Monitoring kidney patients by syntactometric EEG analysis

The EEG of seriously ill kidney patients reflects changes in their condition which can be measured quantitatively by a syntactic pattern recognition technique. 128 s of an EEG were sampled at 100 Hz and segmented into 4 sec blocks, each of which was labelled D (or d), T (or t), N (or n), S (or s), or B (or b) depending on the position of its main peak in the power spectrum: delta band (0-4 Hz), theta band (4-8 Hz), alpha band (8-12 Hz), sigma band (12-14 Hz) or beta band (over 14 Hz). The use of capital or small letters depends on the size of the peak A refinement of the method also takes into account the second largest peak. The distance of the resulting 32-character 'sentences' from a pattern is calculated using a string-to-string metric based on weighted insertions, deletions and substitutions (insertions and deletions are included to allow for artefacts detected in the signal). Elementary weights have been assigned on empirical medical grounds taking into account the neurological significance of the various spectral bands and their correlation with the levels of creatinine and urea in the bloodstream.