Multifrequency tympanometry in chinchillas

On-Demand Synthesis of Antiseptics at the Site of Infection for Treatment of Otitis Media

Otitis media (OM) is the main reason for pediatric antibiotic prescriptions. The current treatment mandates a rigorous regimen of multidose antibiotics over 5-10 days. The systemic antibiotic exposure and often prematurely terminated treatment due to the challenge of drug administration to young patients are believed to breed antibiotic resistance. To address these challenges, we designed a local treatment that converted a metabolic product (H2O2) of an OM pathogen (Streptococcus pneumoniae) into a potent antiseptic (HOBr), a reaction catalyzed by locally administered vanadium pentoxide nanowires. The therapeutic, HOBr, was only synthesized in the presence of the pathogen, enabling on-demand generation of therapeutics for OM treatment. Hypohalous acids are broad-spectrum and have a long history in general disinfection applications without breeding substantial drug resistance. A single dose of the nanowire formulation eradicated OM in a standard chinchilla model in 7 days with no observable tissue toxicity or negative impact on hearing sensitivity.

Review of blast noise and the auditory system

The auditory system is particularly vulnerable to blast injury due to the ear's role as a highly sensitive pressure transducer. Over the past several decades, studies have used a variety of animal models and experimental procedures to recreate blast-induced acoustic trauma. Given the developing nature of this field and our incomplete understanding of molecular mechanisms underlying blast-related auditory disturbances, an updated discussion about these studies is warranted. Here, we comprehensively review well-established blast-related auditory pathology including tympanic membrane perforation and hair cell loss. In addition, we discuss important mechanistic studies that aim to bridge gaps in our current understanding of the molecular and microstructural events underlying blast-induced cochlear, auditory nerve, brainstem, and central auditory system damage. Key findings from the recent literature include the association between endolymphatic hydrops and cochlear synaptic loss, blast-induced neuroinflammatory markers in the peripheral and central auditory system, and therapeutic approaches targeting biochemical markers of blast injury. We conclude that blast is an extreme form of noise exposure. Blast waves produce cochlear damage that appears similar to, but more extreme than, the standard noise exposure protocols used in auditory research. However, experimental variations in studies of blast-induced acoustic trauma make it challenging to compare and interpret data across studies.

Wideband Absorbance Outcomes of Cochlear Implantation: A Comparative Clinical Study

OBJECTIVES

Wideband tympanometry (WBT) measurements show sensitivity to trends in external ear canal/middle ear maturation and changes in middle ear status as a result of different types of dysfunction. This study aims to determine the effects of cochlear implantation (CI) on middle ear status.

MATERIALS AND METHODS

This is a prospective comparative clinical study that has been done in a tertiary referral center. The patients who underwent unilateral cochlear implantation were included in the study. All the participants were under 18 years of age and had congenital bilateral profound sensorineural hearing loss (SNHL). WBT measurements of implanted ears were calculated and compared to those of non-implanted ears (control group) in the same patient group. The differences in these measurements were subjected to statistical analyses.

RESULTS

A total of 48 patients (96 ears) who underwent unilateral CI were included in the study. Our study revealed that significant reductions in the average absorbance ratios occurred at all measured frequencies and that the average resonance frequency increased more significantly in the implanted ears compared with those of control group (p<0.001). The difference in the average peak pressure was not significant among two groups. (p=0.211) CONCLUSION: This study shows that the average absorbance ratio decreases and average resonance frequency increases after cochlear implantation. These findings may be related to increased stiffness in middle and inner ear system. Future studies are needed for more detailed information and recommendations on this topic.

The Year of the Rat: The Rat Genome Database at 20: a multi-species knowledgebase and analysis platform

Formed in late 1999, the Rat Genome Database (RGD, https://rgd.mcw.edu) will be 20 in 2020, the Year of the Rat. Because the laboratory rat, Rattus norvegicus, has been used as a model for complex human diseases such as cardiovascular disease, diabetes, cancer, neurological disorders and arthritis, among others, for >150 years, RGD has always been disease-focused and committed to providing data and tools for researchers doing comparative genomics and translational studies. At its inception, before the sequencing of the rat genome, RGD started with only a few data types localized on genetic and radiation hybrid (RH) maps and offered only a few tools for querying and consolidating that data. Since that time, RGD has expanded to include a wealth of structured and standardized genetic, genomic, phenotypic, and disease-related data for eight species, and a suite of innovative tools for querying, analyzing and visualizing this data. This article provides an overview of recent substantial additions and improvements to RGD's data and tools that can assist researchers in finding and utilizing the data they need, whether their goal is to develop new precision models of disease or to more fully explore emerging details within a system or across multiple systems.

The chinchilla animal model for hearing science and noise-induced hearing loss

The chinchilla animal model for noise-induced hearing loss has an extensive history spanning more than 50 years. Many behavioral, anatomical, and physiological characteristics of the chinchilla make it a valuable animal model for hearing science. These include similarities with human hearing frequency and intensity sensitivity, the ability to be trained behaviorally with acoustic stimuli relevant to human hearing, a docile nature that allows many physiological measures to be made in an awake state, physiological robustness that allows for data to be collected from all levels of the auditory system, and the ability to model various types of conductive and sensorineural hearing losses that mimic pathologies observed in humans. Given these attributes, chinchillas have been used repeatedly to study anatomical, physiological, and behavioral effects of continuous and impulse noise exposures that produce either temporary or permanent threshold shifts. Based on the mechanistic insights from noise-exposure studies, chinchillas have also been used in pre-clinical drug studies for the prevention and rescue of noise-induced hearing loss. This review paper highlights the role of the chinchilla model in hearing science, its important contributions, and its advantages and limitations.

The Chinchilla Research Resource Database: resource for an otolaryngology disease model

The long-tailed chinchilla (Chinchilla lanigera) is an established animal model for diseases of the inner and middle ear, among others. In particular, chinchilla is commonly used to study diseases involving viral and bacterial pathogens and polymicrobial infections of the upper respiratory tract and the ear, such as otitis media. The value of the chinchilla as a model for human diseases prompted the sequencing of its genome in 2012 and the more recent development of the Chinchilla Research Resource Database (http://crrd.mcw.edu) to provide investigators with easy access to relevant datasets and software tools to enhance their research. The Chinchilla Research Resource Database contains a complete catalog of genes for chinchilla and, for comparative purposes, human. Chinchilla genes can be viewed in the context of their genomic scaffold positions using the JBrowse genome browser. In contrast to the corresponding records at NCBI, individual gene reports at CRRD include functional annotations for Disease, Gene Ontology (GO) Biological Process, GO Molecular Function, GO Cellular Component and Pathway assigned to chinchilla genes based on annotations from the corresponding human orthologs. Data can be retrieved via keyword and gene-specific searches. Lists of genes with similar functional attributes can be assembled by leveraging the hierarchical structure of the Disease, GO and Pathway vocabularies through the Ontology Search and Browser tool. Such lists can then be further analyzed for commonalities using the Gene Annotator (GA) Tool. All data in the Chinchilla Research Resource Database is freely accessible and downloadable via the CRRD FTP site or using the download functions available in the search and analysis tools. The Chinchilla Research Resource Database is a rich resource for researchers using, or considering the use of, chinchilla as a model for human disease.

Database URL: http://crrd.mcw.edu

Conductive hearing loss induced by experimental middle-ear effusion in a chinchilla model reveals impaired tympanic membrane-coupled ossicular chain movement

Otitis media with effusion (OME) occurs when fluid collects in the middle-ear space behind the tympanic membrane (TM). As a result of this effusion, sounds can become attenuated by as much as 30-40 dB, causing a conductive hearing loss (CHL). However, the exact mechanical cause of the hearing loss remains unclear. Possible causes can include altered compliance of the TM, inefficient movement of the ossicular chain, decreased compliance of the oval window-stapes footplate complex, or altered input to the oval and round window due to conduction of sound energy through middle-ear fluid. Here, we studied the contribution of TM motion and umbo velocity to a CHL caused by middle-ear effusion. Using the chinchilla as an animal model, umbo velocity (V U) and cochlear microphonic (CM) responses were measured simultaneously using sinusoidal tone pip stimuli (125 Hz-12 kHz) before and after filling the middle ear with different volumes (0.5-2.0 mL) of silicone oil (viscosity, 3.5 Poise). Concurrent increases in CM thresholds and decreases in umbo velocity were noted after the middle ear was filled with 1.0 mL or more of fluid. Across animals, completely filling the middle ear with fluid caused 20-40-dB increases in CM thresholds and 15-35-dB attenuations in umbo velocity. Clinic-standard 226-Hz tympanometry was insensitive to fluid-associated changes in CM thresholds until virtually the entire middle-ear cavity had been filled (approximately >1.5 mL). The changes in umbo velocity, CM thresholds, and tympanometry due to experimentally induced OME suggest CHL arises primarily as a result of impaired TM mobility and TM-coupled umbo motion plus additional mechanisms within the middle ear.

Concurrent development of the head and pinnae and the acoustical cues to sound location in a precocious species, the chinchilla (Chinchilla lanigera)

Sounds are filtered in a spatial- and frequency-dependent manner by the head and pinna giving rise to the acoustical cues to sound source location. These spectral and temporal transformations are dependent on the physical dimensions of the head and pinna. Therefore, the magnitudes of binaural sound location cues-the interaural time (ITD) and level (ILD) differences-are hypothesized to systematically increase while the lower frequency limit of substantial ILD production is expected to decrease due to the increase in head and pinna size during development. The frequency ranges of the monaural spectral notch cues to source elevation are also expected to decrease. This hypothesis was tested here by measuring directional transfer functions (DTFs), the directional components of head-related transfer functions, and the linear dimensions of the head and pinnae for chinchillas from birth through adulthood. Dimensions of the head and pinna increased by factors of 1.8 and 2.42, respectively, reaching adult values by ~6 weeks. From the DTFs, the ITDs, ILDs, and spectral shape cues were computed. Maximum ITDs increased by a factor of 1.75, from ~160 μs at birth (P0-1, first postnatal day) to 280 μs in adults. ILDs depended on source location and frequency exhibiting a shift in the frequency range of substantial ILD (>10 dB) from higher to lower frequencies with increasing head and pinnae size. Similar trends were observed for the spectral notch frequencies which ranged from 14.7-33.4 kHz at P0-1 to 5.3-19.1 kHz in adults. The development of the spectral notch cues, the spatial- and frequency-dependent distributions of DTF amplitude gain, acoustic directionality, maximum gain, and the acoustic axis were systematically related to the dimensions of the head and pinnae. The dimension of the head and pinnae in the chinchilla as well as the acoustical properties associated with them are mature by ~6 weeks.

Chinchilla as a robust, reproducible and polymicrobial model of otitis media and its prevention

There is compelling evidence that many infectious diseases of humans are caused by more than one microorganism. Multiple diverse in vitro systems have been used to study these complex diseases, and although the data generated have contributed greatly to our understanding of diseases of mixed microbial etiology, having rigorous, reproducible and relevant animal models of human diseases are essential for the development of novel methods to treat or prevent them. All animal models have inherent limitations; however, they also have important advantages over in vitro methods, including the presence of organized organ systems and an intact immune system, which promote our ability to characterize the pathogenesis of, and the immune response to, sequential or coinfecting microorganisms. For the highly prevalent pediatric disease otitis media, or middle-ear infection, the chinchilla (Chinchilla lanigera) has served as a gold-standard rodent host system in which to study this multifactorial and polymicrobial disease.

Normative data of multifrequency tympanometry in rabbits

In an experimental study, we evaluated acoustic immittance in rabbits in order to use these data as normative values for further experimental investigations. This study is the first experimental evaluation of both conventional 226 Hz and multifrequency tympanometry (MFT) in rabbits. For the investigation, we used 33 female New Zealand rabbits weighing 3.2–4.4 kg and aged six months. Bilateral measurements using conventional 226 Hz and MFT were performed under general anaesthetic. A 226 Hz tympanogram was recorded for all animals by conducting an air pressure sweep from +200 to −400 daPa at a rate of 50 daPa/s. Subsequent tympanograms were recorded over a wide frequency range from 250 to 2000 Hz. The acoustic impedance device used in this study provided reproducible and evaluable tympanograms. The applied tone frequency of 226 Hz proved to be especially suitable for determining compliance. Normative data obtained from our study reveal the resonance frequency to be 1368 ± 205 standard deviation (SD) for the right side and 1413 ± 216 SD for the left side. The values for physiological acoustic immittance of the middle ear in the rabbit obtained here can serve as normative data in subsequent experimental animal studies.

Multifrequency Tympanometry

HYPOTHESIS

We used multiple-frequency tympanometry (MFT) to evaluate the influence of a newly developed ossicular replacement prosthesis on transmission characteristics of middle ear.

BACKGROUND

Multiple-frequency tympanometry is a technique for evaluating the emittance of the middle ear over a wide frequency range. It has been shown to be sensitive to certain middle ear conditions that are not detected by conventional 226-Hz tympanometry. In the field of experimental evaluation, MFT has been shown in certain animal studies to be useful in monitoring diseases.

METHODS

Thirty-six prostheses composed of titanium dioxide ceramic were implanted into the right middle ear of female rabbits. Bilateral measurements using conventional 226-Hz and MFT were performed before implantation and after 28, 84, and 300 days postoperatively. The results of the preoperative examinations yielded reference values for physiological resonance frequency. After dissecting the temporal bone, we opened the middle ear and analyzed both the surrounding tissue and the position of the prosthesis.

RESULTS

The constant values for compliance revealed by both preoperative and postoperative measurements indicate good reproducibility of 226-Hz tympanometry. Postoperatively, resonance frequency increased continuously up to the 300th day. The observation supports the assumption that the higher stiffness level of connective tissue influenced resonance frequency.

CONCLUSION

The reference values in this study can serve as guidelines for further experimental trials.

Multifrequency immittancemetry in experimentally induced stapes, round window and cochlear lesions

OBJECTIVES

To establish that admittance (Y) and susceptance (B) conductance (G) tympanograms at 2 kHz can reflect the status of the annular ligament and the cochlear pressure.

METHODS

Seven experiments were set up in 22 guinea pigs: ventilation of the bulla, blockage of the stapes and round window membrane (RWM), fistula, fluid removal from the cochlea, injection of saline in the scala tympani and acoustic trauma. Resonance frequency, Y, B and G at 2 kHz and curve shapes were analyzed before and after lesions.

RESULTS

A supplementary peak was observed in Y/G tympanograms in all RWM fistulas and in some cases of acoustic trauma; injection of saline into the scala tympani induced constant, immediate and reproducible changes; RWM and stapes blockages induced foreseeable peaking at 2 kHz; fluid removal from the cochlea induced multiple peak curves.

CONCLUSION

Experimentally induced modifications at the AL result in noticeable, constant and reproducible changes in tympanogram curves at 2 kHz and seem to reflect inner ear pressure.

The development of the middle ear in neonatal chinchillas II. Two weeks to adulthood

Studies of auditory function in the human neonate indicate adult-like hearing sensitivity, mature cochlear function and well-developed responses in the auditory pathway. Paradoxically, measurements of middle ear function are characterized by responses that would be interpreted as abnormal in older subjects. Consequently, there is not an accepted clinical test for middle ear disease in the newborn population. Like human neonates, chinchillas have normal hearing sensitivity at birth, but middle ear function tested by multifrequency tympanometry is abnormal compared to the adult. A previous study from our laboratory indicated that the newborn chinchilla middle ear is free of mesenchyme and other debris. Over the first 2 weeks of life there were no significant changes in tympanic membrane thickness and diameter, tympanic membrane to promontory distance and stapes footplate length. There were small changes in mastoid bulla area and perimeter and in mastoid bulla bone thickness. The most striking difference between the newborn and adult temporal bone was in bone composition, the newborn bone having a less dense, spongy appearance. Impedance characteristics of the newborn chinchilla ear, measured by multifrequency tympanometry, were abnormal relative to adult animals and did not change over the first 2 weeks of life. This investigation is an extension of the previous study, designed to better understand the relationship between middle ear function, hearing sensitivity and the structural changes of the newborn chinchilla middle ear. Twenty animals, aged 2-8 weeks, were studied. Additional adult animals were used as controls. Middle ear function was assessed by a wideband reflectance impedance system. Hearing sensitivity was measured by auditory brainstem response in 2- and 8-week-old animals. Structural characteristics of the temporal bone were analyzed using histopathologic preparations. There was an orderly progression in middle ear impedance and reflectance characteristics as the chinchilla ear matured from 2 to 8 weeks of age. At 8 weeks of age, impedance and reflectance patterns approached, but did not match, those of the adult animal. Hearing sensitivity was unchanged throughout this maturational period. Finally, histological analysis demonstrated no age-related changes in distance from the tympanic membrane (TM) to the promontory and in stapes footplate length. There was a small significant decrease in the TM thickness from 2 weeks to adulthood. The most significant developmental changes were a reduction in mastoid bone thickness and concomitant increases in the perimeters and areas of the middle ear and posterior bulla.

Wideband reflectance tympanometry in chinchillas and human

Wideband reflectance tympanometry was performed on twelve chinchillas ears. The complex input impedance of the middle ear, multifrequency admittance tympanograms, reflectance patterns (reflectance versus frequency), and reflectance tympanograms (reflectance versus ear-canal air pressure) were analyzed and compared to human data. The complex impedance of the chinchilla ear has a lower stiffness reactance at low frequencies, a higher mass reactance at high frequencies, and a lower resistance compared to the human. Multifrequency admittance tympanograms from chinchillas follow the same sequence of patterns as humans for low frequencies (<2 kHz). At higher frequencies tympanograms from both species are poorly organized and do not follow a consistent sequence of patterns. Reflectance patterns of chinchillas and humans are different. However, both species show high reflectance at low frequencies, regions of lower reflectance in mid-frequencies (2-6 kHz), and high reflectance at high frequencies (>8 kHz). Reflectance tympanograms for the two species show a single, centrally located minimum at low frequencies (<2 kHz) and are substantially different at higher frequencies. Results are shown for two animals that underwent eustachian tube obstruction. Reflectance patterns obtained with different ear-canal air pressures are substantially different. Reflectance results at any single ear-canal pressure (including ambient pressure) do not completely characterize the effects of middle-ear pathology.

Development of the middle ear in neonatal chinchillas. I. Birth to 14 days

Measures of middle-ear function in humans show large differences among neonates, infants, and adults. In contrast, hearing sensitivity is essentially mature at birth. Hypotheses that have been proposed to explain the developmental changes in middle-ear function include: (i) contaminating effects of the immature neonatal ear-canal wall and (ii) persistent fetal tissue in the ear canal, tympanic membrane (TM), and middle-ear space. To better understand the relationships between middle-ear function, hearing sensitivity and the structure of the middle ear, 30 chinchillas, aged 1-14 days, were studied. Middle-ear function was assessed by multifrequency tympanometry with probe tones ranging from 226 to 2,000 Hz. Hearing sensitivity was measured by auditory brainstem response using clicks and 1, 2, 4, and 8 kHz tone bursts. Structural characteristics were analyzed from temporal bone histologic preparations. At all frequencies, the acoustic admittance of the neonatal car is very low and tympanometric patterns are complex and irregular, compared to adult animals. The admittance is essentially constant from 1 to 14 days, indicating that developmental changes occur over a much wider age span than that investigated here. Hearing sensitivity of the chinchilla appears to be mature at birth. Histologic analysis indicated that there were no age-related changes in TM thickness, TM diameter, distance from TM to promontory, and stapes footplate diameter. There were small increases in bone thickness, middle-ear area, mastoid bulla area, and in the perimeters of the middle ear and mastoid bulla. There were no significant amounts of loose mesenchyme or other fetal tissue in the middle-ear space.

Resonant frequency pattern in multifrequency tympanograms: results in normally-hearing subjects

This paper presents experimental data on the evaluation of middle ear resonances by multifrequency tympanometry. Multifrequency tympanograms (MFTs) of 18 normally-hearing subjects were recorded with a frequency resolution of 15 Hz. The fine structure found in the MFT patterns was compared with findings in literature. A first approach for the evaluation of this fine structure was made explaining the great variability of the main ossicular resonance frequencies described in previous publications. The consequence of the present investigation is that the concept of the main ossicular resonance has to be revised critically.

Immittance and otoacoustic emissions in rhesus monkeys and humans

The purpose of this study was to compare multifrequency tympanometry and otoacoustic emissions (OAEs) in rhesus monkeys (Macaca mulatta) and humans. Tympanometry and OAEs can be recorded efficiently in Macaca mulatta to assess peripheral auditory function with results comparable to those in humans. Differences include (1) greater admittances and conductances in humans from 226 to 630 Hz, the frequency range validly assessed; (2) larger amplitude transient evoked OAEs (TEOAEs) and noise levels in humans; (3) larger amplitude monkey 2f(1)-f(2) distortion product OAEs (DPOAES) (f(2)s>2 kHz); (4) more prominent DPOAEs other than 2f(1)-f(2) in monkeys; (5) more narrowly tuned human f(2)/f(1) X 2f(1)-f(2) amplitude functions at the lower frequencies tested; and (6) lower 2f(1)-f(2) DPOAE thresholds at f(2)=0.5 kHz and > or = 8 kHz in monkeys.

Multifrequency tympanometry and histopathology in chinchillas with experimentally produced middle ear pathologies

Middle ear lesions were produced in chinchillas by introducing fascia, Gelfoam, silastic or a combination of these materials into the labyrinthine and mastoid bullae. After 1-2 months, conventional 226 Hz and multifrequency tympanometry (MFT) were performed and the animals were sacrificed for histopathological analysis of the middle ear. Specific middle ear lesions were created including abnormal tympanic membrane thickness, tympanic membrane mass, tympanic membrane adhesion, mastoid bulla obstruction, ossicular adhesions and reduced middle ear volume. Several potentially strong associations emerged between tympanometric measures and pathological conditions. The strongest were the combinations of thick tympanic membrane and irregular multifrequency tympanograms, tympanic membrane mass and notched 226 Hz admittance tympanograms, tympanic membrane adhesions and low 226 Hz admittance, and tympanic membrane adhesions and low resonant frequency. 226 Hz static admittance had a sensitivity of 0.73 and a specificity of 0.75 for detecting significant middle ear pathology. Tympanometric width was not an effective diagnostic test, separately or in combination with static admittance. The most effective test based on 226 Hz measures was the combination of low admittance or admittance notch. MFT was superior to 226 Hz tympanometry. The combination of low resonance or double resonance or irregular patterns had a sensitivity and specificity of 0.91 and 1.0, respectively. Combining 226 Hz tympanometry with MFT improved the performance relative to 226 Hz tympanometry alone but not relative to MFT alone. The results support clinical reports that multifrequency tympanometry detects some middle ear pathologies that are not detected by conventional 226 Hz tympanometry.

Middle ear mechanics in subjects with rheumatoid arthritis

The incudo-malleolar and incudo-stapedial joints are true diarthroses and therefore may be subject to the same rheumatic lesions as any other articulation in the body. The existence of this involvement in rheumatoid arthritis (RA), however, is highly controversial. The present study investigates modifications of the mechanical properties of the middle ear in a group of subjects with RA by evaluating the resonance frequency obtained with multiple-frequency tympanometry (MFT). Thirty patients with RA, aged 20 to 68 years (mean age: 45.8 +/- 12.4 years), participated in the investigation. Their data were compared with those obtained in a control group of 48 age-matched subjects. Results obtained in both ears were examined in all subjects. The two groups displayed almost equal hearing levels with mean air conduction thresholds ranging from 10 to 22 dB HL. None of the subjects displayed an air-bone gap greater than 5 dB. Normal resonance frequency, calculated at the 95th percentile from the control group, ranged from 900 to 1250 Hz. Twelve rheumatoid arthritis patients (40 per cent) displayed abnormal resonance values. These findings were monolateral in 9 patients and bilateral in 3. Eleven out of 15 ears with abnormal multiple-frequency tympanometry data were characterized by an increase in resonance and 4 by a decrease. A correlation between abnormal resonance values and more aggressive RA was established. The results of this study suggest that rheumatoid arthritis may involve the incudo-malleolar and incudo-stapedial joints, altering the ossicular mechanics in response to static air pressure modifications. This does not impair sound conduction through the middle ear, but might reduce the protective mechanisms of the middle ear towards high static pressures.