Download Audiometry , BERA, OAE

Audiometry , BERA, OAE
HEARING ASSESSMENT: PURE
TONE AUDIOMETRY
 Instrumentation: Audiometer & transducers
 Main goal: To describe and quantify the amount of
hearing loss
Terms
 Hearing threshold: “ the lowest sound pressure level, at which
under specified conditions, a person gives a predetermined
percentage of correct responses on repeated trial”.
 Threshold tested for AC and BC separately.
 Threshold can be tested in the unmasked (quiet) or masked
condition.

Sound conducted to the cochlea through the bone
stimulates the cochlea in three ways:
1. Compressional / distortional bone conduction
2. Inertial bone conduction
3. Osseotympanic bone conduction

Audiometric test frequencies
and
levels
AC
Frequencies: 125, 250, 500, 750, 1000, 1500, 2000, 3000, 4000, 6000, 8000
Hz.
Some high-frequency audiometers can test up to 20 kHz.
Levels: Usually from -10 dB HL to about 110 dB HL (not for 125, 250, and
8000 Hz)

BC
Frequencies: 250 through 8000 Hz.
Levels: Usually from 50 dB HL at 250 Hz to about 70-80 dB HL at other
frequencies
Test environment
 Done using
 Attenuating headphones (supraaural and circumaural)
 Insert earphones
 Sound-treated booths (best if double-walled)
Test environment, cont’d.
 One room: Tester and patient in the same room
 Two room: Tester and control equipment in one room,
patient in the other.
 Must have adequate attenuation, 60 Hz shielding, and
connections for talkback.
 Patient must not be able to observe the tester.
Masking

1.
2.
When to mask?
Always during bone conduction
In air conduction whenever testing with sounds of 45dB and more
 How much to mask?
1. For Bone Conduction
minimum masking = Bt + (Am – Bm)
where Bt = bone conducton threshold in test ear, Am = air conduction
threshold in masked ear, and Bm = bone conduction threshold in the
masked ( non-test) ear.
2. For air conduction
minimum masking = At – 40 + (Am – Bm)
where At = air conduction threshold in the test ear and 40 is the
accepted minimum interaural attenuation for air conducted sound, & (Am
– Bm) = air bone gap in masked ear
3. The maximum masking level for both:
Bt + 45
Clinical Masking
 Nontest ear can influence thresholds of test ear
 Shadow curve apparent without masking
 Interaural attenuation varies from 40 to 80 dB with air
conduction
 Interaural attenuation is about 0 dB with bone
conduction
Sounds used for masking
 White noise
 Narrow band noise
 Complex noise
Shadow Curve
Normal
Hearing(2)
Types of Hearing Loss
 Conductive
 Bone conduction is normal(
15dB- 20dB) but the air bone
gap is 20dB or more
 Sensorineural
 Bone conduction level is more
than 20dB & if the air bone
gap is 15dB or lesser
 Mixed
 Bone conduction level is worse
than 20dB & the air bone gap
is 20dB or more
Severity of Hearing Loss
Why do we need it?
 Whether the subject has any definite audiometry
disorder?
 Whether the hearing loss is conductive/ sensorineural/
mixed
 If sensorineural, then whether it is cochlear or
retrocochlear
 The degree of hearing dysfunction
 For preop and postop hearing
 For medicolegal purposes
Determine Hearing
Level
 Establish Hearing Threshold Level
(HTL or simply HL)
 What is threshold?
 With earphones or via bone, softest sound
detected 50% of time
 In the soundfield, tests reveal response of better
ear
 Speech Reception Threshold (SRT) is softest level possible to
hear closed set of bi-syllabic words
 Thresholds are measured in decibels (dB) at various
frequencies, reported in Hertz
Speech Reception Threshold
 Softest level of speech that can be understood 50% of
the time
 Bi-syllabic vocabulary may include words tailored for
pediatric patients
 Ear specific, if earphones used
 Obtained via air and/or bone conduction
 Correlates closely with pure tone average at 500 Hz,
1000 Hz and 2000 Hz
Provides estimate of hearing for speech
Speech discrimination score
 The percentage of correctly identified words, when words
from a specially prepared list called “ phonetically
balanced word list” is presented to the subject.
Phonetically Balanced Word Lists
 selection of a group of words so that each phoneme
appears with the same frequency it has in the normal
lexicon. Based on Thorndike-Lorge lists of words and
word frequencies.
 So-called PB word lists-- CID W-22 Lists
 Four lists of 50 words each.
Rollover Indices for the
preceding examples
 Normal: (100 - 100) / 100 = 0.0
 Rollover: (44 - 20) / 44 = 0.54
 Cochlear: (80 - 70)/80 = 0.125
 Rollover Indices of 0.45 or greater indicate a neural (VIIIth nerve)
problem.
Tympanometry
 Measurement of the change of impedance of the middle
ear at the plane of the tympanic membrane as a result of
changes in air pressure in the external auditory meatus.
 Impedance: physical and mechanical property , mixture
of three parameters, viz. stiffness, mass and friction
 Admittance : reciprocal of impedance
 Compliance : reciprocal of stiffness

1.
2.
3.

1.
2.
3.
4.
Pathologies with increased compliance:
Ossicular chain discontinuity
Scarring of the tympanic membrane
Very large tympanic membrane
Pathologies with decreased compliance:
Otosclerosis
Adhesive or secretory otitis media
Tumours in the middle ear like glomus jugulare
Ossicular fixation like fixed malleus syndrome

Pathologies with normal compliance:
1. Eustachian tube obstruction only, without secretory
changes in the middle ear
 Tympanometry provides objective results to determine
status of middle ear
 Acoustic reflexes are part of the test, add diagnostic
information
 May be obtained ipsilaterally and/or contralaterally
Immittance Tests(12)
 Five classifications of results,
referred to as Modified Jerger
Classification System
 Type A(d), A, A(s), B and C
A(d)
A
A(s)
B
C
-400
-200
0
+200
 Ad , ie, normal middle ear
pressure with high compliance,
ossicular chain discontinuity
 As , ie, normal middle ear
pressure low compliance ,
otosclerosis
 Flat tympanogram without any
pressure peak or measurable
compliance
 Jeger’s type B
 Gross secretory otits media or
gross adhesive changes in
middle ear
 Negative middle ear pressure,
normal compliance with a
normal shape and single peak
 Jeger’s type C
 Blocked eustachian tube
without collection of any
significant fluid in the middle
ear
Acoustic/ stapedial reflex tests


1.
2.
3.
4.
Principle
The acoustic reflex tests help the otolaryngologist in
the:
Elimination of middle ear pathology
Differentiation of cochlear and retrocochlear pathology
Detection of some cases of brain-stem pathologies
Objective estimation of average hearing threshold level
 On the afferent side, sound enters one earpasses through the
middle ear reaches the cochleapasses through the 8th cranial
nerve reaches the cochlear nucleus of the same sidepasses to
the superior olivary complex in the brainstem
 At this level there is crossing of pathways and the efferent pathway
is bilateral
 On the efferent side, from the centre of the reflex arc which is in the
superior olivary complex of the brainstem , 7th nerve nucleus of
both sides passes through the facial nerve passes through
nerve to stapedius  stapedius muscle on both sides muscle
contraction
Interpretation of stapedial reflex
test
 Unilateral moderate or severe conductive deafness
 In bilateral conductive deafness
 In unilateral severe sensorineural deafness
 In bilateral sensorineural deafness
 In central lesions
Auditory Brainstem Evoked
Response [ABER]
 Jewett & Wilson (1971)
 It is an exogenous transient response recorded in the 1-
10 ms interval(fast/short) elicited best by very brief
stimuli such as clicks,at moderate to high levels
Introduction
 Auditory brainstem response (ABR) is a neurologic test of
auditory brainstem function in response to auditory
(click) stimuli.
 It’s a set of seven positive waves recorded during the first
10 seconds after a click stimuli. They are labeled as I - VII
PHYSIOLOGY
 Auditory brainstem response (ABR) typically uses a click
stimulus that generates a response from the hair cells of
the cochlea, the signal travels along the auditory pathway
from the cochlear nuclear complex to the inferior
colliculus in mid brain generates wave I to wave V.
ORIGIN OF BAEP
Origin of each wave
Wave
Origin
I
Cochlear nerve
II
Dorsal & Ventral cochlear nucleus
III
Superior olivary complex
IV
Nucleus of lateral lemniscus
V
Inferior colliculus
VI
Medial geniculate body
VII
Auditory radiation(cortex
Electrode placement (Montage)
 Cz (at vertex) (recording electrode)
 Ipsilateral ear lobule or mastoid process (reference
electrode).
 Contra lateral ear lobule (act as a ground)
Procedure





Subject lying supine with a pillow under his head.
Room should be quite.
Clean the scalp & apply electrode.
Check the impedance.
Apply the ear phone (red for the right ear & blue for the
left ear)
 Select the ear in the stimulator & apply masking to the
opposite ear.
Contd..
 Stimulation rate : 11/sec.
 Repetition : 2000
 Find out the threshold of hearing.
 ABR should be done at around 80dB.
 Start averaging process & continue until the required
repetition accomplished.
 Calculate the peak – interpeak latencies for the ABR
waves.
Normal values
 Peak latency of a wave = less than
the next higher no. wave
 Or just add 1 to that wave, latency
will be less than that.
eg. Latency of wave 1 is less than 2.
Wave
Latency
I
<2mSec.
II
<3 m.sec
III
<4 m.sec
IV
<5 m.sec
V
<6 m.sec
VI
<7 m.sec
Normal BERA tracing showing
distinct peaks
BERA parameters that are studied
 Though seven waves can be recorded,the first five waves
are commonly employed and the most prominent
feature, the wave V complex, is used for threshold
estimation
 During ABER recording the brain activity and the noise
level s/b minimum
 Young infants often fall asleep after a feed and on testing,
the stimulus intensity needs to start at around 50 db,so
that a normal hearing baby is not woken by the initial test
sequence
 Older and more disturbed children require sedation or
anaesthesia for testing
 Effects of maturation on ABERs
*from 3 months to 3 years of age, there is no significant
change in the latency of wave I, but wave V latency and IV interval decreases until stable levels are reached by 18
months of age (Gorga et al 1989)
 The amplitude of all waves increases with age from
birth,with wave I reaching adult size by 6 months and
wave V by 2 years.
 In the newborn only wave I and wave V are clearly seen
and wave III becomes prominent at about 2 weeks of age
 The hearing threshold is determined by the lowest
stimulus intensity at which the the AEP is detectable
visually
 As ABER is usually evoked by click stimuli,any information
on hearing is mainly b/w frequencies 2kHz and 4kHz
 Difference b/w the observed ABER threshold and the
behavioural threshold may be b/w 5-25 db
 Differentiation b/w conductive, cochlear and mixed
losses may not be easy during ABER measurement
 As wave I is present at birth and there is no significant
change in latency from 3 months to 3 years,definite
prolongation of wave I latency would suggest a
conductive hearing problem
 Bone conduction ABER testing may further elucidate a conductive
loss
 The relationship b/w stimulus intensity and wave V latency is used
to plot ‘latency-intensity’ function
 In normal hearing, with increasing intensity of stimulation, the
amplitude of the waves are enhanced and the latencies are
reduced,but the interwave latencies are relatively independent of
click intensity
 ABERs also provide useful information on the neurological status
.Pts with multiple sclerosis may have neuronal desynchronization
which abolishes the ABER while the pure tone audiogram remains
normal
 In infants, a prolonged I-V latency with normal threshodls would
suggest neurological damage to the auditory pathways
Interpretation
 Wave I : small amplitude, delayed or absent may indicate cochlear




lesion
Wave V : small amplitude, delayed or absent may indicate upper
brainstem lesion
I – III inter-peak latency: prolongation may indicate lower brainstem
lesion.
III – V inter-peak latency: prolongation may indicate upper
brainstem lesion.
I – V inter-peak latency: prolongation may indicate whole brainstem
lesion. Shortening of wave the interval with normal latency of wave
V indicate cochlear involvement.
APPLICATIONS
 Identifying the hearing loss
 Classification of type of deafness
(conductive or sensorineural)
Contd…
 Identification of retro choclear patholgy
Auditory brainstem response (ABR) audiometry is
considered an effective screening tool in the evaluation
of suspected retrocochlear pathology such as an acoustic
neuroma or vestibular schwannoma.
OTOACOUSTIC EMMISIONS [OAEs]
 First reported by Kemp(1978)
 They reflect a release of acoustic energy which can be
recorded in EAC and are thought to originate from the
OHCs of cochlea
 OAEs canoccur spontaneously in 40-60% of healthy ears
 Clinically useful OAEs are evoked OAEs
Evoked OAEs
Transient OAEs – in response to a click or
tone burst.
TOAEs are present with good low and middle frequency
hearing to click stimuli
TOAEs reflect a hearing threshold of 15-25db or better
TOAEs can be recorded from birth, with large amplitude
emissions,making this an excellent tool for screening in
neonates
Distortion product OAEs - occuring at intermodulation
frequencies when two tones are presented
simultaneously
DPOAEs have been found to be absent if hearing threshold
exceeds 15 db
The main use of EOAEs is in
1. Screening for hearing impairment in neonates
2. Screening cooperative children with a variety of
handicaps where it is not possible to perform
behavioural testing
3. Monitoring of hearing in children on ototoxic agents
4. In identifying the site of a hearing impairment,as
although absent in peripheral auditory disorders, they
are present in central auditory disorders
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