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The Basic Audiologic Evaluation

The Basic Audiologic Evaluation. An introduction to audiometry and impedance testing Nicole J. Lanthier, MA, CCC-A Clinical Audiologist, Reg. CASLPO. What is an Audiologist?.

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The Basic Audiologic Evaluation

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  1. The Basic Audiologic Evaluation An introduction to audiometry and impedance testing Nicole J. Lanthier, MA, CCC-A Clinical Audiologist, Reg. CASLPO

  2. What is an Audiologist? • A professional holding a Master’s degree in Audiology, as well as a professional license or certification, who is educated in the areas of hearing measurement, hearing disorders, aural rehabilitation, amplification, & hearing conservation • Otolaryngologist ~= Opthalmologist • Audiologist ~= Optometrist • HearingAid Dispenser ~= Optician

  3. Who Needs Audiologic Testing? • Infants, children, and adults • people known to be at risk through genetics, noise exposure (ongoing or episodic), oto-toxic drug exposure, aging, related health issues or trauma, those who are concerned about difficulties hearing (or friends/family are concerned about their hearing) • age = birth - 130 years

  4. The Basic (Adult) Audiologic Evaluation • history, reason for referral • otoscopy • tympanometry • stapedial reflexes • pure tone audiometry • air and bone conduction; masking • speech testing (speech audiometry)

  5. Tympanometry • tympanometry = an objective measure of eardrum compliance change as air pressure is varied in the external ear. An assessment of eardrum mobility. Also called dynamic compliance • tympanometric curve = pressure-compliance function

  6. The Tympanogram • Measured on an “impedance bridge” • A tympanogram will give an indication of the status of the middle ear, in terms of compliance • is the middle ear system “stiff” or “floppy” • what is the pressure in the middle ear space • is the eardrum intact

  7. Tympanometric Normsfor Compliance • typically ~ 0.3 cc - 1.5 cc WNL for adults; ~ 0.2 - 1.0 cc for children • lower than this indicates high impedance, higher than this indicates high compliance • low compliance may indicate middle ear effusion or stiffening (otosclerosis) • high compliance could indicate TM scarring (flaccid monomeric areas), ossicular discontinuity

  8. Tympanometric Norms - from Margolis &Heller, 1987 • Compliance Vol. Width • (mmho or cc) (cc) (daPa) • ADULTS • 0.3 - 1.4 0.6 - 1.5 50 - 110 • (X = 0.8) (X=1.1) (X= 80) • CHILDREN(age 3 - 5 years) • 0.2 - 0.9 0.4 - 1.0 60 - 150 • (X = 0.5) (X = 0.7) (X= 100)

  9. Liden-Jerger Classification of Tympanometry • categorical classification of tympanograms • the most commonly used of classification systems; uses “alphabet” category names • normal tympanogram (normal compliance, pressure, morphology) is “Type A”

  10. Type A with Subscript • Type Adeep (Ad) denotes a tympanogram with a peak and normal peak pressure, but increased compliance • e.g. peak pressure + 15 daPa, compliance 1.9cc • Type Ashallow (or As) denotes a tympanogram with a peak and normal peak pressure, but reduced compliance • e.g. peak pressure - 25 daPa, compliance 0.2cc

  11. The Flat Tympanogram • A flat or “type B” tympanogram can indicate • occlusive obstruction in the ear canal • look for smaller EAC volume; otoscopy • a TM which is not moving due to high middle ear impedance • look for normal EAC volume; otoscopy • a perforated TM • look for large volume; otoscopy

  12. Type C Tympanogram- Negative Pressure • When peak pressure is lower than - 150 daPa this is a “Type C” tympanogram • indicates negative middle ear pressure; usually associated with eustacian tube dysfunction • compliance may be normal or reduced • “type C” can be concomitant with, a precursor to, or occur during resolution of middle ear effusion

  13. Stapedial Reflexes(aka Acoustic Reflexes) • Loud acoustic stimulus will cause bilateral contraction (reflex) of stapedius muscles • measured on an “impedance bridge” • loud stimulus delivered to one ear, can measure reflex response on the ipsilateral or contralateral ear - measurement of both “ipsi” and “contra” gives best info

  14. Acoustic Reflex Pathways • START: outer ear -> middle ear -> inner ear -> VIII nerve -> cochlear nucleus -> ipsilateral superior olivary complex • THEN • IPSI - ipsi facial nerve - > ipsi middle ear • OR • CONTRA - contra superior olivary complex -> contra facial nerve -> contra middle ear

  15. Stapedial Reflexes(aka Acoustic Reflexes) • use to detect non-organic hearing loss, investigate facial nerve function, investigate possible retrocochlear pathology • reflex can be also be absent due to middle ear dysfunction or severe hearing loss • look at reflex threshold norms compared to hearing levels

  16. Reflex Decay • reflex decay test - present stimulus tone 10 dB higher than the patient’s reflex threshold for 10 seconds; 500 or 1000 Hz stimulus • measure the amplitude of the reflex for 10 seconds, if it is reduced 50% or more in this time period this is “reflex decay” • suggestive of retrocochlear pathology

  17. Pure Tone Audiometry • Typically tested frequencies include 250 Hz - 8000 Hz • humans can hear ~ 20 Hz - 20 000 Hz but this tested range of frequencies is the area of our most sensitive hearing and the frequencies most used in human speech • may include ultra high frequency testing (>8000 Hz) if monitoring high risk individuals (noise, cisplatin exposure etc.)

  18. Pure Tone Audiometry • A calibrated audiometer is required to ensure that the presented sounds are the proper frequencies and intensities • calibrated earphones required to deliver the sounds • quiet testing area required to ensure detection of sounds is not masked

  19. Earphones • Earphones are sound transducers • Common styles or earphones include • supra-aural earphones • circumaural earphones • insert ear phones • bone conduction transducer/headband • speakers for sound-field presentation

  20. Advantages of Insert Earphones • reduces chance of collapsing ear canals • best reduction of environmental noise • improved comfort • hygiene - usually disposable/cleanable tips • increased inter-aural attenuation • less need for masking • fewer masking dilemmas

  21. Pure Tone Testing • Typically used protocol is a bracketing technique, beginning at 30 dBHL when thresholds unknown, or ~10 dB above known thresholds • if no response at 30 dB, go to 50 dB • bracket “10 down & 5 up” • e.g. response at 30, go to 20, response at 20, go to 10, no response at 10, go to 15; recheck 2-3x

  22. Pure Tone Testing • good idea to test better ear first • if there is an asymmetry in hearing of over 60 dB when using insert phones, or 40 dB using supra-aural phones, you may have problems with crossover and inadvertently stimulate the non-test ear • inter-aural attenuation ~60 dB w/ insert earphones, ~ 40 dB w/ supra-aural headphones

  23. Crossover • E.g. - thresholds of 10 dB left and thresholds over 50 dB right will require masking w/ supra-aural headphones • e.g. thresholds of 10 dB left and thresholds over 70 dB right will require masking with insert earphones • if you do not mask, the sound will cross over via bone conduction

  24. Crossover • To prevent getting responses from the non-test ear in these situations you must use masking noise • for pure tone testing use narrow band noise • for speech testing use speech weighted noise • remember crossover is by bone conduction even if stimulating via air conduction

  25. Masking • Various equations used - example here • For masking for air conduction • threshold of non-test ear, plus 15 dB • want to plateau 15 dB to ensure real threshold • ideally want 30 dB effective masking • remember that masking can also cross over, so you don’t want to overmask and elevate threshold of test ear- remember inter-aural attenuation

  26. Masking Example - AC • E.g. threshold left ear 10 dB, right 75 dB • begin with masking left 25 dB, present tone again right - if response obtained from right, increase masking 5 dB, if no response, increase presenting level to test ear by 5 dB • follow this until you are able to increase masking three times in non test ear with reliable responses from test ear

  27. Bone Conduction • Bone conduction testing uses a vibrating sound generator held to the head to stimulate the inner ear ~ directly • “bypasses” outer and middle ear systems • usually test 250 or 500 - 4000 Hz with BC • usually use pure tone stimuli • typical placement on mastoid, (not touching pinna) can use forehead, teeth, nose

  28. Bone Conduction • Use bone conduction when air conduction thresholds are elevated & want to differentiate b/w conductive and sensorineural hearing loss • conductive hearing loss - hearing loss due to pathology of outer or middle ear systems • AC thresholds elevated, BC thresholds WNL = conductive hearing loss

  29. Air-Bone Gap • The difference b/w the AC and BC thresholds is called the “air-bone gap”, or the “conductive component” • e.g. AC threshold 45 dB, BC threshold 5 dB • air-bone gap, or “conductive component” 40dB • this indicates normal function of the inner ear and auditory CNS, problem OE or ME

  30. Conductive Hearing Loss • Conductive hearing loss associated with • otitis media • otitis externa • TM perforation • ossicular discontinuity • otosclerosis • occluded ear canal/stenosed ear canal

  31. Sensorineural Hearing Loss • if elevated AC and BC thresholds are the same (or very close, 5 dB, together) then the hearing loss is sensorineural • e.g.AC threshold 45 dB, BC threshold 45dB • OR AC = 45 BC = 40 • no air-bone gap, bypassing the OE and ME does not improve threshold, so hearing loss is sensorineural - due to IE/possibly retrocochlear

  32. Sensorineural hearing loss • Called sensorineural since can be sensory or neural: typically sensory, due to IE/cochlea • popular but incorrect, “nerve deafness” • Sensorineural hearing loss associated with • noise exposure -retrocochlear pathology • aging -illness (e.g.meningitis) • ototoxic drugs -labyrinthitis

  33. Mixed Hearing Loss • if there is an air-bone gap, but the BC thresholds are not WNL, then it is a mixed hearing loss • the degree of hearing loss is partly due to OE or ME and partly due to IE • e.g AC threshold 75 dB, BC 40 dB • air-bone gap 35 dB, BC threshold elevated out of normal range (>25 dB)

  34. Mixed Hearing Loss • MHL has a component of CHL and SNHL • Mixed hearing loss can be associated with: • otosclerosis • SNHL with otitis media, • SNHL with cerumen occlusion • SNHL with TM perforation • SNHL with overlay of etc. etc. etc. • post-surgical e.g. cholesteatoma removal

  35. Speech Reception Threshold • SRT - lowest dB HL at which (closed set) speech can be understood • usually obtained by presenting descending levels of spondaic words (spondees) until only 50% score is obtained • use a list of 10-15 familiarized words • spondee - two syllable word with equal emphasis on both syllables (e.g. hotdog)

  36. Speech Reception Threshold • SRT is usually within ~ 6 dB of the pure tone average (PTA = average threshold using 500, 1000, and 2000 Hz) • if hearing loss is steeply sloping or has a “notch” SRT may be lower than PTA, closer to “best threshold” • quick reliability check - if SRT better than thresholds would indicate - ? test validity

  37. Speech Discrimination Testing • Present a list of published phonetically balanced words, usually 25 - 50 words at a level allowing good audibility and comfort • usually ~ 35 - 40 dB over PTA/SRT • NU-6, W-22 • PBK for “kindergarten age” children • modify for special needs (board, write etc.)

  38. Hearing “Sensitivity” vs. Hearing “Clarity” • speech discrimination testing gives an idea about the “clarity” of hearing • patients with identical audiograms (thresholds/sensitivity) may differ significantly in their functional auditory abilities depending on their speech discrimination abilities • unusually poor or asymmetric “discrim” can suggest retrocochlear pathology

  39. Infants/Toddlers • Below age of 6 months use ABR and OAEs • from age ~ 6 - 24 months use visual reinforcement audiometry = VRA • usually done “in the soundfield”, child seated on parent’s lap between loudspeakers in a soundbooth; reinforcing toys hidden behind smoked glass on either side of child • condition child to turn to sound & reinforce

  40. Young Children • Age ~ 2 1/2 - 5 years use play audiometry • usually with earphones, condition child to respond to perceived sounds with a “play” response such as dropping a block in a bucket or putting a sticker in a book • can usually accomplish some speech testing • children/adults with “younger functional ages” can be tested in this manner as well

  41. Amplification? • people with hearing loss affecting the frequency/intensity ranges of spoken language will often benefit from amplification (hearing aids or other varieties of amplification) • good speech discrimination allows better amplified performance • ensure appropriate hearing aid prescription

  42. Other Audiologic Tests • ABR/BAER • ECOG • OAEs • CAP testing • tinnitus counselling

  43. Re-Cap • otoscopy • tympanometry • stapedial reflexes • pure tone audiometry • air and bone conduction; masking • speech testing • other tests as needed to follow up

  44. Abbrevations Used • EAC = external ear canal • WNL = within normal limits • TM = tympanic membrane (eardrum) • SRT = speech reception threshold • PTA = pure tone average • OE = outer ear • ME = middle ear

  45. Abbrevations Used • SNHL = sensorineural hearing loss • CHL = conductive hearing loss • MHL = mixed hearing loss • ABG = air bone gap • AC = air conduction • BC = bone conduction

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