audiometry

1. TOPIC 5
NONBEHAVIORAL
ASSESSMENT
MEASURES
IMMITANCEIMMITANCE
AUDIOMETRYAUDIOMETRY

2. The Functions of Immittance
Audiometry
 Detection of middle ear pathology
 Differentiating cochlear from
retrocochlear pathology
 Estimate sensitivity
 Use in cross-check with pure tone
results

3. Advantages of Immittance
Audiometry
 Non-invasive
 Non-behavioral

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

5. Measurement Technique
“Immittance is a physical characteristic of
all mechanical vibratory systems, of
which the middle ear is one example”

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

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
 Tympanometry
 Acoustic Reflex Thresholds
 Acoustic Reflex Threshold Decay

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

11. Tympanometry
Concepts of immittance applied in practice

12. Normal Tympanogram

13. 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

14. What’s a Normal
Tympanogram?
 Shape
 Pressure: -100 mm H2O or DaPa
 Compliance: 0.3-1.6 cc

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

16. Common Tympanograms
 Type As
 Shape?
 Pressure?
 Compliance?

17. Common Tympanograms
 Type Ad
 Shape?
 Pressure?
 Compliance?

18. Common Tympanograms
 Type B
 Shape?
 Pressure?
 Compliance?

19. Assessing PE Tubes

20. Common Tympanograms
 Type C
 Shape?
 Pressure?
 Volume?

21. Basic Immittance Measures
 Tympanometry
 Acoustic Reflex Thresholds

22. The Middle Ear Muscles and
the Acoustic Reflex
 Tensor tympani
muscle (top figure)
 Stapedius muscle
(bottom figure)

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

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

25. Instrumentation for Acoustic
Reflex Thresholds

26. Normal Acoustic Reflex
Threshold Levels

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

28. Basic Immittance Measures
 Tympanometry
 Acoustic Reflex Thresholds
 Acoustic Reflex Threshold Decay

29. 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.