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TOPIC 5

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.

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TOPIC 5

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  1. TOPIC 5 NONBEHAVIORAL ASSESSMENT MEASURES IMMITANCE AUDIOMETRY

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

  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

  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.

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