Assessment of hearing
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Assessment of hearing

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ways to assess whether a person hears normally or not right from very basic upto advanced by Dr zeeshan ahmad presented in ENT NMCH patna on 10-02-11

ways to assess whether a person hears normally or not right from very basic upto advanced by Dr zeeshan ahmad presented in ENT NMCH patna on 10-02-11

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  • The decibel originates from methods used to quantify reductions in audio levels in telephone circuits. These losses were originally measured in units of  Miles of Standard Cable  (MSC), where 1 MSC corresponded to the loss of power over a 1  mile  (approximately 1.6 km) length of standard  telephone  cable at a frequency of 5000  radians  per second (795.8 Hz), and roughly matched the smallest attenuation detectable to an average listener. Standard telephone cable was defined as " a cable having uniformly distributed resistances of 88 ohms per loop mile and uniformly distributed  shunt   capacitance  of .054 microfarad per mile " (approximately 19 gauge).[ citation needed ] The  transmission unit  (TU) was devised by engineers of the  Bell Telephone Laboratories  in the 1920s to replace the MSC. 1 TU was defined as ten times the base-10 logarithm of the ratio of measured power to a reference power level. [3]  The definitions were conveniently chosen such that 1 TU approximately equaled 1 MSC (specifically, 1.056 TU = 1 MSC). [4]  Eventually, international standards bodies adopted the base-10 logarithm of the power ratio as a standard unit, named the  bel  in honor of the  Bell System 's founder and telecommunications pioneer  Alexander Graham Bell . [5]  The bel was larger by a factor of ten than the TU, such that 1 TU equaled 1 decibel. [6]  For many measurements, the bel proved inconveniently large, giving way to the decibel becoming the common unit of choice.

Assessment of hearing Assessment of hearing Presentation Transcript

    • The incidence of 30/01/11 evening when TWO ON DUTY DOCTORS were shot by a legislator
    We condemn the inhuman and antisocial act DO YOU?
  • ASSESSMENT OF HEARING by:- Dr ZEESHAN AHMAD NMCH PATNA INDIA
  • DECIBEL(dB)=1/10 Bel
    • Bel is a base10 logarithmic ratio of intensity of given sound to threshold of hearing in normal subjects at 1000Hz
    • The decibel originates from methods used to quantify reductions in audio levels in telephone circuits
    • 1MSC=loss in 1 mile = 1.6Km
    • 1.056 TU = 1 MSC)
    • 1TU=1/10 Bel=1dB
    • Named after Alexander Graham Bell who invented the telephone
  • Pathways for air and bone conduction
  •  
  • A uditory cortex M GB I nferior collliculus L ateral lemniscus O livary nucleus(superior) C ochlear nucleus E ight cranial nerve E.COLI-MA PL Dhingra has simplified auditory pathway and made it easier to remember by a mnemonic
  • Tuning Fork Tests
  • Tuning Fork Tests
    • Tuning fork is a device usually made of steel, magnesium or aluminum that is used to tune musical instruments by musicians and we the doctors use it to assess hearing
    • We can set it into vibration by holding
    • the stem/handle in the hand and striking one
    • of the tines against a firm but resilient surface
    • It emits a tone at a particular pitch and has a clear musical quality
    • It vibrates sinusoidally to generate a pure tone
    • When it vibrates properly, the tines move alternately away from and toward one another
    • Several forks are available, each correspond to notes on the musical scale. We have the following frequencies (4096, 2048,1024, 512, 256, 128, 64) Hz
  •  
  • Tuning Fork Tests
    • Used before the development of audiometers with BC and the other sophisticated electronic devices
    • A century ago, they were used widely as an instrument for testing hearing
    • They illustrate the principles involved in certain modern tests
    • Their use has declined but are still used by many physicians in their everyday practice
  • Principle of Tuning Fork Tests
    • CHL (OE or ME Disorder)
    • Sounds delivered to the ear via AC will be attenuated
    • If the sound is delivered to the ear via BC, bypassing the OE & ME, then the sound will be heard normally assuming there is no disorder
    • SNHL (OE & ME Are Free From Disorders)
    • Sounds delivered to the ear via BC will be attenuated
  • Standard Tuning Fork Tests
    • Purpose: to diagnose the type of HL
    • Results from these tests are determined by the presence or absence of an occlusion effect
    • Schwabach Test
    • Bing
    • Rinne
    • Weber
  • Various positions of tuning fork during tuning fork tests On mastoid At the opening of EAC Midline of skull
  • Schwabach Test
    • Was once popular but no longer is in general use
    • It compares pt’s hearing sensitivity with that of an examiner (assuming that he/she has a normal hearing)
    • The fork is set into vibration, stem is placed alternately against the mastoid process of the pt. and of the examiner
    • Pt. should indicate whether the tone is heard or not each time the fork is placed is pressed against his/her mastoid process
    • Vibratory energy of the tines of fork decreases overtime, making the tone softer
    • When the pt. no longer hears the tone, examiner immediately places the stem behind his or her own ear and using a watch, notes the number of seconds the tone is audible after the pt. stops hearing it
  • Schwabach Test
    • Normal Schwabach:
    • Both pt. & examiner stop hearing the tone at approximately the same time
    • Pt. has normal BC
    • Pt. has normal hearing or CHL
    • Diminished Schwabach:
    • Pt. stop hearing the sound much sooner than the examiner
    • Pt. BC is impaired
    • Pt. has SNHL
  • Schwabach Test
    • Can be quantified by recording the number of seconds an examiner continues to hear the tone after a pt. has stopped hearing it
    • Examiner hears the tone 10 sec longer than a pt.  pt. hearing is “Diminished 10 seconds”
    • If pt. has CHL, BC is normal and they are expected to hear the tone for at least as long as the examiner
    • In some CHL, the pt’s hearing in the low-pitch range may appear better than normal, called “Prolonged Schwabach”
    • Disadvantages: Difficulties in the administration and interpretation of test in cases of MHL plus it requires normal hearing by the examiner
  • Bing Test
    • Premise:
    • Persons with Normal hearing and SNHL when they close off the opening of the ear canal, loudness of a tone presented by BC increases “ Occlusion Effect”
    • Observed primarily for low-pitched sounds
    • Absent in pts. with CHL
  • Bing Test
    • Assesses the presence of CHL
    • Tuning fork is placed on the pt.'s mastoid, while the ear canal is alternatively opened and closed by the examiner by depressing tragus and the pt. is asked to state which position is louder
    • When the ear canal is closed on a person with normal hearing or SNHL, low-frequency bone conducted signals are heard more loudly (Occlusion Effect), the is a "Positive Bing“
    • Pts. with CHL will not experience this sensation and the tone will be the same when the ear canal is open and closed and the test will be a "Negative Bing" because the ear already has a conductive impairment
  • Rinne Test
    • Compares pts' hearing sensitivity by BC to their sensitivity by AC
    • The tuning fork is set into vibration and held close the pt's ear
    • Tuning fork is alternatively held to the ear and then the base is placed on the mastoid process
    • pt. is asked to state where the tone is louder, at the ear or at the mastoid
    • Pts. with normal hearing and SNHL will hear the tone louder at the ear (Because AC is a more efficient means of sound transmission to the IE than BC) than behind the ear (Positive Rinne)
    • Pts. with CHL (more than mild) or MHL will hear the tone louder with the stem of the fork behind the ear because their BC hearing is better than their AC hearing (Negative Rinne)
  • Disadvantages
    • In Schwaback test, Bing test and Rinne Test:
    • There is always a danger of getting a response to the tone by the non-test ear (especially if the BC of the non-test ear is more sensitive than the BC of the test ear (
    • False negative results may occur
    • Give rise to improper diagnosis of CHL
  • Weber Test
    • A test of lateralization
    • Used for pts. reporting unilateral HL
    • The examiner places the stem of the tuning fork on the midline against the pt's forehead
    • The pt. should state if the tone is heard in the left ear, right ear, both ears or in the midline
    • Weber effect is based on “Stenger Principle”:
    • If two tones are identical except they are different in loudness, are introduced simultaneously into both ears, only the louder tone will be perceived
    • Two ears, one has poorer BC sensitivity, when the tone is being produced to both ears with equal energy, the tone will be perceived softer or will not be perceived at all in the poor ear
    • If the tone lateralizes to the poorer ear:
    • That ear has improved BC sensitivity
    • CHL in the poor ear
    • If the tone lateralizes to the better/good ear:
    • The cochlea with the best hearing sensitivity will detect the signal
    • SNHL or MHL in the poor ear
    • If the sound is detected in the midline position:
    • Normal hearing
    • or equal amounts of the same type of HL in both ears (CHL, SNHL or MHL)
    • If the sound lateralizes to the ear with greater conductive component:
    • Pt. has a bilateral loss
  • Weber Test
    • Advantages:
    • Quick
    • Easy
    • Often helpful
    • Disadvantages:
    • Difficult to interpret results in cases of unilateral CHL and MHL
  •  
  • Pure Tone Audiometry
  • Pure Tone Audiometry -Audiometer is an electronic device which produces PURE TONES ,the intensity of which can be increased or decreased by 5dB steps -Air conduction thresholds are measured from 125 to 8000 Hz -Bone conduction thresholds from 250 to 4000 Hz -The intensity of sound to be raised above normal to make it hear is a measure of degree of hearing impairment -This is charted on a graph called AUDIOGRAM
  • Those mysterious markings
  • Legends for PTA’s
  • Air conduction Bone conduction
  • How they do it (briefly)
    • Otoscopy + explanation
    • Best ear?
    • Start with AC on best ear
    • Start at 1000Hz at 60dB
    • Down by 10dB until no response
    • Then up by 5dB until reponse (3 out of 5)
    • Up and down frequencies
    • Same for bone
  • Important concept…
    • At Iowa State Fair in 1935, 10 000 young women had their hearing measured
    • This established the normal hearing levels for pure tone Audiometry (0 db Threshold)
  • It’s a Normal PTA Sensorineuronal/conductive abnormality ??
  • Pure Tone Average
    • --Degree of hearing loss is computed by using average of HTL taken at 500 Hz, 1,000 Hz and 2,000 Hz.
    • --The average of these three frequencies is called the Pure Tone Average or PTA and is the degree of hearing loss a person has expressed in dB
  • Hearing Loss Table Classification PTA Profound hearing loss >90 Severe HL 71-90 Moderately severe HL 61-70 Moderate HL 41-60 Mild hearing loss 21-40 Normal 0-20
  • And, we all know BC is not as good as AC, don’t we?
    • So, why does a normal PTA look like this?
  • Conductive Loss What’s this shows
  • Sensorineural Loss
  • Mixed Loss Now what does this one shows
  • Masking
    • Used to prevent non-test ear hearing stimulus presented to test ear
  • Interaural attenuation
    • Bone
    • Assumed to be 0dB, but probably nearer 4-6dB
    • Air
    • Assumed to be greater the 40dB, but varies between patients
    • Masking used to eliminate this confounding factor
  • PTA limitations
    • PTA in NOT always a ‘Gold Standard’ and infallible
    • Limited by : patient, audiologist and equipment
    • Beware on NOHL
    • Try to supplement other simple tests
  • Speech Audiometry
  • Speech Audiometry
    • Speech Reception Threshold using spondaic words
    • Standardized word lists
    • Ascending series of presentation
    • Minimum intensity at which 50% of words are repeated correctly
    • Excellent speech discrimination in conductive hearing loss patients
    • Poor speech discrimination in cochlear hearing loss patients
    • Poorest speech discrimination in retrocochlear hearing loss patients
  • Imepedence Audiometry (Tympanometry + stapedial reflex)
  • Tympanometry
  • Definition:
    • Tympanometry is an electronic and acoustic measurement technique to assess middle ear status
    • Combined with otoscopy, it is an objective, fast, and highly accurate way to rule out outer and middle ear pathology
  • Principles of Tympanometry
    • Introduces a pure tone into ear canal through 3-function probe tip
    • Manometer (pump) varies air pressure against TM (controls mobility)
    • Speaker introduces 220Hz probe tone
    • Microphone measures loudness in ear canal
  • Tympanometry Janet Stockard Sullivan 2003
  • Here’s how it works...
  • These 5 second motion video otomacroscopy (MVOM) samples resent a view of a 58 year male right tympanic membrane during tympanometry. The patulous  pars flaccida  was ejected at the outset of recording from a prior tympanometric trial. The Middle Ear Analyzer was set to run from +400 daPa though -600 daPa. MVOM and tympanograms were video-captured 15 f/s . The time lines between videos are only roughly coincident. The negative slope of the tympanogram corresponds to the period of rapid  pars flaccida  ejection.
  • videos Taken from--- http:// www.rcsullivan.com/www/tympavi.htm
  • Normal tympanogram (Type A)
    • Peak at 0 daPa
    • Best movement of drum when no extra pressure on either side of TM
  • Other Type A tympanograms
    • Peak at 0daPa, but unusually high amplitude
    • ? Ossicular disruption
    Peak at 0daPa, but unusually low amplitude ? Stapes fixation
  • Flat tympanogram (Type B)
    • No Peak
    • No best TM movement at any pressure
  • Flat tympanogram (Type B)
    • When tymp is flat,
    • usually means 1 of 3 things:
    • Artefact
    • Fluid in ME
    • Perforation
    • Look at EAM vol.
    • If large = perf
    • If normal = fluid
  • Negative tympanogram (Type C)
    • Peak at < 0daPa
    • Best movement of drum when negative pressure in EAM thus middle ear pressure must be less than atmospheric
  • Negative tympanogram (Type C)
    • Can be further divided into:
    • C1 – peak between 0 and -200 daPa
    • C2 – peak less than -200daPa
  • Acoustic Reflex Testing
    • The stapedius muscle attaches to the neck of the stapes
    • Upon being triggered by loud sound, contraction of the stapedius dampens motion of the stapes, reducing effectiveness of the ossicular chain
    • In acoustic reflex testing, the probe tip produces a sudden loud tone and simultaneously records any drop in compliance
    • If the compliance drops, the tympanometer records the acoustic reflex as present
      • Interpret as no conductive component, and not more than moderately severe hearing loss
    • If compliance is not affected, the tympanometer records the reflex as absent
      • Subject to wide range of interpretation
  •  
  • Interpreting results of acoustic reflex testing: Summary
    • Reflex present = probable normal middle ear function
    • Reflex absent = possible middle ear problem, severe sensorineural hearing loss, or several other possible explanations
  • OTOACOUSTIC EMISSIONS
  • OAE’s
    • They are low intensity sounds produced by outer hair cells of a normal cochlea
    • Can be elicited by a very sensitive microphone placed in EAC
    • Absent when OHC are damaged
    • Thus serve to test cochlear functioning
    • Outer hair cells
    • Basilar membrane
    • Perilymph
    • Oval window
    • Ossicles
    • Tympanic membrane
    • EAC
  • OAE’s spontaneous evoked Transient (click) Distortion product (paired tones)
  • Spontaneous OAE
    • They are present in healthy normal hearing persons
    • When hearing loss does not exceeds 30 dB
    • May be absent in 50% of normal persons
  • Transient Evoked OAE
    • -Evoked by clicks
    • -Clicks are presented at 80-85 dB
  • Distortion Product OTOACOUSTIC EMISSIONS
  • USES of OAE’s
    • As a screening test for neonates
    • Distinguish cochlear from retrocochlear HL
    • To test hearing in meantally challanged and uncooperative individuals after sedation
    • (Note- sedation doesn’t interferes with OAE’s)
  • Brainstem Evoked Response Audiometry (BERA)
  • BERA Brainstem Evoked Response Audiometry
  • Definition
    • Bera is an objective way of eliciting brain stem potentials in response to audiological click stimuli. These waves are recorded by electrodes placed over the scalp.This   investigation was first described by Jewett and Williston in 1971.
  • The standard electrode configuration
    • --a non inverting electrode over the vertex of the head
    --an inverting electrodes placed over the ear lobe or mastoid prominence. --One more earthing electrode is placed over the forehead
  • Cochlear nerves Cochlear nucleus Superior olivary complex Nulclei of lateral lemniscus   Inferior colliculus 
  • Uses of BERA:
    • 1. It is an effective screening tool for evaluating cases of deafness due to retrocochlear pathology i.e. (Acoustic schwannoma). An abnormal BERA is an indication for MRI scan.
    • 2. Used in screening newborns for deafness
    • 3. Used for intraoperative monitoring of central and peripheral nervous system
    • 4. Monitoting patients in intensive care units
    • 5. Diagnosing suspected demyelinated disorders
  • BERA findings suggestive of retrocochlear pathology:
    • 1. Latency differences between interaural wave 5 (prolonged in cases of retrocochlear pathology)
    • 2. Waves I - V interaural latency differences - prolonged
    • 3. Absolute latency of wave V - prolonged
    • 4. Absence of brain stem response in the affected ear
  • Criteria for screening newborn babies using BERA: 
    • 1. Parental concern about hearing levels in their child
    • 2. Family history of hearing loss
    • 3. Pre and post natal infections
    • 4. Low birth weight babies
    • 5. Hyperbilirubinemia
    • 6. Cranio facial deformities
    • 7. Head injury
    • 8. Persistent otitis media
    • 9. Exposure to ototoxic drugs
  • A COMPARISON Unsuitable for children Suitable for even young children Response begins after 50 - 300 milliseconds after stimulation Responses begin after 1 - 10 milliseconds after stimuli The patient must lie still through out the process Can be performed in awake and restless patients Responses are frequency specific Responses are not frequency specific Tone stimulus is used Click stimulus is used Recording is made from cortical potentials Recording is made from brain stem potentials CERA BERA
  • Electrocochleography
  • Electrocochleography setup The recording electrode is a thin needle passed through the tympanic membrane onto the promontory under L/A or G/A Non invasive Electrode placed on TM Invasive
  • ECochG
    • It measures electrical potentials arising in the cochlea and VIII nerve in response to auditory stimuli within first 5 millisec
    • Response is in the form of Cochlear microphonics, Summation potential and Action potentials
  • Final Thought Tests are not infallible, they are only as good as those taking, administering and interpreting them…
    • A slideshow presentation
    • Prepared by
    • Dr. ZEESHAN AHMAD
    • under guidance of
    • DR(Prof)CHANDRA SHEKHAR
    • (Head ENT deptt)
    • THANK YOU