Search

Many authors emphasize the fundamental and practical importance of investigation of the low-frequency rhythm in the brain and cardiac signals that correlate with the activity of the autonomic control of circulation. However complexity, nonstationarity and high nonlinearity of the system complicate the research and require application of the specialized methods. This study aims to compare the methods of coupling detection that were adapted to the detection of coupling between the loops of autonomic control of circulation. The analysis of the data from healthy subject demonstrated that the methods based on the analysis of phase dynamics and coherence function calculations are adequate for the investigation of coupling patterns in the autonomic control of circulation. However the results of both methods require the control of statistical significance.

Background ― Effective treatment of melanoma is only possible during the early stages of the disease. However, current techniques of cancer diagnostics are not sensitive enough to be reliable during the early stages. Photoacoustic cytometry provides a very perspective method for early diagnostics, which, in principle, can detect even a single melanoma circulating melanoma cell. However, the photoacoustic monitoring system needs to be paired with an effective automated algorithm, which will detect acoustic responses from melanoma cells among normal blood cells. Objective ― The study aims to compare the currently adopted algorithm for the detection of circulating melanoma cells based on a calculation of the standard deviation of the acoustic responses with the new model-based algorithm. Methods ― We tested and compared two different methods of automated detection of melanoma acoustic responses. The first approach was based on a calculation of the deviation of the acoustic responses. The second approach was based on the subtraction of the ensemble average normal acoustic response from melanoma acoustic responses. The resulting differential signals contained positive spikes, which were detected. Results ― The model-based approach demonstrated better sensitivity and specificity when detecting circulating melanoma cells in comparison to the approach based on the calculation of standard deviation of the acoustic responses. Conclusions ― Obtained results suggest that the model-based approach is a more reliable basis for an automated algorithm for the detection of circulating melanoma cells. The model-based approach has an additional advantage of being simpler to calculate and requires less computational power to run in real-time.

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 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.

The goal of our study was to investigate gender-related specificities of photoplethysmogram (PPG) spectral assessment dynamics in healthy individuals during the passive tilt test. Material and Methods — The study involved 38 men (33±7 years old) and 15 women (27±8 years old). The PPG signal was recorded for 10 minutes in the horizontal and vertical positions of the human body (passive tilt test). The following spectral parameters of PPG were calculated: HF%, LF%, and LF/HF. Results — In the horizontal body position, men had significantly higher values of the LF% index. In the course of the passive tilt test, an increase in HF% was observed by almost 1.5 times in men and by more than 5 times in women. Significant differences in the values of vegetative indicators were achieved: in women, HF% values exceeded those in men, while LF% values were noticeably lower. Conclusion — Men displayed signs (assessed by LF%) of augmented sympathetic activity, relative to women, at all stages of their passive tilt test. During the transition from the horizontal to the vertical position, a significant increase in respiratory influences (assessed by HF%) on PPG signal components was established, which was more pronounced in women.

An original method for reconstruction of time-delay systems parameters from time-series was tested on a radiophysical chaotic generator with quadratic nonlinearity and on a periodic radiophysical model of baroreflectory control of the mean arterial pressure. The method in question is based on analysis of synchronous response of the driven system. It was shown that parameters of chaotic generator can be reconstructed (the error is less than 1%) from a time-series which length was less than 2 delay times. The parameters of the periodic model were reconstructed from a time-series which length was 10 delay times.

In many cases, cancers are detected only after they have become untreatable due to development of deadly metastasis. Most treatment is more effective at early cancer stages. We explore early cancer diagnosis at singe cell levels by their irradiation with short laser pulses followed by time-resolved detection of laser-induced acoustic waves. We explored the viability of correlation analysis for analysis of acoustic responses. It was estimated that correlation between cancer cells responses is 0.86±0.06, while correlation between cancer cells responses and responses from human blood is - 0.05±0.06.

Background ― The treatment of the cancer, especially in more aggressive metastatic forms is more effective at early disease stage. However, existing diagnostic techniques are not sensitive enough for early cancer detection. An alternative, perspective diagnostic approach can be based on photoacoustic (PA) method of irradiation of cancer cells in biotissue, blood and lymph by laser pulses. The fast thermal expansion of heated zones into cells associated with intrinsic or artificial PA contrast agents leads to generation of acoustic waves detected with ultrasound transducers. In particular, melanoma cells with melanin as a PA marker are darker than normal red blood cells and, therefore, produce greater acoustic responses. This technique can theoretically detect even a single cancer cell in the tissue and blood background; however, a robust algorithm of automated response detection is yet to be developed. Objective ― The main aim is to develop the approach for data pre-analysis that can improve the sensitivity and noise resistance of the automated in individual cancer cell detection algorithm, based on estimation of the amplitude of the acoustic responses. Methods ― Acoustic responses were obtained from a round polyurethane tube with human blood, or solution of the mouse melanoma cells in 10 mol/L concentration. In control experiments the laser was blocked by an opaque film. Many (up to 1000) acoustic responses were obtained from normal blood cells and pigmented cancer cells. Spectral analysis of the acoustic responses was used to find the spectral ranges that provide valuable diagnostic information with the sufficient signal-to-noise ratio. Results ― It was estimated that relevant diagnostics information in the acoustic responses is limited to the 0-12 MHz frequency band. Application of the 8th order low-pass Butterwort filter with 12 MHz cut-off frequency improved the signal-to-noise ratio from 21.14±10.39 to 110.81±56.94 for the cancer-related responses, and from 1.04±0.1 to 2.23±0.33 for the normal blood responses. Conclusions ― Adoption of low-pass filtering during the pre-analysis of acoustic responses results in better sensitivity of automated cancer cells detection algorithm.

A mathematical model is proposed for the autonomic control of cardiovascular system, which takes into account two separated self-exciting sympathetic control loops of heart rate and peripheral vascular tone. The control loops are represented by self-exciting time-delay systems and their tone depends on activity of the aortic, carotid, and lower-body baroreceptors. The model is used to study the dynamics of the adaptive processes that manifest in a healthy cardiovascular system during the passive head-up tilt test. Computer simulation provides continuous observation of the dynamics of the indexes and variables that cannot be measured in the direct experiment, including the noradrenaline concentration in vessel wall and heart muscle, tone of the sympathetic and parasympathetic control, peripheral vascular resistance, and blood pressure. In the supine and upright positions, we estimated the spectral characteristics of the model variables, especially in the low-frequency band, and the original index of total percent of phase synchronization between the low-frequency oscillations in heart rate and blood pressure signals. The model demonstrates good quantitative agreement with the dynamics of the experimentally observed indexes of cardiovascular system that were averaged for 50 healthy subjects.

Study aims to adopt the cross-recurrence analysis for detection of coupling between the loops of sympathetic regulation of cardiovascular system. To test the applicability of the method and to set its parameters it was applied to the mathematical model of cardiovascular system that has a structure similar to the structure of the real system. To investigate whether the cross-recurrence analysis reflects the dynamics of autonomic control the authors conducted four numerical experiments with gradually decreasing activity of sympathetic regulation. No correlation was found between the results of cross-recurrence analysis and the coupling strengths.

The aim of study is to investigate effectiveness of cross-recurrence analysis for the detection of coupling between the loops of heart rate and vessel tone sympathetic control. The cross-recurrence analysis is applied to the interbeat intervals and photopletysmographic signals from the mathematical model of cardiovascular system and from adults and newborn children. The model is examined under the conditions of the four experiments: with fully operational autonomic control, autonomic control weakened by 40%, autonomic control weakened by 70% and autonomic blockade. The coupling is most pronounced in adult subjects and the model with fully operational autonomic control, while it is absent under the autonomic blockade. Autonomic control is also not fully developed in newborn children. As the result, smaller coupling strength is expected. The results of cross-recurrence analysis of the model and experimental data are compared with the results of coupling detection based on the analysos of phase synchronization. Synchronization index demonstrates good correlation with the coupling strength in the model and weak coupling in newborn children in relation to adult subjects. In both cases, no correlation is observed between the synchronization index and the results of cross-recurrence analysis.

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.

We proposed a method of experimental observation of the Arnold tongues in the study of the synchronization of the contours of autonomic regulation of the heart rate with a characteristic frequency of about 0.1 Hz and respiration. The formulation of a special active experiment made it possible to determine the boundaries of synchronization tongues in 3 subjects. The method allows noninvasive research. The basic idea is to influence the contours of heart rate regulation with a respiratory signal, which has respiratory frequency varying linearly about 0.1 Hz according to the sound signal generated by a special device. The amplitude of the breath is changed by the subjects at the command of the researcher. The study is important for understanding the features of complex multichannel systems of biological nature and their mathematical modeling.

The features of the individual dynamics and interaction of the elements of the autonomous regulation of blood circulation and blood flow fluctuations in the microvasculature of the skin were investigated. Phase synchronization of the laser Doppler flowmetry signal with processes of autonomic regulation is revealed. This may indicate the effect of vegetative regulation on the myogenic range of laser Doppler flowmetry.

A model of human cardiovascular system is proposed which describes the main heart rhythm, the regulation of heart function and blood vessels by the autonomic nervous system, baroreflex, and the formation of arterial blood pressure. The model takes into account the impact of respiration on these processes. It is shown that taking into account nonlinearity and introducing the autonomous loop of mean arterial blood pressure in the form of self-oscillating time-delay system allow to obtain the model signals whose statistical and spectral characteristics are qualitatively and quantitatively similar to those for experimental signals. The proposed model demonstrates the phenomenon of synchronization of mean arterial pressure regulatory system by the signal of respiration with the basic period close to 10 seconds, which is observed in the physiological experiments.

An original method is proposed for reconstructing the parameters of a oscillator operating in periodic modes with delayed feedback. It is compared to other methods by analyzing the time series of a system of biological nature in the presence of dynamic and measurement noises. Our method has advantages in analyzing data sensitive to measurement noise.

We proposed the model of cardiovascular system which describes the sinus rhythm, autonomic regulation of heart and arterial vessels, baroreflex, arterial pressure and respiration process. The model included a self-oscillating loop of regulation of mean arterial pressure. It was shown that suggested model more accurately simulated the spectral and statistical characteristics of heart rate variability signal in comparison with the model proposed earlier by Seidel and Herzel.