Types of Hearing Aids. Enumerate Advantages and Disadvantages – JUNE 2016

DEFINITION - It is a device used to amplify the sounds for pronounced irreversible hearing loss and helps in clarity of hearing. PARTS – a) Microphone which collects the sound and transforms into electrical energy. It has a diaphragm with an electromagnet behind it. b) Amplifier which magnifies electrical impulses by use of transistors and the usual range of amplification of hearing aids is 250 to 400 Hz. c) Receiver which transforms this electrical energy back into sound waves which have much greater amplitude than the one received at microphone. d) Battery and volume control. MECHANISM - input signal -> -microphone stage: acoustic to mechanical -> mechanical to electrical -amplifier stage: boosts electrical signal -> receiver stage: electrical to acoustic -> output to EAC Amplification (gain): Linear: - Direct relationship maintained b/n signal input and output input/output slope = 1.0 Nonlinear: vary gain via amplitude compression or expansioninput/output slope < 1.0; slope reduced by a constantsound level at output remains audible and comfortable over broad range of input intensitycompression most useful for those with reduced dynamic range (threshold of hearing and discomfort)as hearing input increases, the amount of gain is automatically reduced to avoid reaching an uncomfortable level. Saturation Sound Pressure Level: -maximum amount of sound pressure output that a hearing aid can produce. Venting: - reduces the “occlusion effect” (relative increase in low-frequency sounds -> muffled sounds) Acoustic gain of a hearing aid is the amount of amplification which it gives. Output of the aid is sum of input and the gain. Tone control and output limitation for clipping of loud sounds for better tolerance are incorporated in the hearing aid. Automatic volume control (AVC) in hearing aid is designed to overcome recruitment. Types of Hearing Aids- Classification on type of technology- Classification on the basis of Design - Analogue Digitally Programmable True Digital Devices Wearable hearing aids Non-wearable aids Wearable Hearing Aids Non-Wearable Aids • Body worn aids • Post-aural aids • Spectacle aids • In the ear aids • Canal type aids • CROS (contralateral routing of signals) hearing aid for severe unilateral SNHL. • Portable aids • Group hearing aids • Inductance loop systems • Radio transmission aids. ADVANTAGES AND DISADVANTAGES OF HEARING AIDS BY TYPE- Type of Hearing Aid Advantages Disadvantages BTE 1- Severe and profound HL. 2- Allows adequate space to accommodate gain, output, and frequency response. 3- Allow for placement of directional microphone. 1- Earmold Fitting. 2- Compliance. 3- Cosmesis. ITE 1- Cosmetically appealing 2- Placement of microphone takes advantage of pinna and concha effects enhancing amplification in high frequencies. 3- Easier to insert - one component is involved 4- Allows for placement of directional microphone 1- Real ear gain is limited because of feedback problems due to close proximity of microphone and receiver especially in cases of severe-profound HFHL. ITC 1- Cosmesis. 2- Advantage of pinna and concha effects boosting gain in high frequencies 3- Improves localization to sound. 1- Upto Moderate HL 2- Venting options limited 3- Deep placement precludes use of directional microphone CIC 1- Cosmesis is very good 2 -Takes full advantage of pinna and concha effects 3- Reduces occlusion effect 1- Upto Moderate HL 2- Venting options limited 3- Deep placement precludes use of directional microphone. 4- Tailor Made. hearing aids Analogue: -constantly modifies input stimulus Digitally Programmable: -analogue/digital hybrid. -program hearing aid response characteristics into digital memory and control the analogue circuit digitally. True Digital Devices: - improved speech recognition, sound quality and comfort. 1. Body hearing Aids: advantage: allows high level output with low feedback, easy to manage disadvantage: conspicuous, clothes and body may rub against microphone, poor localization of sound 2. Behind the Ear (BTE) 3. In the Ear (ITE) Allows gain for moderate to severe hearing loss 4. In the Canal (ITC) Allows for normal acoustics provided by pinnaIncreases gain in high frequenciesHelps with localization of sound 5. Completely in the Canal (CIC) Maximizes pinna and concha effects greater high-frequency 6. Contralateral routing of signal (CROS)1 Cases of no hearing in one ear and normal hearing in the other.One Microphone is placed on impaired side and signal is transmitted to good ear so patient can use good ear to hear signals from impaired sideBiCROS hearing aids also amplify sound to the better hearing ear 7. Bone conduction aid Patients with existing or recurrent external or middle ear problem.Bone oscillator placed on mastoid.Can be used only with milder hearing losses.Frequency response is not as good as more traditional systems. 8. Bone-anchored hearing aids (BAHA)2 Who cannot use air conduction devices -eg. congenital atresia and chronic middle-ear disorders 9. Middle-ear Implants (MEIs)2 1. Use piezoelectric or electromagnetic principles to drive an output transducer mounted on the ossicular chain 2. Fitted for those with pure SNHL Situation Where Aids Are Required 1. A patient who has hearing problem like presbycusis and which is not treatable by medical or surgical means is an ideal candidate for hearing aid. Hence, it is useful hearing device for deaf mutes along with speech and auditory training3,4. Types of Presbycusis 2. SNHL—however, all patients may not be benefitted with this aid because of distortion of sounds5. Causes of bilateral SNHL is given below. Causes of bilateral SNHL 3. Hearing aids give best results in conductive deafness patients who do not want surgery or are unfit for surgery. Hearing Aids Are Not Indicated If i) Hearing loss for pure tones does not exceed 30 to 35 dB. ii) In monaural deafness. iii) In patient where hearing for tones of low frequency is normal while loss for high frequency sounds is great. iv) Air conduction hearing aids are not given in discharging ears or congenital malformations. Here bone conduction type hearing aids having a bone vibrator should be used. Syndromic Causes of Hearing Loss Syndromic Causes of Hearing Loss Syndromic Causes of Hearing loss Types of Hearing Aids. Enumerate Advantages and Disadvantages of Each. JUNE 2016 Expected Questions On this Topic- What are the components of a hearing aid ?What is gain? What is the advantage of nonlinear gain?What is saturation sound pressure level?Name few syndromic causes of Hearing loss?Types of Presbycusis?Name causes of Bilateral SNHL?What are the advantages of digital hearing aids over analogue?What are the different types of hearing aids ? - JUNE 2016What are the advantages and disadvantages of each? - JUNE 2016What is the indication for bone-anchored hearing aids? What is the maximum threshold that can be serviced? References - 1. Hilly O, Sokolov M, Finkel R, Zavdy O, Shemesh R, Attias J. Hearing in Noise With Unilateral Versus Bilateral Bone Conduction Hearing Aids in Adults With Pseudo-conductive Hearing Loss. Otol Neurotol. 2020;41(3):379-385. doi:10.1097/MAO.0000000000002550 2. Ryberg A, West N, Sass H, Cayé-Thomasen P. [Bone-anchored hearing aids and active middle ear implants]. Ugeskr Laeger. 2019;181(36). https://www.ncbi.nlm.nih.gov/pubmed/31735200. 3. Williger B, Lang F. Managing age-related hearing loss: how to use hearing aids efficiently - a mini-review. Gerontology. 2014;60(5):440-447. doi:10.1159/000357709 4. Cox R, Alexander G, Gray G. Personality, hearing problems, and amplification characteristics: contributions to self-report hearing aid outcomes. Ear Hear. 2007;28(2):141-162. doi:10.1097/AUD.0b013e31803126a4 5. Gates G, Mills J. Presbycusis. Lancet. 2005;366(9491):1111-1120. doi:10.1016/S0140-6736(05)67423-5

Types of Hearing Aids. Enumerate Advantages and Disadvantages – JUNE 2016

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