Audiological Evaluation

A to Z
Dr.Osama Hamed
Audio-Vestibular Medicine Specialist
KAUH
AUDIOLOGY
The study of sound and hearing
Sound=physical stimulus that evoke
sensation of hearing.
Audiometry=the measurement of
hearing sensitivity.
 The nature of sound and hearing
Stimulus:
sound

(sine wave)
MECHANICAL ELECTRICAL/SENSORY
 SOUND

Sound is a form of vibration

Vibration is the to-and-fro motion of an

object (guitar string, vocal folds, diaphragm
on an earphone or loudspeaker, tuning
fork)
 SOUND

For sound to occur, must have a

SOURCE: Something has to be

disturbed.

FORCE: Something has to disturb it.

MEDIUM (e.g. air): Something has to

carry the disturbances.
 When air molecules are
displaced, pressure waves
occur

http://www.glenbrook.k12.il.us/gbssci/phys/Class/sound/u11l1c.html
SOUND: PRESSURE WAVE
 Characteristics of the waveform
(amplitude x time)

CYCLE: One complete period of compression

and rarefaction of a sound wave
 Characteristics of the waveform
(amplitude x time)
PERIOD: The amount of time that it takes to
complete one vibratory cycle.
FREQUENCY: The number of cycles that occur in one
second.
 FREQUENCY

Hertz (Hz): Unit of measurement

of frequency

100 cycles per second = 100 Hz

Pitch: Psychological percept of

frequency.
e.g., low frequency sounds = low pitch
 Frequency Range of Hearing
Sensitivity

Humans: 20 Hz to 20 kHz.
– Below 20 Hz, we feel a vibration rather than hear a
sound.
– Most people have very diminished sensitivity for
frequencies > 8000-10, 000 Hz.
Bats (auditory specialists) : 2 kHz-100 kHz.
The Minimal Audible Pressure Curve (dB SPL)

Indicates the
minimum
average
sound
pressure
levels by
frequency for
a group of
people with
normal
hearing
Amplitude
Intensity

The quantity or
magnitude of
sound.
 AMPLITUDE/INTENSITY

Decibel (dB): Unit of amplitude

used most frequently in clinical
audiology.

Loudness: The psychological

correlate of amplitude (measured in
sones, phons).
Hearing loss prevention
 Noise controls, hearing protectors
– Primary prevention  reduction or elimination of HL
 Screening neonates, school age, elderly, industrial
– Secondary prevention  early identification to reduce
negative effect of HL
 Audiology services (hearing aids, rehab)
– Tertiary prevention  services to deal with adverse effects of
HL
Types of Tests

BEHAVIOURAL OBJECTIVE
– reliable & consistent – no voluntary response
response to sound – infants and young children
– Developmental age – non compliant subjects
– not used in newborn – people with developmental
screening level that doesn’t allow other
testing.
 Age based hearing assessment

BEHAVIOURAL OBJECTIVE

PURE TONE
SCHOOL-

Request
AGED +

AUDIOMETRY Measure
responses
responses
PLAY
AUDIOMETRY
TODDL

Condition
VROA
ER

responses
BOA
Observe
BIR
TH

responses
Need to consider individual’s functional
age
Overview
 Behavioral audiometry
 Tympanometry

 Acoustic reflex measurements

 ECochG

 Auditory Brainstem Response (ABR)

 Otoacoustic Emissions
 Behavioural Observation Audiometry (BOA)

Observing changes in behaviour in response to sounds

Who?
Very young babies (under 6mths corrected) or with similar
functional age.
Test sounds & materials
 Calibrated (known frequency and intensity) noisemakers
 Audiologist records sound level (from sound level meter),
sound type & observed response- observer determines
whether response is present/absent
Infants 7 months-3 years
 Aim: to detect hearing impairment greater than
20-30 dB HL
 Typically use behavioural techiques
– Visual Reinforcement Orientation Audiometry
(VROA) for 6-18 months
– Play audiometry
 May incorporate objective testing if non-
compliant or very difficult to test
Visual Reinforcement Oreintation Audiometry (VROA)

– Uses operant conditioned

response and visual
reinforcement
 Response typically head
turn. Eye turn also
possible
 Complex visual

reinforcement usually
lighted puppet theatre-
colour movement and light
are important
Play audiometry 3-9 years
 Before testing
– Subjective check of audiometer
– Check test environment, audibility of tones
– Avoid visual clues
– Instruct client, demonstrate procedure
– Position headphones
– Present orienting tone (40dBHL) and check client’s
response. Re-instruct if necessary
Screening with Play Audiometry
 use peg board, blocks etc.
– if very young get parents to train child at home
 headphones on desk present 100dB tone
 train child without headphones- Stimulus -

Response
 introduce headphones

 present 40dB HL tone with headphones on.

Repeat
 decrease tone to 20dB HL for screen
Pure Tone Audiometry
 Most common test
 Threshold of audibility
 Activation of auditory system
 Energy formatted into neural
code
 Air conduction assesses entire
system
 Bone conduction assesses
cochlea onwards
Pure Tones
 Auditory acuity
 Spectrally specific
 High frequency tones
stimulate basal turn of
the cochlea
 Low frequency tones
stimulate apical turn of
the cochlea
Assessment of thresholds
 Octave frequencies tested
 Bone conduction thresholds

 Mastoid or forehead used

 Mastoid preferred because less intensity

required
 Occlusion effect

 Ascending series of tone presentations

Ranges of Hearing Loss

 -10 – 25 dB HL = Normal range

 26 – 40 dB HL = Mild hearing loss

 41 – 55 dB HL = Moderate


 56 – 70 dB HL = Moderately Severe

 71 – 90 dB HL= Severe

 Greater than 90 dB HL = Profound

Normal Hearing
Conductive Hearing Loss
Sensorineural Hearing Loss
Mixed Hearing Loss
Speech Audiometry
 Speech Reception Threshold using spondaic words
 Standardized word lists
 Familiarization with spondees
 Ascending series of presentation
 Excellent speech discrimination in conductive hearing loss patients
 Poor speech discrimination in cochlear hearing loss patients
 Poorest speech discrimination in retrocochlear hearing loss patients
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
Shadow Curve
Clinical Masking cont.
 Compare bone conduction threshold of nontest
ear with air conduction threshold of test ear to
determine whether masking is necessary
Plateau method
 Mask nontest ear with
progressively greater
amounts of sound until
threshold does not rise.
 Masking Dilemma
Electrophysiological Tests
 Immittance
 Evoked Potential

 Otoacoustic Emissions
Immittance
 Ear Canal Volume
 Tympanometry

 Static Compliance

 Acoustic Reflex, Decay, & Latency

Ear Canal Volume
 Measure at +200 mmH20
 Provides measure of volume of external ear

canal
 Volumes based on age

 Volumes greater than 2.5 suggest:

– Perforation or
– Patent V. tube
 Tympanometry
 Objective
measure of
the function of
the TM and
middle ear
 5 or 6 basic

shapes
Tympanogram Types
Type A Tympanogram
OE ME IE AN CNS
Type AD Tympanogram
OE ME IE AN CNS
Type AS Tympanogram
OE ME IE AN CNS
Type BLow Tympanogram
OE ME IE AN CNS
Type BHi Tympanogram
OE ME IE AN CNS
Type C Tympanogram
OE ME IE AN CNS
 Static Compliance
(Peak Compliance)
Acceptable Range by Age

Flaccid: disarticulation,
flaccid TM, etc.
0.9 1.4

Normal mobility

0.2 0.3 Stiff: otosclerosis fluid,

tympanosclerosis, etc.
Child Adult
ART
Acoustic Reflex Threshold
 Stapedial muscle contraction
 Temporary increase in middle
impedance
 Bilateral Stimulation
 Adaptation
 Neural network in lower
brainstem
Clinical application of ASR
 Middle Ear Disease
 Otosclerosis
 Cochlear hearing loss and loudness recruitment
 Retrocochlear lesions may abolish the ASR
 Brainstem lesions may abolish the contralateral
reflexes
 Determination of site of a seventh nerve lesion
 Acoustic Reflex Decay
Reflex Decay
otoacoustic emissions
Background
The presence of cochlear emissions was
hypothesized in the 1940’s on the basis of
mathematical models of cochlear nonlinearity.
However, OAEs could not be measured until
the late 1970s, when technology created the
extremely sensitive low-noise microphones
needed to record these responses.

David Kemp first discovered Otoacoustic

emissions in 1978.
Otoacoustic Emissions
 Otoacoustic emissions are sounds that are
produced by healthy ears in response to acoustic
stimulation.

 OAE’s arise because our ears have evolved a

special mechanism to give us extra hearing
sensitivity and frequency responsiveness. The
mechanism is known as the cochlear amplifier and
it depends on a specialized type of cell called
“outer hair cells.”

 It’s the job of the cochlea to receive the sound

energy collected by the outer and middle ear and
to prepare it for neural transmission.
Purpose of OAE’s
 The primary purpose of otoacoustic
emission (OAE) tests is to determine
cochlear status, specifically hair cell
function. This information can be used to
 (1) screen hearing
 (2) partially estimate hearing sensitivity
within a limited range
 (3) differentiate between the sensory and
neural components of sensorineural
hearing loss
 (4) test for functional hearing loss.
 Types of OAE’s

Types

Distortion Product
Spontaneous OAE’s Transient Evoked
OAE’s (DPOAE’s)
(SPOAE’s) OAE’s (TEOAE’s)
Spontaneous OAE’s
 Occurs in the absence of any intentional
stimulation of the ear.
 Prevalence is in about 40-60% of normal
hearing people.
 When you record SOAE’s, you average the
number of samples of sounds in the ear and
perform a spectral analysis.

 The presence of SOAE’s is usually considered to

be a sign of cochlear health, but the absence of
SOAE’s is not necessarily a sign of abnormality.
Distortion Product OAE’s
 Result from the interaction of two simultaneously
presented pure tones.
 Stimuli consist of 2 pure tones at 2 frequencies (ie, f1, f2
[f2>f1]) and 2 intensity levels (ie, L1, L2). The relationship
between L1-L2 and f1-f2 dictates the frequency response.
 DPOAEs allow for a greater frequency specificity and can
be used to record at higher frequencies than TOAE’s.
Therefore, DPOAE’s may be useful for early detection of
cochlear damage as they are for ototoxicity and noise-
induced damage.
 DPOAEs often can be recorded in individuals with mild-to-
moderate
hearing losses for whom TOAE’s are absent.
*DPOAE’s do not occur in the frequency
regions with more than 50-55dB Hearing loss.
* DPOAE’s can be elicited from ears that
have a greater hearing loss than TEOAE’s.
DPOAEs
 2 tone stimuli (F1 and F2)
 Cochlea hair cells generate a resonance
RESPONSE

NOISE
Transient Evoked OAE
 TEOAE’s are frequency responses that follow
a brief acoustic stimulus, such as a click or tone burst.
 The evoked response from this type of stimulus covers the
frequency range up to around 4 kHz.
 In normal adult ears, the click-elicited TEOAE typically falls
off for frequencies more than 2 kHz, and is rarely present
over 4 kHz, because of both technical limitations in the ear-
speaker at higher frequencies and the physical features of
adult ear canals so that is why DPOAE’s would be more
efficacious.
 For newborns and older infants, the TEOAE is much more
robust by about 10 dB and typically can be measured out
to about 6 kHz indicating that smaller ear canals influence
the acoustic characteristics of standard click stimuli much
differently than do adult ears.
 TEOAE’s do not occur in people with a hearing loss greater
TEOAE results

Normal hearing

High
frequency HL

Severe SN HL
TEOAE & DPOAE
Recording OAE’s
 OAEs are measured by presenting a series of very brief
acoustic stimuli, clicks, to the ear through a probe that is
inserted in the outer third of the ear canal. The probe
contains a loudspeaker that generates clicks and a
microphone that measures the resulting OAE’s that are
produced in the cochlea and are then reflected back through
the middle ear into the outer ear canal.
 The resulting sound that is picked up by the microphone is
digitized and processed by specially designed hardware and
software. The very low-level OAEs are separated by the
software from both the background noise and from the
contamination of the evoking clicks.
SOUND TRAVEL FWD BWD TRAVEL SOUND
IN EAR THRU COCHLE COCHLE THRU IN EAR
CANAL ME A A ME CANAL

Response
detected
OAEs
 Otoacoustic emissions
 “Echo”-like response of outer hair cells of the

cochlea
 Can only indicate functioning outer hair cells

and good middle ear function.

Types of OAEs

 Spontaneous
– 20-60% of population, related to age
– Not clinically useful
– Not related to tinnitus
 Evoked
– Present in normal ears
– Not present in ears with SNHL greater than 25-30 dB
– Absent in presence of conductive hearing loss. WHY?
Evoked OAEs
Types
– Click (transient) evoked OAE-
TEOAE
Absent for sensori neural loss
greater than 20-30dB HL
– Distortion product OAE (DPOAE)
Absent in sensori neural losses
greater than 45-55 dB HL
Acquisition
 Not affected by sleep but needs test subject to
be still and compliant
 Very quick
clinical applications

 Quick screening tool

 Good indicator of cochlear reserve- correlated with
hearing
 Monitoring
 TEOAE present with hearing loss up to 30dBHL
 DPOAE present with hearing loss up to 50dB HL
 Monitoring of drug ototoxicity (can affect OAE before HL
present)
 Sensory vs. neural HL
clinical limitations
 Problems because of middle ear disease
 Not sensitive for neonates within 24 hours of

birth
 Results affected by test conditions
– Noise
– Electrical interference
 Not a test of hearing- limited application
electrocochleography
components
 Cochlear microphonic: outer hair cell response
 Summating potential: cochlear activity

 Action potential: Firing of auditory nerve (same

as ABR wave 1)

 All occur within the first 1.5-2 ms after an

acoustic stimulus
stimulus & acquisition
 Recording electrode must be as close to
response as possible (transtympanic)
 Children: general anaesthetic

 Adults: may be done without anaesthetic

 resistant to effects of drugs and subject state of

arousal
 Can be used in pre-implant assessment to test

cochlear function
clinical applications
 Diagnosis of Meniere’s disease

 Diagnosis of cochlear hearing loss/auditory

dysynchrony, sensory vs neural.
 Assessment of hearing status for difficult to test

subjects
clinical limitations
 Auditory information only provided to cochlea
 Very invasive

 Results can vary up to 20dB from actual

hearing
 Limited frequency specificity

 expensive
auditory brainstem response
history
 First complete description in 1970s
 Response found between 1-15ms after stimulation.
 Recording has 7 peaks, peak five being the most
prominent.
– The amplitudes, latencies and relationship of those peaks can
be used to diagnose certain pathological conditions.
 What is an ABR?
 The Auditory Brainstem
Response is the
representation of electrical
activity generated by the
eighth cranial nerve and
brainstem in response to
auditory stimulation
How is an ABR recorded?

 Electrodes are placed on the scalp and coupled via leads to

an amplifier and signal averager. EEG activity from the
scalp is recorded while the ear(s) are stimulated via
earphones with brief clicks or tones.
 A series of waveforms unique to the auditory neural
structures is viewed after time-locking the EEG recording to
each auditory stimulus and averaging several thousand
recordings.
components

Response occurs within 5-6ms

after stimulus is presented
Generators of the ABR
Auditory cortex

V Medial geniculate body

I
Inferior colliculus
V
Lateral lemniscus

Superior & accessory olive area

Dorsal cochlear nucleus
IV Ventral cochlear nucleus

III VIIIth nerve

II
I
 Medial
Ventral &Dorsal Superior Lateral Inferior
Cochlea Geniculate
CochlearNucleus Olive Lemniscus Colliulus
Body

VIII

ACOUSTIC
STIMULATION
V
IV
III
II
I ABR
Latency, ms

0 1 2 3 4 5 6 7 8 9 10
 anatomy

proximal VIIIth nerve Multiple generators

Distal VIIIth nerve
stimulus & acquisition
 Short clicks or tone bursts used
 Rate of around 20/sec or faster

 Responses can be + or – 20dB on true

thresholds, mixed in with EEG

 Electrodes on head (surface electrodes)

 Can be influenced by subject characteristics

(age, gender, body temperature)

 Not affected by arousal state or most drugs
 Differential
Differential
Transducer
Transducer amplifier
amplifier
(HP)
(HP)

Analog
Analog filter
filter
Stimulus
Stimulus
generator
generator
Trigger Signal
Signal averager
averager

Display/analysis
Display/analysis
Example Normal Hearing
18 Month-Old – 2000 Hz Tone-Burst

70 dBnHL

10 dBnHL
clinical applications
 Basis of Newborn screening tests: non-
invasive, high success rate
 Estimation of thresholds for difficult to test

people
 Neurodiagnosis of VIIIth nerve/ brainstem

problems
 Intraoperative monitoring

 Cochlear implant evoked responses

 Test-retest reliability
Why use ABR testing?

DIAGNOSIS SCREENING
OF SOME FOR
CONDITION HEARING
S LOSS

THRESHOL
D TESTING
(FREQ
SPECIFIC)
Left
Right
Auditory
Auditory
cortex
cortex

Cochlea Medial geniculate nucleus

Inferior colliculus

Auditory Superior
nerve fiber Olivary
Ipsilateral
Cochlear nucleus
nucleus