the cochlear promontory.
- Stimulation and recording setup mimicked electrocochleography.
- Measurements were performed on temporal bone specimens.
Main Results:
- CM-like potentials were recorded down to 80 dB HL.
- Similar findings were observed using damp cloths, suggesting non-biological origins.
- Artifacts were suspected at high sound pressure levels.
Conclusions:
- High-level cochlear microphonics are artifacts, not indicators of hair cell function.
- The diagnostic utility of CM at high sound pressure levels is questionable.
- Potential sources of these artifacts are discussed.
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