Techniques of EEG frequency analysis for evaluation of uremic encephalopathy.

In an effort to provide nephrologists with practical, objective, and quantitative methods for evaluating uremic encephalopathy and the severity of uremia, we investigated five techniques for EEG frequency analysis, the selection of EEG samples for analysis, and the normal values for dominant frequency and the percent of EEG power from one through six Hz. The five techniques consisted of 1. handcounting, 2. use of a tape recorder and sonic analysis system to determine EEG power versus frequency, 3. use of the tape recorder and sonic analysis system to determine EEG voltage versus frequency, 4. on-line measurement of % EEG voltage from one through six Hz, and 5. use of base line crossovers to count the number of waves occurring at each frequency. All techniques were found to be satisfactory. The most significant difference between techniques depended on whether wave amplitude influenced the analysis (techniques 2, 3, and 4) or did not (techniques 1 and 5); in the former case slow wave activity was more evident than in the latter case. Our experience indicated that the determination of relative EEG power from each frequency (EEG power versus frequency or power spectral density) was the most practical and revealing mode of analysis, but any of these techniques would be valid and useful if employed with awareness of the difference in the normal range obtained by different techniques.