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Hearing Aids simplified
 

Hearing Aids simplified

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    Hearing Aids simplified Hearing Aids simplified Presentation Transcript

    • M.Khousht M.D.Professor of Audiology Cairo Unsiversity
    •  I- MICROPHONES: FUNCTION: CONvERT SOUNd INTO ElECTRICITy (TRaNSdUCER) PERFECT: ElECTRICal SIgNal IdENTICal TO aCOUSTIC SIgNal. SENSITIvITy: RElaTION bETwEEN THE SIzE OF THE OUTPUT vOlTagE & THE SOUNd OF THE INPUT SOUNd
    •  baSIC FUNCTION: MakE SMall ElECTRIC SIgNal INTO a laRgER SIgNal. aMPlIFIER TakES POwER FROM a baTTERy & TRaNSFER IT TO THE aMPlIFIER OUTPUT IN a MaNNER CONTROllEd by THE INPUT SIgNal. THUS THE wavEFORM IS a laRgER vERSION OF THE INPUT SIgNal.
    • RECEIvERS CONvERT THE aMPlIFIEd & MOdIFIEd ElECTRICal SIgNal INTO aN aCOUSTIC OUTPUT SIgNal.
    • PEak ClIPPINg & dISTORTION: aMPlIFICaTION CaNN’TPROdUCE SIgNalS laRgER THaN SOME SPECIFIEd MaxIMUM EqUal TO OR RElaTEd TO baTTERy vOlTagE. bIggER SIgNalS wIll HavE THEIR PEakS ClIPPEd. THUS THE OUTPUT SIgNal wOUld CONTaIN COMPONENTS THaT aRE NOT IN THE INPUT ‘dISTORTION PROdUCT”.
    • NEwER TECHNOlOgy INvOlvES dIgITIzaTION OF THE SIgNal.advaNTagES:  gREaTER PRECISION.  lESS INTERNal NOISE.  abIlITy TO dO COMPlEx OPERaTIONS IN a SMall “IC” THaT CONSUME lITTlE POwER.
    •  PEakS IN gaIN-FREqUENCy RESPONSE aFFECTS SPEECH INTEllIgIbIlITy & qUalITy OF aMPlIFIEd SOUNd. SPECIally IF THEy RISE by MORE THEN 6 dB abOvE THE RESPONSE. PlaCINg aN aCOUSTIC RESISTOR [daMPER] aT aPPROPRIaTE lOCaTION dECREaSES THE PEakS.
    •  SMall COIl OF wIRE THaT PROdUCES a vOlTagE wHEN aN alTERNaTINg MagNETIC FIEld FlOw THROUgH IT. MagNETIC FIEldS aRE PROdUCEd by lOUdSPEakERS, TElEPHONE RECEIvERS OR INdUCTION lOOP SySTEMS. aN aUdIO SIgNal PROdUCES a MagNETIC FlUx CHaNgINg ITS dIRECTION MaNy TIMES/SEC. [CORRESPONdINg TO THE –vE & +vE SOUNd wavES].
    •  TRaNSMIT aN aUdIO SIgNal TO THE Ha vIa aN ElECTRICal CablE [TaPE RECORdER- MICROPHONE- FM RECEIvERS]. THIS SIgNal wIll bE TREaTEd IN THE SaME way aS IF COMINg FROM THE MICROPHONE. THE SIgNal COMINg FROM IT SHOUld bE THE SaME SIzE aS IF COMINg FROM THE MICROPHONE (1Mv).
    •  important characteristic are: voltage capacity - maximum current provide the increased signal power to the ha user.operation:  generate electricity by putting 2 different materials (electrodes) in proximity in a medium that conduct electricity in the form of ions (electrolytes).
    • 1- perform more complex processing that is possible in analogue ha. the signal shaping is performed with numbers under control of algorithms that provide extremely precise signal changing calculations2-consistent performance resulting in greater fidelity of the signal3- operation can be performed with less power & circuit size.
    • 4- make decisions about how to process the sound depending on hearing environment.5- some of the digital ha can be updated with new processing schemes.6- great reliability over time.
    • Hearing aid styles
    • A new born enter the world wrapped in ablanket of sounds from his own cryingsounds to the sound of his mother’s heartbeats. Then a long journey followsaccompanied by increasing amount of lifesounds. The infant begins to distinguishcertain sounds and attach meanings tothese sounds.
    • As the child grow, sound provides thebasis for communications, he learnswords that projects his ideas, needs anddescriptions of what is around him . Most of the sounds that surrounds uspass unnoticed but not unheard. Theyform a complex background beneath ourawareness.
    • Yet on a subconscious level, thesesounds provide us with a sense of lifeparticipation. Thousands of signals enterour brain everyday and night withoutstop. We cann’t stop it as simply wecann’t close our ears. This flow ofrandom sounds continues throughout ourlives. This flow of information isinterrupted in hearing impaired person.
    • Normal verbal communication, understanding,even the ability to speak clearly. These are theobvious losses, but the more traumatic is theuncoupling of this person from his environment.The flow of information to this person has beenbroken. This closing down of the world forcesthe hard of hearing person inwards with agrowing sense of detachment from theenvironment.
    • Patient with mild degree of hearing loss has no problem in communication in every day situations. His defect will appear only when in poor S/N situations or when the input signal is multiply refracted or in poorly illuminated situations. His main problem would be discrimination.
    • Hard of hearing: Patient with moderate or severe degree of hearing loss. Has a problem in everyday situations. Seek help on his own.Deaf:Patient who lost all his hearing abilities. has a handicap and a problem of discrimination even when aided. Needs total communication schemes.
    •  Normal hearing: sensitivity between – 10 & 15 dB. Slight loss: sensitivity between 16 –25 dB Mild loss: sensitivity between 26-40 dB Moderate loss: between 41- 55 dB Moderately severe: between 56-70 dB Severe: between 71- 90 dB Profound: more than 90 dB.
    •  initially a patient’s decision. some are in doubt & ask the clinician advice.statistics: 10 % to 16 % of adults have hearing problems. 16% of adults have a 4 frequency average more than 25 db hl in the better ear, 7% to 8% greater than 35 db hl. from those with hearing loss only 14% to 24% own ha [ 4 out of 5 have not tried ha]. several reports indicate that at least twice the number using ha can benefit from them.
    •  patient with severe hearing loss benefit enormously from amplification. people with normal hearing drive no benefit from amplification. why is it difficult to get a pta level in between that can truly separate them ???? otherfactors influence the need for amplification more than pta.
    • o motivation is the strongest factor.o acknowledgment of the loss.o need.o consequences.o self image.o expected benefit.o influence of others.o fear or uncertainty.o cost.
    •  the degree of motivation determine the frequency of use of the ha. usually proper counseling lead to people accepting that their hearing loss is the cause of their difficulty & thus encourage them to seek & use ha.
    • the type of loss will affect the benefit from the ha. so in the unaided condition, a conductivepatient will have a poorer speechrecognition than a snhl patient with thesame degree . the condition is reversed in the aidedstate [ distortion at & beyond the cochlea].
    •  extreme low speech intelligibility scores indicate poor benefit from ha. on the other hand, high speech scores do not prove that a person doesn’t have enough hearing loss to benefit from amplification. not a good indicator of improvement in speech discrimination with the ha in various listening conditions.
    •  people who seek amplification by themselves are more aware of their hearing disability. people with the most disability are the ones reported to be mostly helped by amplification. questionnaire to assess handicap is helpful. low self-reported disability reflect a denial of the handicap. a mismatch between reported handicap & pta requires more questionnaires. ( whether to the good or the bad sides).
    • o it is worthwhile to study the patient’s life style for proper counseling.o +ve family re-inforcement is helpful to establish candidacy.o young adults feel the handicap of their hearing loss more than the elderly with the same degree of hearing loss.
    •  many patients are concerned about the visibility of the ha. older patients are less likely to report dissatisfaction with the appearance. adults are concerned that they will be perceived as older if the wear ha [ ha are worn by by a bigger % of elderly (26%)]. some patients consider concern about appearance is vanity & deny it. these people will not use their ha unless properly counseled.
    • any of these conditions halt the processof ha fitting temporarily orpermanently. sudden hearing loss. rapidly progressing hearing loss. fluctuating hearing loss. tinnitus of sudden recent onset ( till diagnose the etiology of it). unilateral hearing loss of unknown origin. otitis externa (till healed). atresia.
    •  the degree of motivation determine the frequency of use of the ha. usually proper counseling lead to people accepting that their hearing loss is the cause of their difficulty & thus encourage them to seek & use ha.
    • research evidence indicate that 2 ha are always better than one.patients usually prefer 1 ha specially older patients.from the clinician point of view: except for a small number with severe asymmetry or with unsatisfactory binaural fusion, bilateral fitting is the best. patients with moderate or severe hearing loss in both ears will benefit more from 2 ha specially with speech understanding in difficult situations.
    •  Why a patient should wear 2 HAs ?? 1-Better understanding of speech: Selective listening is more easily achieved. 2-Better understanding in groups & noisy situations: Improved speech intelligibility. 3-Better ability to tell the direction of sound: Localization. 4-Better sound quality: Stereo system gives the smoothest, sharpest & most natural sound quality.
    • 5-By wearing 2 HA, the patient increase his hearing range to 360ْ .6-Smoother tone quality: 2 instruments require less gain than 1 resulting in less distortion & better reproduced amplified sounds.7-Wider hearing range: A person can hear sounds from a further distance with 2 ears.8-Better sound identification.9-Less hearing deterioration: by keeping both ears active
    • 10-Hearing less tiring & listening more pleasant.11-Feeling balanced hearing12-Greater comfort with loud sounds.13-Reduced feedback & whistling14-Tinnitus masking15-Consumer preference & satisfaction.God has offered us 2 ears why use only one???
    • cost: double the cost for the instruments & maintainance [ including batteries].binaural interference:  poorer discrimination with binaural fitting occur in 10% of elderly.  above % increase with asymmetrical losses.due to deterioration of the signal fusion from the 2 ears. [loss of tunning properties of the cochlea due to ohc loss together with some brain dysfunction]or due to loss of interhemispheric transfer of auditory information through the corpus callosum.
    • association of 2 ha with being older.overly optimistic view of gain from 1 ha.milder hearing losses would postpone the ha for later timing.miscellaneous disadvantageswind noise produce twice the annoyance from a single ha.aid management: for individuals with problem managing one ha, 2 would be a problem.
    • one common strategy is the sequential fitting [over a period of few weeks].advantages: patient make gradual commitment to owing ha. patient acquire necessary skills to manipulate hadisadvantages: patients undergoes 2 periods of adjustment. number of visits to fit the ha doubles.there is no data to substantiate a strategy over the other.clinicians prefer simultaneous approach. sequential may be reserved for patients who refused 2 ha.