impedance audiometry ent ppt

1. IMPEDANCE AUDIOMETRY
By Dr.HEMABALAN K
1st Year PG

2. Introduction
• Objective audiometric test used to access the middle ear function
• Also used to access ET function
• Acoustic impedance refers to resistance to flow of acoustic energy
Admittance definition - Admittance is measuring the ease at which energy
(sound) flows through the system (ear)
Impedance definition- Reflection or refraction of a sound wave when it
encounters a boundary or an interface between 2 tissues.

3. There are three factors that impede the flow
of sound
• Stiffness (TM & ossicles)
• Mass (ossicles)
• Friction or Resistance (ligaments in Middle ear)

4. PRINCIPLE
• Impedance is mainly determined by the stiffness of the middle ear
system and friction has a negligible effect
• Stiff system  more impedance less sound is conducted through it
 offering less admittance
• Flaccid system  impedance is less admittance is more
• MAXIMUM admittance – pressure in the external ear and middle ear
are equal .

5. Procedure
• APPARATUS 1- Consist of ear probe
and probe tip containing three
tubes – placed in middle ear
• Tube is used to deliver the probe
tone generated by 226hz oscillator
driving a miniature receiver
• Microphone is used to pick up the
energy in the canal

6. • Manometer is used to increase or decrease the pressure in the
external canal using air pump

7. Procedure
• APPARATUS 2: Conventional Earphone placed in opposite ear
• Connected to a suitable sound source the delivers signals (pure tone
or noise ) used to measure acoustic reflex threshold

8. Procedure
• WAX or debris in EAC cleared
• Otoscopy to access TM
• Choosing proper Ear tip for air tight seal
• Patient instructed – not to move , avoid deep inspiration , to avoid
talking and swallowing

9. Procedure
• Probe is put in the ear  pressure increased to +200 mm of water 
TM is pushed inward and become fixed
• Leading to more reflection and less compliance
• Reduce pressure serially to 100, 50 and 0 till maximum compliance
• -100, -200 make the TM more rigid and reduce compliance

10. Procedure
• The normal middle ear pressure is +(or)- 25mm of water
• A graph with pressure on the X-axis and Compliance on Y-axis.
(pressure vs compliance function curve)
• Graphical representation is called a tympanogram

11. Tympanogram

12. Inference
• Static compliance – difference between maximum compliance and
compliance at +200mm of water.
• Which is pressure at 0(ear canal + middle ear)-pressure at +200(ear
canal admittance)
• The normal range 0.3-1.7ml

13. Inference
• More than 1.7ml – highly loose ossicular system (laxity)
• Less than 0.3ml – stiff ossicular system
• Positive middle ear pressure is rarely encounter in condition like in
early stage of AOM, after blowing the nose and while crying.

14. Types of tympanogram curves
• Type A : Peak is near 0 pressure – normal
ears
• Type As is peak is at 0 but amplitude of
peak is at low(stiff) - otosclerosis,
tympanosclerosis and thick graft

15. Types of tympanogram curves
• Type Ad: Peak is around 0 but peak
amplitude is abnormally high which means
system is more complaint than normal-
ossicular discontinuity and flaccid or
monomeric membrane
• Type B : Flat curve – pressure change does
not have much change on compliance-
impacted wax, foreign body , SOM ,
Adhesive otitis media , perforated TM, and
a patent grommet

16. Types of tympanogram curves
• Type C: Peak is shifted to negative side –ET
dysfunction , early SOM

18. Acoustic Reflex or (stapedial Reflex)Threshold

19. Acoustic Reflex or (stapedial Reflex)Threshold

20. Acoustic Reflex or (stapedial Reflex)Threshold
• Involuntary contraction of the stapedius muscle on both sides
following a stimulus of a loud sound given to one ear
• Unilateral, ipsilateral, contralateral and bilateral reflexes can be
measured
• Stimulus given at 70-90db sensation level.
• Threshold is the lowest intensity at which reflex is obtained

21. Acoustic Reflex or (stapedial Reflex)Threshold
It is the useful test in the following :
• CHL (ossicular fixation)
• Retrocochlear pathology
• In children to decide on further assessment of hearing
• As a topodiagnostic test in fascial palsy

22. Impedance
• https://www.thieme.de/de/q.htm?p=opn/cs/22/11/19875500-
808517ff

23. THANK YOU