Tests of hearing

Physiology Seminar
18/04/2013
©Dr. Anwar Siddiqui
Tests of
Hearing

Why do we test hearing ?
Is the hearing normal?
What is the degree of hearing loss?
What type of hearing loss is it?

Principles of hearing
Units for measuring sound exposure
 Sound Pressure Level (SPL)
• expressed in μPa or Pa
• range from 20 μPa (hearing threshold) till 20 Pa (pain
threshold),
 Decibel dB of sound pressure level (dB SPL)
• defined as: 20 log10 p1/p0 where p1 is actually measured
sound pressure level of a given sound, and p0 is a reference
value of 20μPa, which corresponds to the lowest hearing
threshold of the young, healthy ear.
• In the logarithmic scale the range of human ear’s audible
sounds is from 0 dB SPL (hearing threshold) to 120-140 dB
SPL (pain threshold)

Table 1: Examples of sound pressure levels in relation to
hearing threshold and pain threshold (in dB SPL)The range
of human ear’s audible sounds goes from 0 dB SPL (hearing
threshold) to 120-140 dB SPL (pain threshold)
Source / observing
situation
Typical sound pressure
level (dB SPL)
Hearing threshold 0 dB
Leaves fluttering 20 dB
Whisper in an ear 30 dB
Normal speech conversation
for a participant
60 dB
Cars/vehicles for a close
observer
60-100 dB
Airplane taking-off for a
close observer
120 dB
Pain threshold 120-140 dB
20dB is 10 times 0dB, 40dB is 10 times
20dB, 60dB is 1000 times louder than 0dB
Source: SCENIHR, Po
health risks of exposure to no
personal music players and
phones including a music p
function (2008) , Section 3.3.3

Bone conduction
Air conduction

Types of hearing loss
 Conductive hearing loss
 Sensorineural Hearing Loss

Types of hearing loss
 Mixed Hearing Loss
 Central Hearing Loss

Severity of hearing loss
Degree of hearing loss Hearing loss range (dB HL)
Normal –10 to 15
Slight 16 to 25
Mild 26 to 40
Moderate 41 to 55
Moderately severe 56 to 70
Severe 71 to 90
Profound 91+
Source: Clark, J. G. (1981). Uses and abuses of hearing loss classification. Asha, 23,
493–500.
The table below shows one of the more commonly used classification systems.
The numbers are representative of the patient's hearing loss range in decibels (dB HL).

Severity of hearing loss
 The American Academy of Ophthalmology and
Otolaryngology (AAOO) guidelines (Revised in
1979) states:
“the ability to understand normal everyday
speech at a distance of about 5 feet does not
noticeably deteriorate as long as the hearing loss
does not exceed an average value of 25 dB at 500,
1000 and 2000 Hz”

Hearing Loss Causes
 Age- The tiny hairs get damaged and are less able to respond to sound
waves. Hearing loss can progress over the course of several years.
 Loud noise-Exposure to loud noises damage the hair cells in the cochlea..
 Infections-During an ear infection, fluid can build up in the middle ear.
 Perforated eardrum-Depending on the size of the perforation, there
may be a mild or moderate hearing loss.
 Tumors- eg acoustic neuroma (vestibular schwannoma) and meningioma.
 Trauma-Injuries such as a skull fracture or a punctured eardrum can
cause severe hearing loss.
 Medications- the aminoglycoside class of antibiotics (streptomycin,
neomycin, kanamycin), large quantities of aspirin, chemotherapy drugs
(cisplatin, carboplatin), Vicodin (in large quantities), macrolide antibiotics
(erythromycin) can cause hearing loss.
 Genes- Genetic hearing loss often begins with hearing loss diagnosed at
birth

 Initial Otoscopic examination
 Tympanometry
 BERA
 EChocG
 OAE (Otoacoustic
Emission)
Assessment of hearing
 Speech test
 Loud
 Whisper
 Tuning fork test
 Weber
 Rinne
 Schwabach
 Audiometry
 Speech audiometry
 Pure Tone Audiometry

Initial Otoscopic examination
 Performed with a hand held otoscope
 Ear canal and tympanic membrane
are observed.
 Tympanic membrane is seen for:
• Light reflection
• Differentiation of its part
• Mobility

Speech test
 Simplest of all
 Involves testing ability to hear words without
using any visual information.
 Patient should repeat 5 words spoken loudly at
a distance of approx. 5 metre.
 The whispered voice test involves the tester
blocking one of patients ears and testing hearing
by whispering words at varying volumes.

Speech test
Ball Point click test

Tuning fork test
 Used to differentiate between conductive and
sensorineural hearing loss.
 Larger forks vibrate at slower frequency.
 Tuning forks with frequency 256 or 512 hz are used

Principle of Tuning fork test
CHL (OE or ME Disorder)
 Sounds delivered to the ear via AC will be
attenuated
 If the sound is delivered to the ear via BC,
bypassing the OE & ME, then the sound will be
heard normally assuming there is no disorder
SNHL (OE & ME Are Free From Disorders)
 Sounds delivered to the ear via BC will also be
attenuated

Weber’s Test
 Vibrating tuning fork is placed on the patient's
forehead (or in the middle line).
 The vibrations are tyransmitted by bone
conduction to cochlea.
 The pt. should state if the tone is heard
in the left ear, right ear, or both ears.
 If the sound lateralizes, the patient may have
either an ipsilateral conductive hearing loss or a
contralateral sensorineural hearing loss

Weber’s Test
a b c
Interpretation

Rinne’s Test
 Compares the level of air and bone conduction
of the same ear.
 base of a tuning fork is placed to the mastoid
area (bone con.), and then after the sound is no
longer appreciated, the vibrating top is placed
near the external ear canal (air con.)

Schwabach’s Test
 compares the patient's bone conduction to that of
the examiner's
 If the patient stops hearing before the examiner,
this suggests a sensorineural loss
 If the patient hears it longer than the examiner,
this suggests a conductive loss
This test is contingent on the examiner having normal hearing…..

Audiometry
 Audiometry (from the Latin audīre, "to hear", and
metria, “to measure) is a branch of Audiology, and
is the science of measuring hearing acuity for
variations in sound intensity and frequency.
 An audiometer is the device used to produce sound
of varying intensity and frequency.
Ear Phone to test
Air conduction threshold
Response switch
Bone oscillator to test
Bone conduction threshold

Pure Tone Audiometry
 A pure tone is a tone having a single specific
frequency. The frequency of the tone is determined
by the rate or speed at which the sound source
vibrates
 Pure tone audiometry is the use of pure tones to
assess an individual’s hearing.
 The results of this testing are plotted on the
audiogram.
 Pure tones are generated by an audiometer and
presented to the patient via headphones or, in
some cases, through loudspeakers.
 Can be air conduction audiometry or bone
conduction audiometry

Pure Tone Air Audiometry procedure
 The audiologist present pure tones of one frequency to
the patient, initially at an intensity level that it is
assumed they can hear quite well.
 The intensity (loudness) of the tone is decreased in 10 to
15 dB steps.
 This is continued, with tones being presented for one to
two seconds, until the patient no longer responds.
 The intensity is then raised in 5 dB steps until the
patient responds, decreased again and increased again
in 5 dB steps until the patient responds.
 This lowest audible intensity is defined as the patient’s
threshold for the particular frequency and is marked as
such on the audiogram

Interaural attenuation and masking
 At certain intensity levels, the signal presented
to the test ear will cross over and be heard in the
non-test ear. The inter-aural attenuation rate, or
the intensity difference at which a sound will be
heard in the non-test ear, is approximately 40
dB for air conduction signals presented through
circumaural earphones.
 the masking noise used for pure tone
audiometry is narrow-band noise;generally the
same frequency as the pure tone being
presented to the test ear.

Pure Tone Air Audiometry audiogram

Pure Tone Air Audiometry audiogram
Sensorineural impairment Conductive disease

Tympanometry
 Tympanometry is an examination used to test
the condition of the middle ear and mobility of
the eardrum (tympanic membrane) and the
conduction bones by creating variations of air
pressure in the ear canal.
 In evaluating hearing loss, tympanometry
permits a distinction between sensorineural and
conductive hearing loss, when evaluation is not
apparent via Weber and Rinne testing

Principles of Tympanometry
 Introduces a pure tone into ear canal through 3-
function probe tip
• Manometer (pump) varies air pressure against TM
(controls mobility)
• Speaker introduces 220Hz probe tone
• Microphone measures loudness in ear canal

Normal tympanogram (Type A)
• Peak at 0 daPa
• Best movement of drum when no extra pressure on either side of TM

Other Type A tympanograms
Peak at 0daPa, but
unusually high amplitude
? Ossicular disruption
Peak at 0daPa, but
unusually low amplitude
? Stapes fixation

Flat tympanogram (Type B)
When tymp is flat,
usually means 1 of 3
things:
1. Artefact
2. Fluid in ME
3. Perforation
Look at EAM vol.
If large = perforation
If normal = fluid

Negative tympanogram (Type C)
Can be further divided
into:
C1 – peak between 0
and -200 daPa
C2 – peak less than -
200daPa

Otoacoustic Emission
 They are low intensity sounds produced by
outer hair cells of a normal cochlea
 Can be elicited by a very sensitive microphone
placed in EAC (External Ear Canal)
 Absent when OHC are damaged
 Thus serve to test cochlear functioning

OAE’s
spontaneous evoked
Transient
(click)
Distortion product
(paired tones)
Otoacoustic Emission

USES of OAE’s
 As a screening test for neonates
 Distinguish cochlear from retrocochlear HL
 To test hearing in mentally challanged and
uncooperative individuals after sedation
(Note- sedation doesn’t interferes with OAE’s)

ElectroCochleoGraphy (EChocG)
 It measures electrical potentials arising in the
cochlea and VIII nerve in response to auditory
stimuli within first 5 millisec
 Response is in the form of
• Cochlear microphonics (CM)
• Summation potential and (SM)
• Action potentials (AP)
 Two methods are widely used:
• Transtympanic
• Extratympanic

ElectroCochleoGraphy(EChocG)
Transtympanic membrane
electrodes: These are needle
electrodes, which are placed over the
promotory by penetrating the ear
drum
Intrameatal electrodes: These
electrodes are placed in the external
auditory canal.

ElectroCochleoGraphy (EChocG)
 Normal electrocochleogram from the tympanic membrane to clicks
presented in alternating polarity at 80 dB HL. The amplitudes of
the Summating Potential (SP) and Action Potential (AP) can be
measured from peak-to-trough (left panel), or with reference to a
baseline value (right panel).
 mean SP/AP amplitude ratio to click stimuli for normal subjects is
approximately 0.25 + 0.10 standard deviations (SD). An SP/AP
amplitude ratio greater than 45 % (2 SDs above the norm) is
considered to be enlarged.

ElectroCochleoGraphy (EChocG) usage
 Objective identification and monitoring of meniere’s
disease and endolymphatic hydrops (EH): Enlarged SP
reflects pathologic condition of EH. SP-AP amplitude
ratio is more consistent with the presence of meniere’s
disease. On average, SP-AP ratio of 0.45 or greater is
considered abnormal.
 Intraoperative monitoring: Surgical operation on
brainstem or cerebellum may bear risk of damage to the
auditory system. ECochG recording during surgery
assess the functional integrity of the peripheral and
brainstem pathway directly during operation.

BERA
 To be dealt in subsequent seminar by Dr. Saif

Final Thought
“Tests are not infallible, they are
only as good as those taking,
administering and interpreting
them…”

Sorry can’t hear you!!!!!!!!!
………………Thank You
Any Queries?

Tests of hearing

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