Papers by Christof Röösli
Audiology and Neuro-otology, May 7, 2010
Vibratory auditory stimulation or bone conduction (BC) reaches the inner ear through both osseous... more Vibratory auditory stimulation or bone conduction (BC) reaches the inner ear through both osseous and non-osseous structures of the head, but the contribution of the different pathways of BC is still unclear. In this study, BC thresholds in response to stimulation at several different locations including the eye were assessed, while the magnitudes of skull bone vibrations were measured on the front teeth in human subjects with either normal hearing on both sides or unilateral deafness with normal hearing on the other side. The BC thresholds with stimulation at the ipsilateral mastoid and ipsilateral temporal region were lower than the BC thresholds with stimulation at the other sites, as reported by previous works. The lower thresholds with stimulation at the ipsilateral mastoid and ipsilateral temporal region matched higher amplitudes of skull bone vibrations measured on the teeth, but only at frequencies below 1 kHz. With stimulation at the eye, the thresholds were significantly higher than those with stimulation at the bony sites in the frequency range of 0.25-4 kHz. While skull bone vibrations as measured on the teeth during stimulation at the eye were low for low frequencies, significant bone vibrations were measured at 3 and 4 kHz, indicating different pathways for BC for either the soft tissue or bony site stimulation. This finding contradicts a straightforward relationship between vibrations of the skull bones and BC hearing thresholds.
Hearing Research, Nov 1, 2017
Background: Bone conduction (BC) is an alternative to air conduction to stimulate the inner ear. ... more Background: Bone conduction (BC) is an alternative to air conduction to stimulate the inner ear. In general, the stimulation for BC occurs on a specific location directly on the skull bone or through the skin covering the skull bone. The stimulation propagates to the ipsilateral and contralateral cochlea, mainly via the skull bone and possibly via other skull contents. This study aims to investigate the wave propagation on the surface of the skull bone during BC stimulation at the forehead and at ipsilateral mastoid. Methods: Measurements were performed in five human cadaveric whole heads. The electro-magnetic transducer from a BCHA (bone conducting hearing aid), a Baha ® Cordelle II transducer in particular, was attached to a percutaneously implanted screw or positioned with a 5-Newton steel headband at the mastoid and forehead. The Baha transducer was driven directly with single tone signals in the frequency range of 0.25 -8 kHz, while skull bone vibrations were measured at multiple points on the skull using a scanning laser Doppler vibrometer (SLDV) system and a 3D LDV system. The 3D velocity components, defined by the 3D LDV measurement coordinate system, have been transformed into tangent (in-plane) and normal (out-of-plane) components in a local intrinsic coordinate system at each measurement point, which is based on the cadaver head's shape, estimated by the spatial locations of all measurement points. Results: Rigid-body-like motion was dominant at low frequencies below 1 kHz, and clear transverse traveling waves were observed at high frequencies above 2 kHz for both measurement systems. The surface waves propagation speeds were approximately 450 m/s at 8 kHz, corresponding trans-cranial time interval of 0.4 ms. The 3D velocity measurements confirmed the complex space and frequency dependent response of the cadaver heads indicated by the 1D data from the SLDV system. Comparison between the tangent and normal motion components, extracted by transforming the 3D velocity components into a local coordinate system, indicates that the normal component, with spatially varying phase, is dominant above 2 kHz, consistent with local bending vibration modes and traveling surface waves. Both SLDV and 3D LDV data indicate that sound transmission in the skull bone causes rigid-body-like motion at low frequencies whereas transverse deformations
Journal of the Acoustical Society of America, Mar 1, 2020
In order to better understand bone conduction sound propagation across the skull, three-dimension... more 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.
International Journal of Pediatric Otorhinolaryngology, Aug 1, 2023
Hearing Research, Aug 1, 2022
BACKGROUND The frequency dependent contributions of the various bone conduction pathways are poor... more 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.
Hearing Research, Dec 1, 2018
Background Bone conduction (BC) is an alternative to air conduction (AC) for stimulation of the i... more 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 boneconducted 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.
Hearing Research, Oct 1, 2016
BACKGROUND: The malleus-incus complex (MIC) plays a crucial role in the hearing process as it tra... more BACKGROUND: The malleus-incus complex (MIC) plays a crucial role in the hearing process as it transforms and transmits acoustically-induced motion of the tympanic membrane, through the stapes, into the inner-ear. However, the transfer function of the MIC under physiologically-relevant acoustic stimulation is still under debate, especially due to insufficient quantitative data of the vibrational behavior of the MIC. This study focuses on the investigation of the sound transformation through the MIC, based on measurements of three-dimensional motions of the malleus and incus with a full six degrees of freedom (6 DOF). METHODS: The motion of the MIC was measured in two cadaveric human temporal bones with intact middle-ear structures excited via a loudspeaker embedded in an artificial ear canal, in the frequency range of 0.5-5 kHz. Three-dimensional (3D) shapes of the middle-ear ossicles were obtained by sequent micro-CT imaging, and an intrinsic frame based on the middle-ear anatomy was defined. All data were registered into the intrinsic frame, and rigid body motions of the malleus and incus were calculated with full six degrees of freedom. Then, the transfer function of the MIC, defined as velocity of the incus lenticular process relative to velocity of the malleus umbo, was obtained and analyzed. RESULTS: Based on the transfer function of the MIC, the motion of the lenticularis relative to the umbo reduces with frequency, particularly in the 2-5 kHz range. Analysis of the individual motion components of the transfer function indicates a predominant medial-lateral component at frequencies below 1 kHz, with low but considerable anterior-posterior and superior-inferior components that become prominent in the 2-5 kHz range. CONCLUSION: The transfer function of the human MIC, based on motion of the umbo and lenticularis, has been visualized and analyzed. While the magnitude of the transfer function decreases with frequency, its spatio-temporal complexity increases significantly.
Hearing Research, Jul 1, 2019
Objective Investigation of bone conduction sound propagation by osseous and non-osseous pathways ... more Objective 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.
Hearing Research, Aug 1, 2023
Hearing Research, Mar 1, 2023
Hearing Research, 2023
The time delay and/or malfunctioning of the Eustachian tube may cause pressure differences across... more 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 degrees 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. Keywords ambient pressure variation micro-computed tomography imaging middle-ear ossicles protection function quasi-static displacement static pressure static pressure loads stereo camera system three-dimensional displacement
Journal of the Acoustical Society of America, Mar 1, 2022
This study is aimed at the quantitative investigation of wave propagation through the skull bone ... more 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.
Hearing Research, Jun 1, 2022
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Hearing Research, Sep 1, 2020
OBJECTIVES Experimental investigation of the contribution of the middle ear to bone conduction (B... more 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.
Hearing Research, 2018
Background: Intra-operative quantification of the ossicle mobility could provide valuable feedbac... more Background: Intra-operative quantification of the ossicle mobility could provide valuable feedback for the current status of the patient's conductive hearing. However, current methods for evaluation of middle ear mobility are mostly limited to the surgeon's subjective impression through manual palpation of the ossicles. This study investigates how middle ear transfer function is affected by stapes quasi-static stiffness of the ossicular chain. The stiffness of the middle ear is induced by a) using a novel fiber-optic 3axis force sensor to quantify the quasi-static stiffness of the middle ear, and b) by artificial reduction of stapes mobility due to drying of the middle ear. Methods: Middle ear transfer function, defined as the ratio of the stapes footplate velocity versus the ear canal sound pressure, was measured with a single point LDV in two conditions. First, a controlled palpation force was applied at the stapes head in two in-plane (superior-inferior or posterior-anterior) directions, and at the incus lenticular process near the incudostapedial joint in the piston (lateralmedial) direction with a novel 3-axis PalpEar force sensor (Sensoptic, Losone, Switzerland), while the corresponding quasi-static displacement of the contact point was measured via a 3-axis micrometer stage. The palpation force was applied sequentially, step-wise in the range of 0.1e20 gF (1e200 mN). Second, measurements were repeated with various stages of stapes fixation, simulated by pre-load on the stapes head or drying of the temporal bone, and with severe ossicle immobilization, simulated by gluing of the stapes footplate. Results: Simulated stapes fixation (forced drying of 5e15 min) severely decreases (20e30 dB) the low frequency (<1 kHz) response of the middle ear, while increasing (5e10 dB) the high frequency (>4 kHz) response. Stapes immobilization (gluing of the footplate) severely reduces (20e40 dB) the low and mid frequency response (<4 kHz) but has lesser effect (<10 dB) at higher frequencies. Even moderate levels of palpation force (<3gF, <30 mN), regardless of direction, have negative effect (10e20 dB) on the low frequency (<2 kHz) response, but with less significant (5e10 dB) effect at higher frequencies. Forcedisplacement measurements around the incudostapedial joint showed quasi-static stiffness in the range of 200e500 N/m for normal middle ears, and 1000e2500 N/m (5e8-fold increase) after artificially (through forced drying) reducing the middle ear transfer function with 10e25 dB at 1 kHz. Conclusion: Effects of the palpation force level and direction, as well as stapes fixation and immobilization have been analyzed based on the measurement of the stapes footplate motion, and controlled application of 3D force and displacement.
Hearing Research, Oct 1, 2016
Under large quasi-static loads, the incudo-malleolar joint (IMJ), connecting the malleus and the ... more Under large quasi-static loads, the incudo-malleolar joint (IMJ), connecting the malleus and the incus, is highly mobile. It can be classified as a mechanical filter decoupling large quasi-static motions while transferring small dynamic excitations. This is presumed to be due to the complex geometry of the joint inducing a spatial decoupling between the malleus and incus under large quasi-static loads. Spatial Laser Doppler Vibrometer (LDV) displacement measurements on isolated malleus-incus-complexes (MICs) were performed. With the malleus firmly attached to a probe holder, the incus was excited by applying quasi-static forces at different points. For each force application point the resulting displacement was measured subsequently at different points on the incus. The location of the force application point and the LDV measurement points were calculated in a post-processing step combining the position of the LDV points with geometric data of the MIC. The rigid body motion of the incus was then calculated from the multiple displacement measurements for each force application point. The contact regions of the articular surfaces for different load configurations were calculated by applying the reconstructed motion to the geometry model of the MIC and calculate the minimal distance of the articular surfaces. The reconstructed motion has a complex spatial characteristic and varies for different force application points. The motion changed with increasing load caused by the kinematic guidance of the articular surfaces of the joint. The IMJ permits a relative large rotation around the anterior-posterior axis through the joint when a force is applied at the lenticularis in lateral direction before impeding the motion. This is part of the decoupling of the malleus motion from the incus motion in case of large quasi-static loads.
European Archives of Oto-rhino-laryngology, May 5, 2020
Objectives To investigate the association between the "ChOLE" classification, hearing outcomes an... more Objectives To investigate the association between the "ChOLE" classification, hearing outcomes and disease-specific healthrelated quality of life (HRQoL). Methods In two tertiary referral centers, patients requiring primary or revision surgery for cholesteatoma were assessed for eligibility. Audiometric assessment was performed pre-and postoperatively. The ChOLE classification was determined intraoperatively and via the preoperative CT scan. HRQoL was assessed pre-and postoperatively using the Zurich Chronic Middle Ear Inventory (ZCMEI-21). Results A total of 87 patients (mean age 45.2 years, SD 16.2) were included in this study. ChOLE stage I cholesteatoma was found in 8 (9%), stage II cholesteatoma was found in 65 (75%), and stage III cholesteatoma was found in 14 (16%) patients. Postoperatively, the mean air-bone gap (0.5, 1, 2, 3 kHz) was significantly smaller than before surgery (14.3 dB vs. 23.0 dB; p = 0.0007). The mean ZCMEI-21 total score significantly decreased after surgery (26.8 vs. 20.7, p = 0.004). No correlation between the ZCMEI-21 total score and both the ChOLE stage and the extent of the cholesteatoma (ChOLE subdivision "Ch") was found. A trend towards worse HRQoL associated with a poorer status of the ossicular chain (ChOLE subdivision "O") was observed. The audiometric outcomes were not associated with the extent of the cholesteatoma. The ChOLE subdivision describing the ossicular status showed a strong association with the pre-and postoperative air conduction (AC) thresholds. Further, the ZCMEI-21 total score and its hearing subscore correlated with the AC thresholds. Conclusion The ChOLE classification does not show a clear association with HRQoL measured by the ZCMEI-21. The HRQoL neither seems to be associated with the extent of the disease nor with the ossicular chain status. Yet, surgical therapy significantly improved HRQoL by means of reduced ZCMEI-21 total scores, which were strongly associated with the AC thresholds. Intraoperative assessment of a cholesteatoma using the ChOLE classification and HRQoL complement each other and provide useful information.
Otology & Neurotology, Oct 1, 2016
Hypothesis: Intracranial pressure and skull vibrations are correlated and depend on the stimulati... more Hypothesis: Intracranial pressure and skull vibrations are correlated and depend on the stimulation position and frequency. Background: A hearing sensation can be elicited by vibratory stimulation on the skin covered skull, or by stimulation on soft tissue such as the neck. It is not fully understood whether different stimulation sites induce the skull vibrations responsible for the perception or whether other transmission pathways are dominant. The aim of this study was to assess the correlation between intracranial pressure and skull vibration measured on the promontory for stimulation to different sites on the head. Methods: Measurements were performed on four human cadaver heads. A bone conduction hearing aid was held in place with a 5-Newton steel headband at four locations (mastoid, forehead, eye, and neck). While stimulating in the frequency range of 0.3 to 10 kHz, acceleration of the cochlear promontory was measured with a Laser Doppler Vibrometer, and intracranial pressure at the center of the head with a hydrophone. Results: Promontory acceleration and intracranial pressure was measurable for all stimulation sites. The ratios were comparable between all stimulation sites for frequencies below 2 kHz. Conclusion: These findings indicate that both promontory acceleration and intracranial pressure are involved for stimulation on the sites investigated. The transmission pathway of sound energy is comparable for the four stimulation sites.
Hearing Research, Oct 1, 2016
Bone conduction (BC) stimulation can be applied by vibration to the bony or skin covered skull (o... more Bone conduction (BC) stimulation can be applied by vibration to the bony or skin covered skull (osseous BC), or on soft tissue such as the neck (non-osseous BC). The interaction between osseous and non-osseous bone conduction pathways is assessed in this study. The relation between bone vibrations measured at the cochlear promontory and the intracranial sound pressure for stimulation directly on the dura and for stimulation at the mastoid between 0.2 and 10 kHz was compared. First, for stimulation on the dura, varying the static coupling force of the BC transducer on the dura had only a small effect on promontory vibration. Second, the presence or absence of intracranial fluid did not affect promontory vibration for stimulation on the dura. Third, stimulation on the mastoid elicited both promontory vibration and intracranial sound pressure. Stimulation on the dura caused intracranial sound pressure to a similar extent above 0.5 kHz compared to stimulation on the mastoid, while promontory vibration was less by 20-40 dB. From these findings, we conclude that intracranial sound pressure (non-osseous BC) only marginally affects bone vibrations measured on the promontory (osseous BC), whereas skull vibrations affect intracranial sound pressure.
Otology & Neurotology, Feb 1, 2011
OBJECTIVE: Use of the SMart piston, a nitinol-based, self-crimping prosthesis in stapes surgery m... more OBJECTIVE: Use of the SMart piston, a nitinol-based, self-crimping prosthesis in stapes surgery may allow improved functional results because of better sound transmission properties at the incus-prosthesis interface because of the elimination of manual crimping. Possible disadvantages include thermal damage or strangulation of the incus and its mucoperiosteum or nickel intolerance. The goal of this study was to morphologically assess the fixation of this prosthesis to the incus, investigate the reaction of the middle ear mucosa to the prosthesis, identify alterations to the incudal bone, and detect deposits of nickel in the tissue around the prosthesis. STUDY DESIGN:: Prospective consecutive case analysis. SETTING:: Tertiary referral center. PATIENTS: Four patients with an unfavorable functional result after primary SMart-piston stapedotomy. INTERVENTION: Revision malleostapedotomy with explantation of the incus and prosthesis for further analysis. MAIN OUTCOME MEASURES: Analysis of intraoperative findings and postoperative examination of the explants using light-and scanning-electron microscopy, energy dispersive x-ray analysis, and atom absorption spectrometry. RESULTS:: The intraoperative, macroscopic, and scanning electron microscopic investigation showed tight circular fixation of the prostheses, whereas a gap between the prosthesis and the lateral incus was found in 1 case. All prostheses were overgrown by mucosa. Superficial localized erosion of the incudal bone was found in 2 cases. There was no elevation in nickel content in the removed tissue samples. CONCLUSION:: The lateral gap between prosthesis and incus did not affect fixation of the prosthesis, neither did covering by a mucosal layer. Bone erosion was most likely caused by laser in one and by the prosthesis in another explant. No signs of increased nickel deposits could be found on energy dispersive x-ray analysis or atom absorption spectrometry. We conclude that a nitinol stapes prosthesis is safe for treatment of stapedial fixation.
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Papers by Christof Röösli