Electrophysiological Tests Course (RHS 428)
Brainstem Evoked Response Audiometry (BERA) Lab
Compass II (Nicolet Biomedical Inc.)
To introduce students to the ABR procedure.
To assist student to interpret ABR results.
Turn the computer on
From the desktop, double click on the folder (EP 317) to open ABR software.
Start preparing your patient (you patient should be laying down on a bed or sitting on a comfortable chair with his/her head and neck supported and in a relaxing position.
Squeeze a bit of abrasive gel (prepping gel) onto a cotton pad and rub gently at placement sites to remove dead skin.
Use alcohol swaps to clean placement sites.
Apply a small amount of the conductive gel(EEG paste) to the electrodes
Attach the electrodes to placement sites carefully using medical tap without touching the placement site with your fingers.
We will be using 1 channel recording, so 3 electrodes should be coming from the pre-amplifier and be attached to the patient's head as follows:
Cz = high forehead, input 1 (+) noninverting /active electrode to channel 1
A1= mastoid of tested ear (TE) = LE, input 2 (-) inverting/reference electrode to channel 1
A2 = mastoid of nontested ear (NTE) = RE, ground/common
Instruct your patient as follows: "this test requires you to be as quiet as possible, we want you to close your eyes and try to relax as much as you can and if you like to take a nap that’s ok we will wake you up when we are done"
Put the headphones on your partner's ears; make sure that you don't change the electrodes positions.
From the main menu, go to “File”, “File Select”, under file name; enter your patient’s name, press “Esc” to save and exit this window.
A new window should open showing the following:
File:C/EP/your patient name.EP
From the main menu, go to "Parameters" then "collection parameters".
Keep all settings as they are, only disable channel 2 (type the letter "d" from the keyboard) because we will be doing only 1 channel recording.
Change the intensity level to 70 dBnHL, change the ear to L (type L), press "Esc" to save and exit this window.
After you make sure that all the three electrodes have been properly connected, test electrodes for skin resistance (impedance), do the following to check impedance:
From the main menu, press "collect", then "impedance"
Impedance values should be less than 10 kΩ (ideally less than 5 kΩ) at each site electrode
Interelectrode difference should not be greater than 2 kΩ
If your values are high, remove the electrodes and re-scrub and re-clean to improve conduction
Record your impedance values before testing begins
When impedance values are ok, press "Esc" to exit this window
From the main menu, go to "Analyze", then “Start”: pt. should be hearing the stimulus now.
Down on the right side of the screen, you will see "Avg", click on it to change it to "1Avg" then at the top of the screen click on “1Pause” to change it to “Pause” to start averaging (ABR recording should start now).
Watch the no. of averaging running at the middle bottom of the screen, recording will stop automatically when no. of averaging reaches (1024).
If noise level is high (EEG activity is high) you can decrease the gain from the right side of the screen under "more functions", the more you click on it, the more it will decrease the gain (not the effect of decreasing the gain on EEG waveform "smoothing effect")
When the averaging is finished, the ABR recording at this particular intensity is completed and the waveform will disappear.
To bring back your first recording (Record 1), from the top menu, go to "load".
A new screen will open for you, click on "Record 1", "channel 1" and "load".
"Record 1" should come up in the testing screen, you can activate your waveform by selecting it, in the top of the screen, below the main menu, click on A1, it should become ¹A
1.Then you can move the cursor by the keyboard arrows to start marking your waves, when you locate your wave peak, from the top menu, click "Mark" and select your waveform number (I, II, III, IV or V)
To display waveform absolute latency, from the main menu, click on "Display", "Information Window", "Marked Point" then record the latency of each wave.
To display waveform interpeak latencies, from the top menu, click "Display", "Information Window", "Interpeak Calculations", record the interpeak latencies.
Perform another ABR recording using lower intensity level (50 dBnHL), use the same steps you used to perform the 70 dBnHL recording.
Press “Esc” to exit the testing window, the main menu window will come, select “Parameters”, then “ Collection Parameters”, change the intensity to 50 dBnHL.
Re-check your impedance values before you run the test.
Mark all ABR waveforms. Record all absolute latency values and interpeak latency values. Make sure that the printer is on and it has papers.
After arranging your records, go to the testing window, from the top menu, to “Print” , “all waves”, it should print out your waveforms, absolute and interpeak latency values, amplitude values and other test information. Please attach your printed results along with your lab assignment papers.
If you want to delete a certain record, select the record, from the right side of the testing screen, go to “More Functions”, “ erase”.
Remove electrodes from your patient. Clean electrodes sites.
Detach electrodes from equipment, remove any excessive gels from electrodes heads, wash electrodes heads (only the heads, not the wire) with water and little bit soap, please hang electrodes to dry.
Keep pressing "Esc" until you completely exit (EP 317) software.
Shut down the computer and the monitor.
Lab Assignment Requirement
Brainstem Evoked Response Audiometry (BERA) Lab
Print out all your marked ABR waveforms.
Print out all ABR waves absolute latencies and interpeak latencies.
What electrode impedance values and interelectorde impedance difference values did you get before you run your ABR test, for both recordings (70 & 50 dB nHL)? Comment on these values.Comment on your patient ABR recordings, discuss your results.