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AUDIOMETRY – PTA,SPEECH TEST,IMPEDENCE,SPECIAL TESTS OF HEARING,BERA,OTOACOUSTIC EMISSIONS

AUDIOMETRY – PTA,SPEECH TEST,IMPEDENCE,SPECIAL TESTS OF HEARING,BERA,OTOACOUSTIC EMISSIONS. Dr nayana v g Senior resident YMc. Learning objective. Aim: To know the basic audiometric investigations and to diagnose type and site of lesion based on the results. Audiometric testing

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AUDIOMETRY – PTA,SPEECH TEST,IMPEDENCE,SPECIAL TESTS OF HEARING,BERA,OTOACOUSTIC EMISSIONS

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  1. AUDIOMETRY – PTA,SPEECH TEST,IMPEDENCE,SPECIAL TESTS OF HEARING,BERA,OTOACOUSTIC EMISSIONS Drnayana v g Senior resident YMc

  2. Learning objective Aim: To know the basic audiometric investigations and to diagnose type and site of lesion based on the results

  3. Audiometric testing • A)Behavioral audiometric testing(subjective) 1.PTA 2.Speech audiometry • B)Objective audiometric testing • 1.Immitence audiometry • 2.OAE • 3.BERA

  4. Objective audiometric testing • Most commonly used method • Based on active, voluntary response from the subject • Can test the entire auditory system • Based on subjective response to tones and speech

  5. PTA • In PTA sensitivity to pure tones is measured by determining the hearing threshold. • Threshold are measured from 125Hz to 8KHz. • Done separately in right and left ears • Thresholds are tested for air and bone conduction separately.

  6. PTA AUDIOMETER : DEVICE TO GENERATE PURE TONES OF VARYING FREQUENCY AND LOUDNESS 125Hz to 8000Hz are delivered Tones are presented to one ear only by air conduction using a head phone. bone conduction by a bone vibrator pressed against mastoid / forehead.

  7. PTA • Amount of intensity to be raised above the normal level -degree of hearing impairment at that frequency • Charted in graph – Audiogram. • THRESHOLD OF BONE CONDUCTION – COCHLEAR FUNCTION • DIFFERENCE BETWEEN AC AND BC –DEGREE OF CONDUCTIVE DEAFNESS. • MASKING

  8. INTEPRETATION OF PTA • With proper calibration and normal sound conduction threshold for both air and bone conduction are equal • If air conduction threshold > bone conduction threshold –CONDUCTIVE HEARING LOSS • If air and bone conduction threshold are increased without much difference between two – SENSORINEURAL HEARING LOSS • If both air and bone conduction thresholds are increased and there is difference between two –MIXED HEARING LOSS

  9. Normal hearing PTA AC- within normal limit BC- within normal limit No AB Gap. PTA - AVERAGE OF AC THRESHOLD AT 500HZ, 1000HZ AND 2000HZ

  10. Conductive hearing loss AC- High threshold BC- Normal AB GAP -Present

  11. Sensorineural hearing loss AC – High Threshold BC- High Threshold AB Gap - nil

  12. Mixed hearing loss • AC- high Threshold • BC- High Threshold • AB Gap - nil

  13. Uses of PTA 1.Measure of threshold of air and bone conduction and thus the degree and type of hearing loss, 2.Record for future reference 3.Prescription of hearing aid 4.Degree of handicap 5.Predict speech reception threshold.

  14. SPEECH AUDIOMETRY • Measures the ability to hear and understand speech. • Principle: speech material is available in standardized form on compact disc and is presented at designated level using an audiometer. • Presented to one ear -> headset • both ears -> loudspeaker in sound field environment.

  15. SPEECH AUDIOMETRY - 2 TYPES 1.SRT(Speech reception threshold) 2.SDS(Speech discrimination score)

  16. SPEECH AUDIOMETRY-Speech reception threshold Minimum intensity at which 50%words are repeated correctly Set of spondee words(baseball,sunlight) to each ear headphone Intensity increased in 5db till 50% words are correctly heard Normally within 10db of PTA

  17. SPEECH AUDIOMETRY –Speech discrimination score Ability to understand speech. List of phonetically balanced words(pin,sin,tinetc) to each ear separately 30-40dB above his SRT and percentage correctly heard is recorded. Normal and Conductive hearing loss – 90-100% obtained. Sensorineural (cochlear) - reaches a plateau. Neural – graph fall after reaching peak. ROLL OVER CURVE

  18. SPEECH AUDIOMETRY Normal hearing – 100% at 30db CoHL – 100% at 50db SNHL – never attains 100% and decline after maximum

  19. SPEECH AUDIOMETRY –Speech discrimination score • Interpretation: SA indicates the percentage of syllable, words or sentence that subject has clearly heard in each test series. • It depends on comprehension, memory and motor speech. • It also depends on native language and vocabulary.

  20. Objective audiometric testing • Impedence audiometry • OAE • BERA • Special tests of hearing Unlike the subjective tests it helps in testing hearing without eliciting an active response from the patient.

  21. IMPEDENCE AUDIOMETRY • IMPEDANCE : It is the measure of the resistance that the system offers to the absorption of sound waves. • COMPLIANCE: Sound absorption is referred as compliance of tympanic membrane. • Middle ear changes sound waves in such a way that it can induce waves in cochlear fluid with little resistance – IMPEDANCE MATCHING OF MIDDLE EAR.

  22. IMPEDENCE AUDIOMETRY TYMPANOMETRY: measurement of impedance changes(reflected sound energy) caused by changing air pressure in sealed EAC STAPEDIAL REFLEX: Acoustically evoked changes of impedance

  23. Tympanometry • Air pressure in EAC and ME is equal to atmospheric pressure -> minimum resistance and maximum compliance and absorbs sound bests. • If pressure in EAC is increased or decreased, acoustic resistance increases and sound absorption or compliance is reduced. • Pathologic changes in middle ear or TM leads to changes in compliance-> change in shape of tympanogram.

  24. Tympanometry • Equipment –snugly fitting probe in EAC with 3 channels A)Deliver tone of 220Hz B)To pick up reflected sound through microphone C) to bring air pressure changes in EAC. TYMPANOGRAM IS THE GRAPHIC REPRESENTATION OF THE TM COMPLIANCE AS THE APPLIED PRESSURE IS VARIED OVER POSITIVE NEGATIVE RANGE +/- 300MMHG.

  25. REFLEXOMETRY • Loud sound 70-100dB above the threshold of hearing of a particular ear, cause bilateral contraction of stapedial muscles. • Tone delivered to one ear reflex picked from same and contralateral • Ipsilateral – CN VIII -> ventral cochlear nucleus -> CN VII -> Ipsilateral stapedius muscle • Contralateral – CN VIII-> ventral cochlear nucleus-> contralateral medial superior olivary nucleus-> contralateral CN VII nucleus-> contralateral stapedius muscle

  26. Oto acoustic emission Low intensity sounds by outer hair cells which are elicited by very sensitive microphone kept in EAC and analyzed by computer Vibrations produced by biomechanical amplifier of cochlea (outer hair cells) ->Middle ear-> tympanic membrane emits vibrations as sound to EAC->microphone probe in EAC.

  27. Oto acoustic emission Used to test the cochlear amplifier. Absent-cochlear damage,present –VIII damage. Outer hair cells are the source of OAE. Requires intact cochlear OHC,middle ear and tympanic membrane 3 Types :Spontaneous OAE Transient OAE DPOAE

  28. Oto acoustic emission • SPONTANEOUS OAES: Emissions without acoustic stimulus. Seen in 50% population, low level continuous tone. • TRANSIENT EVOKED OAES: Emissions in response to a brief stimulus(click) in subjects with normal cochlear function. • DPOAE: Distortions in cochlear amplifier can be detected by 2 different tone of adjacent but different frequency(F1 and F2).frequently used objective audiometric test.

  29. Oto acoustic emission • Application of OAE: 1.Used to screen congenital hearing loss in newborns. 2.To test hearing –mentally challenged /uncooperative patients 2.To rule out non organic hearing loss. 3.To distinguish cochlear and retro cochlear pathology. Disadvantage: Location and degree of hearing loss cant be assessed

  30. Auditory evoked potential • Physiologic process of hearing involve many bioelectric potential changes involving cochlea, auditory nerve and CNS. • Utilized for objective testing of auditory function. • TECHNIQUE: ACOUSTIC STIMULUS TO EAR BY HEADPHONES AND AUDITORY EVOKED POTENTIAL MEASURED FROM SCALP USING SURFACE ELECTRODES.

  31. BERA-brainstem evoked response audiometry Auditory evoked potential used for diagnostic purpose are brainstem potential. Click stimulus Evoked potential recorded after 10 msec. Repeated 1000 to 2000 times and EEG averaged I to VII waves are recorded {EECOLIM} Peaks are unchanged during anaesthesia or sleep.

  32. wave V detected 10db above the hearing threshold.

  33. BERA-brainstem evoked response audiometry • Differentiating between cochlear and retro cochlear disease • Objective measurement of hearing threshold • Diagnosis of retrocochlearpathogy {8th nerve} (acoustic neuroma). • Diagnosis of brainstem disease.(multiple sclerosis,brain stem stroke) • Objective measurement of threshold testing in pediatric population and mentally retarded • Intra op monitoring.

  34. Special tests of hearing1.RECRUITMENT Abnormal growth of loudness Ear which does not hear low intensity sound begin to hear greater intensity sound as louder than normal hearing ear. Intolerable in diseased ear. Lesions of cochlea (menieres disease, presbycusis) Poor candidate for hearing aid. ABNORMAL BINAURAL LOUDNESS BALANCE TEST

  35. 2.Short increment sensitivity index Patients with cochlear pathology distinguish small changes in intensity of pure tone better than normal, conductive or neural pathology. SISI test to differentiate cochlear from retro cochlear pathology

  36. 3.TONE DECAY TEST • Measure of tone fatigue. • Detect retro cochlear pathology. • Normally person can hear tone for 60s. • In nerve fatigue stops hearing early.

  37. summary 1.PTA – thresholod of hearing for 125Hz to 8000Hz 2.Speech audiometry –SRT & SDS Grap 3.Immitence audiometry - tympanometry (A,As,Ad,B,C) and reflexometry –I/L and C/L 4.OAE –spontaneous,TEOAE,DPOAE –present/absent 5.BERA - I to VII waves. Wave V

  38. REFERENCES 1.BASIC OTORHINOLARYNGOLOGY – RUDOLF PROBST,GERHARD GREVERS 2.DISEASE OF EAR,NOSE ,THROAT &Head and neck surgery – P.L DHINGRA.

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