TOPIC 5 NONBEHAVIORAL ASSESSMENT MEASURES IMMITANCE AUDIOMETRY.

TOPIC 5

NONBEHAVIORAL ASSESSMENT MEASURES

IMMITANCE 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 Relationships

Probe 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.