The original objective of this work was to verify the possibility of using electrical pulsatile cerebral impedance measurements as a diagnostic aid for assessing the brain-death condition in adults; a subordinate target was to validate a simple method for detecting perfusional changes in the brain. To this end, impedance signals were recorded, for a comparative study, from both live subjects and brain-dead patients, using a simple four-electrode arrangement. Rather unexpectedly, pulsatile transcephalic impedance waveforms exhibiting a temporal dependance similar to those of live subjects were detected in artificially ventilated, cerebrally dead, adult subjects; distributions of the time delays between impedance peaks and ECG peaks were also recorded for the two groups (dead and live subjects). These data provided no evidence, at the 1% significance level, against the hypothesis that the two sample groups are drawn from identical populations. The detection of impedance variations from brain-dead patients can be explained by the residual persistence of blood flow through the scalp, by mechanical variations synchronous with the heart beat and by the presence of the oscillating flow and the systolic spikes that precede the final blood flow arrest. The fact that impedance variations can be traced back to a multiplicity of causes, unrelated to the normal unidirectional flow, renders the transcephalic impedance method inappropriate for detecting cerebral perfusion changes in adults. This conclusion is also strengthened by some theoretical results recently derived from a multilayer model of the head.

This prospective study was planned to assess whether quantitative EEG (qEEG) can give an estimate of the timing of achievement of three endpoints (loss of activities of daily living, incontinence, and death) in 72 consecutive patients (53 females, 19 males; mean age, 70.8) affected with probable Alzheimer's disease, as defined according to the NINCDS-ADRDA criteria. Power-weighted, log-transformed relative values of the four conventional EEG bands were considered in a central-posterior temporal region for each hemisphere. The hypothesis was tested by the lifereg procedure of the Statistical Analysis System package (first significance level accepted, P < or = 0.01). Because patients were in different stages of the disease, the statistical analysis was performed in the entire group as well as in the subgroup of 41 patients (mean age, 69.6) with mild dementia (scoring 3 or 4 on the global deterioration scale). In the whole group, the loss of activities of daily living was predicted by delta power in either side (P = 0.01), incontinence was predicted by alpha power in the right side (P < 0.01), whereas the statistical significance was not reached for death (P < 0.05). In the subgroup of mild demented patients, the loss of activities of daily living was predicted by delta power in the left side (P = 0.01), incontinence by both delta (P < 0.01) and alpha (P < 0.001) power in the right side, and death was not significantly predicted (P = 0.08). Quantitative EEG is a low-cost, discomfort-free technique which may be used to obtain information on the timing of disease evolution. The results showed in mild Alzheimer's disease appear especially interesting to attempt a prediction of the future time course of the disease from its beginning.

In the present study, quantitative electroencephalographic (EEG) analysis was performed at rest and during photic stimulation (5, 10, and 15 Hz) in nine patients with presenile dementia of the Alzheimer type (AD; mean age at onset, 55 years) and nine sex- and age-matched control subjects. Compared with the normal controls, the AD patients had a significantly lower alpha-2 and beta band power in the resting EEG as well as a significant increase in delta and theta band power. EEG analysis during photic stimulation demonstrated that the AD patients had a significantly lower EEG power during photic stimulation for the alpha (9.8–10.2 Hz) and beta bands (14.8–15.2 Hz) corresponding to photic stimulation at 10 Hz and 15 Hz, respectively. In addition, when we examined EEG changes from rest to the stimulus condition, the AD patients were found to show significantly smaller changes in EEG power mainly over the posterior regions, irrespective of the stimulus frequency. These findings provide evidence that AD patients have EEG abnormalities in both non-stimulus and stimulus conditions, and suggest diminished EEG reactivity to photic stimulation.