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Factors Influencing the ABR (I
- 1. Stimulus, Recording & Patients factors influencing the ABR (I) Chapter 4 馬偕紀念醫院耳鼻喉科 馬偕醫學院聽語系 褚嘉慧MD, MPH
- 2. 可以想見，很多因素可以影響ABR 1.刺激音 2. 紀錄 3. 病患本身
- 3. 4.1.1 Stimulus Intensity As the stimulus intensity Latencies (若沒特別指明就是在講wave V) Amplitudes The latency changes occur slowly for intensities from 90 to 60 dBnHL and then more rapidly at lower intensity levels.
- 5. Latency-intensity function Steeper Non-Linear Above 60dB; wave V latency 0.1~0.2 ms/ Stimulus intensity 10dB Below 60dB; wave V latency 0.5~0.6 ms/ Stimulus intensity 10dB
- 6. At lower intensity levels, wave V is most visible. Earlier components tend to become indistinguishable at 25~35dB. Near the threshold of the response, wave I occurs at approximately 4.0ms; wave V at 7~9ms Wave I latency shifts more than wave V 第一波晚得較多
- 8. 4.1.2 Stimulus Rate When stimulus rate >30/s, latency (of all components), amplitude, clarity, reproducibility Wave V Latency (rate from 10/s to 100/s) Earlier waves Latencies are generally less affected Amplitude 每一個波都 尤其是V明顯慢出現 其他波顯著變小, Latency稍變慢
- 9. When the stimulus rate from 10/s to 100/s 當刺激速率越來越加快的時候 Wave V Latency: by 0.5ms Earlier waves: latencies less affected Earlier waves: Amplitude 比較慢出現 振幅變小
- 10. Lower stimulus rate, better ABR morphology BUT Faster rates can be used in 1. Threshold-seeking ABR 2. Difficult to evaluate tracings cases (個人/環境) 11.3/s, 可能需 700~1000次平均加算(總耗時62~89秒) 27.7/s, 可能需1500~2000次平均加算(總耗時54~72秒) 57.7/s, 可能需2500~3000次平均加算(總耗時43~52秒) 高刺激速率需要更多次平均加算，但整體耗時有機會再縮短 刺激速率快有其存在價值 臨床: 要獲得清晰的反應波形，又不能搞太久 目前一般採用11-20次/秒的刺激速率 比較省時
- 11. 4.1.3 Stimulus Polarity (a) When the speaker diaphragm moves outward, it creates a condensation (b) When the diaphragm moves inward, it creates a rarefaction.
- 13. 4.1.3 Stimulus Polarity Rarefaction A rarefaction stimulus produces an initial inward movement of the earphone diaphragm an outward movement of the footplate an upward motion of the basalmost structures of organ of Corti. Upward motion: depolarizing motion for hair cells, latency is shorter, amplitude is higher for the early components Rarefaction對內耳毛細胞屬興奮性，ABR反應振幅較好 所以一般ABR多用Rar (但Con, Alt也都可以)
- 14. 4.1.3 Stimulus Polarity Condensation Condensation stimuli produce an initial inward movement an outward movement & depolarization of the hair cell latency is longer, amplitude is smaller for the early components. Large latency differences between polarities are observed in individuals. (no conclusion yet…...)
- 18. 4.1.3 Stimulus Polarity Polarity & Peripheral HL The effects of polarity on ABRs are particularly important in patients with high tone sloping HL. Phase reversal can degrade ABR sufficiently interfere with accurate interpretation So in patients with HL, use of a single polarity stimulus is recommended.
- 19. 4.1.3 Stimulus Polarity Alternating polarity Using rarefaction & condensation separately acquiring response signals digitally added together early response of ABR, SNR Clinical applications: Auditory neuropathy, normal OAE When a cochlear response is large When stimulus artifact is large (e.g. supra-aural earphones)
- 20. 交替使用Using rarefaction & condensation separately Wave I之前的耳蝸訊號加總之後, CM不見了
- 21. 4.1.4 Stimulus Duration Standard pulse duration in clinical ABR: 0.1ms ABR: onset sensitive, the duration of stimulus should NOT alter the response Some special applications using different stimulus duration Testing higher frequency regions (>8000Hz) of the cochlea, to monitor ototoxicity 集體放電
- 22. 4.1.4 Rise time 上昇時間Rise time是信號從特定低準位上昇到特定高準位 需要的時間，可用相對於參考輸入的比率或%來表示 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=9817 Points located 10% & 90% up the curve are commonly used.
- 23. Rise time, duration皆為用以形容Toneburst特性的參數 Toneburst是Tone去改良，讓純音變成比較Transient (仿造 Click特性)，所以TB有「起、平台、降」的時間 (例如像ㄇ一樣），ㄇ的寬度就是TB的duration The frequency-dependent duration provides a compromise between rapid onset (necessary to optimize neural synchrony) and spectral definition Tone-burst duration gradually as frequency 2.83 ms at 2 kHz, 2.38 ms at 3 kHz, 2 ms at 4 kHz, 1.69 ms at 6 kHz 低頻TB, duration長
- 24. 4.1.4 Rise time The rise time of stimulus has a marked effect on the ABR Fewer neurons firing simultaneously: Synchrony (hard to read) Rise time > 5ms: fail to generate ABR J Am Acad Audiol 2: 24-31 (1991) Rise time Latency Amplitude Morphology deteriorates
- 25. 4.1.5 Stimulus Frequency ABR can be obtained using TB Trade-off: frequency specificity neural synchrony 4K click versus 4K TB: about the same TB with longer rise time: more frequency specificity but poor neural synchrony affect ABR quality (will be discussed in Ch 6 later, evaluation of hearing sensitivity) Higher frequency stimulus more basal portion stimulated Shorter latency Better neural synchrony 魚與熊掌 高頻相對比較沒差 比較多Basal portion被激發 Latency短, 集體放電效果較佳
- 26. https://www.britannica.com/science/ear/ (A) Fibers of the basilar membrane become progressively wider and more flexible寬度和柔軟 度不同 from the base of the cochlea to the apex. As a result, each area of the basilar membrane vibrates preferentially to a particular sound frequency. (B) High-frequency: maximum vibration of the BM nearest to the basal cochlea (C) Medium-frequency: affect the center of the membrane (D) Low-frequency: preferentially stimulate the apex of the BM
- 27. James W. Hall III, University of Florida
- 28. 4.1.6 Monaural v.s. Binaural Responses to binaural stimuli over monaural stimuli 1. Binaural response is NOT the sum of monaural responses: An average of 60% in amplitude Different response of auditory system to binaural/ monaural stimuli 2. Similar latencies 3. Reflects only the response of the more normal ear, thus will NOT reveal the presence of a unilateral disorder 所以並非直接加乘
- 30. 4.2.1 Electrode Montages Optimal electrodes placement at most conditions Cz (vertex; Lt-Rt/ Nasion-Inion); A1 Lt ear, A2 Rt ear Fpz (ground): can be put anywhere on the body, usually on the forehead
- 32. Wave I-III: more prominent in ipsilateral recordings Wave IV, V: often better separated in contralateral recordings Earlobes sites: less muscle potential and greater wave I amplitude (than mastoid recording sites) Use of non-cephalic site (C7 vertebra): enhance wave V, VI
- 33. 4.2.2 Filter setting Filtering of the physiological response is used to eliminate as much as internal noise (e.g., unrelated muscle potentials), & external electrical noise (from environment 60Hz) as possible. Increasing the high-pass filter cutoff frequency ( low frequency energy) from 30Hz to 100Hz or 150Hz in the amplitude and latency of the response 低頻的濾掉太多, 使wave V變小, 誤判Threshold 把下限設得太高
- 34. Allowing more low frequency information into the average: Amplitude (particularly later components) Latencies slightly Decreasing the low-pass filter cutting frequency (e.g., from 3000Hz to 1500Hz) Some rounding of the peaks, but less effect on amplitude or latency 把上限設得太低 濾掉較多高頻的訊號, Peak變圓圓……太圓又會誤判 所以低頻的波不能濾掉太多, wave V才不會變太小, 誤判Threshold
- 36. 通常至少設在100Hz, 避免日常生活中電器釋放60Hz之電訊干擾; 但這樣的設 定可能使wave V稍微變小, 因而影響到tABR之判讀; 故有時會將filter下限定在30Hz, 避免高估Threshold (低頻的不要濾掉太多, 以 免看不到wave V) 濾掉較多高頻訊號, Peak變圓圓
- 37. Example: Acquisition & stimulus parameters used in ABR
Editor's Notes
- The causality here is pretty straightforward: Compression at the stapes footplate deforms the BM downward, rarefaction at the stapes footplate deforms the BM upward. (This is a closed system, so these pressure pulses are resolved by inward and outward movements at the round window, which is covered by the internal tympanic membrane.)
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