A. D. Nozdrachev

Cardiac Rhythm Variability: Approaches to Mechanisms

Physiological mechanisms of cardiac rhythm variability (CRV) are reviewed. The results of original experiments are discussed together with the history of the problem and data available from the literature. Special emphasis is placed on the spectral analysis of cardiac rhythm. Various mechanisms of the generation of periodic and aperiodic components of CRV are considered. Although the variability of cardiac rhythm has been studied for many years in many laboratories worldwide, fine mechanisms of CRV remain obscure. However, a number of specific features of CRV are presently widely recognized. Periodic CRV components isolated from short-term records in patients at rest are represented by high-frequency, low-frequency, and very low-frequency oscillations. Fourier-transform spectral analysis of cardiac rhythm is the most appropriate method of the detection of these oscillations. High-frequency components are associated with respiration and represent the effects of the parasympathetic nervous system on myocardium. Low-frequency components are due to the activity of the postganglionic sympathetic fibers and represent the processes of cardiac rhythm modulation by the sympathetic nervous system. Genesis of very low-frequency oscillations is still uncertain. Most probably, these oscillations are associated with the effects of suprasegmental (primarily, hypothalamic) centers of autonomic regulation. Aperiodic CRV components represent random events associated with the reflex regulation of the heart rate by external or internal factors. Because aperiodic components significantly modify the results of the CRV analysis, the effects of these factors should be eliminated. It is concluded that because many problems associated with cardiac rhythm variability remain to be solved, extensive research in this direction should be continued.

Modern Methods of Functional Studies of the Autonomic Nervous System

Contemporary methods to assess the functional state of the autonomic nervous system are reviewed. This paper discusses different hypotheses on the nature of the low- and very low-frequency waves (LFand VLF, respectively) that are recorded during the spectral analysis of the heart-rate variability (HRV). Analysis of their own data along with data found in literature enabled the authors to propose the possible parasympathetic nature of the LF-wave generators. The application of the established indices of the absolute power of all the components of the HRV spectrum led to the hypothesis that emotional stress is related to the attenuation in the regulatory effects of the higher levels of the central nervous system.

Postural Influences on the Hormone Level in Healthy Subjects: I. The Cobra Posture and Steroid Hormones

Cortisol, testosterone, dehydroepiandrosterone (DHEA), and aldosterone were measured in the blood serum of healthy subjects who adopted the cobra posture (bhujangasana), a key posture of hatha yoga. The subjects were trained in yoga; blood samples were taken before and after the exercise at an interval of no more than 5 min. As revealed with a new confidence interval–evaluating method developed by A.I. Ivanov, cortisol decreased by 11% with a reliability of 0.99 in all subjects, while testosterone increased by 16% with a reliability of 0.95. Changes in DHEA and aldosterone varied. Proceeding from ideas about motor–visceral interactions, the authors hypothesize that, when the subjects adopted the cobra posture, the production of steroid hormones was controlled by neural mechanisms.

Energy and fractal characteristics of physiological and pathological tremors of the human hand

Tremors (involuntary shaking) were compared in healthy subjects and patients with the tremulous form of Parkinsonism sustaining isometric effort of the hand. For this purpose, fractal analysis and multilevel wavelet decomposition of tremor were used, and the energy characteristics determined on the basis of the spectral density of the energy of detailed components obtained at different levels of decomposition. The calculated fractal and energy characteristics of the tremor of healthy subjects were significantly lower than those of patients. If the patients took antiparkinsonian drugs at their usual doses, the characteristics shifted towards normal values. The decrease in the fractal dimension indicates an increase in the strength of the correlation in the dynamics of involuntary shaking. Thus, the characteristics studied allow not only physiological and pathological tremors to be discriminated, but also the strategy of selection of optimal drugs for relieving Parkinsonian tremor to be developed.

Features of parkinsonian and essential tremor of the human hand

Using spectral, wavelet, multifractal, and recurrence analyses we examined the features of involuntary shaking (tremor) that occur during the performance of a given motor task. The task was to maintain the efforts of fingers under isometric conditions by a healthy subject, a patient with primary bilateral parkinsonism, and a patient with essential tremor syndrome. The physiological tremor was characterized by the lowest amplitude, a broad power spectrum, the lowest energy of the wavelet spectrum, the highest degree of multifractality, the lowest degree of determinism, and the highest entropy of the recurrence time density. In the case of the essential tremor we observed a significant enhancement of the wavelet spectrum energy and a decrease of the oscillation complexity. This was evident via the occurrence of clear peaks in the power spectra, a decrease in the degree of multifractality, the emergence of a quasi-periodic structure in the recurrence diagrams, an increase in determinism and a decrease of the entropy of recurrence time density. All these trends were increased for the parkinsonian tremor data. These characteristics enable us to quantitatively estimate the degree of deviation of motor function from the healthy case.

Nonlinear dynamics of involuntary shaking of the human hand under motor dysfunction

Wavelet and multifractal features of involuntary shaking (tremor) arising during the performance of the motor task (under sustaining isometric effort of fingers of the human hand) have been examined by nonlinear dynamic methods. The wavelet score (the maximum of the global energy of a wavelet spectrum) and multifractal parameters (the width and asymmetry of a singularity spectrum) significantly differ in tremor of healthy subjects and patients with motor dysfunction. The relations between the change of the state of the patients with Parkinson’s disease connected with the drug relief of parkinsonian symptoms and the variations of the parameter values have been obtained. The suggested analytic approach for noninvasive study of integrative activity of the central nervous system, formed as the motor exit during realization of the motor task, enables us not only to estimate quantitatively the degree of deviation of the motor function from the healthy one, but it can help to a clinician to choose the optimal treatment in every particular case.

Analysis of changes in EEG patterns in response to rhythmic photic stimulation under various disruptions of the functional state of the central nervous system

Using the wavelet transform of the electroencephalographic (EEG) fragments we have examined for the first time the photic driving reaction for patients with disruptions of the functional state of the central nervous system arising by cerebrovascular disturbances of various intensity degrees. Background fragments of EEG of patients in the vegetovascular dystonia group are characterized by the smaller values of the wavelet spectrum energy in the α range than the fragments in the control group. Patients in the groups of vertebrobasilar insufficiency and arteriosclerotic damage of cerebral blood vessels have much less energy values in δ range. The wavelet analysis of reactive patterns has demonstrated the different photic driving for β, θ and α ranges for the patients of various groups. The study demonstrates the possibility of the wavelet analysis to estimate quantitatively the human brain lability to percept light stimuli. The results can be applied for appropriate choice of treatment of a patient having cerebrovascular disturbances.

Modern concepts on the mechanisms of encoding visceral nociceptive stimuli

This paper reviews the existing concepts on the physiology of visceral pain and mechanisms of processing nociceptive stimuli at the level of sensor neurons of surface segments of the spinal dorsal horns. Data on the ion channels and receptors involved in the transduction of the pain signals are discussed.

Spatial structure of EEG in depression patients with co-occurring anxiety disorders

This study was carried out on 36 patients with reactive depression and recurrent depressive episodes accompanied by severe anxiety disorder. Cross-correlation analysis of the spatial structure of the brain bioelectric activity has been performed. It have been found that clinical features of depression and anxiety disorder affect the spatial EEG structure depending on the type of anxiety disorder.

A view of the cardiac rhythm control: Intrinsic regulation

Regulation of the cardiac rhythm is intricate and occurs at least at two major levels, intrinsic and extrinsic. In turn, each of these levels can be divided into several sublevels. The factors regulating the cardiac activity eventually affect the duration of spontaneous diastolic depolarization of pacemaker myocytes of the sinoatrial node and, to a far lesser extent, the conduction velocity in the conduction system of the heart. Intrinsic regulation of the heart rate (HR) includes the myogenic sublevel and the sublevels of cell-to-cell communication, the cardiac nervous system, and humoral factors produced within the heart. Myogenic regulation is considered to be the first sublevel in control of the cardiac function. The available data suggest myogenic regulation only for the contractility of the myocardium. The cell-to-cell regulation sublevel involves two principal mechanisms. One depends on the heterogeneous structure of the sinoatrial node and within-node shifts of the dominant pacemaker, which is a group of cells that determine the HR and govern all other cells of the sinoatrial node. The other mechanism is based on the effects of peptides produced by cardiomyocytes and endothelial cells on pacemaker cells of the sinoatrial node. Regulatory peptides are also produced by the cardiac nervous system, which includes sensory and effector autonomic fibers, represents the cardiac part of the metasympathetic system, and forms intramural ganglia. In addition to modulating the HR, these peptides affect the contractility, microcirculation, coronary blood flow, preload, and afterload. Currently available data demonstrate that the autonomic nervous system is far more intricate than believed earlier. Using various neuropeptides, this system provides for fine adjustment of the cell functions, subject to its immediate control.