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?

• 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

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

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)

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

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

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

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)

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”

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

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

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

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

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

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

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

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.)

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

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

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

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

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

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

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

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

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

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

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

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

Conductive Hearing Loss

• Conductive hearing loss associated with– otitis media– otitis externa– TM perforation– ossicular discontinuity– otosclerosis– occluded ear canal/stenosed ear canal

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

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

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)

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

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)

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

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.)

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

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

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

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

Other Audiologic Tests

• ABR/BAER

• ECOG

• OAEs

• CAP testing

• tinnitus counselling

Re-Cap

• otoscopy

• tympanometry

• stapedial reflexes

• pure tone audiometry– air and bone conduction; masking

• speech testing

• other tests as needed to follow up

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

Abbrevations Used

• SNHL = sensorineural hearing loss

• CHL = conductive hearing loss

• MHL = mixed hearing loss

• ABG = air bone gap

• AC = air conduction

• BC = bone conduction