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Purpose: Studies have assessed the trauma and change in hearing function from the use of otological drills on the ossicular chain, but not the effects of partial laser ablation of the incus. A study of the effectiveness of a novel middle-ear microphone for a cochlear implant, which required an incus recess for the microphone balltip, provided an opportunity to compare methods and inform a feasibility study of the microphone with patients. Methods: We used laser Doppler vibrometry with an insert earphone and probe microphone in 23 ears from 14 fresh-frozen cadavers to measure the equivalent noise level at the tympanic membrane that would have led to the same stapes velocity as the creation of the incus recess. Results: Drilling on the incus with a diamond burr created peak noise levels equivalent to 125.1–155.0 dB SPL at the tympanic membrane, whilst using the laser generated equivalent noise levels barely above the baseline level. The change in middle ear transfer function following drilling showed greater variability at high frequencies, but the change was not statistically significant in the three frequency bands tested. Conclusions: Whilst drilling resulted in substantially higher equivalent noise, we considered that the recess created by laser ablation was more likely to lead to movement of the microphone balltip, and therefore decrease performance or result in malfunction over time. For patients with greatly reduced residual hearing, the greater consistency from drilling the incus recess may outweigh the potential benefits of hearing preservation with laser ablation. [ABSTRACT FROM AUTHOR]

• Ear canal and intracochlear pressures become nonlinear at high SPLs. • The saturation point of ossicular transmission is frequency dependent. • High SPL transmission exhibits harmonic distortion consistent with peak clipping. • Results can be used to update and extend hearing hazard assessment tools. Previous reports have suggested that intracochlear pressures (P IC) measured at the base of the cochlea increase directly proportionally with stapes displacement (D Stap) in response to moderately high (<130 dB SPL) level sounds. Consistent with this assumption, we have reported that for low frequency sounds (<1 kHz), stapes displacement and intracochlear pressures increase linearly with sound pressure level (SPL) for moderately high levels (<130 dB SPL), but saturate at higher exposure levels (>130 dB SPL). However, the magnitudes of each response were found to be frequency dependent, thus the relationship between D Stap and P IC may vary at higher frequencies or higher levels. In order to further examine this frequency and level dependence, measurements of D Stap and P IC were made in cadaveric human temporal bones prepared with a mastoidectomy and extended facial recess to expose the ossicular chain. P IC was measured in scala vestibuli (P SV) and scala tympani (P ST) simultaneously with SPL in the external auditory canal (P EAC) and laser Doppler vibrometry (LDV) measurements of stapes velocity (V Stap). Consistent with prior reports, D Stap and P SV increased proportionally with sound pressure level in the ear canal up to a frequency-dependent saturation point, above which both D Stap and P SV showed a distinct deviation from proportionality with P EAC , suggesting that their relationship may remain constant at these high frequencies. Likewise, while the asymptotic value, and SPL at which saturation occurred were frequency dependent in both D Stap and P SV, the reduction in gain with increasing SPL above this level was constant above this level at all frequencies, and the magnitude of responses at harmonics of the driving frequency increased with increasing level, consistent with harmonic distortion via peak clipping. Importantly, this nonlinear distortion shifts the energy arriving at the inner ear to higher frequencies than are present in incident stimulus, thus exposing the high frequency sensitive components of the auditory system to more noise than would be expected from measurement of that stimulus on its own. Overall, responses suggest that the cochlear representation of very high-level air conducted stimuli is limited by nonlinearities in the middle ear, and that this peak limiting leads to increased high frequency cochlear exposures than are present in the driving stimulus. [ABSTRACT FROM AUTHOR]

Tympanometry provides an objective measurement of the status of the middle ear. During tympanometry, the ear-canal pressure is varied, while the response of the ear to sound pressure is measured. The effects of the pressure on the mechanics of the middle ear are not well understood. This study is a continuation of our previous work in which the vibration response of the gerbil eardrum was measured in vivo under quasi-static pressure steps. In this study, we delivered a continuous pressure sweep to the middle ear and measured the vibration response at four locations for six gerbils. Vibrations were recorded using a single-point laser Doppler vibrometer and glass-coated reflective beads (diameter ~ 40 µm) at the umbo and on the mid-manubrium, posterior pars tensa and anterior pars tensa. The vibration magnitudes were similar to those in the previous step-wise pressurization experiments. Most gerbils showed repeatability within less than 10 dB for consecutive cycles. As described in the previous study, as the frequency was increased at ambient pressure, the vibration magnitude on the manubrium increased slightly to a broad peak (referred to as R1) and then decreased until a small peak appeared (referred to as R2), followed by multiple peaks and troughs as the magnitude decreased further. The low-frequency vibration magnitude (at 1 kHz) decreased monotonically as the pressure became more negative except for a dip (about 500 Pa wide) that occurred between − 700 and − 1800 Pa. The lowest overall magnitude was recorded in the dip at mid-manubrium. The vibration magnitudes also decreased as the middle-ear pressure was made more positive and were larger than those at negative pressures. R1 was only visible at negative and small positive middle-ear pressures, while R2 was visible for both positive and negative pressures. R2 split into multiple branches after the middle-ear pressure became slightly positive. No magnitude dip was visible for positive middle-ear pressures. The low-frequency vibration magnitudes at negative middle-ear pressures on the pars tensa were higher than those on the manubrium. R1 was not visible for large negative middle-ear pressures on the pars tensa. R2 appeared as a multi-peak feature on the pars tensa as well, and a higher-frequency branch on the posterior pars tensa appeared as a trough on the anterior pars tensa. The magnitude dip was not present on the pars tensa. The largest overall magnitude was recorded at the R2 peak on the posterior pars tensa. The results of this study expand on the findings of the step-wise pressurization experiments and provide further insight into the evolution of the vibration response of the eardrum under quasi-static pressures. [ABSTRACT FROM AUTHOR]

Objective: Anchoring grafts for tympanic membrane (TM) reconstruction in anterior and subtotal TM defects is essential to prevent medialisation and can be facilitated by cartilaginous bending spring tympanoplasty (CBST). The purpose of this study was to analyse the impact of spring cartilages on middle ear transfer functions and patient hearing levels. Methods: In six fresh-frozen human temporal bones a cartilage graft (measuring 6 × 2 mm with a thickness of 0.1–0.2 mm) was formed into a 'U'-shaped bending spring, to be placed between the medial tympanic wall and the tympanic underlay grafts. The stapes velocity for excitation by exponential sweeps from 400 to 10,000 Hz was measured with a laser Doppler vibrometer. The resulting middle ear transfer functions were compared with the reconstructed middle ear. For clinical evaluation, 23 ears in 21 patients with chronic otitis media and an intact ossicular chain were operated using CBST. At each follow-up visit, the patients underwent pure-tone audiometry and the Freiburg monosyllabic speech test at a presentation level of 65 dB SPL for the word recognition score (WRS). Results: The measured stapes velocities at one-third octave midband frequencies averaged 3.56 × 10–2 ± 9.46 × 10–3 (mm/s/Pa) compared to 3.06 × 10–2 ± 6.86 × 10–3 (mm/s/Pa) with the bending and underlay cartilage in place (p = 0.319; r = 0.32). The bending spring tympanoplasty reduced the transfer function by 1.41 ± 0.98 dB on average. In the clinical part of the study, the graft success rate was 96% (22 out of 23 patients) after a mean follow-up of 5.8 ± 2.4 months (min. 3.5 months, max. 12.0 months). The air–bone gap improved significantly by 6.2 dB (± 6.6 dB; p < 0.001; r = 0.69), as well as the WRS from 61.8 ± 33.3% preoperatively to 80.0 ± 20.9% postoperatively (p = 0.031; r = 0.35). Conclusion: Experimental data as well as initial clinical results suggest that CBST is an effective method for reconstructing anterior or subtotal defects of the tympanic membrane with satisfactory audiologic results and graft success rates comparable to previously described methods. It can, therefore, be added to the arsenal of tympanoplasty techniques for anterior and subtotal TM perforations. [ABSTRACT FROM AUTHOR]

Tympanometry is a relatively simple non-invasive test of the status of the middle ear. An important step towards understanding the mechanics of the middle ear during tympanometry is to make vibration measurements on the eardrum under tympanometric pressures. In this study, we measured in vivo vibration responses in 11 gerbils while varying the middle-ear pressure quasi-statically, with the ear canal at ambient pressure. Vibrations were recorded using a single-point laser Doppler vibrometer with five glass-coated reflective beads (diameter ~ 40 μm) as targets. The locations were the umbo, mid-manubrium, posterior pars tensa, anterior pars tensa and pars flaccida. As described in earlier studies, the unpressurized vibration magnitude was flat at low frequencies, increased until a resonance frequency at around 1.8-2.5 kHz, and became complex at higher frequencies. At both the umbo and mid-manubrium points, when the static pressure was decreased to the most negative middle-ear pressure (- 2500 Pa), the low-frequency vibration magnitude (measured at 1.0 kHz) showed a monotonic decrease, except for an unexpected dip at around - 500 to - 1000 Pa. This dip was not present for the pars-tensa and pars-flaccida points. The resonance frequency shifted to higher frequencies, to around 7-8 kHz at - 2500 Pa. For positive middle-ear pressures, the low-frequency vibration magnitude decreased monotonically, with no dip, and the resonance frequency shifted to around 5-6 kHz at + 2500 Pa. There was more inter-specimen variability on the positive-pressure side than on the negative-pressure side. The low-frequency vibration magnitudes on the negative-pressure side were higher for the pars-tensa points than for the umbo and mid-manubrium points, while the magnitudes were similar at all four locations on the positive-pressure side. Most gerbils showed repeatability within less than 10 dB for consecutive cycles. The results of this study provide insight into the mechanics of the gerbil middle ear under tympanometric pressures. [ABSTRACT FROM AUTHOR]

Hearing damage is one of most prevalent injuries in military personnel and civilians exposed to a blast. However, the mechanism of how the blast overpressure interacts with the tympanic membrane (TM) and impairs the peripheral auditory system still remains unclear. A 3D finite element (FE) model of the human ear has been developed to predict the blast overpressure transmission through the ear (Leckness et al., 2018), but the model needs to be further validated in TM response to blast pressure. This paper reports the first-ever approach using two laser Doppler vibrometers (LDVs) to measure the motion of the TM when the ear was exposed to a blast. Five fresh human temporal bones were used in this study with a pressure sensor inserted near the TM to measure the pressure reaching the TM (P1). The temporal bone was mounted in a "head block" and exposed to blast at the overpressure around 35 kPa measured at the entrance of the ear canal (P0). The movements of the TM at the umbo and the "head block" were measured simultaneously by two LDVs and the exact motion of the TM was determined by subtracting the head block motion from the TM data. Results include that the maximum TM velocity was 12.62 ± 3.63 m/s (mean ± SD) and the displacement was 0.78 ± 0.26 mm. The peak-to-peak displacement normalized by the P0 pressure was 22.9 ± 6.6 μm/kPa. The frequency domain analysis indicated that the spectrum peaks were located at frequencies below 3 kHz. The TM motion was then compared with that calculated from the FE model of the human ear with the measured P0 pressure wave applied at the ear canal entrance. The FE model-derived TM displacement under blast overpressure was consistent with the experimental results. This study provides a new methodology to determine the behavior of the middle ear in response to blast overpressure. The experimental data are critical for validating the FE model of the human ear for blast wave transduction and understanding the TM damage induced by blast exposure. • Movements of human tympanic membrane (TM) under blast exposure are measured. • Dual-laser Doppler vibrometers are established to measure TM vibration under blast. • Delayed movement of the TM with respect to blast overpressure has been observed. • Frequency components of the TM movement induced by blast are below 3 kHz. • The FE model was validated with the TM movement in response to blast in temporal bones. [ABSTRACT FROM AUTHOR]

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

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 3-axis 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 (lateral-medial) 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 0.1–20 gF (1–200 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 5–15 min) severely decreases (20–30 dB) the low frequency (<1 kHz) response of the middle ear, while increasing (5–10 dB) the high frequency (>4 kHz) response. Stapes immobilization (gluing of the footplate) severely reduces (20–40 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 (10–20 dB) on the low frequency (<2 kHz) response, but with less significant (5–10 dB) effect at higher frequencies. Force-displacement measurements around the incudostapedial joint showed quasi-static stiffness in the range of 200–500 N/m for normal middle ears, and 1000–2500 N/m (5–8-fold increase) after artificially (through forced drying) reducing the middle ear transfer function with 10–25 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. [ABSTRACT FROM AUTHOR]

Objective: In order to help a surgeon make the best decision, a more objective method of measuring ossicular motion is required. Methods: A laser Doppler vibrometer was mounted on a surgical microscope. To measure ossicular chain vibrations, eight patients with cochlear implants were investigated. To assess the motions of the ossicular chain, velocities at five points were measured with tonal stimuli of 1 and 3 kHz, which yielded reproducible results. The sequential amplitude change at each point was calculated with phase shifting from the tonal stimulus. Motion of the ossicular chain was visualized from the averaged results using the graphics application. Results: The head of the malleus and the body of the incus showed synchronized movement as one unit. In contrast, the stapes (incudostapedial joint and posterior crus) moved synchronously in opposite phase to the malleus and incus. The amplitudes at 1 kHz were almost twice those at 3 kHz. Conclusions: Our results show that the malleus and incus unit and the stapes move with a phase difference. [ABSTRACT FROM AUTHOR]

• A novel experimental platform was developed. • Stapes footplate movement and cochlear pressure were measured simultaneously. • New methodology for quantitatively measuring energy flux into the cochlea during blast. • Peak experimental values are consistent with published results and modeling data. Blast-induced auditory injury is primarily caused by exposure to an overwhelming amount of energy transmitted into the external auditory canal, the middle ear, and then the cochlea. Quantification of this energy requires real-time measurement of stapes footplate (SFP) motion and intracochlear pressure in the scala vestibuli (Psv). To date, SFP and Psv have not been measured simultaneously during blast exposure, but a dual-laser experimental approach for detecting the movement of the SFP was reported by Jiang et al. (2021). In this study, we have incorporated the measurement of Psv with SFP motion and developed a novel approach to quantitatively measure the energy flux entering the cochlea during blast exposure. Five fresh human cadaveric temporal bones (TBs) were used in this study. A mastoidectomy and facial recess approach were performed to identify the SFP, followed by a cochleostomy into the scala vestibuli (SV). The TB was mounted to the "head block", a fixture to simulate a real human skull, with two pressure sensors – one inserted into the SV (Psv) and another in the ear canal near the tympanic membrane (P1). The TB was exposed to the blast overpressure (P0) around 4 psi or 28 kPa. Two laser Doppler vibrometers (LDVs) were used to measure the movements of the SFP and TB (as a reference). The LDVs, P1, and Psv signals were triggered by P0 and recorded simultaneously. The results include peak values for Psv of 100.8 ± 51.6 kPa (mean ± SD) and for SFP displacement of 72.6 ± 56.4 μm, which are consistent with published experimental results and finite element modeling data. Most of the P0 input energy flux into the cochlea occurred within 2 ms and resulted in 10–70 μJ total energy entering the cochlea. Although the middle ear pressure gain was close to that measured under acoustic stimulus conditions, the nonlinear behavior of the middle ear was observed from the elevated cochlear input impedance. For the first time, SFP movement and intracochlear pressure Psv have been successfully measured simultaneously during blast exposure. This study provides a new methodology and experimental data for determining the energy flux entering the cochlea during a blast, which serves as an injury index for quantifying blast-induced auditory damage. [ABSTRACT FROM AUTHOR]

In both mammals and birds, the mechanical behavior of the middle ear structures is affected by the mechanical impedance of the inner ear. In this study, the aim was to quantify the acoustic impedance of the avian inner ear in the ostrich, which allows us to determine the effect on columellar vibrations and middle ear power flow in future studies. To determine the inner ear impedance, vibrations of the columella were measured for both the quasi-static and acoustic stimulus frequencies. In the frequency range of 0.3–4 kHz, we used electromagnetic stimulation of the ossicle and a laser Doppler vibrometer to measure the vibration response. At low frequencies, harmonic displacements were imposed on the columella using piezo stimulation and the resulting force response was measured with a force sensor. From these measurement data, the acoustic impedance of the inner ear could be determined. A simple RLC model in series of the impedance measurements resulted in a stiffness reactance of K IE = 0.20·10 12 Pa/m³, an inertial impedance of M IE = 0.652·10 6 Pa s 2 /m³, and a resistance of R IE = 1.57·10 9 Pa s/m. We found that values of the inner ear impedance in the ostrich are one to two orders in magnitude smaller than what is found in mammal ears. [ABSTRACT FROM AUTHOR]

This paper presents in vivo experimental measurements of vibrations on the pars flaccida, along the manubrium and at several points on the pars tensa in the gerbil with open middle-ear cavity. The effects of progressive opening of the middle-ear cavity are presented, with up to five different extents of opening. In all manubrial, pars-tensa and pars-flaccida responses, opening the cavity causes an increase in the low-frequency magnitude and a shift of the main middle-ear resonance to lower frequencies and introduces an antiresonance. However, opening the cavity has little or no effect on either the mode of vibration of the manubrium or the breakup frequency of the pars tensa. When the opening is gradually widened, the antiresonance frequency moves to higher frequencies. When the opening is made as wide as anatomically possible, the antiresonance moves to almost 10 kHz. The main increase in the low-frequency response magnitude happens upon making the smallest hole in the cavity wall, and further progressive enlarging of the opening has little or no effect on the low-frequency magnitude. The antiresonance interferes with the response shapes. An identification method is suggested for eliminating the effect of the antiresonance in order to estimate the ideal open-cavity response. The method is validated and then applied to manubrial and pars-tensa responses. Estimating the ideal open-cavity responses will simplify comparison of the data with numerical models which do not include the air cavity. The data collected at intermediate stages of opening will be useful in validating models that do include the cavity. [ABSTRACT FROM AUTHOR]

The purpose of the present work is to investigate the spatial vibration pattern of the gerbil tympanic membrane (TM) as a function of frequency. In vivo vibration measurements were done at several locations on the pars flaccida and pars tensa, and along the manubrium, on surgically exposed gerbil TMs with closed middle ear cavities. A laser Doppler vibrometer was used to measure motions in response to audio frequency sine sweeps in the ear canal. Data are presented for two different pars flaccida conditions: naturally flat and retracted into the middle ear cavity. Resonance of the flat pars flaccida causes a minimum and a shallow maximum in the displacement magnitude of the manubrium and pars tensa at low frequencies. Compared with a flat pars flaccida, a retracted pars flaccida has much lower displacement magnitudes at low frequencies and does not affect the responses of the other points. All manubrial and pars tensa points show a broad resonance in the range of 1.6 to 2 kHz. Above this resonance, the displacement magnitudes of manubrial points, including the umbo, roll off with substantial irregularities. The manubrial points show an increasing displacement magnitude from the lateral process toward the umbo. Above 5 kHz, phase differences between points along the manubrium start to become more evident, which may indicate flexing of the tip of the manubrium or a change in the vibration mode of the malleus. At low frequencies, points on the posterior side of the pars tensa tend to show larger displacements than those on the anterior side. The simple low-frequency vibration pattern of the pars tensa becomes more complex at higher frequencies, with the breakup occurring at between 1.8 and 2.8 kHz. These observations will be important for the development and validation of middle ear finite-element models for the gerbil. [ABSTRACT FROM AUTHOR]

The article discusses a study conducted to assess the impact of removal of the incus body on sound transfer in ossicular chain reconstruction (OCR). It also provides data helpful in making clinical decision regarding ossiculoplasty. The study found that removal of the incus body in OCR by the help of incus strut prosthesis do not change sound transfer function of the middle ear.

Background: Silastic sheeting is commonly used in middle ear surgery to prevent the formation of adhesions between the tympanic membrane and the medial bony wall of the middle ear cavity. This sheeting is often placed, advertently or inadvertently, so as to cover the round window niche. The effects of mechanically shielding the round window niche in the presence of an intact tympanic membrane and ossicular chain have not been empirically studied to date. Objective: To investigate the effect of acoustically shielding the round window with 1 mm thick Silastic sheeting on middle ear sound transmission in otherwise intact cadaveric human temporal bones. Methods: Using a fresh human cadaveric temporal model, a computerized laser Doppler vibrometry system was used to measure vibrations at the umbo and on the stapes footplate in response to sound introduced into the ear canal. Stapes displacement was used as a measure of sound transmission. The measurements were repeated after shielding the round window using 1 mm thick Silastic sheeting. Results: We found that shielding the round window with Silastic produced no significant difference in the measurements at the stapes footplate. At the umbo, a slight increase in vibrations at 250 to 500 Hz was measured after shielding. This was on the order of 3 dB and was not statistically significant. Conclusion: In the presence of an intact tympanic membrane and ossicular chain, shielding the round window with Silastic sheeting has no clinically significant effect on sound transmission by the human middle ear. [ABSTRACT FROM AUTHOR]

A life-size mechanical middle ear model and human temporal bones were used to evaluate three different middle ear transducers for implantable hearing aids: the driving rod transducer (DRT), the floating mass transducer (FMT) or vibrant sound bridge, and the contactless transducer (CLT). Results of the experiments with the mechanical model were within the range of the results for human temporal bones. However, results with the mechanical model showed better reproducibility. The handling of the mechanical model was considerably simpler and less time-consuming. Systematic variations of mounting parameters showed that the angle of the rod has virtually no effect on the output of the DRT, the mass loading on the cable of the FMT has a larger impact on the output than does the tightness of crimping, and the output level of the CLT can be increased by 10 dB by optimizing the mounting parameters. [ABSTRACT FROM AUTHOR]

• Motion of stapes footplate (SFP) under blast was measured using laser vibrometers. • Displacement of the SFP was 68.7 ± 31.6 μm at the blast level around 48 kPa (7Psi). • The major frequency components of the SFP motion were below 4 kHz. • The earplug lowered the displacement and reduced the energy carried by the velocity of SFP. • A new methodology was developed to estimate the blast-induced damage in the ear. Hearing damage is one of the most frequently observed injuries in Service members and Veterans even though hearing protection devices (HPDs, e.g. earplugs) have been implemented to prevent blast-induced hearing loss. However, the formation and prevention mechanism of the blast-induced hearing damage remains unclear due to the difficulty for conducting biomechanical measurements in ears during blast exposure. Recently, an approach reported by Jiang et al. (2019) used two laser Doppler vibrometers (LDVs) to measure the motion of the tympanic membrane (TM) in human temporal bones during blast exposure. Using the dual laser setup, we further developed the technology to detect the movement of the stapes footplate (SFP) in ears with and without HPDs while under blast exposure. Eight fresh human cadaveric temporal bones (TBs) were involved in this study. The TB was mounted in a "head block" after performing a facial recess surgery to access the SFP, and a pressure sensor was inserted near the TM in the ear canal to measure the pressure reaching the TM (P1). The TB was exposed to a blast overpressure measuring around 7 psi or 48 kPa at the entrance of the ear canal (P0). Two LDVs were used to measure the vibrations of the SFP and TB (as a reference). The exact motion of the SFP was determined by subtracting the TB motion from the SFP data. Results included a measured peak-to-peak SFP displacement of 68.7 ± 31.6 μm (mean ± SD) from all eight TBs without HPDs. In five of the TBs, the insertion of a foam earplug reduced the SFP displacement from 48.3 ± 6.3 μm to 21.8 ± 10.4 μm. The time-frequency analysis of the SFP velocity signals indicated that most of the energy spectrum was concentrated at frequencies below 4 kHz within the first 2 ms after blast and the energy was reduced after the insertion of HPDs. This study describes a new methodology to quantitatively characterize the response of the middle ear and the energy entering the cochlea during blast exposure. The experimental data are critical for determining the injury of the peripheral auditory system and elucidating the damage formation and prevention mechanism in an ear exposed to blast. [ABSTRACT FROM AUTHOR]

• Motion of ear structures differ maximally 10 dB in average between fresh frozen and Thiel conserved human specimens. • First report comparing the effect of conservation methods on middle-ear motion using the same specimen. • Conserved specimens have similar middle ear motion to fresh frozen specimens which facilitates long-term experiments. As an alternative to fresh temporal bones, Thiel conserved specimens can be used in the study of ear mechanics. Conserved temporal bones do not decay, permit long-term experiments and overcome problems with limited access to fresh (frozen) temporal bones. Air conduction motion of the tympanic membrane (TM), stapes (ST) and round window (RW) in Thiel specimens is similar to that of fresh specimens according to reports in the literature. Our study compares this motion directly before and after conservation for the same specimens. The magnitude of motion of TM, ST and RW elicited by acoustic stimulation via the external auditory canal was measured using single point laser Doppler vibrometry (LDV) accessed through a posterior tympanotomy. For the initial measurements (10 ears), fresh frozen whole heads were thawed for at least 24 h. Afterwards, the entire whole heads were embalmed according to the Thiel embalming method and measurements were repeated 3 and 12 months later. The magnitudes of TM, ST and RW motion before and after Thiel conservation differed maximally 10 dB on average. A significant increase in TM motion was observed at low frequencies only after long term conservation (12 months). ST motions decreased significantly between 161 and 5300 Hz after 3 months of Thiel conservation. Over the same time period RW motions decreased significantly between 100 and 161 Hz and 489–788 Hz. The ST and RW motions across all measured frequencies were lower after 3 months by 5.7 dB and 7.1 dB, respectively, without further changes after 12 months of conservation. The mean phase shift between ST and RW motion was only 2.1° for frequencies below 450 Hz. Thiel embalming changes motion of TM after long term conservation. ST and RW motion changed mainly after short term conservation. The phase shifts close to 180° between ST and RW motion indicates that the cochlea was still filled with liquid without air bubbles. The results show that Thiel conserved specimens can be used as an alternative model to fresh frozen preparations with some limitations when studying mechanics of the normal human ear, for example, in implant design. [ABSTRACT FROM AUTHOR]