ORTHOSTATIC TACHYCARDIA: DIAGNOSTIC AND PROGNOSTIC VALUE OF VERY LOW FREQUENCY OF HEART RATE VARIABILITY

Abstract

Researched physiological mechanisms of development of orthostatic tachycardia syndrome (POTS) on the basis of a complex spectral structure analysis of heart rate variability (HRV), its nonlinear behavior in relationship to energy oscillations, baroreflex and parasympathetic activity. There were several stages of research. The first stage: created the method of spectral analysis of individual components of Very Low Frequency (VLF). On the basis of comparative Fast Furrier Transform data 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 s oscillations (VLF200, VLF100, VLF50). The second stage: for evaluation of physiological properties of separate oscillations, was analyzed VLF structure in three groups of patients (100 subjects): with a predominance of parasympathetic activity (HF) in the HRV spectrum; with a dominance of 10 s oscillations (LF); 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 partial independence from the changes of peripheral autonomic indices (LF/HF) at loads of low intensity. The third stage: at an active orthostatic test, 20 subjects with orthostatic tachycardia were researched in a comparison to a control group of 20 subjects without tachycardia. Analyzed the specifics of the VLF structure (VLF100 and VLF50) alone and in a conjunction with the LF and HF, as well as heart rate and blood pressure in subjects 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 the VLF structure (VLF100, VLF50) can demonstrate reciprocal relationships at a load among themselves and in the LF/HF ratio, and play an adaptive role in the mechanisms of autonomic provision. Revealed the importance of VLF and its components 100 and 50 s oscillations at an orthostatic test in the prognosis of orthostatic tachycardia development. In patients with dysautonomia at high level of VLF100 power, or high VLF50 indices, tachycardia did not develop. In this case, VLF and its component parts did an important adaptive function and conversely, the low VLF50 indices contribute to orthostatic tachycardia. 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 neurosomatic models of regulation at POTS.