Heart rate variability: for real doctors. Translation from the Russian version of the book, published at Kharkiv, 2010, 131 p.
The basics and practice of the clinical use of the technology of heart rate variability are outlined for doctors of all specialties and students of medical faculties of universities.
Frequency domain indicators
The spectral components of the HRV TP are traditionally associated with the power of the corresponding regulatory links.
Efferent vagal activity is considered an essential component of the HF domain of HRV and its power is justifiably attributed to the power of parasympathetic influences. The capacity of HF is significantly affected by the respiratory center (cardiorespiratory arrhythmia). As we showed above, the respiratory nuclei and the nuclei of the vagus nerves are located close to the brain stem, which is the cause of the modulating effect of the former on the latter. Direct subordination of the respiratory center to the cortical functions mediates direct central influences on the cardiac spectrum. The close functional relationship of the respiratory and parasympathetic nuclei in healthy people and its frequent disturbances in patients with various diseases allow us to assess the quality of this connection in respiratory tests (most often with metronomized breathing of the same frequency), which has a high clinical significance.
LF domain of HRV is considered by some as a marker of sympathetic modulation (especially when expressed in normalized units) and baroreflex control, while others find it an indicator depending both on sympathetic and vagal influences. It is necessary, however, to bear in mind that the sympathetic modulation is carried out in two subcontours – nerve vegetative sympathetic and humoral sympathetic (release of catecholamine by the adrenal glands, CIF-myocardial cells, etc.), supporting and to some extent complement each other. According to LF, the quality of baroreflex control is rather simple in an orthostatic (active and/or passive) sample, when changes in its power are primarily associated with changes in the sympathetic (in the broad sense of the word) control loop.
There is a view that the ratio of LF / HF reflects the sympathovagal balance. Accurately, however, it reflects the proportion of fast and slow regulation.
VLF domain of HRV is associated with thermoregulation, humoral systems, and somatic tone. There is evidence that VLF and LF are sensitive indicators of controlling metabolic processes and well reflect energy deficiency states.
We noticed that between the vegetative sympathetic and humoral contours, as well as between the parasympathetic and sympathetic vegetative branches, in a living organism there are no clear boundaries. The regulation acts as an orchestra with a large number of degrees of freedom and protection. The “fallout” of the anatomical regulation link is diagnosed and has real clinical significance only when this “fallout” merely is irreplaceable or irreparable, that in real life, fortunately, a thing is quite rare.
ULF domain of HRV analyzed by daily records of HRV. Its origin is unknown, but the forecast of sudden death based on it is the most accurate.
Daily changes in HRV are characterized by circadian behavior. In long-term recordings, HF and LF account for about 5% of the TP, and 95% of the TP for ULF and VLF.
When linking the spectral components of HRV with regulation, it is natural to speak not only (or not so much) about its vegetative parasympathetic and sympathetic, humoral, and other links, but also about fast, slow, very slow and ultra-slow regulation.
Differentiating fast, slow, very slow and ultra slow regulation and realizing that each of them is controlled by all links (parasympathetic, sympathetic, humoral, thermoregulatory, other), do not forget that the effects of the parasympathetic nervous system are large in fast, sympathetic – in slow and very slow, and humoral – in very slow and ultra-slow regulation.
In this understanding, the power of HF, LF, VLF, ULF domains, respectively, is a measure of the power of fast, slow, very slow and ultra-slow regulation.
One would like to make a speculative conclusion of the type: “According to this, it is possible to evaluate the state of the parasympathetic, sympathetic and humoral regulation links exclusively using the methods …”. However, it is not. And not because these methods do not allow to single out these regulation links, but because in the integral regulation loop all its links act as a single ensemble, if you wish, we have already introduced an analogy with the orchestra when isolating or isolating any anatomical (or another) link is nothing more than an abstraction. This understanding of regulation is truly the “golden key” to an interpretation of the results of its research using HRV.