In general, anesthetic depth is evaluated by an experienced anesthesiologist based on changes in blood pressure and pulse rate. Therefore, it is difficult to guarantee the accuracy of an evaluation of anesthetic depth. Efforts to develop an objective index for evaluating anesthetic depth have continued, but little progress has been made in this area. The information on the activity if sympathetic and parasympathetic nervous system is provided by heart rate variability, and almost all anesthetics depress autonomic activity. Novel monitoring systems that can simply and exactly analyze the autonomic activity of the cardiovascular system will provide important information for the evaluation of anesthetic depth. We investigated anesthetic depth during the following seven stages: pre-anesthesia, induction, skin incision, before extubation, after extubation, and post-anesthesia. In this study, temporal, frequency, and chaos analysis methods were used to analyze the HRV time series from an electrocardiogram signal. NN10-NN50, mean, SDNN, and RMS parameters were used in the temporal method. For the frequency method, LF, HF, LF/HF ratio, 1/f noise, alpha1, and alpha2 of DFA analysis parameters were examined. In the chaos analysis, CD, entropy, and LPE were used. The chaos analysis method was valuable to estimate the anesthetic depth as compared with the temporal and frequency methods. This is likely because the human body shows chaotic characteristics.
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