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Eclipse

What is ECochG?
Electrocochleography (ECochG) is a measure of the electrical potentials of the cochlea. Typically, the measurement is characterized by the stimulus onset (baseline), the response of the cochlea to the stimulus (summating potential - SP), and response to the synchronous firing of nerve fibers (action potential - AP). The AP is also known as Wave I. The cochlear microphonic (CM) is also part of the ECochG and has its own protocol. Measuring the CM requires slightly different test parameters than the SP and AP and for this reason it is described in a separate quick guide.

Why Perform an ECochG?
Certain vestibular and auditory conditions may be diagnosed with ECochG. The ECochG is primarily used to

diagnose Meniere’s Disease, particularly Cochlear Hydrops. The SP and AP amplitudes, latencies and their

relationship are used to diagnose these conditions. Perilymph Fistula, sudden hearing loss and other pathologies may result in abnormal ECochG results. Recent studies indicate that Superior Canal Dehiscence (SCD) may also result in elevated SP/AP ratios (Devaiah et al., 2009).

How to Test?
Surface electrodes are not adequate for recording ECochG. It is recommended to use Tiptrodes, TM-trodes or Transtympanic electrodes to measure the electrocochleogram. While transtympanic electrodes will result in the most robust response but are not feasible for most clinics. Gold foil Tiptrodes are sometimes used but TM- trodes will produce larger responses as it is closer to the site of generation. The following is an example of preparation and electrode placement performed with a TM-trode. Note the procedure should only be performed by trained professionals.

Patient Preparation is very important. The patient must lie down and should be relaxed or sleeping in a quiet environment during the procedure. An examination of the ear canal and TM must be performed prior to performing the test.

The electrode sites must be prepared and cleaned in order to obtain acceptable low skin impedance. It is recommended to have impedance values be 5kΩ or lower for Tiptrodes. The impedance values between one another should be balanced or similar in value. For TM-trodes the impedance should be 20kΩ or lower. It may be quite difficult to obtain such low impedance on the ECochG test ear electrode and higher levels may be accepted.

Electrode Placement: The ECochG test leads must be used to acquire the waveform. Below is an example of the electrode placement using the TM-trode with the EPA4 and an example of the EPA3 with a TM-trode.
For both examples the TM-trode and the test ear must be prepared prior to placing the TM-trode on the tympanic membrane. To reduce impedance a solution of saline can be used. Drain the ear prior to inserting the TM-trode. The TM-trode can be placed in a saline solution for a few minutes prior to placing it on the TM and should be dipped in electrode contact gel (e.g. Sonaville) prior to placing it at the TM.

EPA4 TM-trode example
When using EPA4 together with a TM-trode the red TM-trode cable is moved when switching ear.

EPA3 TM-trode example
Only 1-channel is needed to perform an ECochG with the TM-trode and for simplicity EPA3 can be used.

Basic ECochG Testing Procedure
The procedure discussed below is simply a suggested process to be used as a guideline. Consult your Instruction for Use or Eclipse Additional Information to learn how to create or modify a protocol.

Choose the protocol ECochG Click
Manual Mode: To begin the manual mode, choose the intensity and select the ear to test on the Record sheet. Next choose Start (or hit F2).

During testing monitor the EEG to assure a collection with minimal noise. The EEG levels should be low and consistent. As averaging commences, the waveform will appear on the screen.

Hint: Waveform Scaling can be increased or decreased by using the arrows on the top left side of the recording window or on your keyboard.
Hint: Window sizing may be changed during testing by selecting one of the arrow keys on the bottom, right side of the recording window or using the arrows on your keyboard.

Marking Peaks and Areas
Waveforms are marked from the Edit sheet during or after testing either manually or automatically. Amplitude Ratio or Area Ratio Calculation will automatically be computed once the required labels are assigned. The ratio selection is found in the General Setup.


To mark a selected waveform, click the appropriate waveform marker in the Edit sheet (or select 1-6 on the keyboard). Now bring the mouse to the correct position on the waveform and click to place the marker (or hit Enter).

Hint: You can use the digital filters to “clean up” noisy data even after a completed test or run. You’ll find this feature in the bottom of the Edit sheet.

Example of Marked Points for Amplitude Ratio

PBSL=Baseline, SP= Summating Potential, AP=Action Potential, BLst=start of baseline, Blend=end of baseline, AP1=start of AP, AP2=end of AP

Example of Marked Points for Area Ratio

PBSL=Baseline, SP= Summating Potential, AP=Action Potential, BLst=start of baseline, Blend=end of baseline, AP1=start of AP, AP2=end of AP

Amplitude ratio: Amplitude ratio is simply marked with the baseline, the summating potential and the action potential. A ratio between the BSL/SP and BSL/AP is calculated automatically by the system.
Abnormal SP/AP amplitudes are exceeding a ratio of 0.53 as the critical value (Devaiah et al., 2009).

Area Ratio: Area Ratio is marked by first marking the start of the baseline (BLst). The BL end will be marked automatically at the next point in the waveform where the amplitude crosses this baseline. If the waveform does not allow this, you can place the BL end manually. Now mark the SP and the AP1 (the beginning of the AP). Next mark the AP peak. Finally mark the AP2, which is where the AP ends and “changes direction”. A ratio is calculated automatically by the system. Abnormal SP/AP area ratios are exceeding a ratio of 1.94 as the critical value (Devaiah et al., 2009).

Reporting
Choose the Report Icon. When complete, choose Save and Exit. 


References
Devaiah, A.K., Dawson, K.L., Ferraro, J.A., & Ator, G.A. (2009). Utility of area curve ratio electrocochleography inearly meniere disease. Arch Otolaryngol Head Neck Surg, 129, 547-551.

July 2016

What is ABR?
The Auditory Brainstem Response is an Evoked Potential that originates at the auditory nerve (Cranial Nerve VIII). This test is used to assess the auditory system’s function from the cochlea through the brainstem. The response is identified by “peaks” that occur typically between 1 and 15 milliseconds from the stimulus onset. The ABR peaks are measured and marked traditionally as I, II, III, IV, and V. Each peak has an expected latency to be considered “normal”. Delayed or missing peaks are consistent with abnormal auditory function. The amplitudes and latencies (both absolute and inter-peak) are used to diagnose certain auditory pathologies.

Why ABR?
ABR testing is traditionally used to help determine the degree of hearing loss in pediatric or difficult to test populations. It is also used for testing the auditory pathway as related to acoustic neuromas and some nervous system abnormalities.

How to Test?
Patient Preparation is very important. The patient should be relaxed or sleeping in a quiet environment. It is preferable that the patient lie down during the procedure to facilitate a calm and comfortable environment. The electrode sites must be prepared and cleaned in order to obtain acceptably low skin impedance. It is re- commended to have impedance values be 3kΩ or lower. The impedance values between one another should be balanced or similar in value.

Electrode Placement: The electrodes must be placed as indicated below. The must be a few centimetres between the white and black electrode. Alternatively the black electrode can be placed at the cheek.
Check the impedance on the preamplifier and place the transducers. Make sure the patient is relaxed prior to starting the test. You can monitor this by watching the EEG Window on the top right of the recording window.

Setting up the Eclipse
The Eclipse comes with pre-programmed protocols so the system is ready to use immediately. Protocols can be created or modified easily to fit your clinical needs. Consult your Additional Information to learn how to create or modify a protocol. The procedure discussed on the next page is simply a suggested process to be used as a guideline.

Basic ABR Testing Procedure

  1. Choose ABR Threshold e.g. Threshold CE-Chirp LS 
  2. Select ear and intensity
    AutoTest Mode: To begin the Automatic Test Protocol simply click on Start or use the F2 key. This will begin the Auto Sequence set up in the Protocol Setup.

    Hint: To move to the next intensity prior to completion of maximum sweeps choose Next Intensity or F3.
    Manual Mode: To begin the manual mode choose the intensity and select the ear to test on the Record sheet. Next choose Start or hit F2 if needed.

  3. Monitor the EEG during testing to assure a collection with minimal noise.
  4. Monitor the Fmp and Residual Noise to verify that a true response is detected.

    Note: Bayesian Weighting, Fmp, and Residual Noise Calculation are important additional features that are described in dedicated Quick Guides.
  5. Monitor the waveform reproducibility
    The line should be black and relatively flat and consistent. As averaging commences, the waveform will appear on the screen. As averaging continues note the Wave Re-reducibility score.

    When a test is performed, an A and B buffer exist. Each receives half of the responses. An automatic calculation of the correlation (similarity) between the two curves is indicated in this area (above left). The time window over which this correlation calculation occurs is part of the test parameter setup. It is indicated by the bold part of the time scale seen above (right). You may change the width or position of this bold bar by dragging it by its ends or by grabbing it with the mouse and sliding it back and forth along the time scale. Wave reproducibility will be recalculated immediately.

    HINT Waveform Scaling can be increased or decreased by using the arrows on the top left side of the recording window.

    HINT Window sizing may be changed during testing by selecting one of the arrow keys on the bottom, right side of the recording window.

Marking Peaks
Waveforms can be marked during a recording or afterwards from the Recording or Edit sheet. Waveforms can be marked manually or automatically. To mark a waveform automatically, use the Suggest Waveform marker:

This feature will place markers within the latency ranges that may be entered in the Latency template.
To mark a selected waveform manually, choose the appropriate marker or select 1-5 on the keyboard. Now drag the mouse to the correct position on the waveform and click to place the marker (or push Enter). The same function is available if you right click in the graph area with the curve selected.

Hint: If you hold down Crtl key while using the Arrow keys the Waveform Marker will jump from peak to peak!
Hint: You can use the digital filters to “clean up” noisy data even after a completed test or run! You’ll find this feature on the bottom of the Edit sheet.

Latency Data and Latency Intensity graphs
The system has an option to load default latency data during installation. You may also create your own (consult your Additional Information for instruction). While marking waveforms manually, a shaded area will appear indicating such latency data to assist with marking.
Once the waveforms are marked, choose the Latency sheet. The shaded area indicates the range of the latency data.

Reporting
Choose the Report Icon
When complete, choose Save and Exit.

July 2016

What is cVEMP?
The cervical Vestibular Evoked Myogenic Potential (cVEMP) is an evoked potential measured from the sternocleidomastoid (SCM) muscle and is used to assess the vestibular system (the saccule and its afferent pathways). An amplitude asymmetry ratio is then calculated to assess if the vestibular system is working normally. VEMP tracings are easily recorded and provide valuable information to medical practitioners to assist them in the diagnosis of various disorders. Loud tone bursts, at slow rates are used to elicit this response.

Why cVEMP?
The cVEMP is a test used in addition to traditional vestibular testing (e.g., VNG) to assist in the assessment of vestibular function. The cVEMP provides information about the saccule and inferior vestibular nerve, assisting medical practitioners in the diagnosis of disorders such as Superior Semicircular Canal Dehiscence (SSCD) (Milojcic et al., 2013) and Meniere’s disease (Rauch et al., 2004).

How to test?
Patient Preparation
is very important. The electrode sites must be prepared and cleaned in order to obtain acceptably low skin impedances. It is recommended to have impedance values of 3kΩ or lower. The impedance values between each electrode should be balanced or similar in value.

There are different suggested activation techniques for the SCM muscle. The patient can either be sitting and instructed to turn the head only to contract/activate the SCM muscle as shown in the image below.
Alternatively, the patient can be in a reclined position and asked to lift the head and turn the neck to contract the SCM muscle. Use of the patient EMG monitor will ensure consistent activation during testing.

Electrode placement (example):

The reference electrodes should be placed on the upper belly of the SCM muscle on both sides. The vertex electrode is placed on the clavicular joint (or on the high forehead) and the ground/common on the low forehead.

Typically, the air-conduction stimulus used is a 500Hz tone burst at high intensity level (e.g., 90/95dBnHL). Ensure that the patient is relaxed prior to starting the test. After confirming impedances.

Setting up the Eclipse
The Eclipse comes with pre-programmed cVEMP protocols so the system is ready to use immediately. Protocols can be created or modified easily to fit your clinical needs. Consult the Eclipse Additional Information manual to learn how to create or modify a protocol. The procedure described below is simply a suggested test process and to be used only as a guideline.

Patient monitor
An adequate contraction of the SCM muscle is essential for a good cVEMP recording. The patient monitor provides information to the patient during testing to ensure a correct head turn/lift and informs the patient about the test time and contraction of the SCM muscle. The information provided on the patient monitor is a guide to the patient and constitutes to a more accurate test procedure which may shorten the overall test time.


EMG controlled stimulus/recording
when the patient contracts the SCM muscle adequately. This can be monitored by the patient either visually Patient EMG Monitor or audibly Monitor Tone. Please see Additional Information manual for a more detailed explanation of monitoring options.

cVEMP testing procedure
Choose a cVEMP protocol from the dropdown menu 
The cVEMP test should be run in the Manual Mode controlling/selecting stimuli manually.

Manual mode

  1. To begin in manual mode, choose the intensity and select the ear to test on the Record sheet. Instruct the patient to turn their head to the right or left to activate the muscle on the testing side. You should pay particular attention to the ongoing EEG and the target range if needed.
  2. Next choose Start or hit F2.
  3. 100-200 sweeps are typically collected per waveform.

Setting up L & R waveform partners
After collection, choose a left or right ear waveform by double clicking the waveform handle. Next, right click the waveform handle of the opposite ear and select Set as VEMP Partner. The selected waveforms are used in the Asymmetry Ratio Calculation.

EMG scaling
The default protocol is setup to scale the curves automatically. Some prefer to scale after the recordings are completed. After the recording is complete, you can right click on the waveform and choose EMG Scaling. Waveforms will then be scaled according to the average prestimulus EMG values recorded throughout the collection. This will make individual recordings comparable, even though slightly different degrees of muscle tonus may have been applied during the different recordings, which provides a reliable tool in calculation of the amplitude asymmetry (McCaslin et al., 2014).

HINT Display Scaling can be increased or decreased by using the arrows on the top left side of the recording window or by using your keyboard arrows.

Marking peaks
The cVEMP response is well documented and is said to be represented by two distinct peaks; P1 occurring at approximately 13 ms and N1 occurring at approximately 23 ms.

Waveforms can be marked from the Record sheet or the Edit sheet. To mark a waveform double click on the waveform handle you would like to mark. Right click and then choose the correct marker. Drag your mouse to the correct area and click. You can also choose 1-4 on the keyboard to bring up the appropriate marker and use Enter to place it.

Normative data
A number of studies report upper limits of normal for cVEMP recordings between 35 – 45% depending on the use of EMG monitoring and scaling of the response. In a study by McCaslin and colleagues (2013), the upper limit of normal was reported as ~31-37 % when both EMG monitoring and scaling was applied.

Example of a cVEMP where P1 and N1 are marked for both ears. The asymmetry ratio is calculated at 0.06. Curves are scaled.


Example of scaled cVEMP waveforms indicating an abnormal asymmetry ratio (0.80) between left and right side, along with lowered cVEMP thresholds on the right. (Curves in the above example are inverted).

Reporting
Choose the Report Icon .
When complete, choose Save and Exit.


References
McCaslin, D. L., Fowler, A., Jacobson, G. P. (2014). Amplitude normalization reduces cervical vestibular evoked myogenic potential (cVEMP) amplitude asymmetries in normal subjects: proof of concept. J Am Acad Audiol, 25(3), 268-277.

McCaslin, D. L., Jacobson, G. P., Hatton, K., Fowler, A. P., & DeLong, A. P. (2013). The effects of amplitude normalization and EMG targets on cVEMP interaural amplitude asymmetry. Ear Hear, 34(4), 482-490.

Milojcic, R., Guinan, J.J., Rauch, S.D., & Herrmann, B.S. (2013). Vestibular evoked myogenic potentials in patients with superior semicircular canal dehiscence. Otol Neurotol, 34(2), 360-367.

Rauch, S. D., Zhou, G., Kujawa, S. G., Guinan, J. J., Herrmann, B. S. (2004). Vestibular evoked myogenic potentials show altered tuning in patients with Ménière’s disease. Otology & Neurotology, 25(3), 333-338.

Young, Y. H., Wu, C. C., & Wu, C. H. (2002). Augmentation of vestibular evoked myogenic potentials: an indication for distended saccular hydrops. Laryngoscope, 112(3), 509-512.

 

September 2017

1 Introduction: eABR overview.

1.1 What is eABR?
An electrical Auditory Brainstem Response (eABR) is a measurement of the ABR using an electrical stimulus. Instead of a traditional acoustic stimulus the cochlear implant (CI) or auditory brainstem implant (ABI) provides the stimuli that evokes the eABR.

1.2 Why eABR?
eABR testing may be performed for the following reasons:

  • To verify adequate placement of the cochlear implant or auditory brainstem implant electrodes during surgery.
  • To estimate electrical thresholds in infants, young children or other patients who cannot be assessed using behavioral techniques.
  • To assist in mapping the cochlear implant or auditory brainstem implant device.
  • To assess interactions between electrode channels.

2 System setup

Stimulation system and acquisition system are required to complete the basic system setup to proceed with eABR test.

2.1 Cochlear device used for stimulation
For stimulation you need the following materials:

  1. Computer.
  2. CI Software.
  3. CI programming device USB interface
  4. Processor connected to the CI programming device.

2.2 Eclipse device used for recording

  1. Eclipse 1.1 (with EP15 or EP25 license), hereafter referred to as ‘Eclipse’.
  2. Eclipse EP software.
  3. USB interface.
  4. Trigger cable for Eclipse 1.1 (see Figure 1).
  5. Preamplifier (manufactured from June,2019 or above serial number # ID114077).
  6. EPA3 cable collector.
  7. Three electrode cables.
This is an image of the trigger cable for Eclipse

Figure 1


3 Hardware set-up

  • Ensure all the hardware components are arranged as guided in Figure 2.
  • Ensure recording electrode cables are twisted to reduce the artefact from the stimulator.
  • Ensure the cables used for stimulation are well separated from the recording cables in order to reduce the artefact.
This is an image showing how the hardware components should be arranged

Figure 2


3.1 Setting up CI programming software:

  • Ensure the ‘CI Software’ is installed on the computer and available for use.
  • Open the CI software, create a new patient profile if needed or access the existing patient profile1.
  • Connect the processor.
  • Proceed an Impedance Measurement for CI and make sure all electrodes are connected before testing eABR.
  • Proceed with eABR test.

3.2 Setting up Eclipse:

  • Turn on the Eclipse and double-Click on OtoAccess icon. This is an image of the OtoAccess icon
  • Create a new client profile/access the existing one2.
  • Click on the EP icon This is an image of the EP icon and the acquisition window appears
  • Choose the eABR protocol for integrity tests and/or eABR recordings see Figure 3 and footnote No. 2).
  • Now the Eclipse is ready to proceed with the eABR test.
This is an image showing where to select the eABR protocol or eABR recordings

Figure 3


4 Patient Preaparation

Patient preparation is very important to achieve the best test results. Optimally, the patient should be lying down, asleep and in a quiet environment. Minimally, the patient should be relaxed with their eyes closed during testing (Note: Usually eABR is not affected by anesthesia but consult with local physician).
Clean the patient skin with the abrasive gel (e.g. Nuprep.) to reduce the impedance. Impedance values at or below 3kΩ will produce cleaner recordings. Arrange electrode cables away from the cochlear implant connections to minimize interference.
Check the impedance (at or below 3kΩms) on the preamplifier (Note: If the impedances are higher than 5 kΩ, remove the surface electrodes, clean the skin and place new surface electrodes. Refer additional information manual for the detailed procedure of preparation of skin and impedance check).

4.1 Eelctrode placement:
Three (3) electrodes are connected to pre-amplifier as shown in the Figure 4.

  • Positive: indicated by white color.
  • Negative: indicated by yellow color.
  • Ground: indicate by black color.
This is an image showing the electrodes connected to a pre-amplifier

Figure 4


4.2 For eABR test:

  • Positive: High forehead.
  • Negative: Chin.
  • Ground: Place on the side close to the implant.

Note: this is the recommended electrode montage position for eABR test (Figure 5)

This is an image showing the recommended electrode positions

Figure 5


An alternative method (see Figure 6) of electrode position, recording from the contralateral side.

  • Positive: High forehead.
  • Negative: Contralateral side.
  • Ground: Low forehead.
This is an image showing an alternative electrode position

Figure 6


5 Test Procedure:

5.1 eABR test:
In general, for eABR testing, few CI-electrodes are tested, from where a general electrical threshold is set across remaining CI-electrodes.

  1. From Eclipse application select the CI side (right/left), click on the intensity level corresponding to the CI electrode number, e.g. if the CI electrode to test is 4, then choose intensity 4dB to match electrode number and the recording label.
  2. Click on ‘Start’ button (now the eclipse is waiting for the Ci software to send the trigger signal to initiate the eABR recordings).
  3. Come back to CI software and set the test parameters for ‘eABR’ testing. Please refer to the CI manufacturer manual see footnote 2.
  4. Note: when conducting post operation eABR, test amplitude and impulse duration should be defined at the comfortable level of the patient.

    • Electrode to test: 4 (recommended are 4,8,12,16).
    • Stimulation rate: 26 Hz.
    • Stimulation starting current level: 80CL (steps of 103).
    • No of Stimulations to average: 4000.
  5. Now Click on Stimulation button (CI software).
  6. The recording has started on Eclipse.
  7. Open EP application on Eclipse.
  8. When sufficient data has been collected (e.g. when residual noise has reached a level of 50nV), press ‘STOP’ button.
  9. Repeat the steps from 1 to 7 of section 5.1 with different electrode number (in CI software, e.g: 4, 8, 12, 16) to cover all the 4 measurements required to complete the eABR test. The example of the eABR, in this case, electrode No. 4 was selected for eABR test and tested to threshold, is shown in the Figure 7.
This is an image showing the example of eABR with electrode 4 selected

Figure 7


5.2 Troubleshooting: (in case of recording problems in eABR test)
In case of too many rejections, change the EEG rejection level.

  • Check the electrodes impedances of both the Eclipse surface electrodes and the CI electrodes.
  • Be sure that recording and stimulation cables are well separated to minimize cross talk.


6 Result interpretation

6.1 How to interpret the eABR results?
The eABR test is to measure the electrical threshold of the individual CI electrode band. In optimum, a stimulus with the current level of 80 CL is used as starting point, from where it is decided to increase or decrease the amplitude/duration based on the presence of the response. The steps are typically increased/decreased in steps of 10.
In the example, electrical threshold of electrode no.4 was measured and typical result is shown in Figure 8.

This is an image showing an example of a typical result

Figure 8


Labels to each waveform can be added. In the example, current level was labeled, see Figure 9.

This is an image showing a label added to a waveform

Figure 9


When comparing eABR to ABR, the following differences can be noted:

  • eABR latency is approx. 2ms seconds earlier than ABR, hence, eABR Wave V is found typically around the 4ms.
  • A minimal latency shift is seen in eABR with decreased stimuli duration.

Note: For more information about the Eclipse, please refer to the Eclipse User Manual.




1 Refer to CI manufacturer Medical User Manual for further details.
2 Refer to Eclipse User Manual for further details.
3 The steps are typically increased if there is no eABR response and decreased if there is an eaBR response.

July 2017

What is oVEMP?
The Ocular Vestibular Evoked Myogenic Potential (oVEMP) is an evoked potential measured from the inferior oblique muscle and is used to assess the vestibular system. There is still some debate over the origin of the response (Piker et al., 2011), however, the oVEMP is largely dependent on the integrity of the superior vestibular nerve (Jacobson et al., 2011).

The oVEMP is recorded using surface electrodes at four sites on the face and an Amplitude Asymmetry Ratio is calculated to determine if the above-mentioned parts of the vestibular system are intact and working normally.

The figure shows oVEMP recordings from a normal young adult (Murnane & Aki, 2009).

Why oVEMP?
The oVEMP is a test used in addition to traditional vestibular testing (e.g., VNG) to assist in the assessment of vestibular function. oVEMP recordings provide value information to medical practitioners to assist them in the diagnosis of disorders such as Superior Semicircular Canal Dehiscence (SSCD) (Watters et al., 2006) and Meniere’s disease (Sandhu, 2012).

How to test?
Patient Preparation is very important. The electrode sites must be prepared and cleaned in order to obtain acceptably low skin impedances. It is recommended to have impedance values of 3kΩ or lower. The impedance value between each electrode should be balanced or similar in value.

The subject is either seated or in a reclined position and is instructed to maintain an upward gaze at 35 degrees for the duration of the recording (Kantner & Gürkov, 2014). Placing a static visual target on the wall or ceiling for the patient to look at during testing will ensure consistent activation of the inferior oblique muscle.

Electrode placement (example)

Use of this electrode montage does not require the active (white) electrode to be shifted during testing and is reported to provide the largest oVEMP amplitude (Piker et al., 2011).

The reference electrodes should be placed as close as possible underneath the eye in the orbital midline. Avoid placement close to the medial canthus (inner corner of the eye) as a null-point exists where there is no oVEMP response present (Sandhu, George & Rea, 2013).

The oVEMP response is recorded from the inferior oblique muscle underneath the contralateral eye. Therefore, the right (red) electrode is placed under the left eye while the right ear is stimulated. Correct positioning of the electrode on the inferior oblique muscle is essential in obtaining a response (Sandhu, George & Rea, 2013).

Alternative electrode placement (examples)

Electrode montage for testing the left ear. For testing of the right ear, move the active (white) electrode to the other side (underneath the red electrode).

Typically, the air-conduction stimulus used is a 500Hz tone burst at high intensity level (e.g., 90/95dBnHL). Ensure that the patient is relaxed prior to starting the test. After confirming impedances.

Setting up the Eclipse
The Eclipse comes with pre-programmed protocols so the system is ready to use immediately. Protocols can be created or modified easily to fit your clinical needs. Consult the Eclipse Additional Information manual to learn how to create or modify a protocol. The procedure described below is simply a suggested test process and to be used only as a guideline. 

oVEMP testing procedure
Choose an oVEMP protocol from the dropdown menu 
The oVEMP test should be run in the Manual Mode controlling/selecting stimuli manually. For more collection parameters details, please refer to instruction for use manual.

Manual mode

  1. To begin in manual mode, choose the intensity and select the ear to test on the Record sheet. Instruct the patient to look up and hold their gaze without moving their head.
  2. Next choose Start or press F2.
  3. 100-200 sweeps are typically collected per waveform.

Setting up L & R waveform partners
After collection, choose a left or right ear waveform by double clicking the waveform handle. Next, right click the waveform handle of the opposite ear and select Set as VEMP Partner. The selected waveforms are used in the Asymmetry Ratio Calculation.

EMG scaling
The EMG scaling is not to be used in the oVEMP testing, as there is no contracted muscle as in cVEMP. The reason for gazing up, is not to contract the oblique muscle, but instead to positioning the inferior oblique muscle closer to to the recording electrode.

Marking peaks
The oVEMP response is well documented and is said to be represented by two distinct peaks; N1 occurring at approximately 10 ms and P1 occurring at approximately 15 ms.

Waveforms can be marked from the Record sheet or the Edit sheet. To mark a waveform double click on the waveform handle you would like to mark. Right click and then choose the correct marker. Drag your mouse to the correct area and click. You can also choose 1-4 on the keyboard to bring up the appropriate marker and use Enter to place it.

Example of an oVEMP where N1 and P1 are marked for both ears.

Normative data
A large study investigating the normal characteristics of the oVEMP by Piker and colleagues (2011) defined an upper limit of oVEMP amplitude asymmetry to be 34% (mean + 2 SD).

Example of scaled oVEMP waveforms indicating an abnormal asymmetry ratio between left and right side, along with lowered oVEMP thresholds on the right.

Reporting
Choose the Report Icon 
When complete, choose Save and Exit.


References
Kantner, C., Gürkov, R. (2014). The effects of commonly used upward gaze angles on ocular vestibular evoked myogenic potentials. Otology & Neurotology, 35(2), 289-293.

Jacobson, G. P., McCaslin, D. L., Piker, E. G., Gruenwald, J., Grantham, S. L., & Tegel, L. (2011). Patterns of abnormality in cVEMP, oVEMP and caloric tests may provide topological information about vestibular impairment. J Am Acad Audiol, 22, 601-611.

Murnane, O. D., & Akin, F. W. (2009). Vestibular-evoked myogenic potentials. Seminars in Hearing, 30(4), 267-280. Piker, E.G., Jacobson, G.P., McCaslin, D.L., & Hood, L.J. (2011). Normal characteristics of the ocular vestibular evoked

myogenic potential. J Am Acad Audiol, 22, 222-230.
Sandhu, J. S., George, S. R., & Rea P. A. (2013). The effect of electrode positioning on the ocular vestibular evoked

myogenic potential to air-conducted sound. Clinical Neurophysiology, 124(6), 1232-1236.
Sandhu, J. S., Low, R., Rea, P. A., & Sauders, N. C. (2012). Altered frequency dynamics of cervical and ocular vestibular

evoked myogenic potentials in patients with Meniere’s disease. Otology & Neurotology, 33(3), 344-440.
Watters, K. F., Rosowski, J. J, Sauter, T., & Lee, D. J. (2006). Superior semicircular canal dehiscence presenting as postpartum vertigo. Otology & Neurotology, 27(6), 576-768.

September 2017

The Auditory Brainstem Response (ABR) is an evoked potential that originates at the auditory nerve (Cranial Nerve VIII) and the response is picked up by surface electrodes typically placed at Vertex and Left and Right mastoids. An ABR test is used to assess the auditory system’s function from the cochlea through the brainstem.

The response to auditory broad band or frequency specific stimuli is identified by “peaks” that occur typicallybetween 1 and 15 milliseconds from the stimulus onset. The ABR peaks are measured and marked traditionally as I, II, III, IV, and V. Each peak has an expected latency range to be considered “normal”. Delayed or missingpeaks are consistent with abnormal auditory function. The presence or absence of responses can be used to estimate hearing thresholds. An ABR threshold is an electrophysiological threshold that can be used to predict the behavioral audiogram. The difference between the two may vary quite a lot, but correction of 20dB at 500Hz, 15dB at 1kHz, 10dB at 2kHz and 5dB at 4kHz are typically applied correction factors.

Threshold recording using 2kHz Tone Burst. Note the large PAM response from the right side caused by the loud stimulus of 80dBnHL. The ABR threshold at 20dB nHL at 2kHz found here would be well within the range of normal hearing - applying a typical correction factor would estimate the behavioral audiogram threshold to be 10dBHL at 2kHz.

Improving Threshold testing with Eclipse
Challenges arise when evaluating hearing thresholds. They can include:

CE-Chirp® Stimulus Family
We know that as we get closer to threshold, the waveform latencies increase and the amplitudes decrease. This presents a challenge in “peak picking”. A solution is the implementation and use of the CE-Chirp® LS and NB CE-Chirp® LS. The CE-Chirp® LS Stimulus Family compares to the traditional click while the NB CE-Chirp® LS compares to traditional tone burst. Research indicates that the use of the CE-Chirp LS® and NB CE-Chirp® LS particularly at modest stimulation levels results in waveform amplitudes up to double that of traditional stimuli (Elberling & Don, 2008; Ferm et al., 2013). This is achieved by simply accounting for timing issues within the cochlea. If amplitudes can be increased, the ability of the user to quickly and accurately identify waveform peaks near threshold increases. This clearly reduces test time and increases user confidence. Please see example below.

The larger amplitudes of the CE-Chirp® LS when compared to the traditional Click allows for faster and more reliable testing. Similar benefits can be found when substituting traditional Tone Bursts with the NB CE-Chirps® LS.

Residual Noise Calculation

Noise levels also create a challenge as noise can eliminate the ability to obtain or view the necessary waveform peaks. Lower noise levels increase the ability to identify the waveform peaks and increase the confidence of the presence or absence of a response.

Traditionally, users run a set number of sweeps in an effort to reduce the amount of noise in the recording. However, the number of sweeps may tell us little about the Residual Noise in the tracing. An objective Residual Noise measure should be used instead. Typically, if Residual Noise levels are 40nV or less, the tracing is sufficiently clean to be able to reveal a response if present. Therefore, Interacoustics implemented the Residual Noise calculation. The use of Residual Noise calculation either by monitoring or as a stop criterion greatly improves the certainty. The Residual Noise bar placed on the right side of the Fmp graph indicates the Residual Noise level and will turn green with a checkmark when the criterion for residual noise is reached (e.g. 40nV).

The Fmp value (red curve) has at this point of testing passed the 99% response confidence criteria, and the Residual Noise level (black curve) has not yet reached the 40nV residual noise level suitable for quality recordings around threshold.

Fmp Calculation & Response Confidence
The Fmp is an indication of the Response Confidence of the recorded response. While looking at the waveform being recorded, a confidence level is calculated, and provided as a percentage of statistical certainty of a response being present in the recorded waveform. This statistical analysis assists the clinician in that it can reduce test time since it relies on statistical information and not solely on the experience of the user. The experienced user can encompass the Fmp values when evaluating response presence or absence. Often the Fmp will detect strong responses sooner than confident eyeballing can reach the same conclusion. On the other hand, Fmp may not identify smaller responses close to threshold, in which case eyeballing is to be applied, being the golden standard in response detection at threshold. When the response confidence reaches the set criteria (e.g. 99%) the bar indicating the Response Confidence turns green with a checkmark indicating that the Response Confidence criterion is met.

Bayesian Weighting
In the best testing scenario that one should always try to obtain, the patient will be very quiet or sleeping and the EEG at a constant and low level throughout the data acquisition. This is not always the case and Bayesian Weighting is of great help in such test situations. It is an averaging technique that weighs each sweep individuallygiving more “weight” or importance to quiet sweeps and less “weight” to sweeps with more noise. This is different from traditional averaging since traditional averaging simply accepts or rejects each sweep and not weighing them individually.

The use of Bayesian Weighting will assist the clinician in situations that are not ideal testing conditions, and will not alter the response waveform’s morphology.

A few additional practical hints


The Rearrange Curves and Group Curves functions in the upper tool bar ensure easy manual positioning of waveforms.


The A&B tool in the upper tool bar allows waveform reproducibility to be evaluated without the need to run repeated waveforms.

Important highlights

  • Use eyeballed (or Fmp based) response identification or Noise Level as stop criteria, not a fixed number of sweeps.
  • Use Bayesian Weighting for lowest residual noise.
  • Use CE-Chirp® LS rather than click for larger response amplitudes.
  • Neither Click nor CE-Chirp® LS is sufficient information on which to fit a hearing aid.
  • Use NB CE-Chirps® LS rather than Tone Bursts for larger response amplitudes, when doing the frequency specific testing needed for hearing aid fitting.
  • Consider typically using a relatively fast rate, as the time to get a low noise level rather than wave morphology is of the essence in threshold testing. If in doubt then lower the rate.
  • Spend your time close to threshold rather than trying to obtain overly beautiful responses at loud intensities.
  • Tough filtering (e.g. Low Pass display filtering at 1500Hz) may help eyeballing responses.
  • Consider using the A&B buffers as your reproducibility tool, rather than spending time actually running double sweeps.
  • Remember Fmp is typically not capable of picking out response presence close to threshold, but may be a valuable tool confirming response quickly well above threshold.
  • A typical good threshold practice requires waveforms around threshold to have a residual noise level of 40nV or less, and requires eyeballing of a repeated responses (or similar A&B) at threshold and no visible response just below threshold.

References
Don, M. & Elberling, C. (1996). Use of quantitative measures of auditory brain-stem response peak amplitude and residual background noise in the decision to stop averaging. J. Acoust. Soc. Am., 99(1).

Elberling, C. & Don, M. (1984). Quality Estimation of averaged auditory brainstem responses. Scand Audiol. (13) 187-197.

Elberling, C., & Don, M. (2008). Auditory brainstem responses to a chirp stimulus designed from derived-band latencies in normal-hearing subjects. J. Acoust. Soc. Am. (124) 3022-3037.

Elberling, C. & Wahlgreen (1985). Estimation of auditory brainstem response, ABR, by means of Bayesian interference. Scand. Audiol (14) 89-96.

Ferm, I., Lightfoot, G. & Stevens (2013). J. Comparison of ABR response amplitude, test time, and estimation of hearing threshold using frequency specific chirp and tone pip stimuli in newborns. International Journal of Audiology, (52) 419-423.

July 2016
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