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This study aims to investigate the strength of synchronization between the autonomic control loops of the cardiovascular system (CVS) in patients with COronaVIrus Disease 2019 (COVID-19). Methods — We calculated the total percent of phase synchronization index (S index) between the loops of autonomic control of heart rate and vascular tone in two sample groups: healthy individuals and COVID-19 patients. Results — The group-average value of the S index in COVID-19 patients is lower comparing to healthy individuals, the Mann-Whitney U-test confirmed that the differences are statistically significant. Conclusion — Obtained results suggest that the decreased value of the S index reflects the presence of a viral disease, and the S index is a promising basis for non-invasive screening diagnostics of viral diseases, particularly of COVID-19.

This work aims to analyze the coupling between autonomic control loops of blood circulation in patients with Covid-19. In this work, we assessed the degree of coupling between the mechanisms of autonomic control using noninvasive signals of the cardiovascular system - RR-intervals signals and photoplethysmogram signals. Statistical evaluation of the study results using the methods of phase synchronization analysis did not reveal significant differences between the VDPSOH RI SDWLHQWV ZLWK ɋRYLG-19 and healthy subjects of the corresponding age group.

this study presents the results of the spectral analysis of the photoplethysmographic signals obtained from the healthy subjects and the patients with early pre-clinical stages of arterial hypertension, coronary artery disease, and aortic valve stenosis patients. The normalized power density of the low-frequency (LF%) oscillations is significantly higher in the cardiovascular patients, while the normalized power density of the high-frequency (HF%) oscillations and the LF/HF ratio are significantly lower in comparison to the healthy subjects. Aging had no significant effect on the spectral indexes. It was shown that the spectral analysis of the photoplethysmographic signals can be used to diagnose the dysfunction of the autonomic control even at early pre-clinical stages of cardiovascular diseases.

Objective: In this work, the development of the features of an autonomic system of blood circulatory regulation from the period of late prematurity to full-term infants is investigated using the example of signals of the photoplethysmogram of blood vessels, electrocardiogram, and respiration. The previous works of foreign and domestic authors show that interdependency between physiological rhythms emerges early in development. Much attention was paid to the study of cardiorespiratory coupling and his development in newborns, nevertheless, there are still many questions in this area. In this study, in addition to studying the standard low-frequency cardiorespiratory effect, we studied the relationships between the low-frequency components of the autonomic regulation of heart rate (using an electrocardiogram) and the tone of the arterial vessels (using photoplethysmogram of blood vessels).Approach: The goal of the work is to estimate the dynamics of the development of the coupling of the autonomic regulatory circuits of the cardiovascular system and respiratory system. In this paper, special attention is paid to the study of phase synchronization of these processes, as well as to the interaction of frequency components. We studied the coherence between heart rate variability, photoplethysmograms of blood vessels, and respiration signals of newborns with a gestational age of 30 weeks to 40 weeks.Main results: No significant changes in the measure of the estimation of phase synchronization with increases in the gestational age of the infant were found. The reason may be a notable change in the degree of connectedness of the studied systems after birth. There was also an assumption about the presence of changes in the direction of connectedness, but not in its strength.Significance: This study carries a fundamental interest - an understanding of the higher risk for negative results at the end of a premature population. Moreover, the continuation of work in this direction may allow creating a tool for the development of early markers of impaired autonomic regulation of the functions of the cardiovascular system and respiration in young children.

We studied the properties of low-frequency (LF) heart rate variability (HRV) and photoplethysmographic waveform variability (PPGV) and their interaction under conditions where the hemodynamic connection between them is obviously absent, as well as the LF regulation of PPGV in the absence of heart function. The parameters of HRV and finger PPGV were evaluated in 10 patients during cardiac surgery under cardiopulmonary bypass (on-pump cardiac surgery) with or without cardioplegia. The following spectral indices of PPGV and HRV were ertimated: the total spectral power (TP), the high-frequency (HF) and the LF ranges of TP in percents (HF% and LF%), and the LF/HF ratio. We assessed also the index S of synchronization between the LF oscillations in finger photoplethysmogram (PPG) and heart rate (HR) signals. The analysis of directional couplings was carried out using the methods of phase dynamics modeling. It is shown that the mechanisms leading to the occurrence of oscillations in the LF range of PPGV are independent of the mechanisms causing oscillations in the LF range of HRV. At the same time, the both above-mentioned LF oscillations retain their activity under conditions of artificial blood circulation and cardioplegia (the latter case applies only to LF oscillations in PPG). In artificial blood circulation, there was a coupling from the LF oscillations in PPG to those in HR, whereas the coupling in the opposite direction was absent. The coupling from the LF oscillations in PPG to those in HR has probably a neurogenic nature, whereas the opposite coupling has a hemodynamic nature (due to cardiac output).

In this paper, we studied the features of the autonomic regulatory system of the heart rate and the tone of the arteries in newborns. During the experiment, we obtained 15 records of synchronous electrocardiograms and photoplethysmograms of newborns. A spectral analysis was conducted, the results of which revealed a number of features, including the presence of an LF peak at a lower frequency than is common in adult subjects. Based on these results, we have chosen new parameters to assess the degree of synchronization of the autonomic regulatory contours of the blood circulation in newborns, which contribute to the greater significance of the results.

Objective ― The purpose of this paper is to study statistical and dynamic properties of the low-frequency (LF) oscillation synchronization in the heart rate variability (HRV) and the finger photoplethysmographic waveform variability (PPGV) in time. Material and Methods ― Our study included 42 healthy men aged 19-21 years. The HRV and the finger PPGV were simultaneously recorded in all subjects during 7,200 seconds at rest. We extracted the LF oscillations in the HRV and the PPGV. To estimate this synchronization we used the method we suggested earlier. Index S was calculated as the relative time of synchronization between the considered LF oscillations. Results ― The sequence of the synchronization intervals between the LF oscillations behaves as a weakly correlated random process, demonstrating the 1/f distribution. However, the distribution of the index S, estimated even for 10-minute records, is close to normal. The results of estimating the S value from realizations of increasing length indicate that S tends to a fixed value with the increase of time series length. Conclusion ― For practical studies we recommend using the experimental records of ECG and PPG with the length of 10 minutes or more, which will provide a standard deviation of the S estimate less than 10%.

We compare the spectral indices of photoplethysmogram variability (PPGV) estimated using photoplethysmograms recorded from the earlobe and the middle fingers of the right and left hand and analyze their correlation with similar indices of heart rate variability (HRV) in 30 healthy subjects (26 men) aged 27 (25, 29) years (median with inter-quartile ranges) at rest and under the head-up tilt test. The following spectral indices of PPGV and HRV were compared: mean heart rate (HR), total spectral power (TP), high-frequency (HF) and low-frequency (LF) ranges of TP in percents (HF% and LF%), LF/HF ratio, and spectral coherence. We assess also the index S of synchronization between the LF oscillations in HRV and PPGV. The constancy of blood pressure (BP) and moderate increase of HR under the tilt test indicate the presence of fast processes of cardiovascular adaptation with the increase of the sympathetic activity in studied healthy subjects. The impact of respiration on the PPGV spectrum (accessed by HF%) is less than on the HRV spectrum. It is shown that the proportion of sympathetic vascular activity (accessed by LF%) is constant in the PPGV of three analyzed PPGs during the tilt test. The PPGV for the ear PPG was less vulnerable to breathing influence accessed by HF% (independently from body position) than for PPGs from fingers. We reveal the increase of index S under the tilt test indicating the activation of interaction between the heart and distal vessels. The PPGV spectra for finger PPGs from different hands are highly coherent, but differ substantially from the PPGV spectrum for the ear PPG. We conclude that joint analysis of frequency components of PPGV (for the earlobe and finger PPGs of both hands) and HRV and assessment of their synchronization provide additional information about cardiovascular autonomic control.