Audiometry for Undergraduate and postgraduate ENT students

Audiometry is one of the essential topic in MBBS.
This presentation helps students to learn about basic audiometry for MBBS level and shall equally be useful for postgraduate ENT students, too.

1. Audiometry
Dr. Krishna Koirala
2018-07-09

2. •PureToneAudiometry:Measuringrelativehearingthreshold
usingpuretones
•Hearingthreshold:lowest(softest)soundlevelneededfora
persontodetectasignalapproximately50%ofthetimes
•Audiometer:deviceusedinthemeasurementofauditory
threshold
•Patients’hearingthresholdismeasuredincomparisonto
idealfixednormalhearinglevel(0dB)andthusisrelative
hearingthresholdmeasurement
•PTAissubjectivetestofhearing

3. Why Pure Tone thresholds?
•Theauditorysystemisorganizedtonotopicallyinthecochlea:
Highfrequenciesrepresentedatthebasalendandlow
frequenciesattheapicalendofthebasilarmembrane
•Damagetosensorycellsofthecochleaataspecificplace
alongthebasilarmembranecanresultinalossofhearingthat
correspondstothefrequenciescodedbythatplace
•Puretonethresholdtestsprovidedetailsthatwouldotherwise
remainunknownifabroadbandstimulussuchasspeechwere
used

4. Pure Tone Audiometer

5. Sound proof / Sound treated room

6. Hearing Threshold Estimation
•HughsonandWestlaketechnique(5up10down)
−Bettereartestedfirst
−Airconductionmeasuredfor1K,2K,4K,8K,500,250and
125Hzviaheadphone
−Boneconductionmeasuredfor1K,2K,4K,500and250Hz
viabonevibratorwithmaskingofotherear
−Ifdifferencebetweentheseoctavesis>20dBthenhalf
octavesi.e.750,1500/3000/6000Hztested

7. •Thestartingintensityofthetesttoneisreducedin10dB
stepsfollowingeachpositiveresponse,untilahearing
thresholdlevelisreachedatwhichthesubjectfailstorespond
•Then,thetoneisraisedby5dB,ifthesubjecthearsthis
increment,thetoneisreducedby10dBandifthetoneisnot
heardthenitisraisedbyanother5dBincrement
•This5dBincrementisalwaysusediftheprecedingtoneisnot
heard,anda10dBdecrementisalwaysusedwhenthesound
isheard
•2correctresponsesoutof3isacceptableandplottedonthe
graph

8. Symbols used in audiogram

9. Normal Audiogram

10. Pure Tone Average
Calculatedbytakingarithmeticmeanofairconduction
thresholdsat500,1000&2000Hz(speechfrequencies)

11. Classification of Deafness (Goodman and
Clark)
P.T.A. (dB) Type
0 -15 Normal
16 –25 Minimal
26 –40 Mild
41 –55 Moderate
56 –70 Moderately severe
71 –91 Severe
> 91 Profound

12. Conductive deafness
•NormalBoneConduction
•ABgap>15dB

13. Sensori-neural deafness
•Both AC and BC
affected
•No AB gap

14. Mixed deafness
•Both BC and AC above
normal Thresholds
•AB gap present

15. Diagnosis of type of deafness
Type Air
Conduction
Bone
Conduction
Air bone gap
ConductiveWorsened Normal Present
Sensori-
neural
Worsened Worsened Absent
Mixed Worsened Worsened Present

16. Low frequency conductive HL
Otitis media with effusion

17. Carhart’s notch (otosclerosis)

18. High frequency SNHL
Presbycusis, ototoxicity, acoustic neuroma

19. Low frequency SNHL (Meniere’s disease)

20. Deafness in Meniere’s disease

21. Acoustic dip (Noise induced deafness)

22. Uses of pure tone audiogram
1.Tofindtypeofhearingloss
2.Tofinddegreeofhearingloss
3.Forprescriptionofhearingaid
4.Predicthearingimprovementafterearsurgery
5.Topredictspeechreceptionthreshold
6.Arecordformedico-legalreference

23. Speech Audiometry
•SpeechReceptionThreshold(S.R.T.)
–Minimumintensityatwhich50%ofspondee
(disyllablewithequalstress)wordsarecorrectly
identified
–Fallsnormallywithin10dBofPureToneAverage
•SpeechDiscriminationScore(S.D.S.)
–Percentageofphoneticallybalanced(single
syllable)wordscorrectlyidentifiedat40dBabove
S.R.T.

24. •UsesofSpeechAudiometry
–Differentiatebetweencochlearandretro-
cochlearlesions
–VolumeofhearingaidfixedatPBmax
score
–Infunctionaldeafness:SRT>+10dBof
puretoneaverage

25. Speech Audiogram

26. Speech Discrimination
Hearing lossSpeech understanding
0 –25 dBNo difficulty with faint speech
26 –40 dBDifficulty with faint speech only
41 –55 dB Difficulty with faint + normal speech
56 –70 dB Difficulty even with loud speech
71 –91 dBOnly understands amplified speech
> 91 dB Can’t understand amplified speech

27. Special Audiological Tests

28. Tests for Recruitment
•Recruitmentisabnormalgrowthinloudnesswith
increasingfrequencyofsound
•Testsofrecruitmentaredonetodiagnosecochlear
pathology
•Testsused:
–ShortIncrementSensitivityIndex(SISI)Test
–AlternateBinauralLoudnessBalance(ABLB)Test

29. S.I.S.I. Test (Jerger, 1959)
•Continuous tone given 20 dB above hearing threshold
and sustained for 2 min
•Every 5 sec, tone intensity increased by 1 dB and 20
such blips are given
•SISI score = % of blips heard
•70-100 % in cochlear deafness
•0-20 % in conductive & nerve deafness

30. A.B.L.B. Test (Fowler, 1936)
•Pure tone is presented alternately to deaf & normal ear
•Intensity heard in normal ear is adjusted to match with
deaf ear
•Test started 20 dB above threshold in normal ear &
repeated with 10 dB raises till loudness is matched in
both ears
•Initial difference is maintained, decreased & increased
in conductive, cochlear and retro-cochlear lesions
respectively

31. Laddergram in A.B.L.B. test

32. Threshold Tone Decay Test
•OlsenandNoffsinger(1974)
•Detectsabnormalauditoryadaptationduetonerve
fatiguecausedbyaretro-cochlearlesion
•Puretonepresented20dBabovehearingthreshold
continuouslyfor1min
•Ifpatientstopshearingearlier,intensityincreasedby
5dBandrestarted
•Testcontinuedtillpthearstonecontinuouslyfor1
minorintensityincrement(decay)>25dB

33. Interpretation
Tone Decay Pathology
dB Type
0-5 Absent Normal
10-15 Mild Cochlear
20-25 Moderate Cochlear
> 25 Severe Retro-Cochlear

34. Impedance Audiometry
•Objective test of hearing
•Consists of
–Tympanometry
–Acoustic reflex
measurements

35. Tympanometry
•Basedontheprincipleofimpedance
•Whenasoundstrikesthetympanicmembrane,someofthe
soundenergyisabsorbedwhiletherestisreflected
•Astiffertympanicmembranewouldreflectmoresoundenergy
thanacompliantone
•AcompliantT.M.givesequalpressureinE.A.C.andmiddleear
•Bychangingthepressuresinasealedexternalauditorycanal
andmeasuringthereflectedsoundenergy,itispossibletofind
thecomplianceorstiffnessofthetympano–ossicularsystem
andthusfindthehealthyordiseasedstatusofthemiddleear

36. •Theequipmentconsistsofaprobewhichsnuglyfitsintothe
externalauditorycanalandhasthreechannels
–Oscillator:todeliveratoneof220Hz
–Microphone:topickupthereflectedsound
–Airpump:tobringaboutchangesinairpressureintheear
canalfrompositivetonormalandthennegative
•Bychartingthecomplianceoftympano-ossicularsystem
againstvariouspressurechanges,differenttypesofgraphs
calledtympanogramsareobtainedwhicharediagnosticof
certainmiddleearpathologies

37. Impedance Audiometer Probe
A = oscillator (220 Hz)
B = air pump
C = microphone

38. Tympanogram parameters
Adult Child
Compliance 0.5 –1.75 ml0.5 –1.75 ml
Middle ear
pressure
+ 100 to -100
Deca Pascal
+ 60 to -100
Deca Pascal
External Auditory
Canal volume
1.0 –3.0 ml 0.5 –2.0 ml

39. Tympanogram Types (Jerger)

40. Types of Tympanogram
Type Pressure Compliance Seen in
A Normal Normal Normal ME
As Normal Decreased Otosclerosis
Ad Normal Increased Ossicular
discontinuity
BNil (flat curve)Nil (flat curve)Fluid in ME, TM
perforation
C Negative Normal ET obstruction

41. Type A

42. Type As

43. Type Ad

44. Type B (fluid in middle ear)
EAC volume = 1.8 ml

45. Type B (T.M. perforation, grommet)
EAC volume = 3.2 ml

46. Type B (E.A.C. obstruction)
EAC volume = 0.4 ml

47. Type C

48. Acoustic Reflex
Loudsound>70dBabovehearingthresholdcauses
B/Lstapediusmusclescontraction,detectedin
tympanometryasdecreaseincompliance

49. Acoustic Reflex
•Principle:
–Aloudsound,70–100dBabovethethresholdof
hearingofaparticularear,causesbilateral
contractionofthestapedialmuscleswhichcan
bedetectedbytympanometry
–Tonecanbedeliveredtooneearandthereflex
pickedfromthesameorthecontralateralear

50. Clinical uses of Acoustic Reflex
•Totestthehearingininfantsandyoungchildren
•Tofindmalingerers
–Apersonwhodoesnotrespondonpuretoneaudiometrybut
showsapositivestapedialreflexisamalingerer
•Todetectcochlearpathology
–Presenceofstapedialreflexatlowerintensities(e.g.40–60
dB)thantheusual70dBindicatesrecruitmentcochlear
typeofhearingloss
•TodetectVIIIthnervelesion
–Ifasustainedtoneof500or1000Hz,delivered10dBabove
acousticreflexthreshold,foraperiodof10s,bringsthe
reflexamplitudeto50%,itshowsabnormaladaptationandis
indicativeofVIIIthnervelesion(stapedialreflexdecay)

51. •Todiagnosethelesionsoffacialnerveandits
prognosis
–Absenceofstapedialreflexwhenhearingis
normalindicateslesionofthefacialnerve
proximaltothenervetostapedius
–Thereflexcanalsobeusedtofindprognosisof
facialparalysisastheappearanceofreflex,afterit
wasabsent,indicatesreturnoffunctionanda
favourableprognosis
•Lesionofbrainstem
–Ifipsilateralreflexispresentbutthecontralateral
reflexisabsent,lesionisintheareaofcrossed
pathwaysinthebrainstem

52. B/L reflexes present

53. Stapedial reflex absent

54. Acoustic Reflex Decay

55. Electro-cochleography
•Measuresauditorystimulusrelatedcochlear
potentialsbyplacinganelectrodewithinexternal
auditorycanal/ontympanicmembrane/
transtympanicplacementonroundwindow
•3majorcomponents:
–Cochlearmicrophonics:fromouterhaircells
–Summatingpotential:frominnerhaircells
–CompoundActionpotential:fromauditorynerve

56. Electrode in ear canal

57. Trans -tympanic electrode

58. Electro-cochleography findings in
Meniere’s disease
•Summation potential : compound action potential
ratio > 30 %
•Widened waveform
•Distorted cochlear microphonics

59. SP –AP Waveform

60. Cochlear Microphonics
Normal
SP/AP
> 30 %
Distorted CM

61. Otoacoustic Emission (Kemp echoes)
•Sounds generated within normal cochlea due to
activities of outer hair cells
•Types:
–Spontaneous: absent in > 25 dB HL
–Evoked: transient; distortion product
•Applications:
–Objective non-invasive test for hearing screening in
neonates & evaluation of non-organic hearing loss

62. Screening of neonates

63. Normal Otoacoustic Emission

64. Brainstem Evoked Response Audiometry
(BERA/ABR)
•Auditoryevokedneuro-electricpotentialsrecorded
within10msecfromscalpelectrodes
•AnObjectivetestfor
–Hearingthresholdforuncooperativept/malingerer
–Hearingthresholdinsleeping/sedated/comatose
–Diagnosisofretro-cochlearpathology
–DiagnosisofC.N.S.maturityinnewborns
–Intra-opmonitoringofauditoryfunction

65. Hearing test of comatose pt

66. Screening of neonates

67. Auditory evoked potentials

68. Anatomy of B.E.R.A. waves

69. B.E.R.A. waves

70. Normal inter-wave latencies

72. Audio Test Cochlear Retro-cochlear
Speech
Audiometry
S.D.S. = 60-80 % < 40 %, Roll over
phenomenon
S.I.S.I. Positive (> 70 %) Negative
A.B.L.B.
Laddergram
Converging Diverging
Tone decayNegative (< 25dB)Positive (> 25dB)
Stapedial reflexReflex at < 60 db
SL; Decay absent
Reflex at > 70 dbSL;
Decay present
B.E.R.A. (Wave
V latency)
<4.2 msec > 4.2 msec