Study of age-related changes in Middle ear transfer function

Interfacing Perforated Eardrums with Graphene-Based Membranes for Broadband Hearing Recovery

Eardrum perforation and associated hearing loss is a global health problem. Grafting perforated eardrum with autologous tissues in clinic can restore low-frequency hearing but often leaves poor recovery of high-frequency hearing. In this study, the potential of incorporating a thin multilayered graphene membrane (MGM) into the eardrum for broadband hearing recovery in rats is examined. The MGM shows good biocompatibility and biostability to promote the growth of eardrum cells in a regulated manner with little sign of tissue rejection and inflammatory response. After three weeks of implantation, the MGM is found to be encapsulated by a thin layer of newly grown tissue on both sides without a significant folded overgrowth that is often seen in natural healing. The perforation is well sealed, and broadband hearing recovery (1-32 kHz) is enabled and maintained for at least 2 months. Mechanical simulations show that the high elastic modulus of MGM and thin thickness of the reconstructed eardrum play a critical role in the recovery of high-frequency hearing. This work demonstrates the promise of the use of MGM as a functional graft for perforated eardrum to recover hearing in the broadband frequency region and suggests a new acoustics-related medical application for graphene-related 2D materials.

Effects of Age and Middle Ear on the Frequency Tuning of the cVEMP and oVEMP

BACKGROUND

Upward shift in the air conducted (AC) frequency tuning of vestibular evoked myogenic potentials (VEMPs) as an effect of aging is hypothesized to be due to the microstructural stiffening changes in the inner ear. However, with an AC stimulus, it may be possible that the shift in the frequency tuning of VEMPs as an effect of aging may also be due to contributions from the middle ear.

PURPOSE

The main aim of this study was to examine the effects of age on the frequency tuning of the cervical VEMP (cVEMP) and ocular VEMP (oVEMP) and determine the role of middle ear transmission characteristics in shaping these effects.

RESEARCH DESIGN

Standard group comparison.

STUDY SAMPLE

One-hundred seven participants divided in three groups: young adult, middle-age, and older adults with "normal" middle ear and negative history of neurological or vestibular complaints.

DATA COLLECTION AND ANALYSES

Middle ear measures included static admittance and middle ear resonant frequency. cVEMP and oVEMPs were elicited with AC tone bursts at 500, 750, and 1,000 Hz.

RESULTS

No significant effect of age was observed on any of the middle ear measures. There was a significant effect of age on the amplitude of the cVEMP, but this effect was frequency specific. The age-related reduction in cVEMP corrected amplitude was only observed when the eliciting stimulus was 500 or 750 Hz, with no significant effect observed with a 1,000 Hz stimulus. For the oVEMP, the effects of age were apparent at all stimulus frequencies. We also observed a general upward shift in the frequency tuning of both the cVEMP and oVEMP for middle-age and older adults, with 750 and 1,000 Hz yielding higher response rates and larger amplitudes among middle-aged and older adults. Measurements of middle ear did not significantly contribute to the observed findings.

CONCLUSIONS

The upward shift in frequency tuning of VEMPs among middle age and older adults could be due to the changes in the vestibular system and not from the middle ear. These results support the use of different frequency stimuli (i.e., 750 or 1,000 Hz) to elicit a VEMP if a response is absent using a 500 Hz stimulus, especially in patients over the age of 40.

Internal vascular channel architecture in human auditory ossicles

The vascular supply of the human auditory ossicles has long been of anatomical and clinical interest. While the external blood supply has been well‐described, there is only limited information available regarding the internal vascular architecture of the ossicles, and there has been little comparison of this between individuals. Based on high‐resolution micro‐CT scans, we made reconstructions of the internal vascular channels and cavities in 12 sets of ossicles from elderly donors. Despite considerable individual variation, a common basic pattern was identified. The presence of channels within the stapes footplate was confirmed. The long process of the incus and neck of the stapes showed signs of bony erosion in all specimens examined. More severe erosion was associated with interruption of some or all of the main internal vascular channels which normally pass down the incudal long process; internal excavation of the proximal process could interrupt vascular channels in ossicles which did not appear to be badly damaged from exterior inspection. An awareness of this possibility may be helpful for surgical procedures that compromise the mucosal blood supply. We also calculated ossicular densities, finding that the malleus tends to be denser than the incus. This is mainly due to a lower proportion of vascular channels and cavities within the malleus.

Effects of age-related tympanic-membrane material properties on sound transmission in the middle ear in a three-dimensional finite-element model

BACKGROUND AND OBJECTIVES

The Young's modulus of the tympanic membrane (TM) is an important modeling parameter in computer simulations of the sound transmission in the ear. Understanding the material mechanics of the TM is essential to improve the coupling between the tympanic membrane and the auditory ossicles. However, the impact of the age-related Young's modulus of the TM on sound transmission is not well known. The objective of this study was to use a comprehensive finite element (FE) model to assess the impact of Young's modulus on sound transmission from the ear canal to the stapes footplate over acoustic frequencies.

METHODS

The FE model of the ear canal, the middle ear, and the inner ear, was constructed. The model was constructed with identical geometries and boundary conditions, but with three different Young's moduli for the TMs. The auditory ossicles, suspensory ligaments and tendons, and manubrium were also modeled as isotropic elastic materials. Beside, we evaluated the age-related Young's moduli of the TMs on sound transmission with the FE element fluid-structural interaction (FSI) model under acoustic loading conditions.

RESULTS

The impact of the age-related Young's moduli on the sound pressure distributions in the ear canal was significant over two frequency ranges of 1.4-3.2 and 8.6-10 kHz. Meanwhile, the significant differences of the displacement of the stapes occurred at around 1.6 kHz, where the displacement of the stapes decreased from 0.352 nm to 0.287 nm.

CONCLUSIONS

The FSI model could demonstrate the influence of Young's modulus of the TM on the transfer of sound-induced vibrations form the ear canal to the stapes footplate. The FE model may provide appropriate information to the medical device development of artificial ossicles and hearing aids.

Morphology of human ear canal and its effect on sound transmission

The ear canal (EC) is essential for sound transfer and crucial for hearing. Some pathological conditions may modify its morphology, leading to EC sound pressure redistribution, and stapes footplate displacement (FPD) gain alteration. However, no consensus regarding pathological EC and its impact on sound transfer has yet been achieved. To address the effect of morphology of EC on sound pressure redistribution and FPD gain. Varied pathological EC finite element (FE) models were constructed and analyzed based on FE analysis. The results indicated that canal wall down mastoidectomy decreases the second resonance frequency of the EC. The canal wall down mastoidectomy, with conchaplasty increased the first resonance frequency, but decreased the second along with the interval sound pressure gain increased, following which the FPD gain was altered. Stenosis of the EC at the internal portion decreased the second resonance frequency with minimal effect to the first part. When the stenosis moved to the outer portion of the EC, the first resonance frequency decreased, and the second one increased, along with the interval sound pressure gain decreased and FPD gain. Finally, the simplified EC model exerted a minimal effect on sound transfer. The minimal change in EC, such as simplification, straightening, canal wall down mastoidectomy, or enlargement, moderately affects the sound transfer; however, the EC stenosis deteriorates the sound transfer remarkably.

The Impact of the Frequency-Specific Preoperative Sensorineural Hearing Loss to Postoperative Overclosure of Bone Conduction in Stapedotomy

OBJECTIVE

To evaluate the frequency-specific relationships between the preoperative sensorineural hearing loss and postoperative overclosure of bone conduction (BC) threshold after stapedotomy.

METHODS

We conducted a retrospective analysis of 207 otosclerosis patients who underwent stapedotomy in our hospital. Pre- and postoperative audiometry were collected between patients with or without preoperative sensorineural hearing loss (SNHL) component (i.e., SNHL group and non-SNHL group, respectively). Overclosure rate (OR), deterioration rate (DR), and their significant values (i.e., SOR or SDR) were compared between the sub-groups at each frequency to access the frequency-specific outcomes.

RESULTS

There were 69 patients in non-SNHL group and 138 patients in SNHL group. Postoperative success rate was similar in non-SNHL group and SNHL group. For frequency-specific outcomes, both the OR and SOR were significantly obvious in all SNHL subgroups than those in non-SNHL subgroups (p < 0.001), except at 4 kHz for SOR. Extent of overclosure and significant overclosure were more obvious in SNHL subgroups than those in non-SNHL subgroups (p < 0.01). The DR and SDR of BC were significantly obvious at 1k to 4 kHz in non-SNHL subgroups than those in SNHL subgroups (p < 0.01), however, not so for the extent of deterioration (p > 0.05). Frequency-specific success rate was similar at each frequency.

CONCLUSION

Stapedotomy was efficient and safe in patients with or without SNHL component preoperatively. Frequency-specific overclosure effect was more obvious in all tone frequencies in SNHL subgroups than those in non-SNHL subgroups. For frequency-specific outcomes, about 50% BC with preoperative SNHL component at tone frequency meet postoperative significant overclosure effect, which was most obvious at low frequencies.

Effect of ossicular chain deformity on reverse stimulation considering the overflow characteristics of third windows

Stimulating the round window membrane via an active actuator of the middle ear implant, named the reverse stimulation, has become an option to help patients with ossicular chain deformity (OCD) to restore hearing. However, there is still no concise description of how OCD affects reverse stimulation considering the overflow characteristics of third windows. In the present study, an impedance model considering the vestibular and cochlear aqueducts was used to investigate the dynamic response of the cochlea to reverse stimulation under OCD. First, a finite-element (FE) model of the middle ear and the ear canal was used to estimate the changes in reverse middle-ear impedance caused by ossicular chain fixation and ossicular chain interruption. Then, the impedance model was used to predict the reverse transfer function, which characterizes the effect of OCD on the dynamic response of the cochlea. The results show that ossicular chain fixation reduces the reverse stimulation's performance. Moreover, the existence of the third windows complicates the effect of ossicular chain fixation on the reverse stimulation and boosts obviously the reverse stimulation's performance at low frequencies. In contrast, regardless of the existence of third windows, ossicular chain interruption enhances the effect of reverse stimulation.

Osteoporosis, bisphosphonate use, and risk of moderate or worse hearing loss in women

BACKGROUND

Osteoporosis and low bone density (LBD) may be associated with higher risk of hearing loss, but findings are inconsistent and longitudinal data are scarce. Bisphosphonates may influence risk, but the relation has not been studied in humans. We longitudinally investigated associations of osteoporosis and LBD, bisphosphonate use, vertebral fracture (VF), hip fracture (HF), and risk of self-reported moderate or worse hearing loss.

DESIGN

Longitudinal cohort study.

SETTING

The Nurses' Health Study (NHS) (1982-2016) and Nurses' Health Study II (NHS II) (1995-2017).

PARTICIPANTS

Participants included 60,821 NHS women, aged 36-61 years at baseline, and 83,078 NHS II women, aged 31-48 years at baseline (total n = 143,899).

MEASUREMENTS

Information on osteoporosis, LBD, bisphosphonate use, VF, HF, and hearing status was obtained from validated biennial questionnaires. In a subcohort (n = 3749), objective hearing thresholds were obtained by audiometry. Multivariable-adjusted Cox proportional hazards models were used to examine independent associations between osteoporosis (NHS), osteoporosis/LBD (NHS II), and risk of hearing loss.

RESULTS

The multivariable-adjusted relative risk (MVRR, 95% confidence interval) of moderate or worse hearing loss was higher among women with osteoporosis or LBD in both cohorts. In NHS, compared with women without osteoporosis, the MVRR was 1.14 (1.09, 1.19) among women with osteoporosis; in NHS II, the MVRR was 1.30 (1.21, 1.40) among women with osteoporosis/LBD. The magnitude of the elevated risk was similar among women who did and did not use bisphosphonates. VF was associated with higher risk (NHS: 1.31 [1.16, 1.49]; NHS II: 1.39 [1.13, 1.71]), but HF was not (NHS: 1.00 [0.86, 1.16];NHS II: 1.15 [0.75,1.74]). Among participants with audiometric measurements, compared with women without osteoporosis/LBD, the mean multivariable-adjusted hearing thresholds were higher (i.e., worse) among those with osteoporosis/LBD who used bisphosphonates.

CONCLUSION

Osteoporosis and LBD may be important contributors to aging-related hearing loss. Among women with osteoporosis, the risk of hearing loss was not influenced by bisphosphonate use.

Numerical analysis of the effects of ossicular chain malformations on bone conduction stimulation

To assess the effects of ossicular chain malformations on the performance of bone conduction hearing aids, a human ear finite-element model that includes an ear canal, a middle ear, and a spiral cochlea incorporating the third windows was established. This finite element model was built based on micro-computed tomography scanning and reverse modelling techniques, and the reliability of the finite element model was verified by comparison with reported experimental data. Based on this model, two main types of ossicular chain malformations, i.e., the incudostapedial disconnection and the ossicles fixation, were simulated, and their influences on bone conduction were analyzed by comparing the trans-cochlear-partition differential pressures. The results indicate that the incudostapedial disconnection mainly deteriorates the bone conduction response at mid frequencies. The stapes fixation has the largest effect among the ossicles fixation with the bone conduction stimulation, which also mainly decreases the mid-frequency response of the bone conduction, especially at 2 kHz. As the speech intelligibility has the most important frequency range at the range between 1 kHz and 2.5 kHz, the mid-frequency deterioration caused by ossicular chain malformations should be compensated in optimizing the design of the bone conduction hearing aids. For treating patients with the ossicular chain malformations, especially for the patients who suffer from the stapes fixation, the output of bone conduction hearing aids' actuator in the middle frequency band should be improved.