ZH-ECochG Bode Plot: A Novel Approach to Visualize Electrocochleographic Data in Cochlear Implant Users.

Background: Various representations exist in the literature to visualize electrocochleography (ECochG) recordings along the basilar membrane (BM). This lack of generalization complicates comparisons within and between cochlear implant (CI) users, as well as between publications. This study synthesized the visual representations available in the literature via a systematic review and provides a novel approach to visualize ECochG data in CI users. Methods: A systematic review was conducted within PubMed and EMBASE to evaluate studies investigating ECochG and CI. Figures that visualized ECochG responses were selected and analyzed. A novel visualization of individual ECochG data, the ZH-ECochG Bode plot (ZH = Zurich), was devised, and the recordings from three CI recipients were used to demonstrate and assess the new framework. Results: Within the database search, 74 articles with a total of 115 figures met the inclusion criteria. Analysis revealed various types of representations using different axes; their advantages were incorporated into the novel visualization framework. The ZH-ECochG Bode plot visualizes the amplitude and phase of the ECochG recordings along the different tonotopic regions and angular insertion depths of the recording sites. The graph includes the pre- and postoperative audiograms to enable a comparison of ECochG responses with the audiometric profile, and allows different measurements to be shown in the same graph. Conclusions: The ZH-ECochG Bode plot provides a generalized visual representation of ECochG data, using well-defined axes. This will facilitate the investigation of the complex ECochG potentials generated along the BM and allows for better comparisons of ECochG recordings within and among CI users and publications. The scripts used to construct the ZH-ECochG Bode plot are provided by the authors.

Influence of the Intracranial Contents on the Head Motion under Bone Conduction.

INTRODUCTION: The mechanism of non-osseous bone conduction pathways, involving the intracranial contents (ICC) of the skull, is still not well understood. This study aims to investigate the influence of the ICC on the skull bone wave propagation, including dependence on stimulation location and coupling. METHODS: Three Thiel embalmed whole-head cadaver specimens were studied before and after the removal of the ICC. Stimulation was via the electromagnetic actuators from commercial bone conduction hearing aids. Osseous pathways were sequentially activated by mastoid, forehead and BAHA location stimulation via a 5-Newton steel headband or percutaneously implanted screw. Non-osseous pathways were activated by stimulation on the eye and dura via a 5-Newton steel headband and a custom-made pneumatic holder. Under each test condition, the 3D motion of the superior skull bone was monitored at ~200 points. RESULTS: The averaged response of the skull surface showed limited differences due to the removal of the ICC. In some isolated cases, the modal pattern on the skull surface showed a trend for an upshift (~1/2 octave) in the observed natural frequencies for drained heads. This was also consistent with an observed trend for an upshift in the transition frequency in the estimated deformation across the lateral surfaces of the temporal bones. Such changes were consistent with the expected reduction in mass and damping due to the absence of the ICC. CONCLUSION: Overall, the ICC affect to a limited extent the motion of the skull bone, with a limited trend for a reduction of its natural frequencies.

Generation of distortion product otoacoustic emissions in infants with a combined air and bone conduction stimulus.

OBJECTIVES: Evaluation of Distortion Product Otoacoustic Emissions (DPOAEs) by combining Air Conduction (AC) and Bone Conduction (BC) stimuli in infants. METHODS: Measurements were performed in 19 normal hearing infants, and in 23 adults serving as a control group. The stimulus consisted either of two AC tones, or of combined AC/BC tones. DPOAEs were measured for f2 at 0.7, 1, 2, 4 kHz, and a constant ratio of f2/f1 = 1.22. Sound pressure level of the primary stimulus L1 was held constant at 70 dB SPL, while the level of L2 was decreased in 10 dB steps from 70 to 40 dB SPL. A response was included for further analysis when DPOAEs reached a Signal to Noise Ratio (SNR) of ≥6 dB. Additional DPOAE responses of <6 dB SNR were included when visual inspection of the measurements indicated clear DPOAEs. RESULTS: DPOAEs could be elicited in infants at 2 and 4 kHz for the AC/BC stimulus. DPOAE amplitudes evoked by the AC/AC stimulus were larger than those by the AC/BC stimulus, with the exception of 1 kHz. The highest amplitudes of DPOAEs were registered for a stimulation level of L1 = L2 = 70 dB, with the exception of AC/AC at 1 kHz, where the highest amplitudes were with L1-L2 = 10 dB. CONCLUSIONS: We demonstrated that DPOAEs can be generated in infants by a combined AC/BC stimulus at 2 and 4 kHz. The high noise floor needs to be further reduced to achieve more valid measurements in frequencies <2 kHz.

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.

Effects of preloads on middle-ear transfer function and acoustic reflex in ossiculoplasty with PORP.

INTRODUCTION: Surgical outcomes in ossiculoplasty with partial ossicular replacement prostheses (PORPs) are greatly influenced by the amount of preload imposed on the PORP. In this study, the attenuation of the middle-ear transfer function (METF) was experimentally investigated for prosthesis-related preloads in different directions, with and without concurrent application of stapedial muscle tension. Different PORP designs were assessed to determine functional benefits of specific design features under preload conditions. METHODS: The experiments were performed on fresh-frozen human cadaveric temporal bones. The effect of preloads along different directions were experimentally assessed by simulating anatomical variance and postoperative position changes in a controlled setup. The assessments were performed for three different PORP designs featuring either a fixed shaft or ball joint and a Bell-type or Clip-interface. Further, the combined effect of the preloads towards the medial direction with tensional forces of the stapedial muscle was assessed. The METF was obtained via laser-Doppler vibrometry for each measurement condition. RESULTS: The preloads as well as the stapedial muscle tension primarily attenuated the METF between 0.5 and 4 kHz. The largest attenuations resulted from the preload towards the medial direction. The attenuation of the METF with stapedial muscle tension was reduced with concurrent PORP preloads. PORPs with a ball joint resulted in reduced attenuation only for preloads along the long axis of the stapes footplate. In contrast to the clip interface, the Bell-type interface was prone to lose coupling with the stapes head for preloads in the medial direction. CONCLUSIONS: The experimental study of the preload effects indicates a direction-dependent attenuation of the METF, with the most pronounced effects resulting from preloads towards the medial direction. Based on the obtained results, the ball joint offers tolerance for angular positioning while the clip interface prevents PORP dislocations for preloads in lateral direction. At high preloads, the attenuation of the METF with stapedial muscle tension is reduced, which should be considered for the interpretation of postoperative acoustic reflex tests.

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.

Three-dimensional quasi-static displacement of human middle-ear ossicles under static pressure loads: Measurement using a stereo camera system.

The time delay and/or malfunctioning of the Eustachian tube may cause pressure differences across the tympanic membrane, resulting in quasi-static movements of the middle-ear ossicles. While quasi-static displacements of the human middle-ear ossicles have been measured one- or two-dimensionally in previous studies, this study presents an approach to trace three-dimensional movements of the human middle-ear ossicles under static pressure loads in the ear canal (EC). The three-dimensional quasi-static movements of the middle-ear ossicles were measured using a custom-made stereo camera system. Two cameras were assembled with a relative angle of 7° and then mounted onto a robot arm. Red fluorescent beads of a 106-125 µm diameter were placed on the middle-ear ossicles, and quasi-static position changes of the fluorescent beads under static pressure loads were traced by the stereo camera system. All the position changes of the ossicles were registered to the anatomical intrinsic frame based on the stapes footplate, which was obtained from µ-CT imaging. Under negative ear-canal pressures, a rotational movement around the anterior-posterior axis was dominant for the malleus-incus complex, with small relative movements between the two ossicles. The stapes showed translation toward the lateral direction and rotation around the long axis of the stapes footplate. Under positive EC pressures, relative motion between the malleus and the incus at the IMJ became larger, reducing movements of the incus and stapes considerably and thus performing a protection function for the inner-ear structures. Three-dimensional tracing of the middle-ear ossicular chain provides a better understanding of the protection function of the human middle ear under static pressured loads as immediate responses without time delay.

Intracochlear pressure in cadaver heads under bone conduction and intracranial fluid stimulation.

BACKGROUND: The frequency dependent contributions of the various bone conduction pathways are poorly understood, especially the fluid pathway. The aim of this work is to measure and investigate sound pressure propagation from the intracranial space to the cochlear fluid. METHODS: Stimulation was provided sequentially to the bone (BC) or directly to the intracranial contents (hydrodynamic conduction, or HC) in four cadaver heads, where each ear was tested individually, for a total of 8 samples. Intracranial pressure was generated and monitored via commercial hydrophones, while the intracochlear sound pressure (ICSP) levels were monitored via custom-made intracochlear acoustic receivers (ICAR). In parallel, measurements of the 3D motion of the cochlear promontory and stapes were made via 3D Laser Doppler Vibrometer (3D LDV). RESULTS: Reliability of the intracochlear sound pressure measurements depends on the immobilization of the ICAR relative to the otic capsule. Regardless of the significant differences in absolute stapes and promontory motion, the ratios between the otic capsule velocity, the stapes volume velocity (relative to the cochlea), and the intracochlear pressure were very similar under BC and HC stimulus. Under HC, the cochlear fluid appears be activated by an osseous pathway, rather than a direct non-osseous pathway from the cerebrospinal fluid (CSF), however, the osseous pathway itself is activated by the CSF pressure. CONCLUSIONS: Data suggests that the skull bone surrounding the brain and CSF could play a role in the interaction between the two CSF and the cochlea, under both stimulation conditions, at high frequencies, while inertia is dominant factor at low frequencies. Further work should be focused on the investigation of the solid-fluid interaction between the skull bone walls and the intracranial content.

Wave propagation across the skull under bone conduction: Dependence on coupling methods.

This study is aimed at the quantitative investigation of wave propagation through the skull bone and its dependence on different coupling methods of the bone conduction hearing aid (BCHA). Experiments were conducted on five Thiel embalmed whole head cadaver specimens. An electromagnetic actuator from a commercial BCHA was mounted on a 5-Newton steel headband, at the mastoid, on a percutaneously implanted screw (Baha® Connect), and transcutaneously with a Baha® Attract (Cochlear Limited, Sydney, Australia), at the clinical bone anchored hearing aid (BAHA) location. Surface motion was quantified by sequentially measuring ∼200 points on the skull surface via a three-dimensional laser Doppler vibrometer (3D LDV) system. The experimental procedure was repeated virtually, using a modified LiUHead finite element model (FEM). Both experiential and FEM methods showed an onset of deformations; first near the stimulation area, at 250-500 Hz, which then extended to the inferior ipsilateral skull surface, at 0.5-2 kHz, and spread across the whole skull above 3-4 kHz. Overall, stiffer coupling (Connect versus Headband), applied at a location with lower mechanical stiffness (the BAHA location versus mastoid), led to a faster transition and lower transition frequency to local deformations and wave motion. This behaviour was more evident at the BAHA location, as the mastoid was more agnostic to coupling condition.

Development of a finite element model of a human head including auditory periphery for understanding of bone-conducted hearing.

A three-dimensional finite-element (FE) model of a human head including the auditory periphery was developed to obtain a better understanding of bone-conducted (BC) hearing. The model was validated by comparison of cochlear and head responses in both air-conducted (AC) and BC hearing with experimental data. Specifically, the FE model provided the cochlear responses such as basilar membrane velocity and intracochlear pressure corresponding to BC stimulations applied to the mastoid or the conventional bone-anchored-hearing-aid (BAHA) positions. This is a strength of the model because it is difficult to obtain the cochlear responses from experiments corresponding to the BC stimulation applied at a specific position on the head surface. In addition, there have been few studies based on an FE model that can calculate the head and cochlear responses simultaneously from a BC stimulation. Moreover, in this study, the intracochlear sound pressure at multi-positions along the BM length was calculated and used to clarify the effect of stimulating force direction on the cochlear and promontory velocities in BC hearing. Also, the relationship between BC and AC stimulation and the basilar membrane velocity in the FE model was used to calculate the stimulation level at hearing thresholds which has been investigated only by psychoacoustical methods.

Transcutaneous and percutaneous bone conduction sound propagation in single-sided deaf patients and cadaveric heads.

OBJECTIVE: To investigate transcranial transmission (TT) and the dampening effect of the skin in patients and cadaver heads. DESIGN: In patients a pure tone bone conduction audiogram for ipsilateral and contralateral stimulation was performed. The TT was defined as the difference between ipsilateral and contralateral hearing thresholds. In cadaver heads ipsilateral and contralateral promontory motion was measured using a three-dimensional Laser Doppler Vibrometer system. STUDY SAMPLE: Seven single-sided deaf patients fitted with a Baha® Connect, fifteen single-sided deaf patients without a bone conduction hearing aid and five Thiel-embalmed cadaver heads were included. RESULTS: The TT decreased with increasing frequency in patients and cadaver heads. No significant difference was seen between patients and cadaver heads. Measurements on patients and cadaver heads showed increasing skin attenuation with increasing frequency. However, the dampening effect was 3-12 dB higher in patients than in cadavers at all frequencies. CONCLUSION: The TT was not significantly different for patients compared to cadaver heads. The value of promontory motion to estimate TT in patients need to be further evaluated. The skin attenuates a BC stimulus by 10-20 dB in patients and by a smaller amount in cadaver heads, probably due to changes in the properties of the Thiel-conserved skin.

Conductive Hearing Loss with Age-A Histologic and Audiometric Evaluation.

A retrospective analysis to quantify age-related changes of the incudo-malleolar joint (IMJ) and incudo-stapedial joint (ISJ), and to analyse changes in the air-bone gap (ABG) with age, was performed. Defined histologic parameters of 153 IMJ and 106 ISJ from subjects aged from birth to 70 years were correlated to age. Additionally, audiograms of 1760 ears of 974 other subjects aged 20 to 80 years were retrospectively analysed and the ABG was correlated to age. The joint space (age group from 0 to 10 compared to 61 to 70 years) became significantly wider with age (IMJ: from a mean of 44 µm to 100 µm, p < 0.001; ISJ: from a mean of 28 µm to 69 µm, p < 0.009. The thickness of cartilage of the incus decreased in the first 20 years of life (IMJ, from a mean of 88 µm to 65 µm, p < 0.01; ISJ: from a mean of 44 µm to 35 µm, p < 0.01). The ABGs of younger ears (20-40 years) was significantly larger at 500 Hz compared to older ears (60-80 years) by 2-4 dB, while it was significantly smaller by 3-5 dB at 4000 Hz (p < 0.0017). Interindividual variations in all age groups were large for both analyses. The increased joint spaces could potentially reduce the stiffness in the joints and explain the increase in ABG at 4000 Hz and the drop at 500 Hz. While the average change is small and of minimal clinical relevance, a larger increase of ABG with age is seen in some subjects.

Contribution of the flexible incudo-malleal joint to middle-ear sound transmission under static pressure loads.

The incudo-malleal joint (IMJ) in the human middle ear is a true diarthrodial joint and it has been known that the flexibility of this joint does not contribute to better middle-ear sound transmission. Previous studies have proposed that a gliding motion between the malleus and the incus at this joint prevents the transmission of large displacements of the malleus to the incus and stapes and thus contributes to the protection of the inner ear as an immediate response against large static pressure changes. However, dynamic behavior of this joint under static pressure changes has not been fully revealed. In this study, effects of the flexibility of the IMJ on middle-ear sound transmission under static pressure difference between the middle-ear cavity and the environment were investigated. Experiments were performed in human cadaveric temporal bones with static pressures in the range of +/- 2 kPa being applied to the ear canal (relative to middle-ear cavity). Vibrational motions of the umbo and the stapes footplate center in response to acoustic stimulation (0.2-8 kHz) were measured using a 3D-Laser Doppler vibrometer for (1) the natural IMJ and (2) the IMJ with experimentally-reduced flexibility. With the natural condition of the IMJ, vibrations of the umbo and the stapes footplate center under static pressure loads were attenuated at low frequencies below the middle-ear resonance frequency as observed in previous studies. After the flexibility of the IMJ was reduced, additional attenuations of vibrational motion were observed for the umbo under positive static pressures in the ear canal (EC) and the stapes footplate center under both positive and negative static EC pressures. The additional attenuation of vibration reached 4~7 dB for the umbo under positive static EC pressures and the stapes footplate center under negative EC pressures, and 7~11 dB for the stapes footplate center under positive EC pressures. The results of this study indicate an adaptive mechanism of the flexible IMJ in the human middle ear to changes of static EC pressure by reducing the attenuation of the middle-ear sound transmission. Such results are expected to be used for diagnosis of the IMJ stiffening and to be applied to design of middle-ear prostheses.

A New Stapes-Head Coupler for the Vibrant Soundbridge System.

INTRODUCTION: The Vibrant Soundbridge (MED-EL Medical Electronics, Austria) is an active middle ear implant with a floating mass transducer (FMT) for patients with conductive, sensorineural, or mixed hearing loss. While the FMT is vertically aligned above the stapes head (SH) with the current Vibroplasty Clip coupler (MED-EL Medical Electronics), the new SH coupler was developed to mount the FMT on the inferior side of the stapes and to fit in the reduced middle ear space after canal-wall-down mastoidectomy. METHODS: Using 11 human cadaveric temporal bones (TBs), placements of the new SH couplers on the stapes were examined, and effective stimuli to the cochlea were evaluated by measuring piston-like motion of the stapes footplate with a current of 1 mA on the FMT. The results were assessed in comparison with the Vibroplasty Clip coupler. RESULTS: The new SH coupler showed perfect coupling on the stapes in 9 out of 11 TBs. A small gap between the SH and the plate of the connection link part was unavoidable in 2 TBs but had negligible effect on vibrational motion of the stapes. Vibrational motion of the stapes with the new SH coupler was reduced at frequencies above 3 kHz compared to the corresponding motion with the current Vibroplasty Clip coupler, but the relative attenuation over all 11 cadaveric temporal bones was <10 dB. CONCLUSIONS: The new SH coupler provides an alternative with more stable fixation when placement of the current Vibroplasty Clip coupler is limited due to insufficient space after canal-wall-down mastoidectomy, while still delivering effective stimuli to the cochlea.

[Experimental Evaluation of the Adhear, a Novel Transcutaneous Bone Conduction Hearing Aid]. / Experimentelle Evaluation des Adhear, eines neuen transkutanen Knochenleitungshörgeräts.

OBJECTIVE: Different bone conduction hearing aids (BCHA) are commercially available. They are attached to the head in different ways. The aim of this work is an experimental evaluation of the performance of a new transcutaneous (surface mounted via adhesive pad) actuator of a BCHA. MATERIAL AND METHODS: Experiments were conducted on a Thiel embalmed whole head cadaver specimen. The electromagnetic actuators from a commercial BCHA (Adhear) was used to provide stepped sine stimulus in the range of 0.1-10 kHz. The BCHA was coupled to a skin surface adhesion that was placed on the mastoid. The response was monitored as motions of the ipsi- and contralateral promontory, and as motions of the ipsi-, top- and contralateral skull surface. Promontory motion was quantified via a three-dimensional laser Doppler vibrometer (3D LDV) system. Analogously, surface motion was registered by sequentially measuring ~200 points on the skull surface (~ 15-20 mm pitch) via 3D LDV. The data were compared to corresponding measurements obtained with a Baha Power that was coupled to skin on the Mastoid via a 5 Newton steelband. RESULTS: Ipsilateral and contralateral promontory vibration for stimulation with the Adhear are comparable to stimulation with the Baha Power on the 5 Newton steelband with regard to frequency dependent amplitude and phase, as well as the contribution of the motion components. The surface motion of the skull experiences a similar complex motion for both stimulation modes. CONCLUSIONS: Although the Adhear is coupled without any pressure to the skin over the mastoid whereas the Baha power is attached with a 5 Newton steelband, the vibration parameters investigated are comparable.

Experimental investigation of the effect of middle ear in bone conduction.

OBJECTIVES: Experimental investigation of the contribution of the middle ear to bone conduction (BC) hearing sensation. METHODS: Experiments were conducted on 6 fresh cadaver whole head specimens. The electromagnetic actuators from a commercial bone conduction hearing aid (BCHA), Baha® 5 SuperPower and BoneBridge (BB), were used to provide stepped sine stimulus in the range of 0.1-10 kHz. The middle ear transfer function (METF) of each cadaver head was checked against the ASTM F2504-05 standard. In a first step, the stapes stimulus into the cochlea, under BC, was estimated based on the differential velocity between the stapes footplate and the promontory. This was based on sequential measurements of the 3D velocity of the stapes footplate and the promontory. In parallel, the differential tympanic membrane (TM) pressure was recorded by measuring sound pressure in the middle ear and in the external auditory canal each measured 1-2 mm from the TM. The measurement procedure was then sequentially repeated, after: a) opening the middle ear cavity; b) ISJ interruption; c) closing the middle ear cavity. At the end, the velocity at each actuator is measured for comparison purposes. Stapes footplate and promontory motion was quantified as the 3D motion at a single measurement point via a three-dimensional laser Doppler vibrometer (3D LDV) system. The combined motion was used for all motion parameters. RESULTS: The METF, based on the combined motion, matches better to the ASTM standard, making the measurements resilient to oblique measurement directions. The Baha actuator produced ∼10 dB SPL more output than the BB above 2 kHz. This resulted in 2-5 dB increase in the differential pressure across the TM, after middle ear cavity opening, for Baha stimulation, and up to 9 dB drop (around 2 kHz) for BB stimulation. The differential stapes motion follows linearly the level of motion of the stimulation area, however, it is affected by actuator resonances in a more complex way. Interruption of the ISJ, reduces the differential motion of the stapes with 1-5 dB, only at 1-3 kHz. CONCLUSION: Combined velocity more objectively describes the stapes and skull motion, than any individual motion component. The state of the ME cavity and the ISJ affect the cochlear input of the stapes, however, the effect is limited in frequency and magnitude.

Comparison of sheep and human middle-ear ossicles: anatomy and inertial properties.

The sheep middle ear has been used in training to prepare physicians to perform surgeries and to test new ways of surgical access. This study aimed to (1) collect anatomical data and inertial properties of the sheep middle-ear ossicles and (2) explore effects of these features on sound transmission, in comparison to those of the human. Characteristic dimensions and inertial properties of the middle-ear ossicles of White-Alpine sheep (n = 11) were measured from high-resolution micro-CT data, and were assessed in comparison with the corresponding values of the human middle ear. The sheep middle-ear ossicles differed from those of human in several ways: anteroinferior orientation of the malleus handle, relatively small size of the incus with a relatively short distance to the lenticular process, a large area of the articular surfaces at the incudostapedial joint, and a relatively small moment of inertia along the anterior-posterior axis. Analysis in this study suggests that structure and orientation of the middle-ear ossicles in the sheep are conducive to an increase in the hinge-like ossicular-lever-action around the anterior-posterior axis. Considering the substantial anatomical differences, outcomes of middle-ear surgeries would presumably be difficult to assess from experiments using the sheep middle ear.

Dependence of skull surface wave propagation on stimulation sites and direction under bone conduction.

In order to better understand bone conduction sound propagation across the skull, three-dimensional (3D) wave propagation on the skull surface was studied, along with its dependence on stimulation direction and location of a bone conduction hearing aid (BCHA) actuator. Experiments were conducted on five Thiel embalmed whole head cadaver specimens. Stimulation, in the 0.1-10 kHz range, was sequentially applied at the forehead and mastoid via electromagnetic actuators from commercial BCHAs, supported by a 5-N steel band. The head response was quantified by sequentially measuring the 3D motion of ∼200 points (∼15-20 mm pitch) across the ipsilateral, top, and contralateral skull surface via a 3D laser Doppler vibrometer (LDV) system, guided by a robotic positioner. Low-frequency stimulation (<1 kHz) resulted in a spatially complex rigid-body-like motion of the skull that depended on both the stimulation condition and head support. The predominant motion direction was only 5-10 dB higher than other components below 1 kHz, with no predominance at higher frequencies. Sound propagation direction across the parietal plates did not coincide with stimulation location, potentially due to the head base and forehead remaining rigid-like at higher frequencies and acting as a large source for the deformation patterns across the parietal sections.

Packaging Technology for an Implantable Inner Ear MEMS Microphone.

Current cochlear implant (CI) systems provide substantial benefits for patients with severe hearing loss. However, they do not allow for 24/7 hearing, mainly due to the external parts that cannot be worn in all everyday situations. One of the key missing parts for a totally implantable CI (TICI) is the microphone, which thus far has not been implantable. The goal of the current project was to develop a concept for a packaging technology for state-of-the-art microelectromechanical systems (MEMS) microphones that record the liquid-borne sound inside the inner ear (cochlea) as a microphone signal input for a TICI. The packaging concept incorporates requirements, such as biocompatibility, long-term hermeticity, a high sensing performance and a form factor that allows sensing inside the human cochlea and full integration into the existing CI electrode array. The present paper (1) describes the sensor packaging concept and the corresponding numerical and experimental design verification process and (2) gives insight into new engineering solutions for sensor packaging. Overall, a packaging concept was developed that enables MEMS microphone technology to be used for a TICI system.

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.