Bone conduction hearing in the blockage of oval and/or round windows in cats

Although human air conduction (AC) and bone conduction (BC) hearing are well investigated, there is a lack of information about BC hearing in most other species, the normal BC hearing thresholds have not been established. And animal model is vital for understanding the physiology of bone conduction hearing. Hence, in our study, the hearing thresholds in the guinea pigs were estimated by a regression of the amplitude of the compound action potential (CAP) with stimulation level and was found robust and gave a high resolution of the threshold level in the frequency range between 2 kHz and 20 kHz. The reference for the BC thresholds was the cochlear promontory bone velocity. This reference enables comparison of BC hearing in animals, both intra and inter species, which is independent on the vibrator and stimulation position. According to our comparable BC threshold, we can do some further research. The vibration was measured in three orthogonal directions where the dominating vibration directions was in line with the stimulation direction, here the ventral direction. The BC thresholds lay between -10 and 3 dB re 1 μm/s. The slopes of CAP growth function were similar for AC and BC at low and high frequencies, but slightly lower for BC than AC at frequencies between 8 and 16 kHz. This was attributed to differences in the stimulus levels used for the slope estimation and not a real difference in CAP slopes between the stimulation modalities. At the same time, the effect of a middle ear lesion, here modelled by severing the ossicles (ossicular discontinuity) and gluing the ossicles to the bone (otosclerosis), is investigated for both AC and BC. Two kinds of middle ear lesions, ossicular discontinuity and stapes glued to the surrounding bone, gave threshold shifts of between 23 and 53 dB for AC while it was below 16 dB when the stimulation was by BC. Statistically different threshold shifts between the two types of lesions were found where the AC threshold shifts for a glued stapes at 2 and 4 kHz were 9 to 18 dB greater than for a severed ossicular chain, and the BC threshold shifts for a glued stapes at 4 and 12 kHz were 8 to 9 dB greater than for a severed ossicular chain. Moreover, the direction of the vibration influences BC hearing also is investigated in our study. This direction sensitivity was investigated guinea pigs by providing BC stimulation in five different directions at the vertex of the guinea pig skull. The hearing thresholds for BC stimulation was obtained in the frequency range of 2 to 20 kHz by measurements of the guinea pigs’ compound action potential. During the stimulation by BC, the vibration of the cochlear promontory was measured with a three-dimensional laser Doppler vibrometer resulting in a set of unique three-dimensional vibration combinations for each threshold estimation. The sets of three-dimensional vibration at threshold were used to investigate six different predictors of BC hearing based on cochlear promontory vibration, three single direction (x, y and z directions in isolation), one linear combination of the three-dimension vibrations, one square-rooted sum of the squared vibration magnitudes, and one sum of the weighted three-dimensional vibrations based on a restricted minimum mean square error (MMSE) estimation. The MMSE gave the best predictions of the hearing threshold based on the cochlear promontory vibration while using only a single direction gave the worst predictions of the hearing thresholds overall. According to the MMSE estimation, at frequencies up to 8 kHz the vibration direction between the right and left side gave the greatest contribution to BC hearing in the guinea pig while at the highest frequencies measured, 16 and 20 kHz, the anteroposterior direction of the guinea pig head gave the greatest contribution. We do the further research to compare the vibrational patterns of human and guinea pig cochleae accurately, we developed and validated a novel finite element model of the guinea pig, leveraging it to analyze vibrational patterns in the cochlea. This approach is mirrored in our examination of the human cochlear model, providing granular insights into the nuances of human bone conduction hearing. The comparative analysis reveals that the guinea pig cochlea mirrors human cochlear vibrational patterns, thus serving as an efficient proxy for exploring human cochlear function. The convenient and comparable sites for bone conduction stimulation are identified as the human mastoid and the upper region of the guinea pig's skull. The cochlear vibration pattern encompasses a mix of rigid, rotational, and compressive motion.

Besides the normal hearing pathway known as air conduction (AC), sound can also transmit to the cochlea through the skull, known as bone conduction (BC). During BC stimulation, the cochlear walls demonstrate rigid body motion (RBM) and compressional motion (CPM), both inducing the basilar membrane traveling wave (TW). Despite numerous measuring and modeling efforts for the TW phenomenon, the mechanism remains unclear, especially in the case of BC. This paper proposes a 3D finite element cochlea model mimicking the TW under BC. The model uses a traditional "box model" form, but in a spiral shape, with two fluid chambers separated by the long and flexible BM. The cochlear fluid was enclosed by bony walls, the oval and round window membranes. Contingent boundary conditions and stimulations are introduced according to the physical basis of AC and BC. Particularly for BC, both RBM and CPM of the cochlea walls are simulated. Harmonic numerical solutions are obtained at multiple frequencies among the hearing range. The BM vibration amplitude ([Formula: see text]) and its relation with volume displacement difference between the oval and round windows [Formula: see text], as well as the pressure difference at the base of the cochlea ([Formula: see text]), are analyzed. The simulated BM response at 12mm from the base is peaked at about 3kHz, which is consistent with published experimental data. The TW properties under AC and BC are the same and have a common mechanism. (1) [Formula: see text] is proportional to [Formula: see text] at low frequencies. (2) [Formula: see text] is also proportional to [Formula: see text], within 5dB error at high frequencies such as 16kHz. This study partly reveals the common quantitative relations between the TW and related factors under AC and BC hearing.

Bone conduction hearing in the Guinea pig and the effect of artificially induced middle ear lesions

The fluids in the cochlea are normally considered incompressible, and the fluid volume displacement of the oval window (OW) and the round window (RW) should be equal and of opposite phase. However, other channels, such as the cochlear and vestibular aqueducts, may affect the fluid flow. To test if the OW and RW fluid flows are equal and of opposite phase, the volume displacement was assessed by multiple point measurement at the windows with a laser Doppler vibrometer. This was done during air conduction (AC) stimulation in seven fresh human temporal bones, and with bone conduction (BC) stimulation in eight temporal bones and one human cadaver head. With AC stimulation, the average volume displacement of the two windows is within 3 dB, and the phase difference is close to 180 degrees for the frequency range 0.1 to 10 kHz. With BC stimulation, the average volume displacement difference between the two windows is greater: below 2 kHz, the volume displacement at the RW is 5 to 15 dB greater than at the OW and above 2 kHz more fluid is displaced at the OW. With BC stimulation, lesions at the OW caused only minor changes of the fluid flow at the RW.

The fact that vibration of the skull causes a hearing sensation has been known since the 19th century. This mode of hearing was termed hearing by bone conduction. Although there has been more than a century of research on hearing by bone conduction, its physiology is not completely understood. Lately, new insights into the physiology of hearing by bone conduction have been reported. Knowledge of the physiology, clinical aspects, and limitations of bone conduction sound is important for clinicians dealing with hearing loss and is the purpose of this review. The data were compiled from the published literature in the areas of clinical bone conduction hearing, bone conduction hearing aids, basic research on bone conduction physiology, and recent research on bone conduction hearing from our laboratory. Five factors contributing to bone conduction hearing have been identified: 1) sound radiated into the external ear canal, 2) middle ear ossicle inertia, 3) inertia of the cochlear fluids, 4) compression of the cochlear walls, and 5) pressure transmission from the cerebrospinal fluid. Of these five, inertia of the cochlear fluid seems most important. Bone conduction sound is believed to reflect the true cochlear function; however, certain conditions such as middle ear diseases can affect bone conduction sensitivity, but less than for air conduction. The bone conduction route can also be used for hearing aids; since the bone conduction route is less efficient than the air conduction route, bone conduction hearing aids are primarily used for hearing losses where air conduction hearing aids are contraindicated.

Gender differences in bone conduction auditory signal processing: Communication equipment design implications

It has been observed frequently that inner ear trouble caused by the chronic inflammatorydiseases of the middle ear. The etiology has not been cleared but the extension of the inflammation by the destruction of the bone. Another possible route of spread of the disease is through the round and oval window which are located between the inner ear middle ear cavity. In the surgical treatment of the chronic otitis media, the condition of the round window has to be studied prior to the surgery disease how to diagnose any defect of round window for the purpose for the restoration of the hearing. For such purpose the permeability of round window was studied. One tenth cc of 10% cocaine hydrochloride was injected through the ear drum into the inner ear cavity of normal ear, middle ear disease and inner ear disease, and the symptons of autonomic nerve reaction was studied in conjunction with the change in the audiograph. Furthermore, various experimental hearing disordes were studied in the animals in order to endorse the results of the clinical experiments.The results of the investigations were as follows:The autonomic nerve reaction and subjective symptoms were obseeved in case with otosclerosis, sequela of otitis media, chronic otitia media with perforation, healthy ear, Meniere's syndrome and nerve deafness. In aminal experiment, symptoms appeared in conductive deafness (produced by cement injection), conductive deafness (otitis media), healythy ear, and perceptive deafness.The change on the audiograph:-In the cases with healthy ear and also perceptive deafness, the decrease in the thereshold both in air and bone conduction was observed below 2048 c.p.s and the increase in the threshold in air and bone conduction over 2048 c.p.s. In conductive deafnes due to inflammatory condition, the threshold was decreased below 3068 c.p.s in air and bone conduction. In those due to non-inflammatory condition, the change was minimal. Also, in case with remarkable autonomic nerve reaction, the increase of the threshold in higth tone, was observed. The tinnitus gave a certain influence to the audible threshold at the same frequency.Consequently, the cocaine solution being injected into the middle ear cavity may cause a certain trouble of inner ear passing through the round window. When there is a thickening of the membrane of round window such as in cases with chronic otitis media, in some cases the permeability is low and this must be kept in mind at the time of surgicol treatment. The condition of round window is clinically able to be evaluated by the injection of cocaine solution.

Objectives: Report the immediate audiologic effect of paper patch myringoplasty to repair iatrogenic tympanic membrane perforations directly over the round window. Methods: Retrospective case-control study of 15 patients treated for inner ear disease with a MicroWick and dexamethasone for 1 month, resulting in 2-mm perforations over the round window. Paper patch myringoplasties were performed to repair the perforations. Audiograms were performed before and immediately after the paper patch myringoplasty. Results: After paper patch placement, there was a significant improvement in air-bone gap at 250 (p < 0.001), 500 (p = 0.003), and 1000 Hz (p = 0.004) and a significant improvement in bone conduction (BC) threshold at 250 (p = 0.002), 500 (p < 0.001), 1000 (p = 0.002), 2000 (p = 0.003), and 3000 Hz (p = 0.02). Conclusions: Paper patch myringoplasty improves both air conduction and BC hearing from small perforations over the round window. The decrease in BC hearing is a result of middle ear mechanics and is not a true sensorineural hearing loss.

Conclusion: In cases of labyrinthine fistulae, we performed complete removal of the cholesteatoma matrix in a one-stage procedure, resulting in a satisfactory bone conduction (BC) hearing preservation rate. Preoperative evaluation of labyrinthine fistulae using high resolution computed tomography (HRCT) detected 86% of cases, and this contributed to favorable results achieved with the surgical treatment of labyrinthine fistulae. We aimed to review cases of labyrinthine fistulae to summarize their outcomes and establish standards of management. Methods: This was a retrospective chart review of 22 patients with labyrinthine fistulae at Kyoto University Hospital from 2001 to 2009. Patient background (age and sex), location and stage of the fistulae, facial nerve status, preoperative and postoperative BC hearing levels, preoperative CT diagnosis, and surgical procedures were analyzed. Results: The incidence rate of the labyrinthine fistulae was 11.2%. All but one patient had labyrinthine fistula due to cholesteatoma. The fistulae were found in the lateral semicircular canal in 17 cases (77%) and in multiple organs in 4 cases (18%). The BC hearing level was preoperatively scaled out in seven cases. Preoperative HRCT scan revealed the presence of fistulae in 19 cases (86%). For all cases of cholesteatoma, the matrix was completely removed in a one-stage procedure and the fistulae were sealed using bone pate, temporal fascia, and temporal bones. Of the 15 cases with residual BC hearing ability, BC hearing was preserved in up to 12 cases. Two cases with postoperative deterioration of BC hearing had stage 4 fistulae in the cochleae.

In the absence of patent cochlear windows, cochlear fluid inertia depends on the presence of a "third window" as a major component of the bone-conduction response. Studies have shown conflicting results regarding changes in air and bone conduction whenever, the round window, oval window, or both windows were occluded. The study was performed in a tertiary university-affiliated medical center. Auditory brain responses to clicks and 1-kHz tone bursts delivered by air and bone conduction were tested in 5 adult-size fat sand rats. The round window membrane (total, 7 ears) was sealed with Super Glue, and auditory brain response testing was repeated. Thereafter, the stapes footplate was firmly fixated, and auditory brain responses were recorded for a third time. Round-window fixation induced a significant increase in air-conduction thresholds to clicks from 36.4 ± 0.9 to 69.3 ± 4.1 dB SPL, with no significant change in bone-conduction thresholds. When the stapes footplate was immobilized as well, air conduction increased by another 20 dB, on average, with no change in bone conduction. A similar deterioration was seen in response to 1 kHz stimulus. These findings support and complement earlier studies in the same animal model, suggesting that when the pressure outlet through the cochlear windows are abolished, still bone conduction displaces the cochlear partition probably because of a functioning "third window."

Cross-head transmission inherent in bone conduction (BC) hearing is one of the most important factors that limit the performance of BC binaural hearing compared to air conduction (AC) binaural hearing. In AC, cross-head transmission is imperceptible leading to a clear understanding of the nature and position of the sound source(s). In this study, the prominence of cross-head transmission in BC hearing is addressed using the fact that ipsilateral cochlear excitation can be canceled by controlled bilateral BC stimulation.A cancellation experiment was conducted on twenty participants with normal hearing at thirteen third-octave frequencies between 250 and 4000 Hz. Both stationary and transient BC stimulation at the mastoid was used. The technique employed multiple stages of masking enabling adjustments of the stimulation level and phase until the tones got canceled in the ipsilateral ear. In addition, the ear canal sound pressure was obtained for ipsilateral and contralateral BC stimulation in isolation, and with bilateral BC stimulation at perceptual cancellation.The inter-aural level differences of both the types of stimulations were found to be the same. Crosstalk was found to be the lowest around 2 kHz and the highest around 1 kHz. The unwrapped inter-aural phase difference from stationary signal cancellation showed an overall increase with frequency starting at around no difference (35°) at 250 Hz to reach 607° at 4 kHz. Cycle-adjusted inter-aural time difference was very low (61 µs) at 250 Hz and increased to 1.1 ms at 800 Hz before falling to 0.6 ms at 4 kHz. It was also found that the ear canal sound pressure was not cancelled at the same phase as the sound in the cochlea.

The goal of this study was to better understand bone-conduction hearing in subjects with normal hearing and in those with otosclerosis through the occlusion effect. With this study, the authors hope to lend credence to commonly accepted theories of bone-conduction hearing and the effect of lateralization during the Weber tuning fork test. There are three accepted theories defining bone-conduction hearing: compressional bone conduction describes an auditory percept produced by the compression and expansion of the cochlea leading to basilar membrane vibration; inertial bone conduction describes the inertia of the ossicular chain as a result of skull vibration during bone conduction testing; whereas skull vibration may also be transmitted to the external auditory canal, surrounding soft tissues, and para-auditory structures to illicit tympanic membrane vibration known as osseotympanic bone conduction. Twenty normal volunteers and 17 unilateral otosclerosis patients underwent external canal sound pressure level measurement during bone-conduction testing using a standardized bone oscillator placement and stimulation paradigm. Sound was detected with a probe microphone placed in the external auditory canal in nonoccluded and occluded conditions after a 50-dB hearing level bone-conduction stimulus. There was no significant difference in sound pressure level between otosclerosis and normal subjects when the external auditory canals were nonoccluded. With occlusion, sound pressure level increased in both groups, but at a statistically significantly higher level for the otosclerosis group. Sound measured in the external canal likely represents energy lost to the environment transmitted through the middle and external ear systems, aided by the effect of both inertial and osseotympanic bone conduction. Occluding the ear leads to sound trapping and amplification. Also, the pressure exerted against the tympanic membrane reduces middle ear compliance and increases the impedance mismatch between air and the middle ear system, reflecting sound back into the external canal. This effect is further enhanced by stapes fixation to explain our data in both groups of subjects. The final common pathway in "lateralization" is probably a product of higher than normal impedance mismatch at the oval window.

Although otosclerosis is essentially a middle ear disease, patients with this disease often exhibit mixed hearing loss. This discrepancy is thought to be explained by the following mechanism: the resonance of the ossicular chain is disturbed by the fixation of stapes, leading to the attenuation of inertial bone conduction. The bone-conduction hearing level usually recovers after stapes surgery. We herein studied the change in air- and bone-conduction hearing after stapes surgery in patients with otosclerosis. Six consecutive patients with otosclerosis who underwent stapes surgery in our department were enrolled. They were 2 men and 4 women, ranging in age from 16 to 74 with an average of 57.2 years. Stapedotomy was performed in 5 patients, and the other patient underwent partial stapedectomy. Their pure tone hearing levels of air and bone conduction were measured before and after surgery. In the air conduction, the hearing levels at 125, 250, 500, 1000, 2000, and 4000 Hz significantly improved after surgery, but showed no significant change at 8000 Hz. On the other hand, in the bone conduction, the hearing levels at 500 and 1000 Hz significantly improved after surgery, whereas those at 250, 2000, and 4000 Hz showed no significant change. The recovery of the bone conduction hearing at 500 and 1000 Hz is explained by the resonance of the ossicular chain. However, the unimproved bone conduction hearing at 2000 Hz is unexplainable, and remains to be further investigated in future studies.

A third window, which is another cochlear fluid pathway different from the oval window and round window, is considered to be a significant factor in bone-conducted hearing. A three-dimensional finite element model of the human ear consisting of the middle ear and cochlea was used to investigate the effect of the third windows on bone-conducted heraing. This study is aimed to find the third window which causes the consistent cochlear responses with previous studies in air-conducted hearing, and causes the asymmetry of the volume velocity ratio between the oval window and round window in bone-conducted hearing. The preliminary result shows that the cochlear aqueduct and the vestibular aqueduct with high impedance do not affect the basilar membrane velocity in air-conducted hearing. On the contrary, in bone-conducted hearing, the direction of the shaking structure for the bone-conducted stimulation as well as the third window can be a significant factor causing the asymmetry of the volume velocity ratio found by Stenfelt et al.

ABSTACTTo ensure the safety and efficacy of implantable hearing aids, animal experiments are an essential developmental procedure, in particular, auditory brainstem responses (ABRs) can be used to verify the objective effectiveness of implantable hearing aids. This study measured and compared the ABRs generated when applying the same vibration stimuli to an oval window and round window. The ABRs were measured using a TDT system 3 (TDT, USA), while the vibration stimuli were applied to a round window and oval window in 4 guinea pigs using a piezo-electric transducer with a proper contact tip. A paired t-test was used to determine any differences between the ABR amplitudes when applying the stimulation to an oval window and round window. The paired t-test revealed a significant difference between the ABR amplitudes generated by the round and oval window stimulation (t = 10.079, α < .0001). Therefore, the results confirmed that the biological response to round window stimulation was not the same as that to oval window stimulation.