23rd B Lec 8 Riphah Immittance Audiometry.ppt

A hearing aid is a small electronic device that you wear in or behind your ear. It makes some sounds louder so that a person with hearing loss can listen, communicate, and participate more fully in daily activities. A hearing aid can help people hear more in both quiet and noisy situations. However, only about one out of five people who would benefit from a hearing aid actually uses one.

A hearing aid has three basic parts: a microphone, amplifier, and speaker. The hearing aid receives sound through a microphone, which converts the sound waves to electrical signals and sends them to an amplifier. The amplifier increases the power of the signals and then sends them to the ear through a speaker.

How can hearing aids help?
Hearing aids are primarily useful in improving the hearing and speech comprehension of people who have hearing loss that results from damage to the small sensory cells in the inner ear, called hair cells. This type of hearing loss is called sensorineural hearing loss. The damage can occur as a result of disease, aging, or injury from noise or certain medicines.

A hearing aid magnifies sound vibrations entering the ear. Surviving hair cells detect the larger vibrations and convert them into neural signals that are passed along to the brain. The greater the damage to a person’s hair cells, the more severe the hearing loss, and the greater the hearing aid amplification needed to make up the difference. However, there are practical limits to the amount of amplification a hearing aid can provide. In addition, if the inner ear is too damaged, even large vibrations will not be converted into neural signals. In this situation, a hearing aid would be ineffective.

1. In the name of Allah, the most beneficent,
the most merciful

2. IMMITTANCE AUDIOMETRY
FUNDAMENTALS - INTERPRETATION
DR MUNIR AHMEDDR MUNIR AHMED
AUDIOLOGIST AND AUDITORY (RE) HAB SPECIALISTAUDIOLOGIST AND AUDITORY (RE) HAB SPECIALIST
E. Mail: E. Mail: [email protected]
Mob : [phone]

3. IMPEDANCE, ADMITTANCE &
IMMITTANCE
Term impedance was coined by Oliver Heaviside (1850-
1925) - a hearing impaired person
He discovered impedance, while he was defining
characteristics of electrical transmission for trans-oceanic
telephone cable
 Acoustic impedance in transmission of acoustic energy
was applied by early telephone engineers
This principle became powerful tool for acoustic system
and is used to design amplifiers

4. Contd--
An Amplifier may be as large as used at sport stadium or
as small as used in Invisible in the canal (IIC) hearing
aids
Terms used to characterized the energy flow are
Impedance, Admittance and immittance
Impedance is an opposition in flow of energy, Admittance
is relative ease in flow of energy through a system and
Immittance is a Generic term; refers either impedance
data or admittance data

5. Contd--
Based on Acoustic Immittance principles; an indirect
method has been developed to measure properties of
middle ear
On the basis of this theory acoustic energy converts into
mechanical energy
This mechanism is so efficient that vibration of eardrum
for sound are difficult to detect at threshold level
Responses of the middle ear structure to sound is
analyzed with this measurement

6. Contd--
Acoustic immittance measured in ear canal is combined
effects of air volume in the external Auditory canal (EAC)
and the characteristics of middle ear
Pathology of the Middle ear produce changing in it’s
function
Changes caused by diseases/ deformities/ obstructions
in conductive system of ear can be recorded by
immittance audiometer ( Middle ear analyzers
Tympanometers )

7. IMMITTANCE MECHANISMMECHANISM
IN CONDUCTIVE SYSTEM OF THE EARIN CONDUCTIVE SYSTEM OF THE EAR
The external Auditory canal (EAC) and the middle ear cavity
is normally filled with air
Enclosed volume of the air on both sides of the tympanic
membrane acts as Acoustic compliance (Acoustic Spring)
The eardrum and the structure within middle ear cavity,
(ligaments, tendons and muscles of middle ear) act as
Mechanical springs that return to its original position, when
stretched and released and ossicles are Mechanical
masses

8. Contd--
Measurement of acoustic Immittance of normal ear form
the basis for determining abnormal middle ear conditions
In fact, by measuring Acoustic Immittance we are
evaluating mechano - acoustic middle ear system
When an acoustic wave strikes the eardrum of normal
ear, a portion of the signal is transmitted via middle ear
to cochlea
Remaining part of the wave is reflected back towards
external canal

9. Contd--
This reflected energy forms a sound wave that travels
outward with amplitude (dependent upon the opposition
encountered at the tympanic membrane)
Energy of reflected wave is greater when the middle ear
system is stiff or immobile as in otitis media with effusion
(OME)
Energy of reflected wave is considerably less into the
canal because of reduce stiffness as in ossicular chain
disruption)

10. Contd--Contd--
 Reflected sound waves recoded with Immittance
audiometer gives lot of information about status of the
middle ear
Immittance audiometry is used to
Identify the presence of fluid in the middle ear
Evaluate the function of Eustachian tube
Predict audiometric findings
Determine the nature of hearing loss
Assist in diagnosing the site of auditory lesions

11. CLINICAL USE IN AUDIOLOGY
 Concept of measuring acoustic immittance was used
clinically in audiology at Denmark in1940
Where Otto Metz worked on differences of impedance in
normal and pathological ear
A group of physicists and physicians of Antwerp university
refined this; clinical test and developed Vanhuys (VAN
EYES-HU) Model to understand effects of middle ear
pathology on tympanometric patterns in 1975

12. Contd--
 Generally, procedure used to evaluate middle ear
function is Tympanometry and its features are recorded
on tympanograph by tympanometer
Features of the tympanogram are
Tympanometric shape
Static acoustic admittance
Tympanometric width
Tympanometric peak pressure
Equivalent ear canal volume

13. QUALITATVE VS QUANTATIVE
APPROACHES
To establish diagnosis: Qualitative or quantitative
approaches are being used in our country
Qualitative Approach
 Diagnosis is established according to the heights and
location of tympanometric peak
Liden (1969) & Jerger (1970) classified tympanogram
qualitatively
Classification of the tympanogram are appended below

14. Contd--
Type “A” Tympanogram
Type “B” Tympanogram
Type “C” Tympanogram
Type ‘D’ Tympanogram
Feldman(1976) added subtypes of “A” Tympanogram,
A
d and A
s to elaborate type ‘D’ Tympanogram

15. Contd--
Type ‘A’ tympanogram has normal peak, height and
location on pressure
axis
Such curves are
found in normal
middle ear functioning

16. Contd--
Type ‘B’ tympanogram is flat and not in the pressure
axis. No point of maximal compliance is observable.
Type ‘B’ Tymp is seen
in patients with
Serous (secretary ) and
adhesive otitis media
some cases of congenital
middle ear malformation
Perforated ear drum
Patent ventilating tube or occluded ear canals with wax

17. Contd--Contd--
Peak of Type ‘C’ tympanogram is displaced towards
negative pressure
This tympanogram represents :
Near normal compliance
–200 dapa Middle ear
pressure or worse
Persistence type ‘C’
tympanogram Infers:
Poor Eustachian tube function in presence of intact
tympanic membrane

18. Contd--Contd--
This curve may or may not
related to the presence
of fluid in the middle ear
but one can conclude
that ear drum still have
some mobility
Valsalva may change type ‘C’ Tympanogram into type ‘A’

19. Contd--
Type “ D” Tympanogram has subtype ‘A
d’ and ‘ AA
s’s’
Type A
d
represents an extremely flaccid eardrum
Type A
d
curve can be seen in
cases of ossicular chain
disruptions

20. Contd--
 In Type In Type A
s
Tympanograph subscript “s” is indicative of
“stiffness” and “ shallowness” of tympanogram
Type A
s curve may
be seen in thickened
or heavily scarred
tympanic membrane
in tympanosclerosis
It also can be seen in
Otosclerosis
s

21. Contd--
Quantitative Approach
Qualitative approach leads to occasional errors and
misinterpretation because, there is no rule to
distinguish type A, A
d
and A
s
To address these issue ANSI bound the manufacturer
to conform the requirement that
Immittance indicator must be calibrated in physical
units and from it’s data one can determine pass/ fail
criteria

22. Contd--
Clinical instrument produced since then have features
like
Compliance
Gradient
Tympanometric peak pressure
 External Canal Value
All above features can be measured in physical units
and one can determine pass/fail criteria

23. Contd--
ComplianceCompliance
Compliance is sensitive to middle ear conditions like,
Otitis media with effusion (OME), Chronic otitis media,
Cholesteatoma and ossicular adhesions
Space occupying lesions such as Glomus tumors,
Ossicular discontinuity, Eardrum perforation
ComplianceCompliance values:
 Less than or equal to 0.25 cm3, generally suggest
low acoustic Immittance (indicative of stiffening
pathologies)

24. Contd--
Greater than or equal to 1.4 cm3
generally indicate abnormally high
immittance (suggestive of ossicular
discontinuity or tympanic membrane
perforation
GradientGradient
Sharpness of tympanometric peak is an indicator of
middle ear pathology

25. Contd--
Width of tympanogram at that point determined in
dapa and wide gradient considered as an indication
of pathology
 Normative data
Children ages 3 to 10 years = (80-159)
adults = (51-114)
Tympanometric Peak PressureTympanometric Peak Pressure(TPP) (TPP)
Air pressure of ear canal at which peak of
tympanogram occurs is TPP

26. Contd--
TPP - 300 dapa indicates significant negative middle ear
pressure
The clinical use of TPP has it’s base on “ex vacuo” theory
of middle ear function
This theory holds that when eustachian tube fails to open
then middle ear mucosa absorbs gases of middle ear cavity
Resulting in negative pressure in middle ear cavity
(frequently observed in children
Restoration of middle ear pressure to ambient level
requires patent eustachian tube

27. Contd--
Mere abnormal TPP is not a reliable indicator for
middle ear diseases
it should correlate with other tympanometric,
audiometric or otoscopic findings
In some patients, particularly in children sniffing may
produce large negative middle ear pressure because
sniffing may cause evacuation of air through
eustachian tube owing to negative pressure in naso-
pharynxs

28. Contd--
Equivalent Ear Canal Volume (ECV)
Tympanometry using 226 Hz probe tones are useful for
estimating volume of air
in front of probe
An opening in tympanic
membrane adds volume
of middle ear space
A flat tympanogram with
large ECV is an evidence of opening in tympanic
membrane

29. Contd--
An estimate of volume of air in front of tube is useful to
determine perforation and evaluation the patency of
grommet
Based on these measurement,
it is possible to distinguish ear
with intact and perforation
ear drum Normal ECV .2 -2 cm
3
A normal ECV does not rule out perforation
Average ECV is about 0.3 cm
3
in 4-months infant: 0.75
cm
3
in preschool aged children 1-1.4 cm
3
in adults

30. CASE - A

31. CASE - B

32. CASE - C

33. CASE -D

34. CASE - E

35. CASE - F

36. CASE -G

37. CASE -H

38. CASE - J

39. CASE - K

40. CASE - L

41. CASE - M

42. First Option

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