The Poincaré graph is a scatter plot: the values of the current RR interval are plotted on the abscissa, and the next RR values are plotted on the ordinate axis. The form of the Poincaré graph is categorized into several functional classes (Fig. 8).

**Fig. 8. Examples of Poincaré plots (the maps show the points with the coordinates Ri Ri + 1 and Ri + 1 Ri + 2 intervals) used to assess the qualities of the sequence of RR intervals: the graphs (a) – (d) are a carefully edited sequence of RR intervals (sinus rhythm); (e) – (j) – records of patients with cardiovascular diseases (Stein**

The Poincare chart contains both generalizing information on heart rate variability and detailed information on its change from systole to systole. The Poincaré chart intersects the line of identity from bottom to top. The position of the point on the line of identity means that the heart rhythm (the duration of the RR intervals) did not change during 2 contractions (

**Figure 9. Method for calculating HRV indices based on the Poincaré graph. Regarding the centroids (average of the RR interval), an ellipse is constructed, whose width is denoted as SD1 (standard deviation perpendicular to the central axis), and length – SD2 (standard deviation along the central axis) (Stein**

Thus, the line of identity is a graph of the function x = y (RRn = RRn + 1). If the point is located above the line of identity, then this means that x

For diagnostics of the functional state, integral indicators are used, calculated on the basis of heart rate variability measures. One of these indicators of the general state of the body is an indicator of the activity of regulatory systems. This indicator is calculated in points based on statistical indicators, histogram indicators and spectral analysis data.

PARS is calculated according to an algorithm based on five criteria:

1. The cumulative effect of regulation in terms of heart rate (PE).

2. Total activity of regulatory mechanisms by the standard deviation (or total spectral power).

3. Vegetative balance on a set of indicators: SI, RMSSD, HF, IC.

4. Activity of the vasomotor center regulating vascular tone (estimated from the power of slow waves of the first order – LF).

5. Activity of the cardiovascular subcortical nerve center, or suprasegmental levels of regulation. These structures regulate vascular tone, and their activity can be assessed by the level of VLF.

The resulting PARS values are expressed in points and range from 1 to 10. Based on these points, the following functional states can be diagnosed:

Based on the analysis of PARS values, the following functional states can be diagnosed:

The state of optimal tension of regulatory systems necessary to maintain the active balance of the organism with the environment (norm, PARS = 1-2).

The state of moderate tension of regulatory systems, when the body needs additional functional reserves to adapt to environmental conditions. Such conditions arise in the process of adaptation to work, under emotional stress or under the influence of adverse environmental factors (PARS = 3-4).

The state of marked tension of regulatory systems, which is associated with active mobilization of defense mechanisms, including increased activity of the sympathetic-adrenal system and the pituitary-adrenal system (PARS = 4-6).

The state of overstressing regulatory systems, which is characterized by a lack of protective and adaptive mechanisms, their inability to ensure an adequate response of the body to environmental factors. Here, excessive activation of regulatory systems is no longer supported by the corresponding functional reserves (PARS = 6-8).

The state of exhaustion (astenisation) of regulatory systems, in which the activity of controlling mechanisms decreases (insufficiency of regulation mechanisms) and characteristic signs of pathology appear. Here, specific changes clearly prevail over non-specific (PARS = 8-10).

**Fig. 10. Rhythmograms recorded in one person at rest (left half) and under stress (right half). A is the sequence of RR intervals in the quiet period, B is the sequence of RR intervals with; C and D are the corresponding scattergrams; E, F, G, I – histograms characterizing the distribution of points on the Poincaré graph**