Distortion product otoacoustic emissions - a tool for assessing the non-linear sound amplification of the ear

摘要

Otoacoustic emissions are a by-product of the non-linear sound amplification of outer hair cells (OHCs) in the cochlea, referred to as the cochlear amplifier (CA), and can be measured non-invasively by means of a microphone in the outer ear canal. Distortion product otoacoustic emissions (DPOAEs) represent cubic distortions of OHCs when stimulated simultaneously by two tones. DPOAEs provide quantitative information about the range and operational characteristics of the CA, i.e., sensitivity, compression, and tuning. The purpose is to show how DPOAEs work in a clinical context and what they are able to achieve in clinical diagnostics.There are several DPOAE measures that are used for assessing the functioning of the CA: DPOAE grams which give information about the fine structure of the behavioural pure-tone thresholds, DPOAE pressure I/O-functions that allow to estimate loss of sensitivity and loss of compression (recruitment), DPOAE iso-suppression tuning curves reflecting frequency selectivity, ipsilateral DPOAE adaptation and contralateral suppression for evaluating the reflex strength of the efferent hearing system which controls OHC motility.The main clinical applications of the DPOAE measures are: topological diagnostics, early detection of OHC impairment during noise exposure or ototoxic drug administration, frequency-specific and quantitative assessment of hearing loss and recruitment, especially in infants in which subjective audiometric tests fail to quantitatively determine cochlear dysfunction. Providing hearing-aid fitting parameters and prediction of cochlear vulnerability to acoustic overexposure are potential applications in the future.