−p < 0.05 in between the indices in the 2nd and 3rd phases.

**Table 2.** Indicators of central hemodynamics at regulated respiration (6 times/min) in different phases of the biological cycle.

The reactivity of all indicators in regulated breathing significantly changed in the III phase compared with the 1st and 2nd phases. No changes occurred in the significance of ATs in all phases, but SI significantly changed in the 3rd phase.

Thus, the major changes in the state of central hemodynamics in the rest of the lying were observed in the luteal phase of the OMC, which disappeared in various loads on the body (respiration 6 times/min, orthopedic, and psychoemotional load).

The cardiovascular system of the human body is one of the most important physiological systems, in the functioning of which involved rhythmic processes that interact with each other. The most important of these is the main cardiac rhythm and breathing.

When analyzing the parameters of the wave structure of the heart rate at rest, it was found that significant differences between their levels, depending on the phase of the OC, were largely absent. The exception is higher values of HFnorm in the III phase of the OC compared with II (65.4 [54.8, 75.0] and 55.4 [42.6, 68.9]%, respectively) and less aLF (11,533 [5449, 23,958] and 17,224 [9769, 26,508] ms2 \*Hz-1, respectively), indicating a higher level of activation of the parasympathetic branch of the autonomic nervous system (VNS) in the follicular and luteal phases.

During orthogonal testing, there were significant changes in the wave structure of the cardiac rhythm that had certain features in different phases of the CMC. Thus, the level of VLF did not change, LF probably (p < 0.05) decreased from 670 [273, 974] to 459 [276, 689] ms2 only in the 2nd phase. Significantly (p < 0.001) in all phases, HF, HFnorm, and TP decreased. Similar changes are the characteristic for this type of load and consist in increasing the tone of the sympathetic link of the CNS [17, 58, 59].

Under conditions of regulated breathing, minor changes in heart rhythm values were observed. Thus, the value of VLF changed in the second phase, and LF in the third phase is devastating with the I and II phases. The value of a LF showed significant changes in all phases (**Table 3**).

At a psychoemotional load, VLF did not change, LF was likely to decrease from 2.0 [1.1, 4.3] to 3.4 [1.8, 5.7] ms2 only in the 2nd phase (p < 0.05). Significantly (p < 0.001) in all phases, HF and aLF increased.

The analysis of the cardiac rhythm reactivity in orthostatic conditions (**Table 4**) showed that in the luteal phase, an increase in the power of low frequency waves of heart rate was observed, which was significantly higher than the amplitude of their decrease in the ovulatory phase. Also, in the 3rd phase, there was a significant increase in the maximum peak in the frequency range of 0.04–0.15 Hz (60.8%).

In regulated breathing, the changes in all phases were in VLF, aLF, and TPover. Insignificant in HF and HFnorm (**Table 5**).

It is noteworthy that the greatest deviation of the values of reactivity to the load is typical for indicators that characterize the frequency range of oscillations R-R from 0.04 to 0.15 Hz.

