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[Otoacoustic emissions and recruitment].
Wiesław Konopka1, Jurek Olszewski
1Zakład Diagnostyki Audiologicznej i Elektrofizjologicznej Katedry Chirurgii Głowy i Szyi Uniwersytetu Medycznego.
Otolaryngologia Polska = the Polish Otolaryngology
|February 14, 2006
Summary
Otoacoustic emissions may detect loudness recruitment in cochlear hearing loss. This study found that DPOAE input/output function slopes differed significantly in patients with cochlear lesions after noise exposure, suggesting a potential diagnostic tool.
Area of Science:
- Audiology
- Otoacoustic Emissions
- Hearing Loss Research
Background:
- Typical high-frequency hearing loss involves loudness recruitment, an exaggerated response to sound above elevated thresholds, often linked to cochlear damage.
- Loudness recruitment, measurable by the Short Increment Sensitivity Index (SISI), is a paradoxical phenomenon in cochlear hearing loss.
- Otoacoustic emissions (OAEs) are proposed as a sensitive method for assessing cochlear changes from noise exposure, potentially more so than pure-tone audiometry.
Purpose of the Study:
- To compare the Short Increment Sensitivity Index (SISI) test, Distortion Product Otoacoustic Emissions (DPOAEs), and DPOAE input/output (I/O) function slopes before and after noise exposure.
- To investigate the sensitivity of DPOAEs in detecting cochlear changes and loudness recruitment compared to traditional audiometric measures.
Main Methods:
- The study compared SISI, DPOAE amplitude, and DPOAE I/O function slopes in 30 ears with cochlear lesions from 40 patients (aged 18-21) before and after noise exposure.
- DPOAE I/O functions were plotted by measuring DPOAE amplitude against increasing primary tone levels (45-70 dB SPL) at frequencies of 1, 2, 3, 4, 6, and 8 kHz.
Main Results:
- Both pure-tone audiometry (PTA) and DPOAE amplitudes significantly decreased after noise exposure in the group with cochlear lesions.
- DPOAE I/O function slopes varied with stimulus levels; amplitudes were reduced at low levels (45-55 dB SPL) but increased above 55 dB SPL compared to pre-exposure.
- These noise-induced changes in DPOAE I/O function slopes were not observed in individuals without cochlear lesions.
Conclusions:
- In patients with cochlear lesions, DPOAE input/output amplitude was elevated at stimulus levels above 55 dB SPL post-noise exposure.
- This observed phenomenon suggests that otoacoustic emissions may reflect loudness recruitment, offering a potential method for its assessment in cochlear hearing loss.