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BERA

BERA. Dr. Supreet singh nayyar, AFMC. For more presentations, visit www.nayyarENT.com. Recording of the synchronous electrical activity recorded by a far-field electrode placed on the scalp in response to a sound presented to the cochlea.

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BERA

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  1. BERA Dr. Supreet singh nayyar, AFMC For more presentations, visit www.nayyarENT.com www.nayyarENT.com

  2. Recording of the synchronous electrical activity recorded by a far-field electrode placed on the scalp in response to a sound presented to the cochlea. • Changes produced by the passage of electrical stimulus generated in the cochlea through the neural pathway www.nayyarENT.com

  3. History • First described by Jewett and Williston in 1971, ABR audiometry is the most common application of auditory evoked responses. www.nayyarENT.com

  4. Uses of BERA • Detection & quantification of deafness in difficult to test patients • Detection of the nature of deafness • Identification of the site of leshion in retrocochlear pathologies • Study of central auditory disorders • Study of maturity of nervous system in newborns • Objective identification of brain death • Assessing prognosis in comatose patients www.nayyarENT.com

  5. Uses of Intraoperative Auditory Brainstem Response Monitoring cochlear function directed at hearing preservation: • Cerebellopontine angle tumor resection (acoustic neuroma surgery) • Vascular decompression of trigeminal neuralgia • Vestibular nerve section for the relief of vertigo • Exploration of the facial nerve for facial nerve decompression • Endolymphatic sac decompression for Mèniére disease Monitoring brainstem integrity: • Brainstem tumor resection • Brainstem aneurysm clipping or arteriovenous malformation resection www.nayyarENT.com

  6. Principle of BERA www.nayyarENT.com

  7. Principle of BERA • Processing at different levels • Generates electrical activity • Monitored by surface electrode • Graphic recording presents a waveform • Depends on the functional integrity of the pathway www.nayyarENT.com

  8. Principle of BERA • Process becomes difficult due to the background potential generated by the brain • Separation of the 2 activities by summation & averaging • Sound evoked electrical potential: time specific • Electrical activity of brain: occurs randomly www.nayyarENT.com

  9. Neurophysiologic Basis of BERA www.nayyarENT.com

  10. Processing of the sound stimulus • ‘Sound conduction time’ • ‘Cochlear transport time’ • Less for high fq sound • High for low fq sound • Passage through cochlear filters • Cochlear filter –build-up time • Broadening of cochlear filters • Synaptic delay • Neural conduction time www.nayyarENT.com

  11. Mechanism of Activation in BERA • Click sound presented to the ear • Earlier stimulation by the high fq sounds • The middle & apical parts don’t contribute much to BERA response • Changes in high fq loss • Relation of intensity of sound stimulus to the latency & amplitude of the waves • Applied Importance www.nayyarENT.com

  12. Auditory evoked potencials • Electrical activity in brain elicited by sound stimulus • Recorded upto 500 millisecs • 3 responses are recorded: • Short Latency Response (10ms) i.e BERA • Middle Latency Response (10-50ms) • Late Latency Response (50-500ms) www.nayyarENT.com

  13. Middle Latency Response • Wave peaks: N0(10ms), P0(10-15ms), Na (16-30ms) ,Pa(25-45ms) and N3(50ms) • Most consistent waves: Na, Pa • Neurogenic & myogenic origin • Affected by sleep, anaesthesia • Origin: Proximal to the midbrain • Assess hearing level between 250-500 Hz • Fitting hearing aid • Elicited by tone pips • Limitations www.nayyarENT.com

  14. 40 Hz Steady State Potencial • Also known as ASSR • Superimposition of BERA & some MLR waves • Recorded as continuous sinusoidal wave • Sound stimuli: 500 Hz of 15 ms duration at 40 stimuli/sec • Indicates a state of arousal • Objective determination of hearing threshold • Used for objective frequency dependent hearing threshold estimation www.nayyarENT.com

  15. Late Latency Response • Recordable between 50-500ms • Originates in the cerebral cortex • Cortical Evoked Response Audiometry (CERA) • 5 wave peaks: P1, N1, P2, N2 & P3 • Tone pips of 1000-2000 Hz • Rate: 1 stimulus every 2-3 secs • P300 Wave peak • Important to neuropsychiatrist & neurotologists www.nayyarENT.com

  16. Pre-requisites of recording BERA • Elicited by click stimulus • 50-60dB above avg. pure tone threshold • Location of electrodes: active, reference & ground • Air conditioned room • Good earthing\ Faraday cages www.nayyarENT.com

  17. Pre-requisites of recording BERA • Position of patient • Relaxed • Sedation in infants & children • Prior PTA • Sound stimulus: Broad Band Clicks (100 microsecs duration) www.nayyarENT.com

  18. Advantages of BBC • Synchronous stimulation of large no. of neurons • Clear, sharp well- marked tracing • Very rapid onset & fall • Easy latency & amplitude measurement • Lowest fq: 100-150Hz • Highest fq: 3000-5000Hz • Total recordings: 2000-4000 • Stimulus rate: 10-40 clicks\sec (11.1/sec) www.nayyarENT.com

  19. Recording • Graph plotted with amplitude (in microvolts) on the ordinate & time (in msec) on the abscissa • 5-7 peaks\waves within 8-10 millisecs • BERA waves: 5 prominent & 2 small • Numbered I-VII www.nayyarENT.com

  20. Site of Neural Generator www.nayyarENT.com

  21. Wave VWave IV • Identified first • Most reliable & easily identifiable • Sharp negative deflection following the peak • Appears at 5.6-5.85 millisecs • Largest & most robust wave • Preceding wave V • Maybe superimposed on wave V • Distinct wave present in 50-60% subjects www.nayyarENT.com

  22. Wave IIIWave II • Upward peak between wave II & IV • Maybe bifid • Maybe fused with II • Preceding wave IV • Around the 3.8 msec • Amplitude: 0.2-0.25 microvolt • Immediately preceding wave III • Latency: 2.8 msec www.nayyarENT.com

  23. Wave I • Sharp peak beyond 1msec mark • Importance of identification: • Presence of wave I in the absence of others: leshion beyond distal nerve end • Delayed wave I: conductive/cochlear pathology • Abolition of wave I: severe peripheral leshions www.nayyarENT.com

  24. Normal BERA tracing www.nayyarENT.com

  25. Parameters Studied • Latency of the wave(s)- absolute, interwave, interaural • Amplitude of the wave(s)- absolute & relative (amplitude ratio) • Wave-form morphology • Latency-intensity functions of wave V www.nayyarENT.com

  26. Latency Studies • Time interval between onset of stimulus & peak of the wave • Measured in millisecs • Also known as Absolute Latency • Most important for clinical measurements • Latency of wave V depends on intensity of sound stimulus • Interwave Latency • Interaural Latency www.nayyarENT.com

  27. Amplitude Studies • Variable • Studies are not very reliable • Used as supplementary evidence • Measured in microvolts • Known as Absolute amplitude of a wave • Relative Amplitude Ratio www.nayyarENT.com

  28. Study of Wave Morphology • Shape of the graph • Normal graph • Graph in newborns • Conditions altering the morphology of the graph: • Acoustic neuroma • Leshion in the auditory pathway • Variation in rate\intensity of stimulus www.nayyarENT.com

  29. Non Clinical Factors affecting BERA • Stimulus rate • Stimulus phase or polarity • Intensity of sound stimulus • Binaural\monoaural stimulation • Filter characters of BERA machine • Nature of sound used • Sex\age of the patient www.nayyarENT.com

  30. Stimulus Rate • No. of clicks presented to the ear/sec • Recommended rate: 10-40/sec • Normally used: 1.1 clicks/sec • Rate >25/sec: increased latency & decreased amplitude • Children: >50/sec • High stimulus rate: Multiple sclerosis www.nayyarENT.com

  31. Stimulus phase or Polarity • Condensation & rarefaction phase • Affects latency, amplitude, morphology of waves • Routine studies: rarefaction waves are used • Alternate phase: reduces the artifacts & also the sharpness of waves www.nayyarENT.com

  32. Intensity of Sound Stimulus • 60 dB suprathreshold • Low intensity: increased absolute latency & decreased amplitude • First to disappear: wave I • Most stable: wave V www.nayyarENT.com

  33. Filter Charactristics • Recording of fixed range of frequencies • Low fq filter: 100-150 Hz • High fq filter: 3000-5000 Hz • Frequencies of the recorded electrical stimulus www.nayyarENT.com

  34. Normal values & Criteria for Abnormality www.nayyarENT.com

  35. Clinical uses of BERA www.nayyarENT.com

  36. Estimation of Hearing Threshold • Useful in newborns, infants, difficult patients • Estimation of hearing threshold • Estimation of type & degree of hearing loss • Avg. pure tone threshold = 0.6 (BERA threshold) • Comparison of latency of wave V at different intensity sounds • Frequency specific audiogram cannot be obtained www.nayyarENT.com

  37. Identification of nature of deafness • Analysis of latency-intensity function • Conductive, sensory or neural • Latency of wave V is recorded for different intensities • Plotted graphically • Conductive loss: upward & parallel shift • Sensory loss: shallow configuration • Neural: steep sloping graph www.nayyarENT.com

  38. Identification of Retrocochlear Pathologies • Most reliably identified • Parameters: • Increased interaural latency difference of wave V • Increase interaural interwave/interpeak latenct between wave I to V • Interwave latency between wave I & III/V www.nayyarENT.com

  39. Derived band stacked BERA • Elicit response from several discrete regions of cochlea • Composite picture of neural activity • Increases sensitivity of the test • Cochlea is divided into 5 segments & response from each is noted www.nayyarENT.com

  40. Derived band stacked BERA • 1st segment: sounds above 8000Hz (extreme basal end) • 2nd segment: 4000-8000Hz (basal end of cochlea) • 3rd segment: 2000-4000Hz (between basal & mid-portion) • 4th segment: 1000-2000Hz (mid portion of cochlea) • 5th segment: 500-1000Hz (apical part of cochlea) www.nayyarENT.com

  41. Derived band stacked BERA www.nayyarENT.com

  42. Stacked BERA • Improvement of derived band BERA • Increases the sensitivity & specificity of BERA for small tumours • Aligning 5 wave Vs of derived band BERA & adding the amplitudes • Reduced in presence of tumours • Useful in patients with U/L SNHL with normal BERA www.nayyarENT.com

  43. ASSR www.nayyarENT.com

  44. Auditory Steady State Response • Objective determination of frequency specific hearing threshold • Overcomes the limitations of BERA: • Idea of hearing threshold for higher frequencies (2000-4000 Hz) • Insensitive for hearing loss above 75-80 Db • Importance in providing hearing aid • Advantage over LLR & LLR www.nayyarENT.com

  45. Modulation of sound • Modulation of pure tone sound: • Amplitude domain (alternate off & on) • Frequency domain (warbling of tone) • Amplitude modulation of 100% is used • Frequency modulation of 20% is used • Restricted narrow area of basilar membrane is stimulated • Frequency specific threshold is determined www.nayyarENT.com

  46. Rate of Modulation • Rate of modulation: • <20 per sec: response from cortical areas • 20-50 per sec: subcortical areas • >60 per sec: brain stem • Recording in sedated infants • Carrier frequency: test frequency • Modulation frequency: no. of times CF is modulated www.nayyarENT.com

  47. Method of recording • Pure tone sounds (500/1000/2000/4000Hz) • Modulation: 90 times/sec • Evoked neural response is pre-amplified, filtered, sampled & analyzed • 90 Hz component of evoked response is measured • Phase coherence is commonly measured www.nayyarENT.com

  48. Consistency of response • Individual presentation of different frequencies • Measurement of fq dependent hearing threshold • Time taken: 45 mins • Determination of behavioral threshold: • Click evoked BERA: 10 dB more • Tone evoked BERA: 20-30 dB more www.nayyarENT.com

  49. Measurement of response • Discrepancy is more in the lower than higher frequencies • Better correlation in high frequency hearing loss • Regression formula for overcoming this • Overcomes the subjective visual factor www.nayyarENT.com

  50. BERA vs ASSR Similarities • Deliver an auditory stimulus • Stimulate the auditory system • Record bioelectric responses from the auditory system via electrodes • Patient does not have to respond volitionally. Differences • BERA stimulus: click or a tone burst presented at a slower rate; ASSR: amplitude or frequency modulated sounds presented rapidly • BERA is dependent on a relatively subjective analysis of amplitude versus latency. ASSR is dependent on a statistical analysis of the probability of a response, usually at a 95% confidence level. • The BERA response is measured in millionths of a volt (microvolts), and the ASSR is measured in billionths of a volt (nanovolts) www.nayyarENT.com

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