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