D-0103906-D – 2019/03 Page 2 of 5
Lead is sometimes soldered onto the reusable cup electrodes by a hospital to improve their conductivity;
producing lower impedances. Reusable electrodes containing lead are not supplied, because of the
hazardous nature of lead.
Reducing Noise
1. Test Room Parameters
The test room and location of the room can greatly effect ABR recordings.
The following test room parameters should be aimed for:
- A magnetically shielded booth/room (if possible)
- A quiet or soundproofed booth or sound treated room. This ensures the patient can relax without
disturbances and the stimulus noise is not masked by background noise
- Use of a dedicated ground (isolated socket) for the ABR equipment
- Lights and other equipment not being used should be turned off or unplugged as the patient can work
as an antenna and picks up electrical interference from these sources
- Separate equipment cables to reduce interference (e.g., braid electrode cables, keep electrode cables
and transducer cables away from each other)
In some cases, it may be necessary to find another test location if there is too much ambient or electrical
noise in the current test room.
Try moving the test bed within the room. It may be placed unknowingly, adjacent to a wall that has
hidden cables and electrical sources.
2. Patient Instructions
The quality of the ABR recordings depends highly on the state of the patient. If the patient is not
physically/mentally relaxed, more unstable, noisy recordings will be seen.
Instruct the patient so that:
- They are relaxed and calm
- Their eyes are closed and that their face and jaw muscles are relaxed
- They are lying down on a comfortable bed or reclining in a comfortable chair. The duration of an
ABR test can be long, so ensure that the patient is as comfortable as possible (use pillows and
blankets as needed)
Note An upright sitting position should be avoided due to contracted neck/head muscles.
- Turn off lights in the test room to avoid electrical interference and to help the patient to relax/go to
sleep. Sleeping during recording will provide the lowest noise from the patient, so a sleeping state is
preferred if possible
- Test infants and children during sleep is recommended as they cannot be instructed to or find
it difficult to relax for the entire test duration
It is important to try and use the same test conditions and parameters for each test when comparing
results.
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