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Review
. 2017 Aug;65(Suppl 2):122-129.
doi: 10.1007/s00106-016-0267-y.

Objective audiometry with DPOAEs : New findings for generation mechanisms and clinical applications

D Zelle  1 , E Dalhoff  1 , A W Gummer  2
Affiliations
Review

Objective audiometry with DPOAEs : New findings for generation mechanisms and clinical applications

D Zelle et al. HNO. 2017 Aug.

Abstract

Background: Distortion product otoacoustic emissions (DPOAEs) and transient-evoked otoacoustic emissions (TEOAEs) are sound waves generated as byproducts of the cochlear amplifier. These are measurable in the auditory canal and represent an objective method for diagnosing functional disorders of the inner ear. Conventional DPOAE and TEOAE methods permit detection of hearing impairment, but with less than desirable accuracy.

Objective: By accounting for DPOAE generation mechanisms, the aim is to improve the accuracy of inner-ear diagnosis.

Methods: DPOAEs consist of two components, which emerge at different positions along the cochlea and which may cause artifacts due to mutual interference. Here, the two components are separated in the time domain using short stimulus pulses. Optimized stimulus levels facilitate the acquisition of DPOAEs with maximum amplitudes. DPOAE and Békésy audiograms were recorded from 41 subjects in a clinically relevant frequency range of 1.5-6 kHz.

Results: The short stimulus pulses allowed artifact-free measurement of DPOAEs. Semilogarithmic input-output functions yielded estimated distortion product thresholds, which were significantly correlated with the subjectively acquired Békésy thresholds. In addition, they allowed detection of hearing impairment from 20 dB HL, with 95% sensitivity and only a 5% false-positive rate. This accuracy was achieved with a measurement time of about 1-2 min per frequency.

Conclusion: Compared to conventional DPOAE and TEOAE methods, separation of DPOAE components using short-pulse DPOAEs in combination with optimized stimulus parameters considerably enhances the accuracy of DPOAEs for diagnosing impairment of the cochlear amplifier.

Keywords: Acoustic stimulation; Auditory threshold; Cochlear amplifier; Hearing; Hearing loss.

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Conflict of interest statement

D. Zelle, E. Dalhoff, and A. W. Gummer declare that they have no competing interests.

The supplement containing this article is not sponsored by industry.

Patient rights. All experiments conducted on humans were performed under permission of the appropriate Ethics’ Committee of the University of Tübingen, in accordance with national laws and the Declaration of Helsinki from 1975 (current, revised version). Informed consent in written form was provided by all subjects.

Figures

Fig. 1
Fig. 1
DPOAE acquisition for direct assessment of the functional integrity of the cochlear amplifier in the human auditory system. DPOAE distortion-product otoacoustic emissions, IHC inner hair cells, OHC outer hair cells
Fig. 2
Fig. 2
Short-pulse stimulation of the cochlea for separating DPOAE components into time and phase signals. a The two stimulus tones at frequencies f1 (30 ms pulsed, “quasi-continuous”) and f2 (“short-pulsed”). b Time signals. Gray line measured time signal. Dark red dashed line envelope of the calculated nonlinear distortion component, p1(t). Light red dashed line envelope of the calculated coherent reflection component, p2(t). Black line envelope of the calculated DPOAE signal, p1(t) + p2(t). Relative to the start of the f2-pulse, p1(t) is delayed by τ1 and p2(t) by τ2. c Phase signals. Gray line measured phase signal. Black line phase signal of the calculated DPOAE signal, p1(t) + p2(t). d Generation of the DPOAE source components. Envelopes of the traveling waves of the tones as function of distance from the basal end of the basilar membrane (BM), xBM. Dark blue line: f2-tone. Light blue line: f1-tone. Red dashed line fDP-tone. p1(t) is generated near the maximum of the traveling-wave envelope of the f2-tone and p2(t) near the envelope maximum of the fDP-tone. DPOAE distortion-product otoacoustic emissions
Fig. 3
Fig. 3
Time-domain representation of short-pulse DPOAEs for constructive (a, b) and destructive (d, e) interference, and corresponding amplitude spectra recorded with conventional continuous stimuli (c, f). Red circles indicate the spectral components at fDP = 2f1-f2
Fig. 4
Fig. 4
High-resolution DP-grams (a) and corresponding low-resolution (conventional) DP-grams (b) for a normal-hearing subject. Red circles indicate examples of frequencies (f2) at which destructive, constructive, and quadrature interference were observed. DPOAE distortion-product otoacoustic emissions
Fig. 5
Fig. 5
Level maps for determining optimal DPOAE stimulus levels, individually for each stimulus-frequency pair and subject. The linear equations give the optimal L1 value for a given L2 value, called the “individual optimum”, L1,ind
Fig. 6
Fig. 6
a Békésy threshold as a function of estimated DPOAE threshold (EDPT) for 41 subjects with normal hearing and sensorineural hearing loss. b ROC curves for the detection of hearing loss using short-pulse DPOAEs (solid lines) in comparison with conventional DPOAE and TEOAE methods (dashed lines). DPOAE distortion-product otoacoustic emissions, TEOAE transient-evoked otoacoustic emissions
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