Aim of the study is to apply the analysis of phase dynamics to investigation of the coupling patterns between heart rate variability, respiration and peripheral circulation in healthy subjects at rest and after moderate physical exercises. Material and Methods ― 30-minutes electrocardiogram (ECG), photoplethysmogram (PPG) and respiration records were obtained from healthy subjects aged 22±2 (mean ± standard deviation) before and after active Martine Kushelevsky test (20 squats in 30 seconds). The coherence function was estimated between all the signals from each subject, and the phase dynamics modeling was used to detect the directional coupling in high-frequency (HF; 0.14-0.40 Hz) and low-frequency ranges (LF; 0.04-0.14 Hz). Results ― At rest (before the physical activity) no statistically significant couplings were detected between the HF rhythms of respiration and heart rate (RR intervals). For the HF rhythms in respiration and PPG, the influence respirationPPG was detected. No couplings were detected between the LF rhythms. After the moderate physical exercise, predominant direction of the influence was RR intervals PPG in the LF range and both RR intervals respiration and PPG respiration in the HF range. The influence PPG respiration was delayed by several seconds. Conclusion ― adaptation to the moderate physical activity has led to the decrease in the overall coherence and changes in patterns of directional coupling between the LF and HF rhythms in respiration, heart rate and peripheral circulation. The obtained results confirm nonlinearity and complexity of the coupling patterns in cardiovascular system.
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 three 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.
Introduction: Communication systems based on the use of dynamical chaos have a number of positive features. Dynamical chaoshas the properties of random processes, which allows systems based on it to ensure the information transmission confidentiality.However, a quantitative security assessment of such systems is a complicated problem, since the methods for evaluating cryptographicstrength are well developed only for the classical encryption algorithms. Purpose: Development of a method for quantitative estimationof confidentiality of a binary signal hidden transmission in a communication system based on a chaotic time-delay oscillator withswitchable delay time. Results: A method is proposed for estimating the confidentiality of a binary information signal transmissionin a communication system using a chaotic time-delay oscillator with switchable delay time as a transmitter. The method is based onestimating the power of the key space for the chaotic communication system under study. We have considered the cases when sometransmitter parameters are known, and the most general case when all the transmitter parameters are unknown. A communicationsystem based on dynamical chaos may have a much higher confidentiality than the classical cryptographic algorithm using a cipher witha key length of 56 bits, but is significantly inferior in terms of cryptographic strength to a cipher with a key length of 128 bits. Practicalrelevance: The proposed method allows us to obtain a quantitative estimation of confidentiality of communication systems based ondynamical chaos, and compare it with the known strength of classical cryptographic algorithms.
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