Intracochlear pressure and temporal bone motion interaction under bone conduction stimulation.

BACKGROUND: Under bone conduction (BC) stimulation, the otic capsule, and surrounding temporal bone, undergoes a complex 3-dimentional (3D) motion that depends on the frequency, location and coupling of the stimulation. The correlation between the resultant intracochlear pressure difference across the cochlear partition and the 3D motion of the otic capsule is not yet known and is to be investigated. METHODS: Experiments were conducted in 3 fresh frozen cadaver heads, individually on each temporal bone, resulting in a total of 6 samples. The skull bone was stimulated, via the actuator of a BC hearing aid (BCHA), in the frequency range of 0.1-20 kHz. Stimulation was applied at the ipsilateral mastoid and the classical BAHA location via a conventional transcutaneous (5-N steel headband) and percutaneous coupling, sequentially. Three-dimensional motions were measured across the lateral and medial (intracranial) surfaces of the skull, the ipsilateral temporal bone, the skull base, as well as the promontory and stapes. Each measurement consisted of 130-200 measurement points (∼5-10 mm pitch) across the measured skull surface. Additionally, intracochlear pressure in the scala tympani and scala vestibuli was measured via a custom-made intracochlear acoustic receiver. RESULTS: While there were limited differences in the magnitude of the motion across the skull base, there were major differences in the deformation of different sections of the skull. Specifically, the bone near the otic capsule remained primarily rigid across all test frequency (above 10 kHz), in contrast to the skull base, which deformed above 1-2 kHz. Above 1 kHz, the ratio, between the differential intracochlear pressure and the promontory motion, was relatively independent of coupling and stimulation location. Similarly, the stimulation direction appears to have no influence on the cochlear response, above 1 kHz. CONCLUSIONS: The area around the otic capsule appears rigid up to significantly higher frequencies than the rest of the skull surface, resulting in primarily inertial loading of the cochlear fluid. Further work should be focused at the investigation of the solid-fluid interaction between the bony walls of the otic capsule and the cochlear contents.

Human middle-ear muscle pulls change tympanic-membrane shape and low-frequency middle-ear transmission magnitudes and delays.

The three-bone flexible ossicular chain in mammals may allow independent alterations of middle-ear (ME) sound transmission via its two attached muscles, for both acoustic and non-acoustic stimuli. The tensor tympani (TT) muscle, which has its insertion on the malleus neck, is thought to increase tension of the tympanic membrane (TM). The stapedius (St) muscle, which has its insertion on the stapes posterior crus, is known to stiffen the stapes annular ligament. We produced ME changes in human cadaveric temporal bones by statically pulling on the TT and St muscles. The 3D static TM shape and sound-induced umbo motions from 20 Hz to 10 kHz were measured with optical coherence tomography (OCT); stapes motion was measured using laser-Doppler vibrometry (LDV). TT pulls made the TM shape more conical and moved the umbo medially, while St pulls moved the umbo laterally. In response to sound below about 1 kHz, stapes-velocity magnitudes generally decreased by about 10 dB due to TT pulls and 5 dB due to St pulls. In the 250 to 500 Hz region, the group delay calculated from stapes-velocity phase showed a decrease in transmission delay of about 150 µs by TT pulls and 60 µs by St pulls. Our interpretation of these results is that ME-muscle activity may provide a way of mechanically changing interaural time- and level-difference cues. These effects could help the brain align head-centered auditory and ocular-centered visual representations of the environment.

Reference velocity of a human head in bone conduction hearing: Finite element study.

A whole head or temporal bone has been used in experiments to understand the mechanism of bone conduction (BC) hearing. In these experiments, two assumptions are generally accepted: (1) a promontory can be a representative point to show the motion of a specimen in BC hearing, and (2) the promontory velocity is proportional to a cochlear response so that the higher the promontory velocity, the better the BC hearing. To confirm the two assumptions, we investigated the velocities of various points corresponding to different BC input types and directions in the head. In this investigation, we used the three-dimensional finite element model of a human head, including an auditory periphery. Results showed that a single promontory was insufficient to be a representative point to show the motion of a specimen because the specimen could have rotational motion at frequencies below 0.5 kHz and the localized deformation at frequencies above 3 kHz. The promontory velocity had the same pattern as the basilar membrane velocity at low and high frequencies. However, at mid-frequencies between 0.5 and 3 kHz, the promontory did not exhibit the same pattern of velocity as the basilar membrane. Therefore, one's BC hearing ability must be carefully determined on the basis of promontory velocity.

Effect of reciprocal headgear forces on the calvarium: A finite element study.

INTRODUCTION: Orthopedic appliances continue to be used for various sagittal, vertical, and transverse corrections of the maxilla. Although cranial growth can continue to adulthood, no study has drawn attention to the effects of headgear forces on the calvarium, in which anchorage is taken. This study focused on the different biomechanical responses on the calvarium of young children wearing a high-pull headgear of varying forces, using a 3-dimensional finite element analysis and the possible implications of such changes on the human skull. METHODS: A 3-dimensional finite element model of a 9-year-old child was designed from the computed tomography scan. The material properties of the juvenile skull were assigned. Varying orthopedic forces (400, 500, and 600 g of force) were applied, and the magnitude of displacement and stresses generated on the cranial bones and sutures were interpreted using ANSYS software (version 12.1; Canonsburg, Pa). RESULTS: Maximum displacement was found for the parietal bone in the inferior direction; parietal and temporal bones in the transverse direction; and frontal, parietal, and temporal bones in the sagittal direction. The least displacement was noted for the occipital bone in all the 3-dimensions. The maximum stresses were concentrated over the region of the lateral margins of the piriform aperture and the medial walls of the orbit. Higher stress values were also found on the parietal bone adjacent to the sagittal suture. The highest value of stresses among the sutures of the craniofacial complex was found to be in the region of the frontonasal, frontomaxillary, and nasomaxillary sutures. CONCLUSIONS: The effects of displacement and stresses obtained from this study suggest a restriction to the growth of the cranial vault and its normal mobility, in turn altering the intracranial tension and causing altered cranial morphology in young, growing children undergoing high-pull headgear therapy. The human cranial system is dynamic throughout life and may be restricted or altered by hereditary or environmental factors.

Round window stimulation with an interface coupler demonstrates proof of concept.

HYPOTHESIS: To mechanically stimulate the round window (RW) membrane, an actuator with an interface coupler (IC) has the potential to improve sound transmission to the cochlea as compared to the most used RW stimulation device implanted today. If a proof-of-concept IC prototype shows promise as compared the most common method for RW stimulation, there is potential that future design development of an IC will be worthwhile. BACKGROUND: A variety of hearing pathologies resulting in mixed and conductive hearing loss can be addressed by mechanically stimulating the RW to transmit sound to the cochlea. The most common method for RW stimulation is with the floating mass transducer (FMT, Med-El). However, the FMT suffers poor sound transmission and unreliable device positioning. The dynamic range and bandwidth of the FMT as a RW stimulator is limited because the entire FMT needs freedom to vibrate. Thus the FMT has difficulty overcoming its own inertia and it cannot be stabilized in a manner that may limit its motion. Here we test an idea of using a generic actuator that vibrates on one side while stationary and held stable on the other (unlike the FMT), and coupling the actuator vibration to the RW membrane with a proof-of-concept IC designed to safely transmit sound to the cochlea. We determine if this proof-of-concept IC can perform as well or better than the FMT in one specimen. If so, further developments of the IC would be worthwhile. METHODS: RW sound transmission comparison was made between an ideally implanted FMT and a proof-of-concept IC prototype driven by a piezoelectric stack actuator with vibrating tip in a fresh human temporal bone. Velocities of stapes, FMT, and IC actuator were measured with laser Doppler vibrometry to determine bandwidth, linearity, and dynamic range of cochlear sound transmission. RESULTS: Stimulation with proof-of-concept prototype of the IC provided increased sound transmission, more linear output for larger dynamic range, and wider frequency range as compared to the FMT. This experiment demonstrates the potential of the IC concept to improve performance, and that it merits further development. However, it was challenging to stabilize the coupling between an external actuator and the proof-of-concept IC prototype. Thus, although we were successful in showing that this IC concept has promise, major design improvements and developments are required in the future. CONCLUSIONS: We demonstrated that the proof-of-concept IC prototype driven with a tip connected to a piezoelectric stack actuator can stimulate the RW membrane with improved acoustic performance as compared to the FMT in one specimen. This study demonstrated proof of concept: that the idea of an IC for sound transmission to the cochlea through the RW has potential, and that it would be worthwhile to pursue the IC idea with further developments. This idea has the potential to provide robust sound transmission to the cochlea via the RW while preventing possible trauma to the cochlea. We also learned that critical design improvements are necessary because coupling the generic external actuator to the IC was challenging. A possible future IC design is to integrate a piezoelectric actuator permanently to the IC, allowing only the soft balloon membrane of the IC to vibrate the RW while the rest of the exterior housing of the combined IC (with actuator) would not vibrate and would be stabilized in a fixed manner.

The dynamic impact behavior of the human neurocranium.

Realistic biomechanical models of the human head should accurately reflect the mechanical properties of all neurocranial bones. Previous studies predominantly focused on static testing setups, males, restricted age ranges and scarcely investigated the temporal area. This given study determined the biomechanical properties of 64 human neurocranial samples (age range of 3 weeks to 94 years) using testing velocities of 2.5, 3.0 and 3.5 m/s in a three-point bending setup. Maximum forces were higher with increasing testing velocities (p ≤ 0.031) but bending strengths only revealed insignificant increases (p ≥ 0.052). The maximum force positively correlated with the sample thickness (p ≤ 0.012 at 2.0 m/s and 3.0 m/s) and bending strength negatively correlated with both age (p ≤ 0.041) and sample thickness (p ≤ 0.036). All parameters were independent of sex (p ≥ 0.120) apart from a higher bending strength of females (p = 0.040) for the 3.5 -m/s group. All parameters were independent of the post mortem interval (p ≥ 0.061). This study provides novel insights into the dynamic mechanical properties of distinct neurocranial bones over an age range spanning almost one century. It is concluded that the former are age-, site- and thickness-dependent, whereas sex dependence needs further investigation.

Chronic Bilateral Cochlear Implant Stimulation Partially Restores Neural Binaural Sensitivity in Neonatally-Deaf Rabbits.

Cochlear implant (CI) users with a prelingual onset of hearing loss show poor sensitivity to interaural time differences (ITDs), an important cue for sound localization and speech reception in noise. Similarly, neural ITD sensitivity in the inferior colliculus (IC) of neonatally-deafened animals is degraded compared with animals deafened as adults. Here, we show that chronic bilateral CI stimulation during development can partly reverse the effect of early-onset deafness on ITD sensitivity. The prevalence of ITD sensitive neurons was restored to the level of adult-deaf (AD) rabbits in the early-deaf rabbits of both sexes that received chronic stimulation and behavioral training with wearable bilateral sound processors during development. We also found a partial improvement in neural ITD sensitivity in the early-deaf and stimulated rabbits compared with unstimulated rabbits. In contrast, chronic CI stimulation did not improve temporal coding in early-deaf rabbits. The present study is the first report showing functional restoration of ITD sensitivity with CI stimulation in single neurons and highlights the importance of auditory experience during development on the maturation of binaural circuitry.SIGNIFICANCE STATEMENT Although cochlear implants (CI) are highly successful in providing speech reception in quiet for many profoundly deaf people, CI users still face difficulty in noisy everyday environment. This is partly because of their poor sensitivity to differences in the timing of sounds arriving at the two ears [interaural time differences (ITDs)], which help to identify where the sound is coming from. This problem is especially acute in those who lost hearing early in life. Here, we present the first report that sensitivity of auditory neurons to ITDs is restored by CI stimulation during development in an animal model of neonatal deafness. These findings highlight the importance of providing early binaural auditory experience with CIs in deaf children.

The biomechanical characteristics of human vestibular aqueduct: a numerical-based model construction and simulation.

Vestibular aqueduct is a precise structure embedded in the temporal bone and plays a key role in the physiological function of inner ear by maintaining the endolymphatic circulation and buffering the impact from intracranial pressure. Although the alterations on the morphology or volume of vestibular aqueduct result in variety of diseases, the approaches of evaluating the condition of vestibular aqueduct are still unsatisfing because the pathological sections utilized for the 3D construction model most likely undergoes morphological changes. In this study, the vestibular aqueduct images obtained by CT scanning were processed by finite element method to construct the 3D model. To assess if this numerical model reflects the actual biomechanical properties of vestibular aqueduct, the fluid-solid coupling calculation was applied to simulate the endolymphatic flow in the vestibular aqueduct. By measuring the dynamics of endolymphatic flow, and the pressure and displacement on round membrane under external pressure, we found the numerical 3D model recapitulated the biomechanical characteristics of the real vestibular aqueduct. In summary, our approach of 3D model construction for vestibular aqueduct will provide a powerful method for the research of vestibular aqueduct-related diseases.

Effectiveness of Bone Conduction Stimulation Applied Directly to the Otic Capsule Measured at Promontory: Assessment in Cadavers.

INTRODUCTION: The aims of this study included: (a) to develop a method of direct acoustic bone conduction (BC) stimulation applied directly to the otic capsule, (b) to investigate the effect of different stimulation sites on the promontory displacement amplitude, and (c) to find the best stimulation site (among 2 located directly on the otic capsule and 1 standard site approved for clinical use) that provides the greatest transmission of vibratory energy. METHODS: Measurements were performed on 9 cadaveric whole human heads. A commercial scanning laser Doppler vibrometer was used. The promontory displacement was recorded in response to BC stimulation delivered by an implant at 3 sites: BC1 on the squamous part of the temporal bone, BC2 on the ampulla of the lateral semicircular canal, and BC3 between the semicircular canals. The displacement of the promontory was analyzed in detail. RESULTS: The results show that BC1 caused an overall smaller promontory displacement than both sites BC2 and 3. BC3 stimulation is more efficient than that at BC2. CONCLUSIONS: BC is an effective method of acoustic stimulus delivery into the inner ear, with the effectiveness increasing when approaching closer to the cochlea. Placing the implant directly on the labyrinth and thus applying vibrations directly to the otic capsule is possible and very effective as proved in this study. The results are encouraging and represent the potential of new stimulation sites that could be introduced in the field of BC hearing rehabilitation as the possible future locations for implantable BC hearing devices.

Bone conduction stimulation of the otic capsule: a finite element model of the temporal bone.

PURPOSE: Bone conduction stimulation applied on the otic capsule may be used in a conductive hearing loss treatment as an alternative to the bone conduction implants in clinical practice. A finite element study was used to evaluate the force amplitude and direction needed for the stimulation. METHODS: A finite element model of a female temporal bone with a precisely reconstructed cochlea was subjected to a harmonic analysis assuming two types of stimulation. At first, the displacement amplitude in the form of air conduction stimulation was applied on the stapes footplate. Then the force amplitude was applied on the otic capsule in the form of bone conduction stimulation. The two force directions were considered: 1) the primary direction, when a typical opening is performed during mastoidectomy, and was coincident with the axis of an imaginary cone, inscribed in the opening, and 2) the direction perpendicular to the stapes footplate. The force amplitude was set so that the response from the cochlea corresponded to the result of air conduction stimulation applied on the stapes footplate. RESULTS: The amplitude and phase of vibration and the volume displacement on the round window membrane were considered as well as vibrations of the basilar membrane, spiral lamina, and promontory. CONCLUSIONS: The cochlear response was comparable for the two types of stimulation. The efficiency of bone conduction stimulation depended on the force direction. For the primary direction, the force was a few times smaller than for the direction perpendicular to the stapes footplate.

Effect of Middle-Ear Pathology on High-Frequency Ear Canal Reflectance Measurements in the Frequency and Time Domains.

The effects of middle-ear pathology on wideband acoustic immittance and reflectance at frequencies above 6-8 kHz have not been documented, nor has the effect of such pathologies on the time-domain reflectance. We describe an approach that utilizes sound frequencies as high as 20 kHz and quantifies reflectance in both the frequency and time domains. Experiments were performed with fresh normal human temporal bones before and after simulating various middle-ear pathologies, including malleus fixation, stapes fixation, and disarticulation. In addition to experimental data, computational modeling was used to obtain fitted parameter values of middle-ear elements that vary systematically due to the simulated pathologies and thus may have diagnostic implications. Our results demonstrate that the time-domain reflectance, which requires acoustic measurements at high frequencies, varies with middle-ear condition. Furthermore, the extended bandwidth frequency-domain reflectance data was used to estimate parameters in a simple model of the ear canal and middle ear that separates three major conductive pathologies from each other and from the normal state.

Reducing Artifacts in Intracochlear Pressure Measurements to Study Sound Transmission by Bone Conduction Stimulation in Humans.

HYPOTHESIS: Intracochlear pressure (ICP) measurements during bone conduction (BC) stimulation may be affected by motion of the pressure sensor relative to the cochlear promontory bone, demonstrating the need to cement the sensor firmly to the cochlear bone. BACKGROUND: ICP is a promising measurement tool for investigating the cochlear drive in BC transmission, but its use is not yet standardized. Previous ICP studies have reported artificially increased pressure due to motion of the sensor relative to the temporal bone. The artifact can be reduced by firmly cementing the sensor to the bone, but this is destructive for the sensor. Previous studies used a custom-made sensor; the use of commercially available sensors, however, is more generic, but also more challenging to combine with the cement. Therefore, the goals of the current study are: firstly, to evaluate a non-destructive cementing method suitable for a commercially available sensor, and secondly, to investigate ICP measurements during BC stimulation in more detail. METHODS: To study the effect of sensor cementing, three fixation conditions were investigated on six fresh-frozen temporal bones: 1) alginate, 2) alginate and dental composite, 3) alginate and dental composite, released from micromanipulators. Pressures in scala tympani and vestibuli were measured simultaneously, while velocity measurements were performed on the cochlear promontory and sensor. The ratio between sensor and promontory bone velocity was computed to quantify the relative motion. RESULTS: For air conduction stimulation, results were in line with those from previous ICP studies, indicating that baseline measurements were valid and could be used to interpret the results obtained with BC stimulation. Results showed that cementing the sensors and releasing them from the micromanipulators is crucial for valid ICP measurements. When the sensors were only sealed with alginate, the pressure was overestimated, especially at low and mid-frequencies. When the sensors were cemented and held in the micromanipulators, the pressure was underestimated. Compared with the scala tympani measurements, ICP measurements showed a lower scala vestibuli pressure below 1 kHz, and a higher pressure above 1 kHz. CONCLUSION: Dental composite is effective as a cement to attach commercially available sensors to the cochlear promontory bone. When sensors are firmly attached, valid ICP measurements can be obtained with BC stimulation.

Video Head Impulse Test in Labyrinthine Fistula due to Middle Ear Cholesteatoma.

OBJECTIVES: To assess and monitor lateral semicircular canal (LSC) function over time in patients affected by chronic otitis media with cholesteatoma (CHO) complicated by fistula of LSC (LSC-F) before and after surgery using video Head Impulse Test (vHIT). MATERIALS AND METHODS: Eight patients aged 18-67 years affected by CHO with imaging-ascertained LSC-F were included in this preliminary prospective study. The following protocol has been applied: oto-microscopic diagnosis with patient's history; computed tomography scan of the temporal bone; surgery with concomitant resurfacing of LSF-F; audiological and vestibular evaluation before surgery (T0) and at 30 days (T1), 6 months (T2), and 1 year after surgery (T3). vHIT was used to assess vestibulo-ocular reflex (VOR) in LSC. RESULTS: None of the patients showed deterioration of bone conduction hearing levels during the different time of evaluation. Three patients showed a reduced VOR gain and catch-up saccades at T0, with VOR gain normalization at T2. This finding remained stable at the 1-year follow-up. The VOR gain in the nonaffected side generally experienced an increase, paralleled by the normalization on the affected side, with statistically significant correlation. The subjects with normal vHIT before surgery did not show any variation following surgery. CONCLUSION: vHIT allows the assessment of LSC function in case of fistula. The adopted surgical fistula repair did not induce deterioration of the auditory or LSC function, but indeed, it could prevent worsening and help promoting recovery to the normal function.

Optimum Coupling of an Active Middle Ear Actuator: Effect of Loading Forces on Actuator Output and Conductive Losses.

INTRODUCTION: The desired outcome of the implantation of active middle ear implants is maximum coupling efficiency and a minimum of conductive loss. It has not been investigated yet, which loading forces are applied during the process of coupling, which forces lead to an optimum actuator performance and which forces occur when manufacturer guidelines for coupling are followed. METHODS: Actuator output was measured by laser Doppler vibrometry of stapes motion while the actuator was advanced in 20 µm steps against the incus body while monitoring static contact force. The occurrence of conductive losses was investigated by measuring changes in stapes motion in response to acoustic stimulation for each step of actuator displacement. Additionally, the electrical impedance of the actuator was measured over the whole frequency range at each actuator position. RESULTS: Highest coupling efficiency was achieved at forces above 10 mN. Below 1 mN no efficient coupling could be achieved. At 30 mN loading force, which is typical when coupling according to manufacturer guidelines, conductive losses of more than 5 dB were observed in one out of nine TBs. The electrical impedance of the actuator showed a prominent resonance peak which vanished after coupling. CONCLUSION: A minimum coupling force of 10 mN is required for efficient coupling of the actuator to the incus. In most cases, coupling forces up to 100 mN will not result in clinically relevant conductive losses. The electrical impedance is a simple and reliable metric to indicate contact.

Inappropriate Use of the "Rosowski Criteria" and "Modified Rosowski Criteria" for Assessing the Normal Function of Human Temporal Bones.

Important research by Rosowski et al. [Twenty-Seventh Meeting of the Association for Research in Otolaryngology, 2004, p. 275] has led to a standard practice by the American Society for Testing Materials [West Conshohocken: ASTM International; 2014] to assess normal function of temporal bones used in the development of novel middle ear actuators and sensors. Rosowki et al. [Audiol Neurotol. 2007; 12(4): 265-76] have since suggested that the original criteria are too restrictive and have proposed modified criteria. We show that both the original and modified criteria are inappropriate for assessing individual temporal bones. Moreover, we suggest that both the original and modified Rosowski criteria should be applied with caution when assessing whether mean data from a study are within physiological norms because the multiple comparisons resulting from verification at each frequency will lead to very liberal rejection. The standard practice, however, has led to the collection of more extensive and consistent data. We suggest that it is now opportune to use these data to further modify the Rosowski criteria.

Experimental investigation of promontory motion and intracranial pressure following bone conduction: Stimulation site and coupling type dependence.

OBJECTIVES: Investigation of bone conduction sound propagation by osseous and non-osseous pathways and their interactions based upon the stimulation site and coupling method of the actuator from a bone conduction hearing aid (BCHA). METHODS: Experiments were conducted on five Thiel embalmed whole head cadaver specimens. The electromagnetic actuator from a commercial bone conduction hearing aid (BCHA) (Baha® Cordelle II) was used to provide a stepped sine stimulus in the range of 0.1-10 kHz. Osseous pathways (direct bone stimulation or transcutaneous stimulation) were sequentially activated by stimulation at the mastoid or the BAHA side using several methods including a percutaneously implanted screw, Baha® Attract transcutaneous magnet and a 5-N (5-N) steel headband. Non-osseous pathways (only soft tissue or intra-cranial contents) were activated by actuator stimulation on the eye or neck via attachment to a 5-N steel headband, and were compared with stimulation via equivalent attachment on the mastoid and forehead. The response of the skull was measured as motions of the ipsi- and contralateral promontory and intracranial pressure (ICP) in the central, anterior, posterior, ipsilateral and contralateral temporal regions of the cranial space. Promontory motion was monitored using a 3-dimensional Laser Doppler vibrometer (3D LDV) system. RESULTS: The promontory undergoes spatially complex motion with similar contributions from all motion components, regardless of stimulation mode. Combined 3D promontory motion provided lower inter-sample variability than did any individual component. Transcranial transmission showed gain for the low frequencies and attenuation above 1 kHz, independent of stimulation mode This effect was not only for the magnitude but also its spatial composition such that contralateral promontory motion did not follow the direction of ipsilateral stimulation above 0.5 kHz. Non-osseous stimulation on the neck and eye induced comparable ICP relative to percutaneous (via screw) mastoid stimulation. Corresponding phase data indicated lower phase delays for ICP when stimulation was via non-osseous means (i.e., to the eye) versus osseous means (i.e., to the mastoid or forehead). Sound propagation due to skull stimulation passes through the thicker bony sections first before activating the CSF. CONCLUSION: Utilization of 3D promontory motion measurements provides more precise (lower inter-sample variability) information about bone vibrations than does any individual component. It also provides a more detailed description of transcranial attenuation. A comprehensive combination of motion and pressures measurements across the head, combined with a variation of the stimulation condition, could reveal details about sound transmission within the skull.

Tympanic membrane surface motions in forward and reverse middle ear transmissions.

Characterization of Tympanic Membrane (TM) surface motions with forward and reverse stimulation is important to understanding how the TM transduces acoustical and mechanical energy in both directions. In this paper, stroboscopic opto-electronic holography is used to quantify motions of the entire TM surface induced by forward sound and reverse mechanical stimulation in human cadaveric ears from 0.25 to 18.4 kHz. The forward sound stimulus was coupled to an anatomically realistic artificial ear canal that allowed optical access to the entire TM surface, and the reverse mechanical stimulus was applied to the body of the incus by a piezo-electric stimulator. The results show clear differences in TM surface motions evoked by the two stimuli. In the forward case, TM motion is dominated by standing-wave-like modal motions that are consistent with a relatively uniform sound-pressure load over the entire TM surface. With reverse mechanical stimulation, the TM surface shows more traveling waves, consistent with a localized mechanical drive applied to the manubrium embedded in the TM. With both stimuli, the manubrium moves less than the rest of the TM, consistent with the TM acting like a compliant membrane rather than a stiff diaphragm, and also consistent with catenary behavior due to the TM's curved shape.

Evaluation of Coupling Efficiency in Round Window Vibroplasty With a New Handheld Probe.

HYPOTHESIS: A handheld measuring probe was developed that analyzes the vibration characteristics of the stapes footplate after backward stimulation of the cochlea in round window vibroplasty. In temporal bone experiments, the measuring accuracy of the probe was tested. BACKGROUND: In round window vibroplasty, the effectiveness of the transmitted vibrations into the inner ear is provided with limited visual and tactile information. Currently, there is no objective measuring tool available. METHODS: In five unfixed temporal bones, a floating mass transducer was coupled to the round window membrane. During the excitation with different voltage levels (0, 5, 25, 100, 300 mV root mean square) corresponding to 0, 80, 94, 106, and 116 dB equivalent ear canal sound pressure respectively, the deflections of the footplate were recorded in parallel by laser Doppler vibrometry and the measuring probe. RESULTS: The probe allowed for differentiation of the coupling efficiency. The measured footplate vibrations from the excitation levels of 106 dB (and 116 dB) were statistically significant compared with the testing without excitation. The footplate deflections determined in parallel by laser Doppler vibrometry showed comparable results. CONCLUSION: In principal, the newly developed measuring probe allows for measuring the quality of retrograde cochlear excitation in a round window vibroplasty by detecting footplate vibrations. Further developments are directed for its application in clinical, intraoperative procedures.

In-vivo assessment of osseous versus non-osseous transmission pathways of vibratory stimuli applied to the bone and the dura in humans.

BACKGROUND: Bone conduction (BC) is an alternative to air conduction (AC) for stimulation of the inner ear. Stimulation for BC can occur directly on the skull bone, on the skin covering the skull bone, or on soft tissue (i.e., eye, dura). All of these stimuli can elicit otoacoustic emissions (OAE). This study aims to compare OAEs generated by different combinations of stimuli in live humans, including direct stimulation of the intracranial contents via the dura, measured intraoperatively. METHODS: Measurements were performed in five normal-hearing ears of subjects undergoing a neurosurgical intervention with craniotomy in general anesthesia. Distortion product OAEs (DPOAEs) were measured for f2 at 0.7, 1, 2, 3, 4, and 6 kHz with a constant ratio of the primary frequencies (f2/f1) of 1.22. Sound pressure L1 was held constant at 65 dB SPL, while L2 was decreased in 10 dB steps from 70 to 30 dB SPL. A DPOAE was considered significant when its level was ≥6 dB above the noise floor. Emissions were generated sequentially with different modes of stimulation: 1) pre-operatively in the awake subject by two air-conducted tones (AC-AC); 2) within the same session preoperatively by one air- and one bone-conducted tone on the skin-covered temporal bone as in audiometry (AC-BC); 3) intra-operatively by one air-conducted tone and one bone-vibrator tone applied directly on the dura (AC-DC). A modified bone vibrator (Bonebridge; MED-EL, Innsbruck, Austria) was used for BC stimulation on the dura or skin-covered mastoid. Its equivalent perceived SPL was calibrated preoperatively for each individual by psychoacoustically comparing the level of a BC tone presented to the temporal region to an AC tone at the same frequency. Simultaneously with the DPOAEs, vibrations at the teeth were measured with an accelerometer attached using a custom-made holder. RESULTS: It was possible to record DPOAEs for all three stimulation modes. For AC-DC, DPOAEs were not detected above the noise floor below 2 kHz but were detectable at the higher frequencies. The best response was measured at or above 2 kHz with L2 = 60 dB SPL. The acceleration measured at the teeth for stimulation on the dura was lower than that for stimulation on the bone, especially below 3 kHz. CONCLUSION: We demonstrate a proof-of-concept comparison of DPOAEs and teeth acceleration levels elicited by a bone vibrator placed either against the skin-covered temporal bone, as in audiometry, or directly against the dura mater in patients undergoing a craniotomy. It was demonstrated that DPOAEs could be elicited via non-osseous pathways within the skull contents and that the required measurements could be performed intra-operatively.

Immunohistochemical localization of megalin and cubilin in the human inner ear.

Megalin and cubilin are endocytic receptors expressed in many absorptive polarized epithelia. These receptors have been implicated in the transport of gentamicin in the inner ear as possible contributors to ototoxic damage. Megalin and cubilin have been characterized in detail in the mouse and rat inner ear, but not in the human inner ear. In this study, megalin and cubilin were localized by immunohistochemistry using affinity-purified antibodies in formalin fixed frozen cryostat and celloidin embedded sections of the human inner ear. In the cochlea megalin and cubilin were localized in marginal cells of the stria vascularis, epithelial cells of the spiral prominence and the Reissner's membrane. In the macula utricle and cristae ampullaris, megalin and cubilin were localized in transitional and dark cells, but not in vestibular hair cells and supporting cells. In the endolymphatic duct megalin and cubilin were localized in the epithelial cells. The localization of megalin and cubilin in the human inner ear is consistent with previous reports in the inner ear of animal models and suggest that these receptors may play an important role in the inner ear endocytic transport, and maybe potential targets for prevention of ototoxic damage or the delivery of medications.