impedance Audiometry impedance Audiometry

impedance Audiometry
impedance Audiometry
impedance Audiometry
impedance Audiometry
impedance Audiometry
impedance Audiometry
impedance Audiometry
impedance Audiometry
impedance Audiometry

1. IMPEDANCE AUDIOMETRY

2. Impedance Opposition to the flow of sound energy is called as IMPEDANCE Opposition of Admittance (Ease with which energy flow)( mho) Impedance of the medium : Complex mixture of 3 parameters- stiffness, mass, friction Middle ear (ME) act as the impedance matching device All ME pathologies alter this impedance , result in lesser sound energy being transmitted to the cochlea

3. Impedance matching by ME system Area of tympanic membrane relative to oval window (Areal Ratio) The lever action of ossicles Mobility of TM

4. Areal Ratio Total area of TM 90mm 2 Functional area of TM is 55mm 2 Area of Stapes footplate is 3.2mm 2 Effective areal ratio is 17:1 Thus by focusing sound pressure from large area of TM to small area of oval window, effectiveness of energy transfer between air to fluid of cochlea is increased.

5. Ossicular Lever Handle of malleus is 1.3 times longer than long process of incus This produce a lever action that convert low pressure with a long lever action at handle of malleus to high pressure with a short lever action at long process of incus

6. Mobility of TM Central part of TM has limited mobility compared to periphery. Result in transfer of most of energy to ossicles. Act as Curved membrane effect.

7. Objective Test Uses of Impedance Audiometry Objective differentiation between CHL and SNHL Measurement of middle ear pressure and evaluation of Eustachian tube function Impedance Audiometry include: Tympanometry Stapedial reflex Eustachian Tube Function Test

8. Principle of Tympanometry Sound strikes the TM – some energy is absorbed and some energy reflected. Stiffer TM – reflects more energy than compliant one. By changing the pressure in a sealed EAC and measuring the reflected sound energy – possible to find the compliance/stiffness of tympano ossicular system.

9. Tympanometer

10. Probe 1.Oscillator producing tone(deliver tone of 226 hz ) 2.Microphone (pick up reflected sound) 3.Air Pump(changes in air pressure in EAC from - ve to normal to + ve )

11. Procedure Otoscopic Examination of EAC and Condition of TM Wax or Epithelial Debris or Discharge Completely blocking the TM Explained to the patient Painless and Objective test Test will take less than 2-3 min, should not swallow or breath very hard Ear tip-  Air tight fashion-- slight discomfort Probe Inserted into EAC in air tight fashion deeply to obtain correct tympanogram (pumping or seal not obtained) Air pressure increased to +200mm of water in EAC and compliance measured at this pressure after that pressure changes from +200mm of water to 0 to -200 mm of water and -600mm of water and compliance measured at different pressure changes. Static Compliance: subtracting the compliance at +200 mm of water from maximum compliance

12. Result of Tympanometry Test displayed graphically with compliance on Y-Axis and Air Pressure on X-Axis known as Tympanogram. Air pressure measured millimeter of water pressure unit Compliance measured in cubic centimeter or milliliter Compliance of TM – Normal range of static compliance –is -0.35 to 1.40 ml ME pressure- Normal pressure is -50 to +50 mm of water

13. Compliance With Increased Compliance Ossi.chain Discontinuity Scarred TM Large TM Post.Stapedectomy ear Decreased Compliance Otosclerosis Adhesive Secretory OM Glomus jugulare Fixed Malleus syndrome Normal Compliance ET obstruction without secretory changes in ME

14. ME Pressure Negative ME Pressure Blocked ET OM with Effusion Normal ME Pressure Otosclerosis Ossi.Chain discontinuity Scarred TM Fixed Mlleus syndrome Positive ME Pressure Early AOM Absence of any pressure peak Adhesive OM Perforated TM Artifact(Blocked probe tip) Patent grommet in TM Wax

15. Feldman description of Tympanogram A)Normal tympanogram : Good mobility with maximum compliance at ambient atmospheric pressure (Corresponds with jerger’s type A)

16. B)Normal middle ear pressure with high compliance (seen in Ossicular discontinuity or scarred TM)

17. C) Normal middle ear pressure with low compliance (Otosclerosis )

18. D) Flat tympanogram without any pressure peak or measurable compliance (Adhesive otitis media)

19. E) Negative middle ear pressure with low compliance (Blockage of ET with some amount of air still present in ME cavity)

20. F) Positive middle ear pressure with normal compliance (Early stage of Acute otitis media)

21. G) Small notched high compliance with normal middle ear pressure H) Broad deep notching of the tympanogram (seen in ossicular discontinuity at high freq. probe 660 or 800hz)

22. Feldman description of Tympanogram I)Negative middle ear pressure with normal compliance with normal shape and single peak(Early stage of ET Obstruction) J)Normal middle ear pressure with minimally low compliance with systemic perturbation(Pulse beat)

23. Fallacies of Tympanometry It is Objective test , it is not without errors Some conditions where tympanogram does not give true picture of ME pathology Mainly when there is two or more ME pathology are present ,compliance is representative of the more lateral ME pathology Examples A patient with otosclerosis and Eustachian tube dysfunction (from a cold) may show negative middle ear pressure and low compliance on tympanometry, mimicking otitis media with effusion. This can lead to a misdiagnosis. A patient with a scarred tympanic membrane but developing otosclerosis may present a Type Ad tympanogram with high compliance. This pattern usually suggests ossicular chain discontinuity.

24. Fallacies of Tympanometry 3. A patient with tympanic membrane thickening but otherwise normal hearing, this patient will present with As type of graph which is particular for Otosclerosis. If this patient may develop tubal dysfunction from a cold, causing a negative pressure, low compliance tympanogram. This can falsely suggest OME, even when no middle ear fluid is present.

25. EUSTACHIAN TUBE FUNCTION TEST Physiological function of ET: Maintenance of equality of air pressure between the middle ear and the ambient atmosphere(ventilatory function) Drainage of the mucus from the ear to the nasopharynx ( mucociliary clearance function)

26. William’s Test Test of Tubal Function with intact TM Measure the middle ear pressure in three condition 1) resting phase 2) while patient swallows 3) finally after performing Valsalva. Normally at resting phase middle ear pressure is at or near environmental atmospheric pressure, become negative while swallows and become positive after Valsalva Any deviation as abnormal Partially impaired ET function : middle ear pressure become negative at swallows but remain negative after Valsalva Grossly impaired ET function : Middle ear pressure does not change at all during swallows or valsalva

27. Toynbee’s Test Done in patient with Perforated TM Artificially increased or decreased pressure in the middle ear and then record the change of middle ear pressure each time patient swallows Carried out for fixed duration of time (min.40 sec to max. 160 sec) Air pressure at middle ear end of ET is changed either +250 or -250 mm of water. Ask patient to swallow repeatedly- pressure will be partially neutralized with each swallow Normally pressure should be totally neutralize after 3 to 4 swallow If some residual pressure persist even after 5 swallow – partially Can not be neutralize at all by repeated swallowing –grossly.

28. Acoustic / Stapedial Reflex Test Non invasive Objective Can be carried out in new born

29. Principle Loud sound reach the ear Stapedius and tensor tympani muscle contract reflexly Pull the stapes outward and upward, tympanic membrane inward Change the impedance of middle ear system Changes are monitored and analyzed by electroacoustic bridge and result displayed accordingly

30. Acoustic Reflex Threshold The signal enters the right ear, travels through the outer, middle (ME), and inner ear (IE), along the VIII nerve to the brainstem. When the signal reaches the brainstem, the signal arrives first at the cochlear nucleus (CN). From here, the signal travels to both right and left superior olivary complexes and both right and left facial nerve (VII) nuclei. The signal is sent from both facial nerve nuclei to both facial (VII) nerves, which results in a contraction of both stapedius muscles. Thus, both stapes bones are pulled outward and downward, in a direction away from the inner ear. This action makes it harder for energy to travel through the middle ear (increase in impedance/decrease in admittance). The lowest intensity level at which this contraction is measurable is the ART.

31. Clinical significance of Stapedial Reflex To test hearing in infants and young children Objective Test Screening tool To detect cochlear pathology Presence of stapedial reflex at lower intensities (40 to 60db instead of the usual 70 to 105db )(recruitment) To detect Retro cochlear pathology If a sustained tone of 500 or 1000hz is delivered 10db above ART for a period of 10sec , if amplitude falls to less than 50% - it shows abnormal adaptation- indicative of retro cochlear pathology Tone decay due to nerve fatigue

32. Clinical significance of Stapedial Reflex Lesion of facial nerve Stapedial reflex absent( if injury is before the origin of the nerve of stapedius) Stapedial Reflex present ( if injury is beyond the origin of the nerve of stapedius) To find malingerers Doesn’t give response on PTA, shows positive stapedial reflex

33. Afferent pathway IL middle ear disease causing moderate to severe CHL Lesion in IL cochlea or 8 th cranial nerve (causing severe SNHL ) Lesion in IL cochlear nucleus or superior olivary complex

34. Efferent pathway Lesion in facial nerve nucleus at brain stem level Facial nerve paralysis before proximal to origin of nerve of stapedius Disease of Stapedius muscle like myasthenia gravis

35. The Four Reflex Categories Right IL Pathway Right CL Pathway Left IL pathway Left CL pathway

36. Cochlear Pathology

37. Retrocochlear Pathology

38. Facial Nerve Pathology

39. ME pathology

40. Intra-Axial Brain Stem Pathology (Small and Large lesion)

41. Thank You