Analyzing autonomic activity in electrocardiography about general anesthesia by spectrogram with multitaper time-frequency reassignment

Autonomic nerve activities in human body under general anesthesia are dynamic and diverse. Respiratory sinus arrhythmia is associated with depth of anesthesia, which exists in the high-frequency region of RRI (beat-to-beat R-peak interval) spectrum. Analyzing RRI variation in electrocardiography by classical power spectrum is insufficient because of the lack of temporal resolution. To better understand autonomic activity during anesthesia, we used spectrogram of RRI to extract its instantaneous information. For improving visual resolution, we choose a newly developed technique, multitaper time-frequency reassignment (MTFR), to estimate spectrograms. The technique provides time-varying spectrogram for RRI with good performance in time-frequency resolution and low fluctuation. Real-life cases are used to demonstrate the variety of autonomic activity presented clearly by the MTFR spectrogram, compared with Gabor spectrogram. Their implications in depth of anesthesia are discussed.