Neurophysiology of delirium

The objective of this thesis was to characterize the neurophysiology of delirium and to assess whether alterations in the neurophysiology of delirium, could provide opportunities for delirium detection. In the first part of the thesis, it is shown that by the analysis of the electroencephalogram (EEG) and electrocardiogram (ECG) we can expand our knowledge of the neurophysiological characteristics of delirium. Patients with delirium suffer from decreased functional connectivity and loss of small world topology in their EEG when compared to patients without delirium. These findings are consistent with altered functional connectivity and network topology in other diseases that affect cognitive functioning, such as schizophrenia and Alzheimer’s disease. In addition, delirious patients have less complex EEG signals with increased spectral variability. The reduced complexity corresponds with results in Alzheimer’s disease. The analysis of heart rate variability (HRV) derived from the ECG, revealed that that the balance between parasympathetic and sympathetic activity (sympathovagal balance) may not be altered during Intensive Care Unit (ICU) delirium. In the second part of the thesis, the results of studies assessing the opportunities for delirium detection using EEG, eye movements and body temperature were presented. It was described that several EEG parameters were significantly different during delirium compared to non-delirium even when these were measured by only two electrodes and over a short period of time. Furthermore, the number of eye movements, especially blinks, were significantly decreased during delirium and had a longer duration. Moreover, temperature variability was increased in ICU patients with delirium, when compared to ICU patients without delirium.