Mai EchoG and OAEs ENT [Recovered].pptx

Audiology

1. ECochG and OAEs By: Dr/Mai El Ghazaly Lecturer of Audio-vestibular Medicine

2. Electro- cochleography ( ECochG ) refers to the recording of the stimulus-related electro-physiological events occurring within the cochlea and the auditory nerve. Cochlear evoked potentials: 1. Cochlear microphonic (CM) 2. Summating potential (SP) 3. Action Potential (AP) Cochlea Auditory nerve

3. The cochlear microphonic (CM) is an alternating current (AC) derived from the movement of the outer hair cells . The waveform resembles the electrical form of the stimulus. Summating potential (SP) is a DC potential arising in from the non-linear vibration of the basilar membrane and IHCs movements.

4. The compound action potential (CAP) is the result of synchronous activity of the auditory nerve fibres . It is an AC voltage . The first and largest wave (N1) is identical to wave I of ABR. Following this is N2, which is identical to wave II of the ABR.

5. ECochG Recording 1. Invasive techniques: transtympanic ecochg : Promontorial needle. Round window ball electrode.

6. 2. Noninvasive techniques a- TM- ECochG : Flexible tube with cotton ball at the end.

7. b- Extratympanic ET- ECochG : Foam plug ear canal Leaf-type ear canal

8. ECochG recording With the right electrodes, virtually any ABR equipment can be used to record ECochG . It is an “early” or “short-latency” AEP that is similarly measured within a latency epoch of 0-5 milliseconds (ms) following stimulus onset.

9. Stimulus type: BB CLICK: most popular stimulus for short-latency AEPs because it excites synchronous discharges from a large population of neurons TONE BURST: More for research purposes. Provide a higher degree of response frequency specificity than clicks, and allows for better visualization of the SP and CM.

10. Stimulus rate : 7.1-21.1 depending on the electrode used  Polarity: Alternating polarity: will often get the best SP possible, a very nice AP, but no CM (cancelled out).  Single polarity: CM direction will be opposite for rarefaction and condensation.

11. Stimulus intensity: A high stimulus intensity is required when we are recording a diagnostic ECochG .  Transducers: Insert earphones. Amplification :   A gain of 75,000 or less can be used.  Analysis time (window): 0 - 5 milliseconds. Filter bandpass : 10Hz – 1500Hz (or 10 – 3000 hz )

12. Ecochgm Interpretation Testing parameters include latencies and amplitudes of SP and AP, and SP/AP amplitude ratio, and area under the curve of SP/AP ratio. Normal SP amplitudes: 0.1 - 0.8 microvolts (Mean 0.4 microvolts ). Normal AP amplitudes: Range : 0.6 - 2.7 microvolts (Mean 1.4 microvolts ). AP-N1 latency is identical to the latency of ABR wave I. At 95 dB HL, our normal N1 latencies generally range from 1.3 - 1.7ms (Mean1.5 ms) Mean SP/AP amplitude ratio to click stimuli for normal subjects is approximately 0.25  +  0.10 SD . SP/AP amplitude ratio > 45 % (2 SDs above the norm) to be enlarged. 

13. Clinical applications 1- Meniere disease Changes in the SP response can reflect pressure differences between the  scala media  and the  scala vestibuli , indicating excessive fluid pressure, thus deforming the  basilar membrane  toward the  scala tympani , so that enhanced-amplitude SP is thought to reflect EH. SP/AP ratio is the most common parameter for diagnosis of EH. 60%-65% of patients with Meniere’s disease were found to have large SP amplitudes when compared to AP amplitudes.  SP/AP ratio > 0.45 (SP > 45% of AP). Increased ratio occurs with increased ear fullness.

14. 2 . Auditory neuropathy spectrum disorder (ANSD) Normal otoacoustic emissions (OAEs) were recorded in patients with very abnormal pure tone hearing threshold or patients with no detectable ABR.

15. The normal tracings illustrate ABR components along with cochlear microphonic (CM) and summating potential (SP), which can be enhanced or reduced by adding or subtracting responses to C and R clicks. In the auditory neuropathy tracings, CM and SP are seen in the absence of ABR components

16. 3. Enhancement of ABR wave I N1 of ECochG is similar to ABR wave I, but due to close recording to the generator in the cochlea, the former is twice in amplitude. If ABR wave I is not readable, and therefore I-V IPL is immeasurable, one can measure the latency of N1 as an alternative to ABR wave I .

17. 4. INTRAOPERATIVE MONITORING (IOM) D uring surgeries that involve the peripheral auditory system; such as acoustic tumor removal, facial nerve exploration , and sac decompression . Esp. CPA surgeries. Such monitoring usually is done to help the surgeon avoid potential trauma to the ear/nerve in an effort to preserve hearing. IOM by ECochG is superior to IOM by ABR because; 1- Direct measuring of 8th nerve activity renders it more sensitive to subtle trauma to the nerve. 2- Intraoperative prediction of postoperative hearing thresholds is more accurate using ECochG . However , ABR is easier to record (surface electrodes)

18. 5- Estimation of Auditory Threshold Prior to the emergence of ABR as a clinical procedure, ECochG was the technique of choice for electrophysiological assessment of auditory function in young children and other difficult to-test patients.

19. Otoacoustic emissions

20. Otoacoustic emissions (OAEs) are sounds generated by the normal cochlea both spontaneously and in response to acoustic stimuli. OAEs are the only audiological test to selectively assess cochlear dysfunction. Fortunately enough those sounds can travel in an opposite direction to the incoming sound back to the middle & outer ear. The initial source of OAEs is the electromotility of the three outer rows of the cochlea’s sensory hair cells, the outer hair cells (OHCs).

21. OHCs acts as

22. Transient evoked OAEs OAEs are measured by presenting clicks to the ear through a probe with a soft flexible tip that is snugly inserted into the ear canal probe. It contains: 1. A loudspeaker that generates the sounds. 2. A sensitive microphone that measures the resulting OAEs. 3. A signal separating processor that can discriminate the sound of the OAE from the stimulus sound and other noise.

23. Parameters Affecting Recording & Analysis of TEOAE I) Stimulus parameters a) Stimulus type 1- Clicks: most commonly used 2-Tone bursts: are superior to clicks in that they don’t ring the probe. b) Stimulus intensity Response amplitude increases linearly with stimulus intensity up to 70 dBSPL when it saturates.

24. II ) Response Parameters a - Waveform reproducibility: odd & even numbered responses are averaged separately (A&B) and correlated together to obtain an overall reproducibility & band-specific reproducibility in percentage. b- Analysis time (windowing): 10-20 msec

25. Distortion Product OAEs The DPOAE is an evoked emission in response to two simultaneously presented primary tones called F1 & F2. The DPs are many, but the most prominent in humans is the 2F1-F2 product.

26. Instrumentation for DPOAE

27. Response Parameters of DPOAEs I. DP-gram ( OHCell -o-gram !) It is the plot of the DP level in dBSPL as function of the frequency of the second primary (F2). Analysis of the DP-Gram: 1- DP levels are above noise floor at all freqs by 5dB, DP levels are > -10 dB & the DP-gram replicates: interpretation: normal DP-gram 2- DP levels are within noise floor at all freqs : interpretation: failed DP-gram

28. Effect of hearing loss on OAES I . Conductive HL 1- Negative ME pressure : OAE abolished only if air-bone gap exceeds 15 dB. 2- TM perforation : OAE recorded if no ossicular lesion or active ME disease ( otitis media or cholesteatoma ). 3- Ventilation tube: OAE can be recorded if tube is patent in 50% of cases. 4- SOM: no OAEs if air bone gap > 15 dB at all freqs . 5- Otosclerosis : OAEs are absent at any freq & for any degree of hearing loss.

29. II. Cochlear HL Both T & DP OAEs are intact in normal hearing (<20 dB HTL). Neither T or DP OAEs can predict degree of loss above 30 dB HTL. TEOAE is superior to DP in detecting HL.(higher sensitivity) DPOAE is superior to TEOAEs in terms of better freq specificity.

30. Clinical Applications of the OAEs 1- Newborn hearing screening: Prons : - can reliably be recorded in infants. - can be recorded in nursery settings. - are absent in modest HLs (high sensitivity) - require brief time to record. - may be recorded by less-trained personnel. Cons: - poor specificity (75%) due to noise. - CHL due to vernix or debris invalidate test.

31. Criteria & Guidelines for Screening with TEOAEs 1- Peak click intensity 74-83 dB SPL 2- Stimulus stability of 75% or more. 3- Flat click spectrum between 1 & 4000 Hz. 4- One of following criteria must be met for a “Pass”: - Overall reproducibility of 75% or more. - Repro for octave bands from 1600 to 4000 Hz of 70% or more. - OAE to noise difference of 6 dB SPL or more. - Overall response level of 23 dB SPL or more.

32. 2- Diagnostic pediatric audiometry : Electrophysiologic test, brief testing time, can be applied during sleep, provide ear-specific & freq-specific audiologic information. 3- Help in test battery of CAPD: to rule out peripheral lesion at the cochlear level. 4- Assessment in suspected non-organic HL . 5- Monitoring ototoxicity : OAEs are site specific as toxic agents primarily affect outer hair cells. Also OAEs can detect subtle cochlear dysfunction at pre-clinical stages.

33. 6- Diagnosis of auditory neuropathy: Together with the ABR, OAEs, when they are intact, have become the cornerstone in diagnosing AN since cochlear function is normal in AN, but retrocochlear neural structures, as shown by the ABR, are not.