This ABR was acquired using an Intelligent Hearing Systems evoked potentials system. The look of ABRs changes a bit from one company to another.
This first case is to acquaint you with a normal ABR and the completion of the report summary form. Only the ipsilateral traces are shown. The latency of the ipsilateral peaks is written onto the ABR traces, on or near the peaks of the waves. The initial and the trace replication are superimposed. The summation of those two traces is below; the peaks are marked and the latencies are displayed. Note that testing was conducted at two rates: 21.7 and 71.7. (If the 21.7 data were not normal, it would be appropriate to slow the rate further and increase the intensity to determine if clearer runs can be obtained.) Use the 21.7 clicks/second latency data in completing report summary forms.
In the attached PDF document (click on it to open it – you probably need to print it out to enter the data), the left ear latency values are filled in, and one right ear latency was also entered so that you can see how the interaural latency difference is calculated and displayed. Complete the rest of the form. Write in the latencies for the right ear and compute the interaural latency differences. If any of the latencies fell outside the normal range (the normal range is provided in the summary form), then I would advise circling it, to make it stand out on the report.
The form asks you to interpret the number of artifact rejections. That wasn’t shown to you in this first case. Sweeps rejected are one indicator of how much muscle movement contaminated the recordings. In this case, that was not problematic.
The control runs are shown below the stimulus runs in the figure above. In theory, when no stimulus is present, the line should be entirely flat. Of course, in reality, it is never entirely flat. Examine the largest size “humps” in the control run. That is the size of a wave that can happen by chance, without stimuluation. The two rules are
1. Don’t mark a wave that is not at least as large as the size wave seen in a control run
AND
2. The wave must replicate before you mark the wave as present.
(There will be exceptions to this 2nd rule in threshold testing.)
- Please complete the case 1 summary form.