Changes In Auditory Function Research Articles

Assessment Criteria for Rotated Stereociliary Bundles in the Guinea Pig Cochlea

Our study examined the relationship between variant stereociliary bundles of cochlear outer hair cells (OHCs) and auditory function to analyze assessment criteria for rotated stereociliary bundles in the guinea pig cochlea. Auditory brainstem response and distortion product otoacoustic emission (DPOAE) were recorded on 100 guinea pigs. Variant hair cells were identified and counted by scanning electron and light microscopy. The most common variation observed was rotation of stereociliary bundles in the first-row OHCs (OHC1), with most 13.3% variant OHC1 rotated 90 degrees and a few 2.5% rotated 180 degrees. Occasionally, the length and angle of the 2 arms of an OHC deviated from the norm. The auditory brainstem response threshold of affected animals increased only slightly, 20- to 30-dB sound pressure level. More importantly, amplitude of DPOAE increased significantly (40.5 dB sound pressure level). Our study suggests that rotation of stereociliary bundles in the cochlear OHC was found to be prevalent in 28% of the animals. We established the assessment criteria for rotated stereociliary bundles that were more than 10% OHC1 rotated. This hair bundle seemed to be rotated by 90 degrees from the normal orientation and was accompanied with changes of auditory function. Increased amplitude of DPOAE is associated with the variation of rotated OHC that might result in hearing loss.

Auditory Brainstem Responses in Patients under Treatment of Hemodialysis

This study evaluated the effects of end stage chronic renal failure (CRF) on auditory function and changes in auditory function following a single session of hemodialysis. The experimental group included 31 patients with end-stage renal failure on chronic hemodialysis. The control group consisted of 31 healthy volunteers. The patients were examined prior to and following a session of hemodialysis. Measurements included pure tone audiometry, tympanometry and acoustic reflex measurements, auditory brainstem responses (ABR), and blood now chemistry parameters. Controls underwent the same test battery, with the exception of biochemical and hematological assessment. Prior to hemodialysis sessions, all ABR latencies except interpeak latency I–III were significantly prolonged in the experimental group. A comparison between controls and the experimental group following hemodialysis indicated that wave V absolute latency and interpeak latencies III–V and I–V were significantly prolonged in the slow repetition rate paradigm. In the fast repetition rate, absolute latencies of waves I and V and III–V interpeak latencies were prolonged in the experimental group. Comparison of ABR recordings prior to and following hemodialysis showed overall significant difference between the measures. Post hoc analysis showed a significant improvement in wave I and V latencies in the slow repetition rate and wave V latency in the fast repetition rate. This study showed that neural conduction along the auditory pathway is delayed in patients with end stage CRF as compared to healthy subjects. Dialysis sessions improve overall neural auditory function. However, patients with end stage CRF show delayed conduction even after a session of hemodialysis.

Effects of GSM Cellular Phones on Human Hearing: The European Project “GUARD”

The European multicenter project named GUARD involved nine centers and aimed to assess potential changes in auditory function as a consequence of exposure to low-intensity electromagnetic fields (EMFs) produced by GSM cellular phones. Participants were healthy young adults without any evidence of hearing or ear disorders. Auditory function was assessed immediately before and after exposure to EMFs, and only the exposed ear was tested. The procedure was conducted twice in a double blinded design, once with a genuine EMF exposure and once with a sham exposure (at least 24 h apart). Tests for assessment of auditory function were hearing threshold level (HTL), transient otoacoustic emissions (TEOAE), distortion product otoacoustic emissions (DPOAE), and auditory brainstem response (ABR). The exposure consisted of speech at a typical conversational level delivered via an earphone to one ear, plus genuine or sham EMF exposure. The EMF exposure used the output of a software-controlled consumer cellular phone at full power for 10 min. A system of phone positioning that allowed participants to freely move their heads without affecting exposure was used. Analysis of the data showed there were no effects of exposure to GSM mobile phone signals on the main measures of the status of the auditory system.

Intraoperative Monitoring of Hearing During Cerebellopontine Angle Tumor Surgery Using Transtympanic Electrocochleography

To investigate the use of transtympanic electrocochleography (TT-ECochG) analyzed on-line by a detector strategy software that made possible automatic extraction of TT-ECochG components intraoperatively in real-time domain.Fifteen patients with cerebellopontine angle tumor among 50 patients were included in this study.All subjects were operated on via middle fossa or retrosigmoid approach. Pure-tone average (PTA) was measured at 0.5, 1.0, and 2.0 kHz, and calculations were performed before and after surgery. Auditory function was monitored intraoperatively via TT-ECochG, and analyzed data were displayed on-line.TT-ECochG changes in morphology were described. Postoperative PTA elevation level correlated with TT-ECochG morphology changes occurring intraoperatively.Analyzed on-line, TT-ECochG data were displayed as first negative peak of compound action potential amplitude and latency in time domain every 3 to 5 seconds. A good correlation between postoperative PTA elevation and TT-ECochG morphology changes was showed (Spearman rank test, R = +0.93; t(N-2) = 9.00; p < 0.0001).TT-EcochG seemed to effectively mirror even minimal changes in auditory function during intraoperative monitoring in real-time domain. Developed strategy of on-line analysis makes the intraoperative hearing status assessment faster and easier.

Early Changes in Auditory Function As a Result of Platinum Chemotherapy: Use of Extended High-Frequency Audiometry and Evoked Distortion Product Otoacoustic Emissions

The objective is to describe progressive changes in hearing and cochlear function in children and adolescents treated with platinum-based chemotherapy and to begin preliminary evaluation of the feasibility of extended high-frequency audiometry and distortion product otoacoustic emissions for ototoxicity monitoring in children. Baseline and serial measurement of conventional pure-tone audiometry (0.5 to 8 kHz) and evoked distortion product otoacoustic emissions (DPOAEs) were conducted for 32 patients age 8 months to 20 years who were treated with cisplatin and/or carboplatin chemotherapy. Seventeen children also had baseline and serial measurement of extended high-frequency (EHF) audiometry (9 to 16 kHz). Audiologic data were analyzed to determine the incidence of ototoxicity using the American Speech-Language-Hearing Association criteria, and the relationships between the different measures of ototoxicity. Of the 32 children, 20 (62.5%) acquired bilateral ototoxicity in the conventional frequency range during chemotherapy treatment, and 26 (81.3%) had bilateral decreases in DPOAE amplitudes and dynamic range. Of the 17 children with EHF audiometry results, 16 (94.1%) had bilateral ototoxicity in the EHF range. Pilot data suggest that EHF thresholds and DPOAEs show ototoxic changes before hearing loss is detected by conventional audiometry. EHF audiometry and DPOAEs have the potential to reveal earlier changes in auditory function than conventional frequency audiometry during platinum chemotherapy in children.

Characterizing the auditory changes in tumor metastasis to the bilateral internal auditory canals

We report the changes in auditory function in a patient with tumor metastasis to the bilateral internal auditory canals (IAC). The hearing gradually deteriorated at frequencies below 1 kHz and above 4 kHz, with the auditory brainstem response (ABR) eventually becoming absent in both ears. However, distortion product otoacoustic emissions (DPOAE) were present at low frequencies, which suggests that the organ of Corti in its upper turn remained unaffected by tumor invasion. Metastatic tumors in the bilateral IAC have been reported to mimic neurofibromatosis type 2, and radiological differentiation from acoustic schwannoma is difficult. We characterize the hearing deterioration caused by metastasis of malignant tumors in the IAC.

Efficacy of the Antioxidant N-acetylcysteine (NAC) in Protecting Ears Exposed to Loud Music

Antioxidants have been reported to be effective in reducing acoustic trauma in animal models but have not been studied in humans. In this study, the antioxidant N-acetylcysteine (NAC) was evaluated to determine if it would reduce temporary changes in auditory function as a result of exposure to loud music in humans. Pure-tone thresholds and distortion product otoacoustic emissions (DPOAEs) were collected in 31 normal-hearing participants, using a randomized, double-blind, placebo-controlled design, before and after two hours of live music in a nightclub. Using repeated measures analysis of variance, no statistically significant differences were found between participants who received NAC versus a placebo for any of the outcome measures. Across all subjects, the largest pure-tone threshold shift occurred at 4 kHz. DPOAE measures were characterized by reductions in amplitude and a trend for shorter group delay values. When the 3 and 4 kHz data were examined by imposing specific criteria of greater than 2 dB DPOAE amplitude reductions and 10 dB or greater pure-tone threshold shifts, DPOAE reductions occurred more often at 3 kHz, and pure-tone shifts occurred more often at 4 kHz.

Aging Effects on Vestibulo-Ocular Responses in C57BL/6 Mice: Comparison with Alteration in Auditory Function

Age-related changes in auditory function are well documented in animal models; however, this is not the case as regards vestibular function. In this study, we evaluated age-related changes in vestibulo-ocular responses in C57BL/6 mice that are considered as a model of presbycusis. The functional data were substantiated by the findings of histological analysis of vestibular and auditory peripherals. The gain in vestibulo-ocular reflex, which reflects functionality of the vestibular system, increased in an age-dependent manner until 12 weeks and exhibited limited functional loss due to aging after 24 weeks. By contrast, no alteration in the thresholds of the auditory brainstem response (ABR) was observed from 3 to 12 weeks of age; however, ABR thresholds were significantly elevated from age 24 weeks and onwards. Histological analysis demonstrated that the degeneration of auditory peripherals was closely related with functional loss due to aging. Vestibular peripherals also exhibited age-related degeneration morphologically, although age-related dysfunction was not apparent. Age-related changes in the vestibular function of C57BL/6 mice followed a different time course when compared to changes in auditory function. These findings indicate that mechanisms for age-related changes in vestibular function differ from those of auditory function.

Prior Heat Acclimation Confers Protection against Noise-Induced Hearing Loss

Exposure to intense noise stress can cause a permanent noise-induced hearing loss which is thought to be due to elevation of reactive oxygen species in excess of the inherent antioxidant mechanisms of the cell. However, preconditioning to low levels of stress of one type can activate cellular mechanisms leading to the elevation of antioxidant levels so that the cell is then better able to tolerate subsequent severe stress of a different type. This has been called cross-tolerance. Here, we tested this hypothesis by acclimating rats to a moderate heat stress (30 days at 34°C). The rats were exposed to 113 dB SPL noise for 3 days (12 h/day) in three different groups: heat acclimated then noise exposed; noise exposed and then heat acclimated; heat acclimated, then noise exposed and then heat acclimated again. Permanent changes in auditory function – auditory nerve brainstem evoked responses (ABR) and distortion product otoacoustic emissions (DPOAEs) – were evaluated in each of these animals and compared with those in rats exposed to noise only and in control groups of rats. Statistical evaluation of the results showed that when assessed with ABR, each of the heat-acclimated, noise-exposed groups was protected from the noise, even the group that was heat-acclimated after the noise exposure. When assessed with DPOAE, protection was statistically apparent only in the group that was heat acclimated, then exposed to noise, and not in the other groups. Thus, heat acclimation provides protection against permanent noise-induced hearing loss.

Gamma knife radiosurgery for acoustic neuromas performed by a neurotologist: early experiences and outcomes.

To assess early outcomes after Gamma knife radiosurgery of acoustic neuromas and other skull base tumors. Gamma knife radiosurgery is one of the available methods to treat acoustic neuromas, in addition to micro-surgical resection. Neuro-otologists have long been associated with microsurgical resection of these tumors; however, the application of Gamma knife radiosurgery to the treatment of these tumors by neuro-otologists has not been previously described. Acoustic Neuroma and Skull Base Surgery Program / Tertiary Referral Center. STUDY DESIGN/PATIENTS/INTERVENTION: Prospective clinical study of all patients treated by the senior author and our gamma knife team beginning in June 2000. Preoperative MRI, audiometry, vestibular testing and facial nerve electromyography were completed. At six-month intervals postoperatively, audiometry, caloric testing and MRI were performed to determine thresholds and speech discrimination ability, vestibular function, and the size of the tumor. From June 2000 until March 2004, 38 patients were treated, and these included 33 acoustic neuromas, two meningiomas, one glomus jugulare tumor, and two facial neuromas. Greater than 36 month follow-up was available in 7 patients, > 24 months in 24, > 12 months in 31, and > 6 months in 34 patients. Statistically significant reduction in tumor size was seen over time, and tumor control was achieved in all but two patients. Various patterns of changes in auditory function, both in threshold and speech discrimination were observed in either positive or negative directions. Preliminary experience with Gamma knife radiosurgery indicates that this treatment method represents another option for neuro-otologists to use in managing patients with skull base tumors.

Preservation of residual hearing in cochlear implantation

Objectives: Many cochlear implant candidates have measurable hearing prior to implantation. Recent reports indicate that residual hearing can be preserved. By comparing pre- and postimplantation auditory thresholds, this study examines the Texas Children’s Hospital experience with conservation of residual hearing. Methods: Children with bilateral profound sensorineural hearing, implanted at least 6 months prior to this study, were eligible for enrollment. A multi-channel device was implanted by the same surgeon in each patient using a round window approach. Preimplantation auditory steady-state responses (ASSR) were available for each patient. Postoperative ASSR were obtained and compared to preimplant thresholds. The nonimplanted ear served as control. Results: Twelve patients (mean age, 4.9 years; 42% male) were studied. Paired t tests indicated no statistically significant differences ( P < 0.05) between the pre- and postimplant ASSR thresholds at 250, 500, 1k, 2k, 4k, and 8k Hz in the implanted ear. There was no difference ( P < 0.05) over the same time period for ASSR thresholds in the nonimplanted control ears at the same frequencies. Conclusion: With the use of a round window approach, by 6 months postimplantation, there is no statistically significant change in auditory function in the implanted ear. Furthermore, by using the nonimplanted ear as a control, this study demonstrates the ASSR to be a stable measure over time. Preservation of residual hearing requires serious consideration as technological advances in electrode development and changing selection criteria for implantation occur.

The Neonate Has a Temporary Conductive Hearing Loss due to Fluid in the Middle Ear

Postnatal functional changes in the activity of the ear and auditory pathway in neonatal guinea pigs [from day of birth (postnatal day, PND = 0), PNDs 1–4, 7 and then weekly up to 7 weeks] were studied as a model of maturation of hearing in human neonates. On the day of birth there were signs of a conductive hearing loss: negative middle ear pressure, auditory nerve brainstem evoked response (ABR) threshold elevation, ABR wave 1 latency prolongation and low amplitude otoacoustic emissions. The conductive hearing loss is probably a result of the (amniotic) fluid found in the neonatal middle-ear cavity. Over the next PNDs, this conductive hearing loss was resolved. In order to confirm this neonatal conductive hearing loss and its resolution, saline was instilled into the middle ear of guinea pigs. This induced signs of a conductive hearing loss similar to those seen in the neonatal guinea pigs which disappeared with clearance of this fluid. Therefore it may be concluded that most of the changes in auditory function seen over the first PNDs are due to absorption of amniotic fluid from the middle-ear cavity.

Pharmacokinetics of Caroverine in the Inner Ear and Its Effects on Cochlear Function after Systemic and Local Administrations in Guinea Pigs

Caroverine, an N-methyl-D-aspartate and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist, has been shown to protect the inner ear from excitotoxicity and to be effective in the treatment of cochlear synaptic tinnitus. Local administration of caroverine on the round window membrane (RWM) could be a more effective means of administration to avoid systemic side/adverse effects. The present study investigates the pharmacokinetics of caroverine in the perilymph, cerebrospinal fluid (CSF) and plasma following intravenous and local applications at different dosages. High-performance liquid chromatography was used to determine the drug concentrations. Our results show much higher caroverine concentrations in the perilymph with lower concentrations in CSF and plasma following local applications compared with systemic administration. Auditory brainstem responses were measured to evaluate the changes in auditory function. The effects on hearing were transient and fully reversible 24 h after local caroverine applications. The findings suggest that local application of caroverine on the RWM for the treatment of excitotoxicity-related inner ear diseases, such as tinnitus and noise-induced hearing loss, might be both safe and more efficacious while avoiding high blood and CSF caroverine levels seen with systemic administration.

Auditory neuropathy/dys-synchrony: diagnosis and management.

Auditory brainstem responses (ABRs) and otoacoustic emissions (OAEs) are objective measures of auditory function, but are not hearing tests. Normal OAEs reflect normal cochlear outer hair cell function, and an ABR indicates a synchronous neural response. It is quite possible for a patient to have normal OAEs but absent or grossly abnormal ABR and a behavioral audiogram that is inconsistent with either test. These patients, who may constitute as much as 10% of the diagnosed deaf population, have auditory neuropathy/dys-synchrony (AN/AD). To diagnose AN/AD accurately, ABRs are obtained in response to condensation and rarefaction clicks to distinguish cochlear microphonics (CM) from neural responses. Appropriate management is confounded by variation among patients and changes in auditory function in some patients over time. Recommendations for management include visual language exposure through methods such as American Sign Language (ASL), Cued Speech, or baby signs, and closely following patients.

Development of form and function in the teleost auditory system

While much is known about form and function in the adult fish ear, there is little information available a to how auditory function changes developmentally in fish. This paper briefly reviews what is known about the development of form and function of the teleost ear and discusses the importance this may have to both the aquaculture setting and to fisheries managers.

Cochlear implants in five cases of auditory neuropathy: postoperative findings and progress.

To review our experiences with some of the preoperative and postoperative findings in five children who were diagnosed with auditory neuropathy and were provided with cochlear implants. We describe changes in auditory function, which enabled these children to have significant improvement in their hearing and communication skills. Pre- and postoperatively, these children received complete medical examinations at Mayo Clinic, including related consultations in audiology, pediatrics, neurology, medical genetics, otolaryngology, psychology, speech pathology, and radiology. These children typically had additional medical and audiological examinations at more than one medical center. The hearing assessments of these children included appropriate behavioral audiometric techniques, objective measures of middle ear function, acoustic reflex studies, transient (TOAE) or distortion product (DPOAE) otoacoustic emissions, auditory brainstem responses (ABR), and, in some cases, transtympanic electrocochleography (ECoG). After placement of the internal cochlear implant devices (Nucleus CI24), intraoperatively we measured electrode impedances, visually detected electrical stapedius reflexes (VESR) and neural response telemetry (NRT). These intraoperative objective measures were used to help program the speech processor for each child. Postoperatively, each child has had regular follow-up to assure complete healing of the surgical incision, to assess their general medical conditions, and for speech processor programming. Their hearing and communication skills have been assessed on a regular basis. Postoperatively, we have also repeated electrode impedance measurements, NRT measurements, otoacoustic emissions, and electrical auditory brainstem responses (EABR). We now have 1 year or more follow-up information on the five children. The five children implanted at Mayo Clinic Rochester have not had any postoperative medical or cochlear implant device complications. All of the children have shown significant improvements in their sound detection, speech perception abilities and communication skills. All of the children have shown evidence of good NRT results. All but case D (who was not tested) showed evidence of good postoperative EABR results. Otoacoustic emissions typically remained in the non-operated ear but, as expected, they are now absent in the operated ear. Our experiences with cochlear implantation for children diagnosed with auditory neuropathy have been very positive. The five children we have implanted have not had any complications postoperatively, and each child has shown improved listening and communication skills that have enabled each child to take advantage of different communication and educational options.

Age-related changes in auditory function of rhesus monkeys ( Macaca mulatta)

The purpose of this study was to investigate the changes in auditory function associated with aging in rhesus monkeys ( Macaca mulatta) as a model for age-related changes in humans. One advantage of using monkeys from the Wisconsin Regional Primate Research Center was that lifestyle factors such as diet and excessive noise exposure were controlled. Twenty younger (mean: 10 years, 9 months, S.D.=±6 months) and 20 older (mean: 25 years, 11 months, S.D.=±11 months) monkeys were used in this study. Cochlear function in these monkeys was measured with distortion product otoacoustic emissions (DPOAEs); neural function was measured with auditory brainstem responses (ABRs) and middle latency responses (MLRs). Older monkeys had (1) significantly smaller DPOAEs, (2) significantly smaller ABR peak amplitudes, and (3) significantly longer ABR peak latencies compared to younger monkeys. Overall, these results suggest that older monkeys have decreased cochlear and neural function to the level of the brainstem as compared to younger monkeys. The decrease in DPOAE level and the increase in age accounted for approximately 70% of the increase in peak IV latency.

Effect of Long-Term Noise Exposure on the Developing and Developed Ear in the Rat

There have been reports that the developing ear is more sensitive than the adult ear to noise-induced hearing loss. This was investigated by testing auditory function in rats, both electrophysiologically and histologically, following exposure to broad-band noise (12 h/day for 15 days) at different stages of auditory development (neonates and adults), and also in age-matched controls. An exposure of 90 dB SPL broad-band noise caused no long-term change in auditory function in either age group. A higher exposure (102 dB SPL) caused greater long-term changes in hearing in the adult compared to the young noise-exposed rats, although histology showed greater damage to hair cells in the younger animals. Therefore, functionally, the developing ear does not seem more vulnerable than the developed ear to acoustic trauma.

Conservative management of acoustic neurinomas: prospective study of long-term changes in tumor volume and auditory function.

Recently reported retrospective analysis on the natural courses of acoustic neurinomas have disclosed that 26-86% of tumors show very slow, or no, growth for many years. To our knowledge, however, there have been no prospective analyses of the natural course of these tumors. We prospectively analyzed tumor growth as well as auditory function changes in 12 patients (13 tumors) managed conservatively. All 12 patients were advised to undergo both pure tone audiometry and magnetic resonance imaging at 3-4 month intervals for the first follow-up year and at 1-2 year intervals thereafter. Then, in the event of either significant tumor growth (> 20% volume increase) or hearing deterioration (> 10 dB), a decision would be made as to whether the patient should undergo either surgery or radiosurgery. A significant increase in tumor volume was confirmed in seven of the 13 tumors during the mean observation period of 564 days (88-1269 days). In another patient, though neither tumor growth nor worsening of auditory acuity was significant, the patient complained of subjective change in the symptoms. Therefore, we decided to treat eight (62%) of the 13 tumors. In contrast, neither tumor growth nor worsening of auditory acuity has as yet occurred in the remaining five tumors (38%) which have been observed for a mean period of 627 days (342-1377 days). Careful follow-up of these five patients is ongoing. Although further long-term follow-up is clearly necessary, conservative treatment appears to be a reasonable alternative to immediate treatment for selected patients with acoustic neurinomas.

How body size affects middle-ear structure and function and auditory sensitivity in gekkonoid lizards.

Gekkonoid lizards increase in body size throughout life, and the present study investigates whether changes in auditory function accompany these increases. Middle-ear structures in four groups of animals, adults and juveniles of two gekkonoid species (Eublepharis macularius and Oedura marmorata), were examined. Tympanic membrane velocity and phase were also measured in all four groups. An indication of peripheral auditory function was obtained for each group by measuring compound action potentials (CAPs) from the round window membrane. The middle-ear contribution to CAP thresholds was obtained by comparing threshold levels of the CAP response with and without an intact middle-ear system. The results from these studies indicated that significant changes occurred in middle-ear structure, tympanic membrane velocity and CAP threshold between the younger and older animals. In addition, the adults of both species exhibited better auditory function when the acoustic stimulus was delivered to the tympanic membrane than when it was delivered to the columella footplate. The findings show clearly that increased body size (or age) is accompanied by functional changes in the auditory periphery.