"Altered Short-Term Dynamics of Cardio-Respiratory Interaction during Propofol-Induced Yawning".

"Cardiac and respiratory oscillations have been shown to interact with each other. This interaction could reflect autonomic nervous system functionality. Propofol-induced yawning during anesthesia induction seems to be associated with sympathetic activation. Presumptively, there is high linearity among interaction of different physiologic system behaviors. Recently, investigators used coherence analysis to quantify the existence and strength of linearity between system signals for study of cardio-respiratory interaction under different physiological conditions. In this investigation, we used a method of time-frequency coherence function to analyze ECG and respiration signals to investigate the linearity of cardio-respiratory dynamics in patients undergoing routine propofol induction procedures for elective surgery. In this prospective, observational clinical study, a total of 84 eligible patients were enrolled. The patients were categorized into yawning and no-yawning groups during propofol induction. During induction, both groups demonstrated significant reduction in high frequency coherence (coh-HF) with simultaneously significant increase in very low frequency coherence (coh-VLF) compared to the pre-induction period. As yawning occurred, the yawning group had more significant changes of cardio-respiratory coherences than the no-yawning group at coh-LF and coh-VLF bands. The yawning group also showed loss of linearity at high frequency band (coh-HF > 0.5) as compared with the pre-induction period, and also showed increases in linearity at low (coh-LF > 0.5) and very low (coh-VLF > 0.5) frequency bands compared with the no-yawning group. Propofol-induced yawning alters cardio-respiratory dynamics with changes of linearity between cardio-vascular and respiratory system behaviors."