Complex structure and nonlinear behavior of very low frequency of heart rate variability: Model of analysis, and practical applications

Researched the structure of Very Low Frequency (VLF) spectrum of heart rate variability (HRV) and its nonlinear behavior in a relationship with the energy of oscillations, baroreflex and parasympathetic activity at functional tests of low intensity in 100 subjects (seven-test, deep breathing), including active orthostatic test of 32 subjects with orthostatic tachycardia in comparison to the control group of 20 subjects.
There were three stages of research. The first stage: created the method of spectral analysis of separate components of VLF. On the basis of comparative data of Fast Furrier Transform with Welch filters, autoregression, continuous wavelet analysis and Hilbert–Huang transform, for the first time it was shown that VLF has separate 200, 100 and 50 sec oscillations (VLF200, VLF100, VLF50). The second stage: for evaluation of physiological properties of the separate oscillations, was conducted the analysis of VLF structure in three groups of patients: (a) with a predominance of parasympathetic activity (HF) in the VLF spectrum, (b) with a dominance of 10 sec oscillations (LF), (c) with a severe depression of energy in all components of the spectrum. It was established that the individual components of VLF (VLF100 and VLF50) have a certain stability and partiall independence from the changes of peripheral autonomic indices (LF/HF) at loads of low intensity. The third stage: analyzed features of VLF structure (VLF100 and VLF50) alone and in a conjunction with LF and HF, as well as heart rate and blood pressure in humans with orthostatic tachycardia with a predominance of parasympathetic activity at functional tests of low intensity (seven-test deep breathing) and at an active orthostatic test. Based on these studies it was concluded that the individual components in VLF structure (VLF100, VLF50) can demonstrate reciprocal relations at a load among themselves and in the LF/HF ratio, and play an adaptive role in the mechanisms of autonomic provision. Previously found regularities that are characteristic for the subjects with orthostatic tachycardia in the form of high-level LF turned out to be insufficient for the prognosis. Revealed the importance of VLF and its components, 100 and 50 sec oscillations at an orthostatic test in the prognosis of orthostatic tachycardia development. In 35% of patients with dysautonomia at high level of VLF100 power, tachycardia did not develop. In this case, VLF and its component parts did an important adaptive function. The analysis of a complex VLF structure contributes to the differential treatment and detection of central mechanisms of adaptation. Adaptive VLF functions were mainly registered at orthostatic load. In the proposed model of the descending neurosomatic control of autonomic regulation of HRV a very important role plays both neurogenic ways of regulation, and neuro-hormonal-metabolic ways, manifested in the complex VLF structure. Regarded the choice of ways and optimal models of regulation.