Aim -Investigation of features of interaction between the loops of autonomic control of heart rate and vascular tone under the ataractanalgesia and spinal block. Material and Methods -The contemporary nonlinear methods developed for the analysis of complex non-periodic signals were applied to the study of electrocardiogram (ECG) and photoplethysmogram (PPG) signals from women during minor gynecological operations. The registered signals were the single-channel ECG at the II standard lead and

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... ee channels of PPG (from earlobe, right ring finger, and right second toe). These signals were recorded under resting conditions at 60 minutes before the surgery and during the main stage of operation under the spinal anesthesia and ataractanalgesia. The signals were sampled at a frequency of 250 Hz and filtered in the 0.05-0.15 Hz band, which includes the rhythms of autonomic control of heart rate and vascular tone. Results -The analysis of phase dynamics of the studied oscillatory systems revealed that the spinal anesthesia suppresses the coupling between the rhythms of autonomic control of heart rate (extracted from ECG) and vascular tone (extracted from PPG) but in a less degree than general anesthesia induced by ataractanalgesia. The strength of the detected coupling between the heart rate variability and PPG depends on the distance between the body parts from which the ECG and PPG signals were recorded. The coupling was found out to be stronger for smaller distances. Conclusion -The obtained results may have not only diagnostic, but also prognostic importance for the estimation of circulatory failure during operations under surgical anesthesia.