Quantification of Subject Wakefulness State during Routine Eeg Examination

The wakefulness state of healthy subjects tends to be an early drowsy state because of the prolonged times required for electroencephalography (EEG) measurements. In such cases, clinicians should consider accurate diagnosis of the wakefulness state of the subjects in order to interpret EEG signals accurately. The aim of the present study was to quantitatively evaluate the wakefulness state (early drowsy or fully awake) of subjects using a novel index for determining the degree of alpha wave prominence and suppression in the time domain over the occipital lobe. This index was based on approximate entropy (ApEn) during routine EEG examination. EEG recordings were acquired from 45 healthy adult subjects in either fully awake or light drowsy groups. ApEn parameters were chosen based on the results that produced a statistical significant difference between the two groups. The proposed index outperformed other best conventional indices used for evaluating the wakefulness status of subjects, including relative delta sub-band power (2-4Hz) (R.δ), relative theta sub-band power (6-8Hz) (R.θ), power ratios between theta and alpha (Pθ/α) and between theta and beta band (Pθ/β) over the occipital lobe. Our proposed index is superior to R.δ, R.θ, Pθ/α and Pθ/β, with 5.6%, 1.1%, 4.5%, and 20% respectively.