1. Dr. Supreet Singh Nayyar, AFMC For more presentations, visit www.nayyarENT.com www.nayyarENT.com Electrocochleography 22-07-2012 www.nayyarENT.com

2. Headings Introduction Principles Recording techniques Interpretation Clinical applications 22-07-2012 www.nayyarENT.com

3. Introduction Electrocochleography (ECochG) Method for recording the electrical potentials of the cochlea Stimulus-related Often includes measurement of the whole nerve or compound action potential (AP) of the auditory nerve. 22-07-2012 www.nayyarENT.com

4. Principles CM An alternating current voltage that mirrors the waveform of the acoustic stimulus at low-moderate levels of stimulation Generated predominantly by the outer hair cells Phase and duration are stimulus dependent 22-07-2012 www.nayyarENT.com

5. Principles SP A Direct Current generated predominantly by the outer hair cells Seen as a DC shift in the CM baseline Duration is dependent on the duration of the acoustic stimulus Independent of stimulus phase 22-07-2012 www.nayyarENT.com

6. Principles AP AC potential that represents the summed response of the synchronous firing of several thousand auditory nerve fibers N1 and N2 are virtually the same components as waves I and II of the ABR Independent of stimulus phase and duration. 22-07-2012 www.nayyarENT.com

7. Principles The normal SP duration is b/w 0.30 and 0.45 ms, and the absolute amplitude of the SP can range from 0.1mV to 1.0 mV AP has a latency of 1.5 ms(1.3 ms to 1.7 ms) duration is normally between 0.80 ms and 1.25 ms, absolute amplitude can vary greatly, ranging from 0.6 mV to 3.0 mV 22-07-2012 www.nayyarENT.com

8. Principles Normal SP/AP ratios generally range from 0.1 to 0.4 across subjects with a mean value of 0.25. Graphic Angle Measurement (GAM) Technique 22-07-2012 www.nayyarENT.com

9. Recording techniques There are two, general approaches for recording ECochG Transtympanic (TT) Extratympanic (ET ) 22-07-2012 www.nayyarENT.com

10. Recording techniques Recording parameters 22-07-2012 www.nayyarENT.com

11. Recording techniques The following suggestions are offered to help to reduce stimulus artifact ▫ test subjects in sound booth with the examiner and AEP unit located outside of the booth; the windows of the booth should be shielded with a copper screen; ▫ plug the AEP unit into an isolated electrical socket equipped with a true-earth ground; ▫ use a grounded cable for the primary electrode (such cables are commercially available); ▫ turn off lights in the testing room and unplug unnecessary electronic equipment (it also may be necessary to turn off the lights in the examiner room); ▫ consider encasing the transducer in grounded Mu metal shielding. 22-07-2012 www.nayyarENT.com

12. Interpretation Normal electrocochleogram from the tympanic membrane to clicks presented in alternating polarity at 80 dB HL 22-07-2012 www.nayyarENT.com

13. Interpretation Normal electrocochleogram from the tympanic membrane to a 2,000 Hz toneburst presented in alternating polarity at 80 dB HL 22-07-2012 www.nayyarENT.com

14. Clinical applications Menieres’ disease/ Endolymphatic hydro The reported incidence of an enlarged SP and SP/AP amplitude ratio in the general Meniere’s population is only approximately 60%-65% 22-07-2012 www.nayyarENT.com

15. Clinical applications Enhancement of wave I Wave I is absent in the conventional ABR tracings but recordable with the ECochG 22-07-2012 www.nayyarENT.com

16. Clinical applications Intraoperative monitoring of inner ear and auditory nerve status during surgeries identification of anatomic landmarks (such as the endolymphatic sac) 22-07-2012 www.nayyarENT.com

17. Clinical applications Other applications Estimation of hearing thresholds 22-07-2012 www.nayyarENT.com

18. Thank you For more presentations, kindly visit www.nayyarENT.comwww.nayyarENT.com 22-07-2012 www.nayyarENT.com