Analysis and classification of nasopharyngeal electroencephalogram in "brain death" patients.

Nasopharyngeally-derived electroencephalogram (EEG) was recorded and digitized in 12 "brain death" subjects with flat-line scalp EEG and loss of auditory brain stem response. The nasopharyngeal EEGs of these cases were classified into three types: Type Ia with complete flat-line, Type Ib with almost but incomplete flat-line EEG, and Type II with low-amplitude slow fluctuations. Digitization of the nasopharyngeal EEG showed that equivalent electric potentials in low frequency bands (delta and/or theta 1) remained within the values of healthy volunteers in Types Ib and II. These results suggested that the tissue in or around the brain stem still functioned in Type 1b and II "brain death" patients. The origin of nasopharyngeal EEG was also discussed in this paper.