Synchronous recording of magnetocardiographic and electrocardiographic signals.

We present a system for simultaneous recording of the electrocardiogram and the magnetocardiogram. The measurement system contained of printed carbon electrodes and SERF magnetometer. The use of this system confirms that the position of the end of the magnetic T wave extends further than the electric T wave, which is an important indicator for the diagnosis of cardiological patients and for drug arrhythmogenicity. We analyze this phenomenon in depth, and demonstrate, that it originates from the fundamental difference between electric and magnetic measurements. The measured value is always bipolar since the electric measurements require two electrodes. We demonstrate how the dual electric and magnetic measuring system adds a new information to the commonly used electrocardiographic diagnosis. The ECG should be interpreted as the spatial asymmetry of the electric cardiac potential, and not as the potential itself. The results seem to prove, that the relation between the magnetic and the electric imaging of neural activities may be broadly applied for the benefit of medical diagnosis in cardiology and many other fields, where the neural activity is measured. This is a pilot study which requires further confirmation at the clinical level.

Finite velocity of ECG signal propagation: preliminary theory, results of a pilot experiment and consequences for medical diagnosis.

A satisfactory model of the biopotentials propagating through the human body is essential for medical diagnostics, particularly for cardiovascular diseases. In our study, we develop the theory, that the propagation of biopotential of cardiac origin (ECG signal) may be treated as the propagation of low-frequency endogenous electromagnetic wave through the human body. We show that within this approach, the velocity of the ECG signal can be theoretically estimated, like for any other wave and physical medium, from the refraction index of the tissue in an appropriate frequency range. We confirm the theoretical predictions by the comparison with a direct measurement of the ECG signal propagation velocity and obtain mean velocity as low as v=1500 m/s. The results shed new light on our understanding of biopotential propagation through living tissue. This propagation depends on the frequency band of the signal and the transmittance of the tissue. This finding may improve the interpretation of the electric measurements, such as ECG and EEG when the frequency dependence of conductance and the phase shift introduced by the tissue is considered. We have shown, that the ECG propagation modifies the amplitude and phase of signal to a considerable extent. It may also improve the convergence of inverse problem in electrocardiographic imaging.

Heart rate variability comparison between young males after 4-6 weeks from the end of SARS-CoV-2 infection and controls.

Due to the prolonged inflammatory process induced by infection of the novel severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), indices of autonomic nervous system dysfunction may persist long after viral shedding. Previous studies showed significant changes in HRV parameters in severe (including fatal) infection of SARS-CoV-2. However, few studies have comprehensively examined HRV in individuals who previously presented as asymptomatic or mildly symptomatic cases of COVID-19. In this study, we examined HRV in asymptomatic or mildly symptomatic individuals 5-7 weeks following positive confirmation of SARS-CoV-2 infection. Sixty-five ECG Holter recordings from young (mean age 22.6 ± 3.4 years), physically fit male subjects 4-6 weeks after the second negative test (considered to be the start of recovery) and twenty-six control male subjects (mean age 23.2 ± 2.9 years) were considered in the study. Night-time RR time series were extracted from ECG signals. Selected linear as well as nonlinear HRV parameters were calculated. We found significant differences in Porta's symbolic analysis parameters V0 and V2 (p < 0.001), α2 (p < 0.001), very low-frequency component (VLF; p = 0.022) and respiratory peak (from the PRSA method; p = 0.012). These differences may be caused by the changes of activity of the parasympathetic autonomic nervous system as well as by the coupling of respiratory rhythm with heart rate due to an increase in pulmonary arterial vascular resistance. The results suggest that the differences with the control group in the HRV parameters, that reflect the functional state of the autonomic nervous system, are measurable after a few weeks from the beginning of the recovery even in the post-COVID group-a young and physically active population. We indicate HRV sensitive markers which may be used in long-term monitoring of patients after recovery.

Asymmetric multiscale multifractal analysis (AMMA) of heart rate variability.

Objective.The physiological activity of the heart is controlled and modulated mostly by the parasympathetic and sympathetic nervous systems. Heart rate variability (HRV) analysis is therefore used to observe fluctuations that reflect changes in the activity in these two branches. Knowing that acceleration and deceleration patterns in heart rate fluctuations are asymmetrically distributed, the ability to analyze HRV asymmetry was introduced into MMA.Approach. The new method is called asymmetric multiscale multifractal analysis (AMMA) and the analysis involved six groups: 36 healthy persons, 103 cases with aortic valve stenosis, 36 with hypertrophic cardiomyopathy, 32 with atrial fibrillation, 59 patients with coronary artery disease (CAD) and 13 with congestive heart failure.Main results. Analyzing the results obtained for the 6 groups of patients based on the AMMA method, i.e. comparing the Hurst surfaces for heart rate decelerations and accelerations, it was noticed that these surfaces differ significantly. And the differences occur in most groups for large fluctuations (multifractal parameterq > 0). In addition, a similarity was found for all groups for the AMMA Hurst surface for decelerations to the MMA Hurst surface-heart rate decelerations (lengthening of the RR intervals) appears to be the main factor determining the shape of the complete Hurst surface and so the multifractal properties of HRV. The differences between the groups, especially for CAD, hypertrophic cardiomyopathy and aortic valve stenosis, are more visible if the Hurst surfaces are analyzed separately for accelerations and decelerations.Significance. The AMMA results presented here may provide additional input for HRV analysis and create a new paradigm for future medical screening. Note that the HRV analysis using MMA (without distinguishing accelerations from decelerations) gave satisfactory screening statistics in our previous studies.

A quantitative model of relation between respiratory-related blood pressure fluctuations and the respiratory sinus arrhythmia.

In order to propose an interpretation of recent experimental findings concerning short-term variability of arterial blood pressure (ABP), heart rate variability (HRV), and their dependence on body posture, we develop a qualitative dynamical model of the short-term cardiovascular variability at respiratory frequency (HF). It shows the respiratory-related blood pressure fluctuations in relation to the respiratory sinus arrhythmia (RSA). Results of the model-based analysis show that the observed phenomena may be interpreted as buffering of the respiratory-related ABP fluctuations by heart rate (HR) fluctuations, i.e., the respiratory sinus arrhythmia. A paradoxical enhancement (PE) of the fluctuations of the ABP in supine position, that was found in experiment, is explained on the ground of the model, as an ineffectiveness of control caused by the prolonged phase shift between the the peak of modulation of the pulmonary flow and the onset of stimulation of the heart. Such phasic changes were indeed observed in some other experimental conditions. Up to now, no other theoretical or physiological explanation of the PE effect exists, whereas further experiments were not performed due to technical problems. Better understanding of the short-term dynamics of blood pressure may improve medical diagnosis in cardiology and diseases which alter the functional state of the autonomous nervous system. Graphical Abstract A simple mathematical model of cardiorespiratory dynamics. A novel class of mathematical models of blood pressure dynamics in humans allows to represent respiratory modulation of Arterial Blood Pressure. The model shows how the phase shift in neural control of the heart rate may produce Paradoxic Enhancement of respiratory Blood Pressure fluctuations. Observed in experiment. The model has many options for further development.

Cardiorespiratory coupling in young healthy subjects.

OBJECTIVE: To quantify the presence of cardiorespiratory interaction in a group of 41 healthy subjects performing a subset of the Ewing test battery. APPROACH: We measure the empirical distribution of the cardiorespiratory coupling time (RI), defined as the time from inspiration onset to R peaks in the ECG. The study protocol is a subset of the Ewing test battery. The respiratory function was measured with a thoracic belt and heart rate was obtained from a two channel ECG measurement. Both series of fiducial points were determined using custom software. Additionally, we determine the presence of cardiorespiratory coupling (CRC) and cardiorespiratory interaction (CRI) using Shannon entropy, synchrograms and coordigrams. MAIN RESULTS: We observe that the RI distribution is asymmetric and nonuniform. These features are a manifestation of the causal relation between heart action and respiration. The preceding R peak strongly affects a position of inspiration onset. From the asymmetry of the RI distribution we conclude that this relation is stronger than the relation between inspiration onset and the following R peak. We use a suitable choice of surrogate data to prove that the result cannot be falsified. We observe a dual structure of the RI histograms, which may be related to the respiratory rhythmogenesis. We compare the sensitivity of RI histograms with other measures of CRI and CRC. In 46% of subjects, CRC appears in at least one stage of the examination, most often in resting states. In states of increased stress-orthostasis or physical (exercise)-the strength of coupling is visibly diminished. The nonuniform structure of the RI histogram is more sensitive to the presence of CRI than synchrograms or coordigrams are, as is well visible in the group averages. We also refer to the question of the most proper mathematical description of cardiorespiratory dynamics (phase domain or time domain). Finally, we formulate the hypothesis that the arterial blood pressure is a common driver of cardiac and respiratory rhythms. SIGNIFICANCE: Analysis of the asymmetry of RI histograms is an interesting and sensitive method to study cardiorespiratory interaction and autonomic balance, in order to assess physical and mental health. The dual structure of the RI histograms which we have observed suggests the possible presence of a twofold mechanism for respiratory rhythmogenesis, as proposed by Galletly and Larsen.

Influence of home-based telemonitored Nordic walking training on autonomic nervous system balance in heart failure patients.

INTRODUCTION: Rehabilitation positively affects the modulation of the autonomic nervous system (ANS). There are no papers evaluating the influence of Nordic walking training (NW) on ANS activity among chronic heart failure (CHF) patients. The aim of study was to assess the influence of NW on ANS activity measured by heart rate variability (HRV) and heart rate turbulence (HRT) in CHF patients and its correlation with physical capacity improvement measured by peak oxygen consumption (peak VO2 [ml/kg/min]) in the cardiopulmonary exercise treadmill test (CPET). MATERIAL AND METHODS: The study group comprised 111 CHF patients (NYHA class II-III; ejection fraction (EF) ≤ 40%). Patients were randomized (2 : 1) to 8-week NW (five times weekly) at 40-70% of maximal heart rate (training group - TG) (n = 77), or to a control group (CG) (n = 34). The effectiveness of NW was assessed by changes (delta (Δ)) in peak VO2, HRV and HRT as a result of comparing these parameters from the beginning and the end of the programme. RESULTS: Eventually, 36 TG patients and 15 CG patients were eligible for HRV and HRT analysis. In the TG low/high frequency ratio (LF/HF) decreased (1.9 ±1.11 vs. 1.7 ±0.63, p = 0.0001) and peak VO2 increased (16.98 ±4.02 vs. 19.70 ±4.36 ml/kg/min, p < 0.0001). Favourable results in CG were not observed. The differences between TG and CG were significant: Δpeak VO2 (p = 0.0081); ΔLF/HF (p = 0.0038). An inverse correlation was found between the decrease in ΔLF/HF and the increase in Δpeak VO2 (R = -0.3830, p = 0.0211) only in the TG. Heart rate variability did not change significantly in either group. CONCLUSIONS: Nordic walking positively affects the parasympathetic-sympathetic balance in CHF patients, which correlates with the improvement in Δpeak VO2. No significant influence of NW on HRT was observed.

Complex activity patterns in arterial wall: results from a model of calcium dynamics.

Using a dynamical model of smooth muscle cells in an arterial wall, defined as a system of coupled five-dimensional nonlinear oscillators, on a grid with cylindrical symmetry, we compare the admissible activity patterns with those known from the heart tissue. We postulate on numerical basis the possibility to induce a stable spiral wave in the arterial wall. Such a spiral wave can inhibit the propagation of the axial calcium wave and effectively stop the vasomotion. We also discuss the dynamics of the circumferential calcium wave in comparison to rotors in venous ostia that are a common source of supraventricular ectopy. We show that the velocity and in consequence the frequency range of the circumferential calcium wave is by orders of magnitude too small compared to that of the rotors. The mechanism of the rotor is not likely to involve the calcium-related dynamics of the smooth muscle cells. The calcium-related dynamics which is voltage-independent and hard to be reset seems to actually protect the blood vessels against the electric activity of the atria. We also discuss the microreentry phenomenon, which was found in numerical experiments in the studied model.

HRV strongly depends on breathing. Are we questioning the right suspect?

The fact that the heart rate variability (HRV) depends on breathing is well known. The HRV is an important phenomenon which reflects the functional state of the autonomous nervous system (ANS), although there are some doubts concerning the actual interpretation of spectral components of HRV and their postulated balance. The assessment of the functional state of the ANS is the task of paramount importance in risk stratification of cardiological patients. HRV is considered to depend mainly on the properties of the sinus node (SN), which achieves neurohumoral input from the ANS. Interestingly, there is growing evidence that the relation between the heart rate (HR) and breathing rate (BR) is really strong. The variety of breathing-related effects that are present in HRV is very rich, including respiratory sinus arrhythmia (RSA), cardiorespiratory synchronization and vivid heart rate response to breathing disorders. If the mean frequency of any of rhythms is changed, the other rhythm adjusts itself. This provokes the question on the actual source of the dynamics observed in the HRV. Is it possible that we observe mainly the dynamics of the respiratory rhythm which is just transduced by the heart effector? What might be the role of the intrinsic dynamics of this effector? Is the RSA a product of neural regulation or rather a by-product: what is its teleological role? In consequence: if we concentrate on the sinus node and its properties in order to understand the nature of the HRV - are we questioning the right suspect? The reasoning is supplied by suitable choice of literature and by the analysis of the computational model. Various consequences are discussed.

[Oscillations in the cardiovascular system--physical models for the interpretation of physiological phenomena]. / Oscylacje w ukladzie sercowo−naczyniowym--modele fizyczne w interpretacji zjawisk fizjologicznych.

We discuss the foundations of the theory of homeostasis within the framework of modern physics. We analyse the paradigm of homeostasis, which is based on the physical assumption that the internal environment undergoes random fluctuations around a steady state equilibrium. We show how the notion of homeodynamics extends the concept of homeostasis. We introduce the paradigm of the phase sensitivity of regulatory activity which supplements the classical paradigm of the tonic character of such activity.

Concealed conduction effects in the atrium.

A one-dimensional (1-D) model of the atrium together with the sinoatrial (SA) and atrioventricular (AV) nodes is presented in this article. The two nodes are each modeled by 15-element, diffusively coupled, modified van der Pol oscillator chains, while the atrium tissue is represented by a 90-element chain of diffusively coupled FitzHugh-Nagumo (FHN) equations. The modified van der Pol oscillators are able to reproduce physiologically important properties, such as the refraction period, phase-sensitivity properties, and modes of change of the action potential frequency. The activity of both branches of the autonomous nervous system may be introduced into the model in a simplified way. The model enables the study of the effect of the magnitude of the action potential conduction rate in the nodes on interspike intervals (ISIs; equivalent of RR intervals) and explains the occurrence of RR-interval alternans in certain patients. The effect of breathing modulation of heart rate and of a single deep breath can also be modeled. Finally, concealed conduction effects in the atrium are studied, yielding results comparable with recorded heart rate variability data.

On the nature of heart rate variability in a breathing normal subject: a stochastic process analysis.

Human heart rate is moderated by the autonomous nervous system acting predominantly through the sinus node (the main cardiac physiological pacemaker). One of the dominant factors that determine the heart rate in physiological conditions is its coupling with the respiratory rhythm. Using the language of stochastic processes, we analyzed both rhythms simultaneously taking the data from polysomnographic recordings of two healthy individuals. Each rhythm was treated as a sum of a deterministic drift term and a diffusion term (Kramers-Moyal expansion). We found that normal heart rate variability may be considered as the result of a bidirectional coupling of two nonlinear oscillators: the heart itself and the respiratory system. On average, the diffusion (noise) component measured is comparable in magnitude to the oscillatory (deterministic) term for both signals investigated. The application of the Kramers-Moyal expansion may be useful for medical diagnostics providing information on the relation between respiration and heart rate variability. This interaction is mediated by the autonomous nervous system, including the baroreflex, and results in a commonly observed phenomenon--respiratory sinus arrhythmia which is typical for normal subjects and often impaired by pathology.

Day-to-day reproducibility of Holter beat-by-beat analysis of repolarisation.

UNLABELLED: Reproducibility of Holter QT analysis is not well established and has been assessed only in one study. STUDY DESIGN: We evaluated the day-to-day reproducibility of different QT parameters--mean and max (four beats basis) 24h QT and QTc (Bazett formula), QT for heart rate 55-60 [QT60], 75-80 [QT80] and 95-100 [QT100] beats/min and QT/RR slope (calculated in moving window of 3000 beats in 50 beat steps). QT intervals were measured from 48h digital ECG (sampled at 256 Hz) recordings using Del Mar Medical's QT software in beat-to-beat fashion. The analysed group consisted of 6 women and 24 men--13 patients with hypertrophic cardiomyopathy, 5 healthy family members of the patients with hypertrophic cardiomyopathy, 7 patients with CAD and 5 with other diseases (hypertension, arrhythmia, aborted sudden death without organic heart disease). Reproducibility was analysed with the methods proposed by Bland and Altman. RESULTS: The overall reproducibility of repolarisation parameters was acceptable. Coefficient of reproducibility for mean 24h QT was 24ms, mean QTc 12ms, max QT 22ms, max QTc 24ms. The best reproducibility was observed for QT60, QT80 and QT100 - 12ms, respectively. The poorest day-to-day reproducibility was recorded for the QT/RR slope parameters, which was related to lower heart rate reproducibility. CONCLUSIONS: We can conclude that day-to-day reproducibility of Holter repolarisation analysis is acceptable. QT measurement in narrow heart rate windows has the best reproducibility. Accurate QT analysis requires good quality recording, T wave amplitude above 0.2mV and an interactive QT measurement tool which includes verification, editing abilities.