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.

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Currently, vegetative dysfunction considered to be one of principal mechanisms in the pathogenesis of cardiovascular pathology, which causes a cascade of events leading to changes in the properties and a structure of vascular wall. This review article contains literature from various databases (Russian science citation index, PubMed, Google Shcolar, Scopus). It presents the methods for assessing vegetative imbalance. In particular, the method of photoplethysmography (PPGV) is considered for recording periodic fluctuations at various frequencies in the distal vascular bed which characterize physiological processes (cardiac activity, respiratory influences, neurogenic, myogenic and endothelial activity). In addition, other diagnostic capabilities of PPGV such as heart rate (HR) assessment, determining the properties of vascular wall and the level of blood saturation are elucidated. This paper demonstrates a wide range of PPGV applications. The simplicity of PPGV reproduction and its cost-effectiveness make it feasible both in routine clinical practice for the purposes of screening for cardiovascular pathology, and for individual health monitoring incorporated in smart devices.

The purpose of this work is to study the interaction between the autonomic regulatory loops of blood circulation from long time series. Methods ― We simultaneously recorded four-hour signals of electrocardiogram and photoplethysmogram from the ear and finger of ten healthy adults. We determined the intervals of phase synchronization of the studied regulatory loops and analyzed the dependence of their length on the recording time. The deviations of the total percentage of phase synchronization (index S) from its mean value were estimated in moving non-overlapping windows. Results ― For studied signals we found no significant correlation between the length of synchronization epoch and the time of its beginning. A sharp increase in the deviation of the index S from its mean was shown at the end of the experiment. Conclusion ― The increase in the deviation from the mean at the end of our records is most likely associated more with psychosomatic influences than with hormonal regulation or immobilization stress.

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.

Aim: to compare the results of examination conducted among oil and gas refinery employees, obtained during yearly periodic medical examination with the results obtained during cardioscreening. Material and Methods – 47 employees (64% - men, mean age 52 ± 8 yrs) of large oil and gas refinery were examined by cardiologist in 2018. Six months before the cardioscreening all employees underwent yearly periodic medical examination. The data of anamnesis, laboratory and instrumental findings (blood glucose, lipids, ECG) of examinees were analyzed. Revealed risk factors, the levels of risk SCORE, diagnosis and recommendations made during periodic medical examination and during cardioscreening were compared. Results – In the studied group dyslipidemia was observed in 39 employees (83%). Elevated blood glucose was revealed in 30 examinees (64%). Left ventricle hypertrophy on ECG was determined in 6 patients (13%). Hypertension was diagnosed in 35 subjects (75%) by cardiologist vs 26 subjects (55%) by therapeutist, diabetes mellitus was diagnosed in 8 (15%) vs 4 (8,5%) subjects by cardiologist and therapeutist correspondingly, smoking – in 20 (43%) and 16 (34%) of employees correspondingly (p < 0,001). Mean systolic BP was 152±20 mm Hg during cardioscreening versus 133±24 mm Hg during periodic medical examination (p < 0,001). High and very high risk SCORE have had 26 subjects (55%) according the data of cardiologist and 15 subjects (32%) according the data of therapeutist (p < 0,001). Conclusion – In the companies with abusive working conditions it is necessary to distinguish high and very high cardiovascular risk groups by means of cardioscreening.

We performed a mathematical analysis of functional connectivity in electroencephalography (EEG) of patients with obstructive sleep apnea (OSA) (N = 10; age: 52.8 ± 13 years; median age: 49 years; male/female ratio: 7/3), compared with a group of apparently healthy participants (N = 15; age: 51.5 ± 29.5 years; median age: 42 years; male/female ratio: 8/7), based on the calculation of wavelet bicoherence from nighttime polysomnograms. Having observed the previously known phenomenon of interhemispheric synchronization deterioration, we demonstrated a compensatory increase in intrahemispheric connectivity, as well as a slight increase in the connectivity of the central and occipital areas for high-frequency EEG activity. Significant changes in functional connectivity were extremely stable in groups of apparently healthy participants and OSA patients, maintaining the overall pattern when comparing different recording nights and various sleep stages. The maximum variability of the connectivity was observed at fast oscillatory processes during REM sleep. The possibility of observing some changes in functional connectivity of brain activity in OSA patients in a state of passive wakefulness opens up prospects for further research. Developing the methods of hypnogram evaluation that are independent of functional connectivity may be useful for implementing a medical decision support system.

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