Fig. 1From: Time-trend analysis of the center frequency of the intrinsic mode function from the Hilbert–Huang transform of electroencephalography during general anesthesia: a retrospective observational studyAn EEG signal and its mean with the upper and lower envelopes This EEG signal was obtained from a 28-year-old woman during the anesthesia maintenance phase. The length and the sampling rate were 8 s and 128 Hz, respectivelyBack to article page