[New options for rehabilitation of conductive hearing loss : Tests on normal-hearing subjects with simulated hearing loss]. / Neue Möglichkeiten der Rehabilitation bei Schallleitungsschwerhörigkeit : Tests an normalhörenden Probanden mit simulierter Schwerhörigkeit.

BACKGROUND: Bone conduction hearing aids can be worn as noninvasive devices using a clip or soft band that exerts pressure on the skin, or they can be surgically implanted. ADHEAR (MED-EL GmbH, Innsbruck, Austria) is a novel noninvasive bone conduction hearing aid that is attached behind the ear using an adhesive adapter and does not exert pressure on the skin. ADHEAR is indicated for patients with conductive hearing loss and normal inner ear function. The aim of this study was to evaluate the achievable hearing improvement with ADHEAR. MATERIALS AND METHODS: Twelve subjects with normal hearing participated in this study. To mimic conductive hearing loss, the participants' ear canals were occluded unilaterally with a foam ear plug. The resultant conductive hearing loss was assessed with pure tone air- and bone-conduction threshold audiometry. Hearing ability was tested with and without ADHEAR via free-field tone audiometry, number perception, and monosyllable perception, with the contralateral ear plugged depending on test requirements. RESULTS: Using ADHEAR, the free-field hearing threshold improved by 13.7 dB at 500 Hz, by 17.9 dB at 1 kHz, by 17.2 dB at 2 kHz, and by 9.8 dB at 4 kHz. In the higher frequencies, a significant pure-tone gain of 14.4 dB at 6 kHz and of 16.5 dB at 8 kHz was observed. Number perception with ADHEAR was mean 69.2% at 35 dB, 97.9% at 50 dB, 100% at 65 dB, and 100% at 80 dB. Monosyllable perception with the ADHEAR was mean 35.0% at 35 dB, 72.3% at 50 dB, 93.5% at 65 dB, and 98.8% at 80 dB. CONCLUSION: Hearing performance was significantly better with ADHEAR under all test conditions except those where maximum perception was already achieved without ADHEAR.

Finite element modelling of sound transmission in the Weberian apparatus of zebrafish (Danio rerio).

Zebrafish, an essential vertebrate model, has greatly expanded our understanding of hearing. However, one area that remains unexplored is the biomechanics of the Weberian apparatus, crucial for sound conduction and perception. Using micro-computed tomography (µCT) bioimaging, we created three-dimensional finite element models of the zebrafish Weberian ossicles. These models ranged from the exact size to scaled isometric versions with constrained geometry (1 to 10 mm in ossicular chain length). Harmonic finite element analysis of all 11 models revealed that the resonance frequency of the zebrafish's Weberian ossicular chain is approximately 900 Hz, matching their optimal hearing range. Interestingly, resonance frequency negatively correlated with size, while the ratio of peak displacement and difference of resonance frequency between tripus and scaphium remained constant. This suggests the transmission efficiency of the ossicular chain and the homogeneity of resonance frequency at both ends of the chain are not size-dependent. We conclude that the Weberian apparatus's resonance frequency can explain zebrafish's best hearing frequency, and their biomechanical characteristics are not influenced by isometric ontogeny. As the first biomechanical modelling of atympanic ear and among the few non-human ear modelling, this study provides a methodological framework for further investigations into hearing mechanisms and the hearing evolution of vertebrates.

Is human underwater hearing mediated by bone conduction?

In-air and underwater audiograms and directional hearing abilities were measured in humans. The lowest underwater thresholds were 2.8 µW/m2 or 3.6 mPa at a frequency of 500 Hz. The underwater hearing thresholds were 4-26 dB and 40-62 dB higher than in-air hearing thresholds when measured in intensity and pressure units, respectively. This difference is considerably smaller than what has been reported earlier. At frequencies below 1 kHz, when measured in units of particle velocity, the underwater threshold was much lower than published bone conduction thresholds, suggesting that underwater hearing is not always mediated by bone conduction pathways to the inner ear, as previously thought. We suggest it is the resonance of air in the air-filled middle ear that produces the low underwater thresholds, at least at frequencies below 1 kHz. The ability to determine the direction of a 700 Hz underwater sound source while being blindfolded was extremely poor, with submerged test subjects showing only coarse directional hearing abilities at azimuths of less than 50˚. The physical cues to sound direction are different in air and water, and the poor directional hearing abilities indicate that, in spite of low hearing thresholds, humans have no special adaptations to process directional acoustic cues under water.

How flexibility and eardrum cone shape affect sound conduction in single-ossicle ears: a dynamic model study of the chicken middle ear.

It is believed that non-mammals have poor hearing at high frequencies because the sound-conduction performance of their single-ossicle middle ears declines above a certain frequency. To better understand this behavior, a dynamic three-dimensional finite-element model of the chicken middle ear was constructed. The effect of changing the flexibility of the cartilaginous extracolumella on middle-ear sound conduction was simulated from 0.125 to 8 kHz, and the influence of the outward-bulging cone shape of the eardrum was studied by altering the depth and orientation of the eardrum cone in the model. It was found that extracolumella flexibility increases the middle-ear pressure gain at low frequencies due to an enhancement of eardrum motion, but it decreases the pressure gain at high frequencies as the bony columella becomes more resistant to extracolumella movement. Similar to the inward-pointing cone shape of the mammalian eardrum, it was shown that the outward-pointing cone shape of the chicken eardrum enhances the middle-ear pressure gain compared to a flat eardrum shape. When the outward-pointing eardrum was replaced by an inward-pointing eardrum, the pressure gain decreased slightly over the entire frequency range. This decrease was assigned to an increase in bending behavior of the extracolumella and a reduction in piston-like columella motion in the model with an inward-pointing eardrum. Possibly, the single-ossicle middle ear of birds favors an outward-pointing eardrum over an inward-pointing one as it preserves a straight angle between the columella and extrastapedius and a right angle between the columella and suprastapedius, which provides the optimal transmission.

Effects of bacterial biofilm on hearing restoration with titanium partial ossicular prosthesis replacement / 医用生物力学

Objective To study effects of the bacterial biofilm at different growth stages on dynamic behavior of the titanium partial ossicular replacement prosthesis (PORP), so as to provide theoretical references for clinical treatment of diseases such as secretory otitis media. Methods Based on the CT scan images of normal human right ear and combined with the self compiling program, a 3D finite element model of the ear was reconstructed for dynamic analysis on sound conduction, and compared with the experimental data. The model was computed by harmonic response analysis method, and the sound conduction effect of bacterial biofilm grown on PORP at different growth stages was analyzed. Results The simulated amplitude of umbo and stapes footplate was in accordance with experimental measurements, which confirmed the validity of this numerical model. The existence of biofilm would cause 0-1.6 dB hearing loss at low frequencies. The growth of biofilm in the radial direction of PORP would cause 0-12 dB hearing loss at intermediate and high frequencies, especially at 8 kHz, and the hearing loss could be as high as 11.2 dB. Conclusions The bacterial biofilm has an impact on hearing by reducing the hearing at low frequencies while raising a little at high frequencies. The biofilm grown in the radial direction of PORP will reduce hearing, and affect the working efficiency of PORP on hearing restoration.