CHAPTER TEN
ABR test
88
ABR test procedure
Electrical noise indicators
The bars on the left of the screen indicate the electrical noise levels. The
lower the test noise the more rapidly an ABR response will be detected.
Electrical noise has multiple sources:
• Interference from other electrical devices (mains/powerline noise)
• Noise from muscle activity (myogenic noise)
• Noise from brain activity (EEG)
The right hand bar (labelled PN) estimates the level of noise from electrical
wiring and other devices. This level is high if there is a lot of interference from
electrical noise and/or one or more of the electrodes is poorly connected (has
high impedance). If impedance levels are acceptable but the PN noise level
remains high try:
• Turning off or moving other electrical appliances (including lights)
• Moving to a different test location
The left hand bar (labelled TN) estimates the total level of noise from
everything except other electrical devices. If this level is high it is likely that
the patient is moving or is not relaxed. Try to settle the subject and ensure
that the neck is supported and muscles are relaxed.
If either level remains high refer to
6.2
ABR test problems
.
Further advice on ...