Impedance audiometry

A presentation of impedence audiometry .

1. Impedance Audiometry Preparation by: Dr. Nagham Ghalyouni ENT resident doctor at National H ospital, Lattakia , Syria

2. Sound Pathways

3. Types of Hearing Loss Conductive Sensorineural Mixed Central

4. Resistance to the flow of acoustic energy Admittance : Ease of which acoustic energy flows Impedance : Immitance is a term derived from the terms for two inversely related processes for assessing middle ear function : Acoustic Immitance

5. Impedance Audiometry

6. Impedance Audiometry Includes: * Tympanometry * Acoustic Reflex Measurements * External Canal Volume (ECV)

7. Tympanometry Definition : A way of measuring how acoustic immittance of the middle ear system changes as air pressure is varied in the external ear canal. Purpose : Main purpose of tympanometry is to give us information on middle ear and rule out middle ear disorders/diseases.

8. Principle : When a sound strikes tympanic membrane, some of the sound energy is absorbed while the rest is reflected . A stiffer tympanic membrane would reflect more of sound energy than a comliant one . Air pressure is varied + ve and – ve relative to ambient or atmospheric pressure and is measured by detecting reflected sound energy from T.M . When air pressure is equal on both sides of T.M , this creates least Stiffness and most Compliance .

9. Tympanometry The equipment consists of a probe which has three channels: 1- Loudspeaker 2- Microphone 3- Air pump

10. Advantages of Tympanometry Objective test Quick Inexpensive Non-invasive Easily tolerated by most subjects Requires no behavioral response Reveals M.E abnormalities that may not be detected by behavioral tests No need for sound-treated room

11. Tympanogram It is the graphic representation of Tympanometry. There are 5 main types of Tympanograms obtained which are diagnostic of certain M.E pathologies : A , B , C , As , Ad

12. Type A Inverted “V” or Mountain. Normal. Equal pressure on both sides of T.M . No CHL . Maybe SNHL .

13. Type B Flat or dome-shaped graph (No peak) . T.M movement is minimal or totally absent . Seen in outer and\or middle ear disorders : Otitis Media or M.E effusion*** Thick T.M Perforated T.M Occluded ear canal

14. Type C Inverted “V” off center to left (Retracted T.M) . Negative M.E pressure . Eustachian Tube function is abnormal .

15. Type As “S” for Shallow . Peak compliance is very low (shallow) . Seen in : Ossicular fixation (stiffness) T.M scarring Tympanosclerosis

16. Type Ad “D” for Disarticulation . Peak compliance is very high or off chart . Seen in : Ossicular disarticulation Thin and Lax T.M

17. Testing function of Eustachian Tube Intact or Perforated T.M - ve or + ve pressure is created in M.E Person is asked to swallow Equilibrating the pressure = normal EU tube function

18. Tympanometry and Ventilation tube Tympanometry can also be used to find the patency of grommet placed in T.M in cases of Serous Otitis Media .

19. Acoustic Reflex ( Stapedius Reflex) A loud sound , 70 – 100 dB above the threshold of hearing of a particular ear , causes bilateral reflexive contraction of the Stapedial muscles which can be detected by Tympanometry. Contraction of the Stapedial muscle tilts the anterior stapes away from the oval window and stiffens the ossicular chain and thus decreasing the transmission of sound energy into the Inner ear to protect it from loud sounds .

20. Acoustic Reflex Arc

21. Acoustic Reflex This test is useful in several ways : To test the hearing in infants and young children (objective method) . To find malingerers . To detect VIIIth nerve ( Vestibulocochlear ) lesions. Lesions of VII nerve (Facial) . Lesions of Brainstem . Lesions of Auditory ossicles (e.g. Otosclerosis ) . Gives an idea about the level of Hearing loss and Threshold .

22. THANK YOU