ORIGINAL ARTICLES   

Otorinolaringologia 1999 September;49(3):125-30

Copyright © 2000 EDIZIONI MINERVA MEDICA

language: Italian

Distorsion products modifications after acoustic overload

Albera R., Giordano L., Rosso P., Ricca G., Ferrero V.

Università degli Studi - Torino Dipartimento di Fisiopatologia Clinica II Sezione di ORL

Background. Distorsion product otoacoustic emission (DPOAEs) are actually considered to represent the active process of cochlear outer hair cells and can be applied as a useful, objective and non-invasive test to evaluate the cochlear function. A possible field of application of this test is the determination of infraclinical noise induced cochlear suffering in order to identify subjects more sensible to noise damage.
Aim of the study. The authors’ aim is to evaluate the DPOAEs amplitude modifications after white noise exposure without any audiometric measurable threshold shift.
Methods. Forty normally hearing volunteeers were submitted to the test. Each subject was submitted to the following protocol in 4 different days. Pure tone audiometry (PTA) and DPOAEs recording at 4 KHz without any acoustic stimulation; PTA and DPOAEs recording pre and after 5’ 90 dB white noise acoustic stimulation; PTA and DPOAEs recording pre and after 5’ 100 dB white noise acoustic stimulation; PTA and DPOAEs recording without any acoustic stimulation.
Results. After acoustic stimulation no PTA worsening was obtained except at 6 KHz. After acoustic overload, DPOAEs at 4 KHz were reduced in amplitude in 24 subjects and increased in 10. In 6 cases the pattern was not regular.
Conclusion. The study shows that after acoustic overload two possible DPOAEs modifications can be recorded. One group of subjects shows a reduction of DPOAEs amplitude demonstrating an outer hair cells suffering while in a second group the response is characterized by an increasing of DPOAEs amplitude as the consequence of a selective damage of efferent cochlear system that could precede outer hair cell suffering. Further studies are necessary to correlate this different pattern of DPOAEs answer to acoustic overload with noise induced hearing loss susceptibility.