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For almost a decade, we have measured intracochlear sound pressures evoked by air conducted (AC) sound presented to the ear canal in many fresh human cadaveric specimens. Similar measurements were also obtained during round window (RW) mechanical stimulation in multiple specimens. In the present study, we use our accumulated data of intracochlear pressures and simultaneous velocity measurements of the stapes or RW to determine acoustic impedances of the cochlear partition, RW, and the leakage paths from scala vestibuli and scala tympani, as well as the reverse middle ear impedance. With these impedances, we develop a computational lumped-element model of the normal ear that illuminates fundamental mechanisms of sound transmission. To calculate the impedances for our model, we use data that passes strict inclusion criteria of: (a) normal middle-ear transfer function defined as the ratio of stapes velocity to ear-canal sound pressure, (b) no evidence of air within the inner ear, and (c) tight control of the pressure sensor sensitivity. After this strict screening, updated normal means, as well as individual representative data, of ossicular velocities and intracochlear pressures for AC and RW stimulation are used to calculate impedances. This work demonstrates the existence and the value of physiological acoustic leak impedances that can sometimes contribute significantly to sound transmission for some stimulation modalities. This model allows understanding of human sound transmission mechanisms for various sound stimulation methods such as AC, RW, and bone conduction, as well as sound transmission related to otoacoustic emissions., (Copyright © 2018 Elsevier B.V. All rights reserved.)

After initially successful preservation of residual hearing with cochlear implantation, some patients experience subsequent delayed hearing loss. The etiology of such delayed hearing loss is unknown. Human temporal bone pathology is critically important in investigating the etiology, and directing future efforts to maximize long term hearing preservation in cochlear implant patients. Here we present the temporal bone pathology from a patient implanted during life with an Iowa/Nucleus Hybrid S8 implant, with initially preserved residual hearing and subsequent hearing loss. Both temporal bones were removed for histologic processing and evaluated. Complete clinical and audiologic records were available. He had bilateral symmetric high frequency severe to profound hearing loss prior to implantation. Since he was implanted unilaterally, the unimplanted ear was presumed to be representative of the pre-implantation pathology related to his hearing loss. The implanted and contralateral unimplanted temporal bones both showed complete degeneration of inner hair cells and outer hair cells in the basal half of the cochleae, and only mild patchy loss of inner hair cells and outer hair cells in the apical half. The total spiral ganglion neuron counts were similar in both ears: 15,138 (56% of normal for age) in the unimplanted right ear and 13,722 (51% of normal for age) in the implanted left ear. In the basal turn of the implanted left cochlea, loose fibrous tissue and new bone formation filled the scala tympani, and part of the scala vestibuli. Delayed loss of initially preserved hearing after cochlear implantation was not explained by additional post-implantation degeneration of hair cells or spiral ganglion neurons in this patient. Decreased compliance at the round window and increased damping in the scala tympani due to intracochlear fibrosis and new bone formation might explain part of the post-implantation hearing loss. Reduction of the inflammatory and immune response to cochlear implantation may lead to better long term hearing preservation post-implantation., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Conclusions: Reconstruction of the ossicular chain differentially affects the motion of the tympanic membrane (TM) and the stapes., Objectives: To determine the effect of different ossicular replacement procedures on the sound-induced motion of the TM and stapes., Methods: A combination of digital stroboscopic holography and laser Doppler vibrometry was used to determine the sound-induced motion of the TM and stapes in cadaveric temporal bones in which the ossicular chain was reconstructed using 12 varied standard techniques. The variations included the use of total or partial ossicular prosthesis, size of cartilage interposed between the TM and the prosthesis, and the length or fit of the prosthesis between the TM and stapes. The measurements were carried out in repeated measures format, so that each manipulation was performed in each temporal bone., Results: The volume displacement of the TM was in general reduced by reconstruction, with the largest reductions occurring with high-frequency stimulation in the reconstructions with a 'large' cartilage oval interposed between the TM and the prosthesis. Larger stapes motions in response to low-frequency sound were observed with either 'loose' or 'best' fit TORP with a 'small' cartilage plate between the TM and the prosthesis.

Objectives: We describe the histopathologic findings in the temporal bones of a patient who had, during life, received a diagnosis of superior canal dehiscence (SCD) syndrome., Methods: The patient was found to have SCD syndrome at 59 years of age. She became a temporal bone donor, and died of unrelated causes at 62 years of age. Both temporal bones were prepared in celloidin and examined by light microscopy., Results: The patient developed bilateral aural fullness, pulsatile tinnitus, and difficulty tolerating loud noises after minor head trauma at 53 years of age. The symptoms were worse on the right. She also had Valsalva-induced dizziness and eye movements, as well as sound-induced dizziness (more prominent on the right). Audiometry showed a small air-bone gap of 10 dB in the right ear. Vestibular evoked myogenic potential testing showed an abnormally low threshold of 66 dB on the right, and a computed tomography scan showed dehiscence of the superior canal on the right. Histopathologic examination of the right ear showed a 1.4 x 0.6-mm dehiscence of bone covering the superior canal. Dura was in direct contact with the endosteum and the membranous duct at the level of the dehiscence. No osteoclastic process was evident within the otic capsule bone surrounding the dehiscence. The left ear showed thin but intact bone over the superior canal. Both ears showed focal microdehiscences of the tegmen tympani and tegmen mastoideum. The auditory and vestibular sense organs on both sides appeared normal. No endolymphatic hydrops was observed., Conclusions: The findings were consistent with the hypothesis put forth by Carey and colleagues that SCD may arise from a failure of postnatal bone development, and that minor trauma may disrupt thin bone or stable dura over the superior canal.

Hypothesis: Round window (RW) stimulation with a floating mass transducer (FMT) can be studied experimentally and optimized to enhance auditory transduction., Background: The FMT (MED-EL Vibrant Soundbridge) has been recently implanted in patients with refractory conductive or mixed hearing loss to stimulate the RW with varying degrees of success. The mechanics of RW stimulation with the FMT have not been studied in a systematic manner., Methods: In cadaveric human temporal bones, measurements of stapes velocity with laser vibrometry in response to FMT-RW stimulation were used to optimize FMT insertion. The effect of RW stimulation on hearing was estimated using simultaneous measurements of intracochlear pressures in both perilymphatic scalae with micro-optical pressure transducers. This enabled calculation of the differential pressure across the cochlear partition, which is directly tied to auditory transduction., Results: The best coupling between the FMT and RW was achieved with a piece of fascia placed between the RW and the FMT, and by "bracing" the free end of the FMT against the hypotympanic wall with dental impression material. FMT-RW stimulation provided differential pressures comparable with sound-induced oval window stimulation greater than 1 kHz. However, less than 1 kHz, the FMT was less capable., Conclusion: Measurements of stapes velocity and intracochlear sound pressures in scala vestibuli and scala tympani enabled experimental evaluation of FMT stimulation of the RW. The efficacy of FMT-RW coupling was influenced significantly by technical and surgical factors, which can be optimized. This temporal bone preparation also lays the foundation for future studies to investigate multiple issues of relevance to both basic and clinical science such as RW stimulation in stapes fixation, nonaerated middle ears, and third-window lesions, and to answer basic questions regarding bone conduction.

The anatomy of the distal incus, including the lenticular process, was examined in histological sections from 270 normal cadaveric human temporal bones aged between less than 1 month and 100 years. All but nine of these sectioned specimens showed signs of a bony connection between the long process of the incus and the flattened plate of the lenticular process, and in 108 specimens a complete bony attachment was observed in a single 20 microm section. In these 108 ears, the bony lenticular process consisted of a proximal narrow "pedicle" connected to a distal flattened "plate" that forms the incudal component of the incudo-stapedial joint. A fibrous joint capsule extended from the stapes head to the pedicle of the lenticular process on all sides, where it was considerably thickened. Three-dimensional reconstructions made from serial 20 microm sections of four bones provided views from all directions that easily convey the anatomical features of this region. Morphometric measurements of the bony architecture of the distal incus in 103 temporal bones were made, including lengths and cross-sectional areas, estimates of the percentage of lacunae containing osteocytes, and the degree of bone resorption. These measurements, analyzed as a function of age, provided an anatomic description over a large age range that can serve as a normal baseline against which structural pathology can be compared. Although none of the bony dimensions showed significant age dependence, the estimated percentage of bony lacunae that contain osteocytes decreased significantly with age. The results have implications for the roles of specific components on the coupling of ossicular motion across the incudo-stapedial joint, and provide insights regarding bone resorption at the level of the distal incus, which occurs clinically in some patients with chronic otitis media or after stapedectomy.

We present the first simultaneous sound pressure measurements in scala vestibuli and scala tympani of the cochlea in human cadaveric temporal bones. The technique we employ, which exploits microscale fiberoptic pressure sensors, enables the study of differential sound pressure at the cochlear base. This differential pressure is the input to the cochlear partition, driving cochlear waves and auditory transduction. In our results, the sound pressure in scala vestibuli (P (SV)) was much greater than scala tympani pressure (P (ST)), except for very low and high frequencies where P (ST) significantly affected the input to the cochlea. The differential pressure (P (SV) - P (ST)) is a superior measure of ossicular transduction of sound compared to P (SV) alone: (P (SV)-P (ST)) was reduced by 30 to 50 dB when the ossicular chain was disarticulated, whereas P (SV) was not reduced as much. The middle ear gain P (SV)/P (EC) and the differential pressure normalized to ear canal pressure (P (SV) - P (ST))/P (EC) were generally bandpass in frequency dependence. At frequencies above 1 kHz, the group delay in the middle ear gain is about 83 micros, over twice that of the gerbil. Concurrent measurements of stapes velocity produced estimates of cochlear input impedance, the differential impedance across the partition, and round window impedance. The differential impedance was generally resistive, while the round window impedance was consistent with compliance in conjunction with distributed inertia and damping. Our technique of measuring differential pressure can be used to study inner ear conductive pathologies (e.g., semicircular dehiscence), as well as non-ossicular cochlear stimulation (e.g., round window stimulation and bone conduction)--situations that cannot be completely quantified by measurements of stapes velocity or scala vestibuli pressure by themselves.

Direct acoustic stimulation of the cochlea by the sound-pressure difference between the oval and round windows (called the "acoustic route") has been thought to contribute to hearing in some pathological conditions, along with the normally dominant "ossicular route." To determine the efficacy of this acoustic route and its constituent mechanisms in human ears, sound pressures were measured at three locations in cadaveric temporal bones [with intact and perforated tympanic membranes (TMs)]: (1) in the external ear canal lateral to the TM, P(TM); (2) in the tympanic cavity lateral to the oval window, P(OW); and (3) near the round window, P(RW). Sound transmission via the acoustic route is described by two concatenated processes: (1) coupling of sound pressure from ear canal to middle-ear cavity, H(P(CAV) ) identical withP(CAV)P(TM), where P(CAV) represents the middle-ear cavity pressure, and (2) sound-pressure difference between the windows, H(WPD) identical with(P(OW)-P(RW))P(CAV). Results show that: H(P(CAV) ) depends on perforation size but not perforation location; H(WPD) depends on neither perforation size nor location. The results (1) provide a description of the window pressures based on measurements, (2) refute the common otological view that TM perforation location affects the "relative phase of the pressures at the oval and round windows," and (3) show with an intact ossicular chain that acoustic-route transmission is substantially below ossicular-route transmission except for low frequencies with large perforations. Thus, hearing loss from TM perforations results primarily from reduction in sound coupling via the ossicular route. Some features of the frequency dependence of H(P(CAV) ) and H(WPD) can be interpreted in terms of a structure-based lumped-element acoustic model of the perforation and middle-ear cavities.

A human temporal-bone preparation was used to determine the effects of various degrees of artificial ossicular fixation on the sound-induced velocity at the input-side (the umbo of the malleus) and the output-side (the stapes) of the ossicular chain. Construction of various degrees of attachment between an ossicle and the surrounding temporal bone provided a range of reduction in ossicular mobility or "fixations". The results demonstrate different effects of the fixations on the umbo and stapes velocity: fixations of the stapes or incus produce larger reductions in sound-induced stapes velocity (as much as 40-50 dB with extensive stapes fixation), than reductions in umbo velocity (typically less than 10 dB). Fixations of the malleus produce similar-sized changes in both umbo and stapes velocity. These differential effects are consistent with significant flexibility in the ossicular joints (the incudo-malleolar joint and the incudo-stapedial joint) that permits relative motion between the coupled ossicles. The existence of flexibility in the ossicular joints indicates that joints in the ossicular chain can effect a loss of sound-induced mechanical energy between the umbo and the stapes, with a concomitant reduction in the sound-induced motion of the stapes. The introduction of such losses in sound transmission by the joints raises questions concerning the utility of three ossicles in the mammalian ear. The consequences of ossicular flexibility to ossicular-chain reconstruction is discussed. Also, as examined in a more clinically directed paper [Laryngoscope 115 (2005) 147], the different effects of the various ossicular fixations on the motion of the umbo and malleus may be useful in the diagnosis of the site of fixations in humans with conductive hearing losses caused by such pathologies.

Objective: To investigate the mechanics of Type III tympanoplasty by developing a cadaveric temporal bone model., Background: Type III stapes columella tympanoplasty involves the placement of a tympanic membrane graft, usually made of temporalis fascia, directly onto the stapes head. The procedure is usually done in conjunction with a canal wall down mastoidectomy. Postoperative hearing results vary widely, with air-bone gaps of 10 to 60 dB. The structural features responsible for the wide range in hearing results have not been systematically investigated., Methods: Canal wall down Type III procedures were performed in eight cadaveric temporal bones. Acoustic stimuli were presented in the ear canal, and round window velocity VRW (used as an index of hearing) was measured, while systematically varying stapes mobility, mechanical properties of tympanic membrane graft, and tightness of connection between tympanic membrane graft and stapes. The effect of interposing a thin cartilage disc between the tympanic membrane graft and stapes head was also assessed., Results: When the middle ear was aerated and the stapes was mobile, VRW was 15 to 30 dB lower than in an intact, normal ear. Stapes fixation led to a significant reduction in VRW; reduction was greatest at low frequencies. There was little effect of varying the tightness of connection between the tympanic membrane graft and stapes head. Sound energy was transmitted from the graft to the stapes as long as the graft was in physical contact with the stapes head. Different tympanic membrane graft materials with a range of mechanical properties (stiffness and mass) resulted in little variation in VRW. Interposing a thin cartilage disc between the tympanic membrane graft and stapes improved VRW in the lower frequencies by 5 to 10 dB. The authors hypothesize that the disc acted to increase the effective vibrating area of the graft., Conclusions: The feasibility of using a cadaveric temporal bone model to study the mechanics of Type III tympanoplasty was demonstrated. A mobile stapes and aerated middle ear were essential for a successful Type III tympanoplasty. There was little effect of varying the mechanical properties of the tympanic membrane graft or changing the tightness of connection between the graft and stapes head. Improved results were achieved by interposing a thin cartilage disc between the graft and stapes head to increase the effective vibrating area of the graft.

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

A study of clinical records and temporal bone histopathology from a woman with bilateral otosclerosis who was treated with lateral semicircular canal fenestration procedures as well as stapedectomy. [ABSTRACT FROM AUTHOR]

We present the first simultaneous sound pressure measurements in scala vestibuli and scala tympani of the cochlea in human cadaveric temporal bones. The technique we employ, which exploits microscale fiberoptic pressure sensors, enables the study of differential sound pressure at the cochlear base. This differential pressure is the input to the cochlear partition, driving cochlear waves and auditory transduction. In our results, the sound pressure in scala vestibuli ( PSV) was much greater than scala tympani pressure ( PST), except for very low and high frequencies where PST significantly affected the input to the cochlea. The differential pressure ( PSV − PST) is a superior measure of ossicular transduction of sound compared to PSV alone: ( PSV− PST) was reduced by 30 to 50 dB when the ossicular chain was disarticulated, whereas PSV was not reduced as much. The middle ear gain PSV/ PEC and the differential pressure normalized to ear canal pressure ( PSV − PST)/ PEC were generally bandpass in frequency dependence. At frequencies above 1 kHz, the group delay in the middle ear gain is about 83 μs, over twice that of the gerbil. Concurrent measurements of stapes velocity produced estimates of cochlear input impedance, the differential impedance across the partition, and round window impedance. The differential impedance was generally resistive, while the round window impedance was consistent with compliance in conjunction with distributed inertia and damping. Our technique of measuring differential pressure can be used to study inner ear conductive pathologies (e.g., semicircular dehiscence), as well as non-ossicular cochlear stimulation (e.g., round window stimulation and bone conduction)—situations that cannot be completely quantified by measurements of stapes velocity or scala vestibuli pressure by themselves. [ABSTRACT FROM AUTHOR]

Abstract: The cochlea is normally driven with “forward” stimulation, in which sound is introduced to the ear canal. Alternatively, the cochlea can be stimulated at the round window (RW) using an actuator. During RW “reverse” stimulation, the acoustic flow starting at the RW does not necessarily take the same path as during forward stimulation. To understand the differences between forward and reverse stimulation, we measured ear-canal pressure, stapes velocity, RW velocity, and intracochlear pressures in scala vestibuli (SV) and scala tympani (ST) of fresh human temporal bones. During forward stimulation, the cochlear drive (differential pressure across the partition) results from the large difference in magnitude between the pressures of SV and ST, which occurs due to the high compliance of the RW. During reverse stimulation, the relatively high impedance of the middle ear causes the pressures of SV and ST to have similar magnitudes, and the differential pressure results primarily from the difference in phase of the pressures. Furthermore, the sound path differs between forward and reverse stimulation, such that motion through a third window is more significant during reverse stimulation. Additionally, we determined that although stapes velocity is a good estimate of cochlear drive during forward stimulation, it is not a good measure during reverse stimulation. This article is part of a Special Issue entitled “MEMRO 2012”. [Copyright &y& Elsevier]

Sound-induced motions of the surface of the tympanic membrane (TM) were measured using stroboscopic holography in cadaveric human temporal bones at frequencies between 0.2 and 18 kHz. The results are consistent with the combination of standing-wave-like modal motions and traveling-wave-like motions on the TM surface. The holographic techniques also quantified sound-induced displacements of the umbo of the malleus, as well as volume velocity of the TM. These measurements were combined with sound-pressure measurements near the TM to compute middle-ear input impedance and power reflectance at the TM. The results are generally consistent with other published data. A phenomenological model that behaved qualitatively like the data was used to quantify the relative magnitude and spatial frequencies of the modal and traveling-wave-like displacement components on the TM surface. This model suggests the modal magnitudes are generally larger than those of the putative traveling waves, and the computed wave speeds are much slower than wave speeds predicted by estimates of middle-ear delay. While the data are inconsistent with simple modal displacements of the TM, an alternate model based on the combination of modal motions in a lossy membrane can also explain these measurements without invoking traveling waves. [ABSTRACT FROM AUTHOR]

Abstract: Sound-induced stapes velocity (Vs) was measured intraoperatively in 14 patients undergoing cochlear implantation. All 14 patients had no history of middle-ear pathology, and their ossicular chains appeared normal on intraoperative inspection and palpation. The magnitude of the mean Vs (normalized by simultaneously-measured ear-canal sound pressure) was stiffness-dominated at frequencies below 1kHz, increased up to ∼4kHz, and then decreased at higher frequencies. The phase of the mean velocity was +0.2 periods at 0.3kHz, and gradually became a phase lag at higher frequencies. The mean Vs measured in this study was similar to that of seven ears reported in the only other published study of live human measurements (). We also made measurements of Vs in fresh cadaveric temporal bones using a technique identical to that used in live ears, including similar measurement angles and location. The mean Vs measured in the cadaveric ears under these conditions was similar to the mean Vs measurements in the 14 live ears. This indicates that middle-ear mechanics are similar in live and cadaveric ears. In addition, interspecies comparisons were made between our live human Vs and the Vs reported in different animal studies. There were some clear similarities in Vs across species, as well as differences. The primary interspecies differences were in the magnitude of the Vs as well as in the frequency of transitions in the magnitudes’ frequency dependence from rising to flat or falling. [Copyright &y& Elsevier]

Methodological differences in sound-induced stapes velocity (Vs) measurements in live and cadaveric ears were examined using fresh cadaveric temporal bones. On average, differences in preparation (sectioning the stapedius tendon, removing the facial nerve, and widely opening the facial recess) had statistically insignificant effects on measured Vs. Differences in the achievable measurement angle (with respect to the axis of piston-like stapes motion) had a significant effect on measured Vs below 2 kHz. These results suggest that much if not all of the differences in Vs measurements between live and cadaveric ears can be explained by the differences in measurement angle between the two preparations. Measurement angle was found to have minimal effect on measured Vs above 2 kHz. This demonstrates that the commonly used method of estimating stapes translational velocity by dividing the measured velocity by the cosine of the measurement angle is not valid above 2 kHz. [ABSTRACT FROM AUTHOR]

The response of the tympanic membrane (TM) to transient environmental sounds and the contributions of different parts of the TM to middle-ear sound transmission were investigated by measuring the TM response to global transients (acoustic clicks) and to local transients (mechanical impulses) applied to the umbo and various locations on the TM. A lightly-fixed human temporal bone was prepared by removing the ear canal, inner ear, and stapes, leaving the incus, malleus, and TM intact. Motion of nearly the entire TM was measured by a digital holography system with a high speed camera at a rate of 42 000 frames per second, giving a temporal resolution of <24 μs for the duration of the TM response. The entire TM responded nearly instantaneously to acoustic transient stimuli, though the peak displacement and decay time constant varied with location. With local mechanical transients, the TM responded first locally at the site of stimulation, and the response spread approximately symmetrically and circumferentially around the umbo and manubrium. Acoustic and mechanical transients provide distinct and complementary stimuli for the study of TM response. Spatial variations in decay and rate of spread of response imply local variations in TM stiffness, mass, and damping. [ABSTRACT FROM AUTHOR]