**4. Discussion**

The research is aimed at finding markers of complex pathological processes that occur in COVID-19 and lead to a significant reduction in functional reserves, low stress resistance of the body and as a result - to severe disease and recovery processes in COVID-19. For this purpose (proposed by the authors), the temporal, spectral, correlation analysis of AOG [19–21] was used. The method is based on the adaptation of the mathematical analysis of heart rate variability (HRV) of the electrocardiographic signal [8, 9, 14, 24–34]. to the analysis of variability of the arterial pulsations registered during measurement of arterial pressure by means of the electronic tonometer of BAT 41–2.

The AOG method was developed by the authors for the first time. It is based on the personal experience of scientific researches on morphological, temporal, spectral, correlation analysis of 3500 AOG people of different ages and health conditions. In healthy people AOG was registered at rest and after exposure to various (mechanical, thermal, physical, psychological, etc.) factors. Patients with diseases of the cardiovascular, respiratory and nervous systems were submitted to oscillographic examination [19].

To substantiate the reliability of the results of arterial oscillography, a comparative analysis of the results of mathematical analysis of ECG and AOG synchronously registered at rest (54 people). Cases of strong correlation between Mo, heart rate are obtained. RMSSD (0.97 ± 0.02, p < 0.05) on synchronously recorded ECG and AOG make it possible to conclude that the observed indicators characterize not only the level of control of the heart, but also blood vessels "peripheral heart" [8, 9, 14, 24–34] and confirms the high informativeness of the selected research methods which ECG does not register [19–21].

For this study, we used temporal, spectral, correlation analysis of AOG, conducted and evaluated in 67 patients with severe COVID-19. The results compared with AOG of 28 patients at the closed ward of the psychoneurological hospital and 548 healthy (including 68 people after exercise and after 2 minutes of rest).

In patients with COVID-19, dysfunction, coordination and communication at all (four) levels of regulation of CVS activity, which is a universal indicator of adaptive activity of the whole organism [9]. There was a significant decrease in functional reserves and low stress resistance of the body due to the lack of sympathetic-adrenal response and centralization of body defense control, disruption of communication and coordination at all levels of the adaptive vertical. This is confirmed by the following research results.


*Aplication Arterial Oscilography to Study the Adaptive Capacity of Subject with COVID-19… DOI: http://dx.doi.org/10.5772/intechopen.98570*

	- A. At patients with COVID-19 mechanisms of decrease in adaptive ability of an organism, disturbance of a functional condition of cardiovascular, autonomic, central nervous systems, mental frustration are revealed and proved. The obtained results will help doctors to pay attention to possible variants of mechanisms of development of pathogenetic processes at COVID-19 and to consider them at a choice of means of correction of the noted disturbances and to include in the protocol of diagnosis, treatment and rehabilitation of patients with COVID-19 at inpatient and outpatient stages of treatment.
	- B. Informative and effective application of arterial oscillography (according to D.V. Vakulenko, L.O. Vakulenko), which can be a mean of finding markers of complex pathological processes that occur in COVID-19. It can be used to improve methods of diagnosis, treatment, rehabilitation, control of longterm results of this dangerous disease in clinical and family medicine.
	- C. For implementation in practice new models of electronic blood pressure monitors it is necessary to provide the possibility of using the AOG

method (D. Vakulenko, L. Vakulenko). The device has the ability to record the values of cuff pressure during compression and export the values for further analysis. AOG includes: measurement of blood pressure, sending data to the personal account of VEP-service Oranta-AO, obtaining the results of the analysis in the form of values of indicators and recommendations of the expert system for further decision-making by the doctor.

