Since the discovery of distortion product otoacoustic emissions (DPOAE) there has been a controversial discussion about their cochlear generation sites. Suppression experiments suggest that the place near f2 is the main generation site. On the other hand, the fact that DPOAE can be perceived subjectively indicates that there is also a cochlear excitation at the place of 2f1−f2 resulting in a stimulus frequency otoacoustic emission (SFOAE). The contribution of this SFOAE to the overall emission is still unknown. Different studies showed contradictory results. We demonstrate a secondary generator by successive suppression of the SFOAE with a sine wave close to the frequency 2f1−f2. Suppression growth functions (SGF) showed a three-step behavior. For low suppressor levels, the emission either decreased or increased when increasing the suppressor. For intermediate suppressor levels, DP amplitude was constant and independant of suppressor level. For high suppressor levels, the emission always decreased with further increase of the suppressor. The behavior of the SGF in the first section depends on the fine structure of the DP-gram, which shows minima and maxima. Emissions at a maximum decreased while emissions at a minimum increased in the first section of the SGF. We conclude that the fine structure of the DP-gram is produced by alternate constructive and destructive interference of the two generators. By adding a third tone near 2f1−f2 the SFOAE and thus the interference are suppressed. The fine structure of the DP-gram vanishes and the resulting DP-gram should be more closely related to the cochlear status near f2.

There is strong evidence for a link between intact cochlear function and otoacoustic emissions (OAE). However, all attempts to find a close correlation between auditory thresholds and amplitudes of distortion product otoacoustic emissions (DPOAE) have failed. As an explanation for these findings, we have studied DPOAE fine structure and its dependence on increasing primary sound levels. Errors due to different calibrations of equipment for measuring DPOAE and auditory thresholds were also investigated. DPOAE were measured in 16 subjects using a frequency range of 500-1000 Hz. Frequencies were changed in 12.5 Hz steps at primary levels of 55, 60, 65 and 70 dB SPL. DPOAE amplitudes were found to vary by up to 20 dB for a frequency step of 50 Hz. Some fine structures showed narrow dips that shifted in frequency and diminished in amplitude with increasing primary levels. These findings demonstrated that sampling DPOAE amplitudes at widely spaced frequencies gave incomplete information about true course. DPOAE growth functions measured close to a dip in the DPOAE fine structure were rendered useless by interference with either the frequency shift or amplitude variations of the dip at different primary levels.

Today, the standard method to predict output levels of active middle ear implants (AMEIs) before clinical data are available is stapes vibration measurement in human cadaveric ears, according to ASTM standard F2504-05. Although this procedure is well established, the validity of the predicted output levels has never been demonstrated clinically. Furthermore, this procedure requires a mobile and visually accessible stapes and an AMEI stimulating the ossicular chain. Thus, an alternative method is needed to quantify the output level of AMEIs in all other stimulation modes, e.g. reverse stimulation of the round window. Intracochlear pressure difference (ICPD) is a good candidate for such a method as it correlates with evoked potentials in animals and it is measurable in cadaveric ears. To validate this method we correlated AMEI output levels calculated from ICPD and from stapes vibration in cadaveric ears with outputs levels determined from clinical data. Output levels calculated from ICPD were similar to output levels calculated from stapes vibration and almost identical to clinical data. Our results demonstrate that both ICPD and stapes vibration can be used as a measure to predict AMEI clinical output levels in cadaveric ears and that ICPD as reference provided even more accurate results.

Objective:The purpose of the present study was to determine the fraction of patients with mixed hearing loss who can or cannot expect benefit from power hearing aids (HAs) after stapes surgery. Design: The audiological outcome of 374 stapes surgeries was used to calculate the patients' individual postoperative requirements in terms of gain and output of HAs. These requirements were compared to the available gain and output provided by state-of-the-art power HAs at 0.5, 1.0, 2.0, and 4.0 kHz. According to these comparisons, ears were divided into three groups. For G0, required gain and output lay within the corresponding technical limits of the HAs at all frequencies. In G1, one or both requirements could not be fulfilled at 1 frequency. G2 combined all ears where the requirements lay beyond the HA's technical limitations at 2 or more frequencies. Results: Stapes surgery resulted in an improvement of air-bone gap (ABG) in 84.5% of the cases by 15.7 dB on average. Based on pure-tone average (0.5, 1.0, 2.0, 4.0 kHz), 40.6% of all cases showed an ABG ≤10 dB. 44.9% of all cases did no longer need a HA after stapes surgery. A power HA would fulfill both audiological criteria at all 4 frequencies in 81.6% of cases that needed a HA postoperatively. However, 18.4% would not be sufficiently treatable at 1 or more frequencies (15.0% in G1, 3.4% in G2). Conclusions:The present study identified a subset of patients with mixed hearing loss after stapes surgery that cannot be treated sufficiently with available power HAs. As the residual ABG is an important reason for this lack of treatment success, the advancement of alternative hearing devices that circumvent the middle ear, such as powerful active middle ear implants, is indicated.

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