Distortion product otoacoustic emissions: Sensitive measures of tympanic -membrane perforation and healing processes in a gerbil model.

Distortion product otoacoustic emissions (DPOAEs) evoked by two pure tones carry information about the mechanisms that generate and shape them. Thus, DPOAEs hold promise for providing powerful noninvasive diagnostic details of cochlear operations, middle ear (ME) transmission, and impairments. DPOAEs are sensitive to ME function because they are influenced by ME transmission twice, i.e., by the inward-going primary tones in the forward direction and the outward traveling DPOAEs in the reverse direction. However, the effects of ME injuries on DPOAEs have not been systematically characterized. The current study focused on exploring the utility of DPOAEs for examining ME function by methodically characterizing DPOAEs and ME transmission under pathological ME conditions, specifically under conditions of tympanic-membrane (TM) perforation and spontaneous healing. Results indicated that DPOAEs were measurable with TM perforations up to ∼50%, and DPOAE reductions increased with increasing size of the TM perforation. DPOAE reductions were approximately flat across test frequencies when the TM was perforated about 10% (<1/8 of pars tensa) or less. However, with perforations greater than 10%, DPOAEs decreased further with a low-pass filter shape, with ∼30 dB loss at frequencies below 10 kHz and a quick downward sloping pattern at higher frequencies. The reduction pattern of DPOAEs across frequencies was similar to but much greater than, the directly measured ME pressure gain in the forward direction, which suggested that reduction in the DPOAE was a summation of losses of ME ear transmission in both the forward and reverse directions. Following 50% TM perforations, DPOAEs recovered over a 4-week spontaneously healing interval, and these recoveries were confirmed by improvements in auditory brainstem response (ABR) thresholds. However, up to 4-week post-perforation, DPOAEs never fully recovered to the levels obtained with normal intact TM, consistent with the incomplete recovery of ABR thresholds and ME transmission, especially at high-frequency regions, which could be explained by an irregularly dense and thickened healed TM. Since TM perforations in patients are commonly caused by either trauma or infection, the present results contribute towards providing insight into understanding ME transmission under pathological conditions as well as promoting the application of DPOAEs in the evaluation and diagnosis of deficits in the ME-transmission system.

Factors affecting sound energy absorbance in acute otitis media model of chinchilla.

Acute otitis media (AOM) is a rapid-onset infection of the middle ear which results in middle ear pressure (MEP), middle ear effusion (MEE), and structural changes in middle ear tissues. Previous studies from our laboratory have identified that MEP, MEE, and middle ear structural changes are three factors affecting tympanic membrane (TM) mobility and hearing levels (Guan et al., 2014, 2013). Sound energy reflectance or absorbance (EA) is a diagnostic tool increasingly used in clinical settings for the identification of middle ear diseases. However, it is unclear whether EA can differentiate these three factors in an AOM ear. Here we report wideband EA measurements in the AOM model of chinchilla at three experimental stages: unopened, pressure released, and effusion removed. These correspond to the combined and individual effects of the three factors on sound energy transmission. AOM was produced by transbullar injection of Haemophilus influenzae in two treatment groups: 4 days (4D) and 8 days (8D) post inoculation. These time points represent the relatively early and later phase of AOM. In each group of chinchillas, EA at 250-8000 Hz was measured using a wideband tympanometer at three experimental stages. Results show that the effects of MEP, MEE, and tissue structural changes over the frequency range varied with the disease time course. MEP was the primary contributor to reduction of EA in 4D AOM ears and had a smaller effect in 8D ears. MEE reduced the EA at 6-8 kHz in 4D ears and 2-8 kHz in 8D ears and was responsible for the EA peak in both 4D and 8D ears. The residual EA loss due to structural changes was observed over the frequency range in 8D ears and only at high frequencies in 4D ears. The EA measurements were also compared with the published TM mobility loss in chinchilla AOM ears.

Audiologic changes after pinna augmentation.

No studies to date have objectively assessed whether pinna morphology affects sound intensity detected within the external auditory canal (EAC). Commonly performed procedures on the EAC are carried out for acquired and congenital pathology, together with correction of ear deformities. Our aim was to use an experimental model to identify whether a relationship exists between pinna shape and its subsequent effect on the hearing subject. An anatomically accurate and life-size model made of rubber composite was used for this study. Serial sections (small wedge, defect open; small wedge, defect closed; large wedge, defect open; large wedge, defect closed [equivalent to a protruding ear]; and pinnectomy) were undertaken, and the sound intensity changes assessed at the junction between the EAC and middle ear (tympanic membrane position) using an AURICAL Plus (Otometrics; Taastrup, Denmark) sound processor. A statistically significant loss was demonstrated for wedge-excised models, which was greatest at 180° azimuth. This loss was significantly reduced when the wedge defects were closed. A statistically significant improvement was demonstrated in the protruding ("bat") ear model compared with the normal ear at 0° azimuth. In this model, gain in sound intensity is adversely affected by pinna wedge resection. Because this change may be increased in those with protruding ears, this factor is important to consider for all cosmetic and noncosmetic operations to the pinna, and it supports the notion that the pinna is not a simple funnel.

First results of a novel adjustable-length ossicular reconstruction prosthesis in temporal bones.

OBJECTIVES/HYPOTHESIS: The performance of an ossicular replacement prosthesis (ORP) is influenced by its alignment and appropriate tension between the tympanic membrane and the stapes footplate. A novel ORP with a flexible element that potentially allows for length adjustment in situ is presented and tested for acoustic performance. STUDY DESIGN: Laser Doppler vibrometry in fresh human cadaveric temporal bones was used to test the acoustic performance of the adjustable ORP relative to standard prostheses used for ossiculoplasty. METHODS: The three-dimensional (3D) velocity of the stapes posterior crus was measured in the 0.2- to 20-kHz range using a Polytec CLV-3D laser Doppler vibrometer. The middle ear cavity was accessed through a facial recess approach. After measuring the normal response, the incus was removed and stapes velocity was measured in the disarticulated case, then after insertion of the new prosthesis, a conventional prosthesis (Kurz BELL Dusseldorf type), and a sculpted autologous incus prosthesis in each temporal bone. The 3D stapes velocity transfer function (SVTF) was calculated for each case and compared. RESULTS: The novel ORP design restored stapes velocity to within 6 dB (on average) of the intact response. No significant differences in 3D-SVTF were found between the new, conventional, or autologous ORPs. CONCLUSIONS: The inclusion of an in situ adjustable element into the ORP design did not adversely affect its acoustic performance. The adjustable element may increase the ease of achieving optimal ORP placement, especially through a facial recess approach. LEVEL OF EVIDENCE: NA Laryngoscope, 126:2559-2564, 2016.

Chronic Conductive Hearing Loss Leads to Cochlear Degeneration.

Synapses between cochlear nerve terminals and hair cells are the most vulnerable elements in the inner ear in both noise-induced and age-related hearing loss, and this neuropathy is exacerbated in the absence of efferent feedback from the olivocochlear bundle. If age-related loss is dominated by a lifetime of exposure to environmental sounds, reduction of acoustic drive to the inner ear might improve cochlear preservation throughout life. To test this, we removed the tympanic membrane unilaterally in one group of young adult mice, removed the olivocochlear bundle in another group and compared their cochlear function and innervation to age-matched controls one year later. Results showed that tympanic membrane removal, and the associated threshold elevation, was counterproductive: cochlear efferent innervation was dramatically reduced, especially the lateral olivocochlear terminals to the inner hair cell area, and there was a corresponding reduction in the number of cochlear nerve synapses. This loss led to a decrease in the amplitude of the suprathreshold cochlear neural responses. Similar results were seen in two cases with conductive hearing loss due to chronic otitis media. Outer hair cell death was increased only in ears lacking medial olivocochlear innervation following olivocochlear bundle cuts. Results suggest the novel ideas that 1) the olivocochlear efferent pathway has a dramatic use-dependent plasticity even in the adult ear and 2) a component of the lingering auditory processing disorder seen in humans after persistent middle-ear infections is cochlear in origin.

Adaptive categorization of sound frequency does not require the auditory cortex in rats.

A defining feature of adaptive behavior is our ability to change the way we interpret sensory stimuli depending on context. Rapid adaptation in behavior has been attributed to frontal cortical circuits, but it is not clear if sensory cortexes also play an essential role in such tasks. In this study we tested whether the auditory cortex was necessary for rapid adaptation in the interpretation of sounds. We used a two-alternative choice sound-categorization task for rats in which the boundary that separated two acoustic categories changed several times within a behavioral session. These shifts in the boundary resulted in changes in the rewarded action for a subset of stimuli. We found that extensive lesions of the auditory cortex did not impair the ability of rats to switch between categorization contingencies and sound discrimination performance was minimally impaired. Similar results were obtained after reversible inactivation of the auditory cortex with muscimol. In contrast, lesions of the auditory thalamus largely impaired discrimination performance and, as a result, the ability to modify behavior across contingencies. Thalamic lesions did not impair performance of a visual discrimination task, indicating that the effects were specific to audition and not to motor preparation or execution. These results suggest that subcortical outputs of the auditory thalamus can mediate rapid adaptation in the interpretation of sounds.

Otitis media.

Acute otitis media (AOM) is diagnosed based on visualization of a full or bulging tympanic membrane with middle ear effusion. The distribution of bacteria causing AOM in North America under the influence of pneumococcal conjugate vaccination and antibiotic selection pressure has resulted in a predominance of ß-lactamase-producing Haemophilus influenzae followed by penicillin-resistant Streptococcus pneumoniae. Although guidelines continue to endorse amoxicillin as the preferred treatment, amoxicillin/clavulanate in high dosage would be the preferred treatment based on the otopathogen mix currently. Antibiotic prophylaxis has fallen into disfavor as a preventative strategy for AOM recurrences.

The tympanic membrane displacement analyser for monitoring intracranial pressure in children.

PURPOSE: Raised intracranial pressure (ICP) is a potentially treatable cause of morbidity and mortality but tools for monitoring are invasive. We sought to investigate the utility of the tympanic membrane displacement (TMD) analyser for non-invasive measurement of ICP in children. METHODS: We made TMD observations on normal and acutely comatose children presenting to Kilifi District Hospital (KDH) at the rural coast of Kenya and on children on follow-up for idiopathic intracranial hypertension at Evelina Children's Hospital (ECH), in London, UK. RESULTS: We recruited 63 patients (median age 3.3 (inter-quartile range (IQR) 2.0-4.3) years) at KDH and 14 children (median age 10 (IQR 5-11) years) at ECH. We observed significantly higher (more negative) TMD measurements in KDH children presenting with coma compared to normal children seen at the hospital's outpatient department, in both semi-recumbent [mean -61.3 (95 % confidence interval (95 % CI) -93.5 to 29.1) nl versus mean -7.1 (95 % CI -54.0 to 68.3) nl, respectively; P = 0.03] and recumbent postures [mean -61.4 (95 % CI -93.4 to -29.3) nl, n = 59) versus mean -25.9 (95 % CI -71.4 to 123.2) nl, respectively; P = 0.03]. We also observed higher TMD measurements in ECH children with raised ICP measurements, as indicated by lumbar puncture manometry, compared to those with normal ICP, in both semi-recumbent [mean -259.3 (95 % CI -363.8 to -154.8) nl versus mean 26.7 (95 % CI -52.3 to 105.7) nl, respectively; P < 0.01] and recumbent postures [mean -137.5 (95 % CI -260.6 to -14.4) nl versus mean 96.6 (95 % CI 6.5 to 186.6) nl, respectively; P < 0.01]. CONCLUSION: The TMD analyser has a potential utility in monitoring ICP in a variety of clinical circumstances.

Prosthetic reconstruction from the tympanic membrane to the stapes head or to the stapes footplate? A laser Doppler study.

BACKGROUND: In the absence of the incus, many surgeons believe that reconstruction from the tympanic membrane to the stapes head is more effective than reconstruction to the stapes footplate. This has rarely been tested empirically. Published better clinical results with reconstruction to the stapes head might simply reflect less underlying disease in ears with an intact stapes superstructure. OBJECTIVE: To compare vibration transmission of these two forms of prosthetic reconstruction. METHODS: A fresh human cadaveric temporal bone model was used. Round window vibrations in response to sound in the ear canal were measured with a laser Doppler vibrometer. After incus removal, the discontinuity was repaired using a titanium prosthesis. Reconstruction from the tympanic membrane to the stapes head was compared to reconstruction to the stapes footplate. RESULTS: Reconstruction of both types decreased round window vibrations by 10 to 15 dB between 500 and 3000 Hz compared to the intact middle ear. Reconstruction to the stapes head performed 5 to 10 dB better at lower frequencies (500-2000 Hz), but this was only statistically significant at 1 and 2 kHz. CONCLUSIONS: There is only a 5 to 10 dB mechanical advantage gained by reconstruction from the tympanic membrane to the stapes head compared to reconstruction to the footplate for frequencies between 1 and 2 kHz.

Effect of middle ear fluid on sound transmission and auditory brainstem response in guinea pigs.

Combined measurements of middle ear transfer function and auditory brainstem response (ABR) in live guinea pigs with middle ear effusion (MEE) are reported in this paper. The MEE model was created by injecting saline into the middle ear cavity. Vibrations of the tympanic membrane (TM), the tip of the incus, and the round window membrane (RWM) were measured with a laser vibrometer at frequencies of 0.2-40 kHz when the middle ear fluid increased from 0 to 0.2 ml (i.e., full fill of the cavity). The click and pure tone ABRs were recorded as the middle ear fluid increased. Fluid introduction reduced mobility of the TM, incus and RWM mainly at high frequencies (f > 1 kHz). The magnitude of this reduction was related to the volume of fluid. The displacement transmission ratio of the TM to incus varied with frequency and fluid level. The volume displacement ratio of the oval window to round window was approximately 1.0 over most frequencies. Elevation of ABR thresholds and prolongation of ABR latencies were observed as fluid level increased. Reduction of TM displacement correlated well with elevation of ABR threshold at 0.5-8 kHz. Alterations in the ratio of ossicular displacements before and after fluid induction are consistent with fluid-induced changes in complex ossicular motions.

Transtympanic electrical stimulation for immediate and long-term tinnitus suppression.

Tinnitus is a common symptom which often becomes disabling, affecting the emotional and psychosocial dimensions of life. There are many reports describing tinnitus suppression or attenuation through electrical stimulation of the ear, provided either by cochlear implants or by transtympanic stimulation. Our study project aims to assess the effects of electrical promontory stimulation (EPS) on persistent disabling tinnitus. We enrolled 11 patients affected by postlingual monoaural or binaural profound hearing loss and disabling tinnitus in the worse ear. EPS was performed with direct continuous positive current delivered by an active platinum-iridium needle electrode connected to a promontory stimulator device. The short-term effect on tinnitus was assessed during and immediately after the stimulation. Long-term effects were estimated after one month by comparing pre- and post-EPS Tinnitus Handicap Inventory (THI) scores. Immediately after EPS, five patients (45.4%) reported complete suppression and four (36.4%) reported attenuation of tinnitus. Two patients (18.2%) said it was unchanged. After one month, the THI score was reduced in five patients (45.4%) and remained unchanged in the other six patients (54.6%). The beneficial effects of EPS on tinnitus might be explained by interference with tinnitus generating circuits such as the dorsal cochlear nucleus and the inferior colliculus and by modification of cortical activity. EPS is to be considered a worthwhile attempt at tinnitus suppression, and could help select candidates for the positioning of an implantable electrical stimulator that might provide longer-term beneficial effect on tinnitus.

Non-ossicular signal transmission in human middle ears: Experimental assessment of the "acoustic route" with perforated tympanic membranes.

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.

Multifield coupled finite element analysis for sound transmission in otitis media with effusion.

In this paper, a newly constructed three-dimensional finite element (FE) model of the human ear based on histological sections of a left ear temporal bone is reported. The otitis media with effusion was simulated in the model with variable fluid levels in the middle ear. The interfaces among the air, structure, and fluid in the ear canal and middle ear cavity were identified and the acoustic-structure-fluid coupled FE analysis was conducted when the middle ear fluid level was varied from zero to full fill of the cavity. The results show how the displacements of the tympanic membrane and stapes footplate or the middle ear transfer function is affected by fluid in the cavity across the auditory frequencies. Comparison of model results with measured data in temporal bones indicates that this model has the capability to extend FE analysis into pathological ears such as otitis media with visualized fluid-air interfaces inside the middle ear structures.

Clinical comparison of tympanic membrane displacement with invasive intracranial pressure measurements.

A non-invasive method of assessing intracranial pressure (ICP) would be of benefit to patients with abnormal cerebral pathology that could give rise to changes in ICP. In particular, it would assist the regular monitoring of hydrocephalus patients. This study evaluated a technique using tympanic membrane displacement (TMD) measurements, which has been reported to provide a reliable, non-invasive measure of ICP. A group of 135 hydrocephalus patients was studied, as well as 13 patients with benign intracranial hypertension and a control group of 77 volunteers. TMD measurements were carried out using the Marchbanks measurement system analyser and compared between the groups. In 36 patients, invasive measurements of ICP carried out at the same time were compared with the TMD values. A highly significant relationship was found between TMD and ICP but intersubject variability was high and the predictive value of the technique low. Taking the normal range of ICP to be 10-15 mmHg, the predictive limits of the regression are an order of magnitude wider than this and therefore Vm cannot be used as a surrogate for ICP. In conclusion, TMD measurements do not provide a reliable non-invasive measure of ICP in patients with shunted hydrocephalus.

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.

[Tympanic electrocochleography with disposable electrode].

Extratympanic recording of electrocochleography (ECochG) has played an important role in the differential diagnosis of inner ear diseases. We used a special electrode, which was wrapped in a cotton ball at the tip and covered with a silicon sheath over the entire length, and recorded ECochG from the tympanic membrane (tympanic ECochG). Our method was found to be more convenient and less traumatic than recording with an ear canal electrode. Tympanic ECochG records from 10 normal volunteers showed no influence of iontophoretic anesthesia on the tympanic membrane. The effects on the conductive hearing mechanism were negligible. The input-output curve of the action potential (AP) by click stimuli was fairly stable and comparable to that obtained with transtympanic recording. We performed tympanic ECochG in patients with Meniere's disease or other sensory hearing loss, and compared the amplitude ratios of the summating potential (SP) and AP (SP/AP ratio) with those in normal hearing subjects. The SP/AP ratios in patients with Meniere's disease were significantly increased, an observation consistent with the results of other studies. The SP/AP ratio was also elevated in patients with autoimmune sensory hearing loss or perilymphatic fistula. Based on the results of the present study, we speculate that it is possible to diagnose an inner ear disorder by comparing the tympanic ECochG findings with not only records from normal subjects, but also the contralateral record of tympanic ECochG from the same subject. We conclude that tympanic ECochG using disposable electrodes can provide useful information on inner ear function, because of its convenience, non invasiveness and safety in clinical use. We found tympanic ECochG to be useful in the glycerol dehydration test and for monitoring inner ear function during acoustic neurinoma surgery.

[Noninvasive assessment of intracochlear pressure and patency of the cochlear aqueduct in normal probands with TMD (tympanic membrane displacement) analysis]. / Nicht-invasive Beurteilung des intracochleären Druckes und der Durchgängigkeit des Aquaeductus cochleae bei Normalpersonen mittels TMD-Analyse.

The intracochlear pressure cannot yet be evaluated in patients with certain audiological neuro-otological diseases. However, it seems to be of importance in the diagnosis and pathogenesis of Ménière's disease and related disorders. The present paper is aimed at introducing a setup to indirectly assess intracochlear and intracranial pressure changes and the design and philosophy of this technique. It is possible to describe a normal range of the measured values in healthy controls although large interindividual variations occur. In addition, the positional changes of the registered parameters enable assessment of the patency of the cochlear aquaeduct. This seems to be important in some diseases, such as stapes gusher.

Stapedius reflex and EABR thresholds in experienced users of the Nucleus cochlear implant.

Evoked auditory brainstem responses (EABR) and stapedius reflex thresholds were established in 7 experienced users of the Nucleus cochlear implant. Even using biphasic 400 microseconds/phase clicks for the EABR, responses were observed in only 5 patients; no stapedius reflex (SR) was seen in 3 patients, 2 of whom had a history of middle-ear disorder. The EABR threshold varied widely between subjective threshold and uncomfortable loudness level (ULL) for the same stimulus. The average SR threshold was found somewhat more consistently at 66% of the dynamic range between threshold and ULL, but grossly overestimated the most comfortable level (MCL) in most cases. To obtain equal loudness at the same current level we suggest that broad clicks (300 microseconds/phase) be used for EABR measurements, thus compensating for the lower repetition rate of EABR stimulus compared with the device fitting stimulus.

Temporary threshold shift caused by hearing aid use.

Temporary threshold shift (TTS) over a wide range of frequencies was found after 4 hours of hearing aid use by a 15-year-old student with severe sensorineural hearing loss who was using real-ear insertion gains 10 to 20 dB greater than those recommended by the current National Acoustic Laboratories (NAL) procedure for selecting the gain and frequency response of hearing aids. Measurements were made of her noise exposure during hearing aid use with a noise dosimeter. The real-ear insertion response and input-output function of her hearing aid were measured with a real-ear gain analyzer and were used to calculate in-ear noise levels from the noise levels measured by the dosimeter. The amount of TTS could be predicted from the in-ear noise levels and the student's hearing levels (HLs) by means of a mathematical model consisting of the Modified Power Law (MPL) of Humes and Jesteadt (1991) combined with equations for predicting TTS in listeners with normal hearing published by Mills, Gilbert, and Adkins (1979). The mean of the instantaneous A-weighted in-ear noise levels proved to be the appropriate equivalent continuous level (ECL) for use in the predictions. The MPL was also used to determine safety limits for TTS due to hearing aid use. The observed TTS exceeded the safety limits at all frequencies up to and including 2000 Hz. It was therefore considered desirable for the girl to use less gain at frequencies from 500 to 1500 Hz.