Immittance audiometry

immitance audiometry summarized

1. NONBEHAVIORAL
ASSESSMENT MEASURES
IMMITANCE AUDIOMETRYIMMITANCE AUDIOMETRY

2. The Functions of
Immittance Audiometry
Detection of middle ear pathology
Differentiating cochlear from retrocochlear pathology
Estimate sensitivity of hearing loss
Cross referencable with pure tone results
The Role of Immittance Audiometry in
Detecting Middle Ear Disease
John T. Jacobson

3. Acoustic immitance
◦Impedance:
◦Resistance to the flow of acoustic energy
◦Useful diagnostic tool to detect presence of
fluid in the middle ear, evaluate EU tube
function, help evaluate the facial nerve and
help predict audiometry
Admittance
◦Ease of which acoustic energy flows
Immitance is a term derived from the terms for two inversely related
processes for assessing middle ear function
◦Impedance
◦Admittance

4. Compliance vs Impedance
Compliance
Ease with which
energy flows through a
system
Impedance
Resistance to energy
flow through a system

5. Advantages of Immittance
Audiometry
“Immittance is a physical characteristic of all mechanical vibratory
systems, of which the middle ear is one example”
Non-invasive
Non-behavioral

6. Instrumentation
Major components
Probe tone oscillator and
loudspeaker
Monitor microphone
Pressure pump and
manometer
Ipsilateral reflex oscillator
and loudspeaker
Probe tip

7. Auditory Immittance
“ A way of assessing the manner in which energy flows through the
outer and middle ear into the cochlea”

8. Immittance Relationships
Probe tone
energy
passed
Probe tone
energy
reflected
Compliance
High
impedance
Low High Low
Low
impedance
High Low High

9. Basic Immittance
Measures
Static compliance
Tympanometry
Acoustic Reflex Thresholds
Acoustic Reflex Threshold Decay

10. Static compliance
Measure of ear canal volume under two specific physical condition
200mH20 of positive air pressure is applied to ear canal and a volume is
read
Second volume reading occurs at a pressure value of maximum eardrum
compliance
Under normal mddle ear conditions, maximum eardrum compliance occurs
when atmospheric pressure is equal on both sides of TM (0mmH2O)
Two volumes are subrtracted from one another and remaining volume
represents the static compliance of the middle ear
Because wide variety of middle ear pathologies produce overlapping
compliance values, static compliance is least applicable measure of
immitance test battery.

11. Tympanometry
“A way of measuring how acoustic immittance of the middle ear
system changes as air pressure is varied in the external ear
canal”

12. Tympanometry
Yields information about
◦Air pressure status of the middle ear
◦Static acoustic immitance (establishing parameters of stiffness or flaccidity at
the ear drum)
◦The integrity and mobility of the eardrum and ossicular chain
◦Resonance point of the middle ear system

13. Tympanometry
Concepts of immittance applied in practice

14. Normal Tympanogram

15. Impedance as Equivalent
Volume
When the amount of reflected probe tone pressure is
high, it’s as if the volume has decreased. As volume
increases, sound pressure decreases

16. What is a Normal
Tympanogram?
Shape
Pressure: -100 mm H
2
O or DaPa
Compliance: 0.3-1.6 cc

17. Common Tympanograms
Normal tympanogram
(Type A)
Shape?
Pressure?
Compliance?

18. Common Tympanograms
Type A
s
Shape?
Pressure?
Compliance?

19. Common Tympanograms
Type A
d
Shape?
Pressure?
Compliance?

20. Common Tympanograms
Type B
No peak compliance
Little change in
compliance with various
pressures
Middle ear effusion,
total perforation, or
impacted wax

21. Assessing PE Tubes
TYPE B (BLOCKED PE TUBE) PATENT PE TUBE

22. Common Tympanograms
Type C
Peak compliance in
negative ranges
often beyond -100db
Eustachian tube
dysfunction,
inadequate
ventilation of ME

23. Tympanometry in very young
children
0 – 6 months
High frequency probe required
1000Hz for babies younger than
3months
3 – 9 months, initially use 1000hz, if
fails repeat tone with 226hz probe
Tympanometry with 226 and 1000 Hertz tone
probes in infants 2012
 
Luciana Macedo de Resende
I
; Juliana dos Santos
Ferreira
II
; Sirley Alves da Silva Carvalho
III
;
Isamara Simas Oliveira
IV
; Iara Barreto Bassi
V

24. Basic Immittance
Measures
Tympanometry
Acoustic Reflex Thresholds

25. ASR
Defined as the lowest intensity required to elicit a stapedial muscle
contraction
Neural connection located in lower brainstem, with influences of higher
CNS structures on the reflex via the olivocochlear bundle
Afferent portion of the reflex is the ipsilateral eight nerve to cochlear
nuclei
Efferent limb is the facial nerve which innervates stapedial muscle
Contraction of the stapedial muscle tilts the anterior stapes away from
the oval window and stiffens the ossicular chain and results in
increased impedence, which is measured as small decrease in
compliance by the ear canal probe

26. ASR
3 primary acoustic reflexes characteristics commonly evaluated
◦1. presence or absence of the stapedial reflex
◦2.acoustic reflex threshold
◦3 acoustic reflex decay or adaptation
The time delay of acoustic reflex is thought to be 10ms
Acoustic reflex thresholds for tones in patients with normal hearing are usually
70 to 80 db above their tone thresholds and about 5db greater for the
contralateral threshold

27. The Middle Ear Muscles and
the Acoustic Reflex
Tensor tympani muscle
Stapedius muscle

28. Acoustic Reflex Pathways
Ipsilateral
Right ear
Left ear
Contralateral
Probe right
Probe left

29. Acoustic Reflex Threshold
“the lowest intensity at which a middle ear immittance change can
be detected in response to sound”

30. Instrumentation for
Acoustic Reflex
Thresholds

31. Normal Acoustic Reflex
Threshold Levels

32. Interpretation of an Absent
Acoustic Reflex Threshold
Possible pathologies that might lead to an absent
contralateral probe left reflex (right crossed)

33. CN VIII lesions
Demonstrate absent acoustic reflex when stimuli presented to affected
ear
Acoustic reflexes differ from cnVIII lesion versus cochlear lesion
◦cnVIII refles will be absent or abnormal regardless of degree of hearing loss
◦Cochlear lesion usually dependent on degree of hearing loss
Abnormal reflexes also recorded when stapedial muscle function is altered by
myopathic disease such as Myasthenia Gravis and Eaton – Lambert
syndrome or hyperthyroidism

34. Basic Immittance
Measures
Tympanometry
Acoustic Reflex Thresholds
Acoustic Reflex Threshold Decay

35. Time Course of the Acoustic
Reflex Threshold Decay
The test is carried out by presenting a 10 s signal
at 10 dB above the ART.

36. Thank you.