TOPIC 5 NONBEHAVIORAL ASSESSMENT MEASURES IMMITANCE 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 LowHighLow Low impedance HighLowHigh

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 H 2 O or DaPa Compliance: cc

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

Common Tympanograms Type A s Shape? Pressure? Compliance?

Common Tympanograms Type A d 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.