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It is possible to have a bilateral hearing loss where one ear is better than the other ear.  This does not however, mean that the “better” ear has hearing levels that are within normal limits.
Hearing problems that are not medically or surgically treatable will be addressed by your hearing healthcare professional. Send Home Our method Usage examples Index Contact StatisticsWe do not evaluate or guarantee the accuracy of any content in this site. How to cite this article:Kim DK, Park Y, Back SA, Kim HL, Park HE, Park KH, Yeo SW, Park SN. Correspondence Address:Shi-Nae ParkDepartment of Otolaryngology-Head & Neck Surgery, Seoul St.
It may also be a combination of any or all of these areas with one area being more involved than others. Protective effect of unilateral and bilateral ear plugs on noise-induced hearing loss: Functional and morphological evaluation in animal model.
Olivocochlear efferents: Anatomy, physiology, function, and the measurement of efferent effects in humans. Contralateral excitation of cochlear nucleus neurons following conductive impairment may involve olivocochlear pathways. Tonic activity of the crossed olivocochlear bundle in guinea pigs with idiopathic losses in auditory sensitivity.
Asymmetry in noise-induced hearing loss: Relevance of acoustic reflex and left or right handedness. Effect of electrical stimulation of the crossed olivocochlear bundle on temporary threshold shifts in auditory sensitivity.
Unilateral hearing losses alter loud sound-induced temporary threshold shifts and efferent effects in the normal-hearing ear. Comparison of functional and morphologic characteristics of mice models of noise-induced hearing loss. Cochlear pathology induced by aminoglycoside ototoxicity during postnatal maturation in cats. A controlled investigation of in-field attenuation performance of selected insert, earmuff, and canal cap hearing protectors. The effects of acoustic environment after traumatic noise exposure on hearing and outer hair cells. Neural and infranuclear region changes in outer hair cells in acoustically exposed rabbits.
Mary's Hospital, 505 Banpo-dong, Seocho-gu, Seoul 137-701 KoreaSource of Support: This research was funded by grants from Seoul St.
In the case of bilateral hearing loss, one or two hearing aids may be recommended, depending upon the degree of hearing loss and your lifestyle needs. When inner ear nerves become damaged and do not properly transmit their signals to the brain.
We performed the present experiment to prove immediate effect of unilateral or bilateral ear plugs from noise by both audiological and histological methods.In this study, we investigated efferent nerve endings of medial olivocochlear system (MOC) as well as the organ of Corti, after noise exposure.
Sensorineural hearing loss not only reduces the intensity of sound, but it might also introduce an element of distortion resulting in sounds being unclear even when they are loud enough.
MOC fibers, which are thick and myelinated, originated from medial part of superior olivary complex and terminate on OHCs of both ipsilateral and contralateral side cochlea. Hearing aids can help treat the symptoms of sensorineural hearing loss, however they cannot perfectly reverse symptoms like eyeglasses do.Degree of Hearing LossDegree of hearing loss refers to the severity of the loss.
This inhibition can protect cochlea from noise and in noisy background, can actually enhance auditory nerve responses to transient sounds. Some authors reported functional changes in contralateral ear, like tonic hyperactivity of MOC system, [9] or changes of suprathreshold cochlear neural responses, [6] but another said no functional changes of that.
The person may start to find it difficult to hear and understand people when in a noisy place. Synaptophysin, an intrinsic membrane protein of synaptic vesicles, is present in the efferent synaptic terminals of neurons innervating both the inner and OHCs in a variety of species and have been used to show damage of efferent nerve from noise in several papers. All procedures were performed in accordance with the national ethics guidelines and this study was approved by the institutional review board of our Hospital (CUMC-2011-0076-02).
These hair cells change the sound waves into electrical impulses that travel along the auditory (hearing) nerve to the brain. Earplug insertion Spongy type custom-made hearing protective earplugs (Ohropax, Germany, single number rating = 32 dB) were selected.
Experimental mice were divided into four groups and the description and the included number of ears of each group were as in the following. The first group (normal control [G1], N = 24) was normal-control group and was not exposed to noise, the second group (bilaterally plugged group [G2], N = 8) had earplug inserted in both ears and the third group was inserted earplugs in a single ear (left side). Each ear of G3 was subdivided as plugged ear subgroup and unplugged ear subgroup and evaluated separately (G3a, N = 16; G3b, N = 16).
It usually happens because the Chemotherapy drug has been absorbed into the fluid that surrounds the hair cells.


We used a specially designed, separated, pie-shaped wire cage to avoid inappropriate exposure to noise caused by the mice gathering together and hiding their heads during noise stimulation and the detailed explanation of the apparatus is described in our previous paper. Swelling or a tumor pressing on the nerve can keep the nerve from working properly.Age-related hearing loss (presbycusis) The aging process is a very common cause of sensorineural hearing loss.
ABR test The evoked acoustic brainstem response thresholds were differentially recorded from the scalps of the mice. Depending on the level of hearing loss and the pitches that are affected, the audiologist may suggest that the patient try hearing aids. Responses were recorded using subdermal needle electrodes at the vertex, below the pinna of tested ear (reference) and below the contralateral ear (ground) and the responses was recorded in both ear one by one. Unfortunately,  hearing aids are not like glasses, in the sense, they will not give a patient normal hearing. Hearing aids may help make some sounds easier to hear that they may not have heard well before.
Evoked potentials were amplified (×200,000), bandpass filtered (100-3000 Hz) and averaged over 1024 sweeps. With hearing aids, speech may still sound distorted to the patient, because hearing loss affects the inner ear in different ways.
The responses are recorded during 12 ms after stimulus onset and thresholds were determined for a broadband click stimuli by decreasing the SPL in 10-dB decrements until the lowest level at which a distinct ABR wave pattern recognizable by two of the investigators was reached. Making sound loud enough for a patient to hear does not always make sound easier to understand.The goal of any treatment is to improve your hearing. ABR measurements were taken with an Intelligent Hearing System Smart EP System, running IHS high-frequency software (ver.
An etymotic 10B+ probe was inserted into the external ear canal and used in conjunction with two different types of transducers depending on the range of the stimulation frequency. Jude Children’s Research HospitalAmerican Speech-Language Hearing Association If you, or your friends and family, think that your hearing is getting gradually worse, see your doctor immediately. Light microscopy At 1 day after noise exposure, 4 cochleae of each group were harvested for light microscopic examination.
Complete Scientific Proofs Weight Loss Surgery May Cause Liver Failure : Bariatric Surgery Side Effects Postpartum Psychosis Symptoms : What is Postpartum Psychosis ? The cochleae were then rinsed with 0.1 M phosphate buffered saline (PBS) and incubated in 1% osmium tetroxide overnight, followed by immersion in 5% ethylenediaminetetraacetic acid (EDTA) for 2-4 days. The decalcified cochleae were then dehydrated in ethanol and propylene oxide and embedded in Araldite 502 resin (Electron Microscopy Sciences, Fort Washington, PA, USA).
A modified rank-order grading method [18],[19] was used to rate the general shape of the organ of Corti. The averaged regional values for the organ of Corti in the base turns were obtained from each group. Scanning electron microscopic (SEM) study Three cochleae of each group were subjected to SEM. After microdissection, cochleae were submerged in PBS and chemically dehydrated in a series of acetone solutions from 50% to 100% respectively (12 h at each concentration). All samples were gold coated using a sputter coater and examined under a JSM-5410 LV SEM (JEOL, Tokyo, Japan) operated with an accelerating voltage of 15 kV. Schematic drawings of mice cochleae from a previous study [20] showing the percent distance plotted were adopted for the observation of specific sites (8-, 16- and 32-kHz areas) in dissected cochleae and morphologic differences between exposed-to-noise group and protected-by-earplug group of P1mo C57 mice were compared.
Whole mount cochlear immunohistochemistry Four cochleae of each group were tested for whole mount immunohistochemistry, 1 day after noise exposure. To evaluate MOC efferent innervation patterns in the cochlea, tissues excised from P1mo C57 mice were subjected to whole mount immunohistochemical staining for synaptophysin and α-synuclein. The cochleae of each group of P1mo C57 mice were perfused with 2% paraformaldehyde and maintained in fixative overnight at 4°C.
The otic capsule was then removed, followed by the removal of the lateral wall, Reissner's membrane and the tectorial membrane. Polyclonal antibodies against synaptophysin (Zymed, South San Francisco, CA, USA) and α-synuclein (BD Bioscience, San Jose, CA) were used to visualize efferent nerve endings.
Tissues were examined under a Zeiss confocal microscope with LSM imaging software (version 3.5, Zeiss, Germany).
The cochlea homogenate was centrifuged (6500 rpm, 4°C, 20 s) and protein concentration in the supernatant was determined using a BCA protein assay. Equal amounts of protein were resolved by sodium dodecyl sulfate polyacrylamide gel electrophoresis and transferred to a nitrocellulose membrane.
Membranes were probed with an anti-α-synuclein (BD Bioscience, San Jose, CA) primary antibody and appropriate horseradish peroxidase-conjugated secondary antibodies as per the manufacturer's recommendations. All western blots were performed in duplicate and visualized using an enhanced chemiluminescence system (Las3000, Fujifilm, Tokyo, Japan).Statistical analysis was performed using statistical package for the social sciences (SPSS) software (ver. G4 and G3b also demonstrated significantly higher threshold than bilateral earplug group (G2) and plugged ear subgroup of unilateral ear plug group (G3a), which were protected from noise. Unplugged ear of G3 (group of unilateral ear plug) and noise control group (G4) show signifi cantly higher mean ABR thresholds and lower responses at DPOAEClick here to viewG4 and G3b also showed significantly lower response than G1 at 6, 7, 10, 20 KHz in DPOAE tests.


G2 and G3a, which were protected from noise by earplugs showed no functional defect of OHCs when compared with G1 [Figure 2]b. Degenerations of the OHCs were observed at G4 and G3b, especially severe at the base region. Unlike them, G2 and G3a did not show severe degeneration of OHCs and especially G2, showed pretty much the same base organ of Corti grade with G1. SEM also revealed major morphological abnormality in G3b and G4, especially in base region, while not shown in G3a, G2 and G1 [Figure 4].
Mean morphologic grades of organ of Corti in normal control group (G1) and bilateral ear plug group (G2) were higher than those of unplugged ear of G3 and noise control (G4). Unilaterally plugged ear of G3 shows intermediate value between bilaterally plugged ear and unplugged ear of G3 in morphologic evaluation of organ of CortiClick here to viewFigure 4: Scanning electron micrographic study of each group in the same frequency area (at 32 KHz) demonstrates damage and missing (asterisks) of outer hair cells in the cochlea of unplugged ear of G3 and noise control (G4).
Much more intense and distinct staining of efferent nerve buttons with by synaptophysin and α synuclein were observed in control (G1), bilaterally plugged ears (G2) and plugged ear of G3 than those of unplugged ear of G3 and noise control (G4) (a).
Signifi cant differences were observed in mean diameters (b) and numbers (c) of efferent buttons between bilaterally plugged ears and unilaterally plugged ears and between plugged and unplugged ears of unilaterally plugged group (G3). In audiological study, we observed the difference of changes in hearing thresholds of ABR and responses of DPOAE tests after noise exposure between groups, there were not any functional damage of both bilaterally and unilaterally protected ear from noise. It has been know that wearing HPD, regardless of its kind, can attenuate noise around 20 dB at frequencies 0.5-8 kHz under field conditions. Ear plug as a HPD, also can provide protection equivalent to ear muffs, if properly inserted.
Especially, bilaterally plugged ear showed nearly normal appearance on all exams which was quite comparable to that of non-exposed control group. Hearing threshold and OHC function were perfectly preserved in the plugged ears after such intense noise exposure and the morphology of organ of Corti and OHCs were not changed at all in the group with plugged ear.Interesting results of our study are audiologic and histologic results of G3, because comparing the results between plugged and unplugged side in this group could provide some information about MOC system.
The main function of MOC efferents has been known to inhibit cochlear responses by decreasing the gain of cochlear amplifier and its effects tend to be largest on low-level responses, where the contributions of the cochlear amplifier are greatest. However, this midline-crossed MOC fibers (to contralateral side) consists the arch of ipsilateral MOC acoustic reflex, because axons of cochlear nucleus cross the brainstem to innervate contralateral side MOC neurons. For example, unilateral cochlear destruction in guinea pig renders the opposite ear less vulnerable to acoustic injury for days to weeks after destruction because of tonic hyperactivity in the MOC system.
There is a well-designed long-term study suggesting no functional change of contralateral ear by MOC activity change following ipsilateral ear manipulation.
Larsen and Liberman [13] have reported similar results with ours that ipsilateral manipulation including tympanic membrane removal, or an acoustic overstimulation designed to produce a reversible or irreversible threshold shift, did not produced any systemic changes in contralateral cochlear responses, either in ABRs or DPOAEs.
Unilaterally plugged ear showed the reduction of the mean number and diameter of efferent buttons in immunohistochemistry of synaptophysin.
This phenomenon seems to be related with the decrease of synaptic vesicles within the efferent nerve endings due to the contralateral reflex of MOC efferent nerves.
In noisy environment, the efferent nerve endings of unilaterally plugged ear, would release synaptic vesicles due to the contralateral reflex of MOC system caused by the strong afferent stimuli of the contralateral unplugged ear. Furthermore, if the noise become intense and harmful, the efferent nerve endings of plugged side also could be changed or damaged with the reduction of storage of synaptic vesicles and transmitter substances due to fatigue effect. Damage of ipsilateral side efferent nerve endings from noise was proven by a study using electron microscopy. These morphological changes of ipsilateral efferent nerve degeneration after noise exposure also could be applied to contralateral side efferent nerve endings even in plugged condition in our study. The effects of asymmetrical noise exposure and the different morphological changes in unilaterally plugged cochleae and MOC efferent nerve endings shown in our study were interesting. There was a tendency of reduction of the organ of Corti grade as well as more degeneration of MOC efferent nerve endings of unilaterally plugged ear compared to those of bilaterally plugged ears. Further study which will show the real effect of MOC efferent nerves and the mechanism of contralateral effect of unilateral ear plugging will be necessary. In the present study, we could observe the reduction of α-synuclein in efferent nerve terminals and cochlear homogenates of noise exposed mice, which might be due to degeneration of efferent nerve terminals or reduction of synaptic vesicles within nerve terminals. This is a novel finding of morphological and biochemical proof of α-synuclein reduction within the efferent nerve endings after noise exposure.
Our morphologically and functionally proven role of ear plug can be used as educational purpose to the workers in noisy environment to emphasize the preventable NIHL. Although, there were not any functional changes of both bilaterally and unilaterally protected ear after noise exposure, there were some mild changes in the grade of the organ of Corti and efferent nerve endings of unilaterally plugged ear in morphologic study.
Reduction of α-synuclein was also observed at the efferent terminal of noise damaged cochlea. Further long-term and ultrastructural study investigating the protective effect of ear plug on OHC damage as well as efferent nerve endings will be necessary.



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