TOPIC 5 NONBEHAVIORAL ASSESSMENT MEASURES IMMITANCE AUDIOMETRY IMMITANCE AUDIOMETRY
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TOPIC 5
NONBEHAVIORAL ASSESSMENT MEASURESIMMITANCE AUDIOMETRYIMMITANCE AUDIOMETRY
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
Advantages of Immittance Audiometry
Non-invasive
Non-behavioral
Instrumentation Major components
Probe tone oscillator and loudspeaker
Monitor microphone Pressure pump and
manometer Ipsilateral reflex
oscillator and loudspeaker
Probe tip
Measurement Technique
“Immittance is a physical characteristic of all mechanical vibratory systems, of which the middle ear is one example”
Compliance vs Impedance Compliance
Ease with which energy flows through a system
Impedance
Resistance to energy flow through a system
Auditory Immittance
“ A way of assessing the manner in which energy flows through the outer and middle ear into the cochlea”
Immittance RelationshipsProbe tone energy passed
Probe tone energy reflected
Compliance
High impedance
Low High Low
Low impedance
High Low High
Basic Immittance Measures
Tympanometry Acoustic Reflex Thresholds Acoustic Reflex Threshold Decay
Tympanometry
“A way of measuring how acoustic immittance of the middle ear system changes as air pressure is varied in the external ear canal”
Tympanometry
Concepts of immittance applied in practice
Normal Tympanogram
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
What’s a Normal Tympanogram?
Shape Pressure: -100 mm H2O or DaPa Compliance: 0.3-1.6 cc
Common Tympanograms
Normal tympanogram (Type A)
Shape? Pressure? Compliance?
Common Tympanograms
Type As Shape? Pressure? Compliance?
Common Tympanograms
Type Ad Shape? Pressure? Compliance?
Common Tympanograms
Type B Shape? Pressure? Compliance?
Assessing PE Tubes
Common Tympanograms
Type C Shape? Pressure? Volume?
Basic Immittance Measures
Tympanometry Acoustic Reflex Thresholds
The Middle Ear Muscles and the Acoustic Reflex
Tensor tympani muscle (top figure)
Stapedius muscle (bottom figure)
Acoustic Reflex Pathways
Ipsilateral Right ear Left ear Contralateral Probe right Probe left
Acoustic Reflex Threshold
“the lowest intensity at which a middle ear immittance change can be detected in response to sound”
Instrumentation for Acoustic Reflex Thresholds
Normal Acoustic Reflex Threshold Levels
Interpretation of an Absent Acoustic Reflex Threshold
Possible pathologies that might lead to an absent contralateral probe left reflex (right crossed)
Basic Immittance Measures
Tympanometry Acoustic Reflex Thresholds Acoustic Reflex Threshold Decay
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.
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