Principle of Air
Conduction (AC) and Bone conduction (BC)
The sound can be transmitted to the cochlea in a two ways
-
1. Air Conduction
• It involves the transmission of sound to the cochlea via
outer and middle ear.
• For testing AC, a charged tuning fork is placed vertically
about 2 cm away from the EAC opening.
• The sound waves transmitted through tympanic
membrane –Middle ear ossicles - Inner ear
.2. Bone Conduction
• It involves the transmission of sound to cochlea via
vibration of the skull bone by passing the outer and
middle ear for testing BC, the base of the charged
tuning fork is placed on the mastoid bone.
• Bone conduction testing only the cochlear function.
• Normally air conduction is louder and heard twice
longer than the bone conduction.
Uses of Tuning Fork
• Used in musical instruments
• Used in clock and watches
• Used in medical and Scientific uses
Limitations of Tuning Fork Tests
• Cannot differentiate between mixed and
conductive hearing loss .
• Time consuming
• The examiner should be wall trained in doing the TFT and should have knowledge of TFT.
• Tuning fork are not calibrate in terms of intensity
the harder you hit them, the louder they sound;
different result each time.
Type of Tuning Fork Tests
• Rinne test
• Weber test
• Schwabach Test
• Bing Test
• ABC test (Absolute bone conduction test)
• Gelle’s Test
Rinne Test
• It was first developed by Polonsky.
• It was developed by Heinnich Rinne in 1855.
What is Rinne test ?
• It is a tuning fork test where the air conduction
and bone conduction of the test ear are
compared.
• It is the test which is based on the concept that
patients with conductive hearing loss hear better
via bone conduction than air conduction for the
patient with SNHL, they hear better via the AC
than the BC.
Principles:-
• The Rinne’s Test compares the hearing sensitivity
by the bone conduction to the hearing sensitivity
by the air conduction.
Purpose:-
• To differentiate between a conductive hearing
loss and preceptors hearing loss.
• Assisting the audiologist in a diagnosis of the
type of hearing loses that a particular patient
exhibit.
Instruction:-
• I will present you two tones, one from the front
part of the ear(EAC) and another from the back
or behind the ear. You have to listen carefully to
the tones and tell me which side the ear the
tone was louder (front or back).
Procedure:-
There are two ways/methods to perform a Rinne’s
test they are:-
1. The threshold comparison method.
2. The loudness comparison method
The Threshold Comparison Method
• In this method, firstly strike the tuning fork
against any objects like rubber pad, and place
the tuning fork in vibration 2.5 cm away from the
EAC holding it vertically for 2 to 3 seconds.
• If the patients reports that he can no longer hear
the sound produced by the tuning fork, then
quickly place the foot piece of the tuning fork on
to the mastoid process of the patient and ask if
he/she can again hear the sound or not.
Loudness Comparison Method
• In this method, firstly we strike the tuning fork
on the bony surface and places it on the EAC and
then to mastoid process alternately. Then ask
the patient which sound was louder.
• This is better method because ear has a property
of adaptation and patient will not hear it if
tuning fork is kept continuously over the mastoid.
Interpretation:-
• The following are the interpretation drown from
Rinne’ s Test.
Positive Rinne
• Rinne test is said to be positive if the air
conduction (through EAC) is louder or longer
than the bone conduction (via mastoid process).• The positive rinne is basically seen in the people
with normal hearing and sensorineural hearing
loss.
• It is also seen with those subject with an incident
conductive loss or with a conductive component
up to 20 dB in a mixed loss.
• Normally, the people with normal hearing will
hear the tone more louder by air conduction
than by bone conduction. For the SNHL, the
attenuation produced will be of some degree of
loss by air conduction as by bone conduction.
Negative Rinne
• The negative rinne is seen in the people with
conductive hearing loss and mixed hearing loss.
• It also seen with the patient with severe sensor
neural loss predominantly on the test side due to
the BC stimulus being cross heard by the better
cochlea on the non- test ear.• This condition can be differentiated by applying a
Barany’s noise box to the opposite ear.
• This masking noise raises the threshold of
hearing in the non test ear to such a level that
tuning fork cannot be heard in that ear by cross
hearing.
False Positive Rinne/ Rinne False positive
• It may be seen in cases with mild / slight
conductive hearing loss.
• In this patient report that he hears the tone
louder via EAC than the bone conduction, the
weber lateralize to normal ear.
• This basically happens when the conductive
components is less.
False Negative Rinne
• It is seen in profound or severe unilateral SNHL
where the patient doesn't hear any sound of AC
but responds to only BC.• This response to BC is due to cross hearing of
tone by better ear.
• To avoid the contribution by the other ear, we
have to perform masking.
Rinne Equivocal
• Here air conduction is equal to bone conduction
and it indicates mild conductive hearing loss.
Limitations:
• Before a negative Rinne can be obtained, the
audiometer must have exhibited more than a
slight conductive loss.• So the slight conductive loss will not overcome
the normal differential between air and bone
conduction and test result will be positive rinne,
even through the patients impairment is actually
of conductive type.
• Interns of those patient with unilateral severe
sensor neural impairment, the Rinne’s test will
be / shows negative Rinne(BC better than AC).
• So, the result might lead the audiologist to
diagnose a conductive loss which of course
would be grossly wrong.• With a unilateral hearing loss, however the
audiologist can check the results of the Rinne against
the results of the weber.
Some Important Things That You Need To Consider
are:-
• Whether the fork is touching the auricle.
Force of application.
Force with which the fork is excited.
Remove the patient glasses when testing bone
conduction.
ØRinne test has high specificity but low sensitivity.
Weber Test
• It was first described by Schmalz.
• It was detailed by wilhelms weber in 1825.
• What is Weber’s Test?
• It is a tuning fork test where in bone conduction
of the both ears are compared at the same time.
• It is a test of lateralization that is the patient
must state where they hear the tone (left ear,
right ear, both ears or in the midline)
Principles :-
• It works on following test.
A. Stenger principle
• It states that if 2 tones that are identical in all
ways except loudness are introduced
simultaneously into both the ears, only the
louder tone will be perceived.
• Weber effect in SNHL cases is based on stenger
principle
B. It compares the bone conduction of both the
ears.
Purpose:-
• To differentiate between the conductive hearing
loss and sensorineural hearing loss.
Instruction:-
• We will give you one sound. You have to listen
carefully to it and tell us which side of the ear it
was louder. You can hear the sound at the
middle of the head, from both the ears or from
either side of the ear. So you have to tell us from
which side did you hear louder.
Placement:-• The stem should be placed on the midline of the
patient skull which included the following:-
ØThe top or the back of the head
ØForehead
ØBridge of the nose
ØThe upper teeth (incisors)
ØThe chin
Procedure:-
• Strike the TF against the bony surface and place
anyone of the listed placement.
• Basically the TF at the bridge of the noise is
preferred because the skin between the fork and
the bones is thinnest here.
• The vertex placement can be effective with bald
patient.
• Then ask the patient from which direction
he/she heard the sound.
Interpretations:-
• Following are the interpretation of weber test:-
1. Centralized ( )
• It is seen with the people with normal hearing. In
this the sound is perceived as the used image at
the center
• Thus, binaural fusion phenomenon takes place
whereby the sound of equal frequency, intensity
and loudness are perceived equally by both the
ears and thus combines to form one single image
of the centre.
2. From both the ears( )
• It is seen with the patient with normal hearing and
bilateral sensorineural hearing loss.
3. Lateralized to poorer ear
• It is seen with the people suffering from conductive
hearing loss.
• Why do weber lateralized to poorer ear?
• Occlusion effect it is the impression of increased
loudness of a bone conduction tone when the outer
ear is tightly covered.• We know that our pinna mainly act as a high
pass filter which allows high frequency wave to
pass through but De-emphasis the lower
frequency wave.
• So, when we press the tragus in ward we are
occluding the low frequency wave.(does not
allow the loudness is chanced and we hear
better from poorer ear.)
Causes of lateralization
• Theories:a) Ambient sound theory (noise theory)
• It is the sound present in the atmosphere.
Normally, tuning fork sound is not heard because
ambient sound is heard.
• In conductive deafness, ambient sound is not
heard, so tuning fork sound is heard well.
b) Theory of dispersion
• Vibration from the tuning fork conducted via the
bone is dispersed in all directions; middle ear,
external auditory canal and inner ear when it
reaches the medial wall of the middle ear in
conductive deafness.• All the sound from the tuning fork is transmitted
to the inner ear and not the exterior due to the
pathology and hence sound is heard better in the
ear with conductive deafness.
• A lateralized weber’s test in a conductive hearing
loss may indicate a hearing loss of only 10-15 dB
4. lateralized to better ear/ cochlea
• It is seen in those patient with sensorineural hearing
loss.
• The lateralization is based on stranger principle.
Limitations:-
• They are poorly understood in conductive hearing
loss.
•
It cannot confirm normal hearing because it does
not measure sound sensitivity in a quantitative
manner.
•
Hearing defects affecting both ears equally as in
presbycusis will produce an apparently normal
results
Bing’s Test
• It was developed by Albert Bing in 1891.
What is Bing Test?
• It is the test for the comparison of bone
conduction thresholds of the same subject when
its EAC occluded and unoccluded.
• It is present more at low frequency ranging from
250 Hz – 1 KHz.
• It is not present beyond 2 KHz.
Principle :-
• It uses is based on the concept of occlusion
effect.
• Occlusion effect:- It is the impression of
increased loudness of a bone – conduction tone
when outer ear is tightly closed (occluded).
• Compare the bone conduction of same patient
when it is occluded and unocculuded.
Purpose :-
• It differentiate between conductive hearing loss
and sensorineural hearing loss.
• Sensitive is detecting up to 9dB of conductive
hearing loss.
Instruction :-
• We will do another test. I will present a tone on
the back of your one ear. You have to listen
carefully and tell me whether there is a change
in loudness of the sound when I cover your EAC
or there is no change.
Procedure:-
• The test may be performed by either of the
method:-
a) Loudness comparison method
• In this method, firstly we strike the tuning fork
against some bony surface. Then we places this
vibrating tuning fork on the mastoid process and
let the subject hear the sound for 2-3 seconds
and then we occlude the EAC by pressing the
tragus inward.• Now, ask the subject about the change in
loudness like whether there was increased in
loudness when we pressed/ covered the EAC by
tragus or there was no change.
b)Threshold comparison method
• In this method, firstly we strikes the tuning fork
against bony surface. Then, place on to the
mastoid process with tuning fork in vibration.
• Listen to the sound carefully until the vibration
gets exhausted and then occlude the EAC and
ask if he can hear any sound or not.
Interpretations:-
a) Bing Positive
• A Bing test is said to be positive if the patient
hears louder sound when EAC is occluded
(due to the occlusion effect ) and hears a softer
sound when EAC is not occluded (because the
ambient noise is heard by ear, which makes the
sound and is heard softer).
• It is seen in those patient with normal hearing or
has sensorineural hearing loss.
(b) Bing Negative
• A Bing test is said to be negative if the patients
appreciate no change in hearing.
• It is seen in those patient with conductive
hearing loss or mixed hearing loss.
Limitations :-
• Cannot differentiate between conductive
hearing loss and mixed hearing loss.
• Cannot differentiate between normal hearing
and sensorineural hearing loss.
• Cannot detect the degree of hearing loss.
Schwabach Test
What is Schwabach’s Test?
• It is a tuning fork test where the bone
conduction of the patient is compared to the
bone conduction of the examiner, assuming that
the bone conduction of the examiner is normal.
Here EAC is not occluded.
• It is the clinical equivalent of what is done in
bone conduction audiometry.
Principles:-
• The test compares the patient’s ability to hear a
tuning fork by bone conduction with that of a
normally hearing person.
Purpose:-
• Differentiates between the conductive hearing
loss and sensorineural hearing loss.
• Finds the degree of hearing losses (it is quantify
inters of time)
Instruction:-
• We will do another test, I will present a tone on
the backside/ behind the ear. You have to
carefully listen to the tone and report me when
no longer sound is heard.
Procedure:-
• In this method, firstly strike the tuning fork
against the bony surface and place the foot piece
of a vibrating tuning fork on patient's mastoid
process. Ask the patient to say when the tuning
fork is no longer heard.• As soon as he/she indicates the point has been
reached, the foot piece of the tuning fork is
transferred to the mastoid process of a normal
hearing person (examiner). Then we compare the
duration of bone conduction heard by the patient to
the bone heard by the examiner.
Interpretations:-
a) Prolong Schwabach Test
A schwabach test is described to be prolonged if the
bone conduction heard by the patient is longer than
the bone conduction heard by the examiner. (P>E)• These type of result is seen on the patient with
conductive hearing loss or mixed hearing loss.
• The prolonged Schwabach response on conductive
hearing loss is primarily due to the exclusion of
masking effects of ambient noise which applies to
usual test conditions or due to the occlusion effect
caused by the presence of ear wax or due to the
infection of middle ear.
b) Diminished Schwabach Test
• A schwabach test is described to be shortened or
diminished if the bone conduction heard by the
patient is shorter than the bone conduction heard by
the examiner (P<E).
• It is observed with patient with SNHL.• It is observed with patient with SNHL.
Limitations:-
• Cannot differentiate conductive hearing loss
from mixed hearing loss.
• It is not that accurate.
• You lose time transferring the tuning fork.
• The examiner must have normal hearing.
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