Abstract

Intrioution. The heart rate variability is based on measuring (time) intervals between R-peaks (of RR-intervals) of an electrocardiogram and plotting a rhythmogram on their basis with its subsequent analysis by various mathematical methods. Using nonlinear methods in HRV and ECG analysis has proven to be very advantageous. Time irreversibility is a fundamental parameter of a system, it defines justification and necessity of applying nonlinear methods for analysis of a system’s dynamics. Objective. We propose an algorithm for testing the probability of a time series' irreversibility, showing its effectiveness in the process of HRV analysis. In this article, complexity of HRV will be described by two parameters: entropy EnRE [18] and correlation dimension D2 [19]. Naturally, the chosen parameters EnRE and D2 in no way can be used for comprehensive description of complexity of HRV, but we will be able to tress the necessary sufficiency of such an approach. Materials and methods. We used long-term HRV records by Massachusetts Institute of Technology – Boston’s Beth Israel Hospital (MIT-BIH) from [15], a free-access, on-line archive of physiological signals for Normal Sinus Rhythm (NSR) RR Interval, Congestive Heart Failure (CHF) RR Interval and Atrial Fibrillation (AF) Databases [16]. In [17], we have developed a special modification to the classic Mann-Whitney (MW) U-test in order to use the test for comparison of Time Series with an equal number of elements N – Time Series MW M-test. Here the new statistical -test was proposed for finding the probability of time series' irreversibility. Conclusion. In this article, we propose a statistical -test for assessment of probability of irreversibility of time series. It has been shown that the new statistical -test accurately identifies times series reversibility and irreversibility in known cases of synthetic data. For long-term HRV records of MIT-BIH database for NSR, CHF and AF groups, we have compared values of z-score, which statistically defines the limit of irreversibility of time series, and values of HRV complexity indicators: entropy EnRE [18] and correlation dimension D2 [19]. We have noted the following: HRV is time irreversible nonlinear dynamic process, with the exception of AF episodes; nonlinear indicators of HRV complexity – entropy EnRE and correlation dimension D2 – have been analyzed, and there is a conclusive difference between NSR and analyzed pathological states; analyzed time series have been presented in D2-z-EnRE phase space, and their reliable separability has been shown. It can be stated that the analyzed D2-z-EnRE phase space is sufficient for research of nonlinear HRV events in this case.

Highlights

  • The heart rate variability is based on measuring intervals between R-peaks of an electrocardiogram and plotting a rhythmogram on their basis with its subsequent analysis by various mathematical methods

  • It has been shown that the new statistical test accurately identifies times series irreversibility in known cases of synthetic data, including: Linear Gaussian Process (LGP), a linear auto-regressive model of second order driven by a white noise AR(2); irreversible classic chaotic systems Lorenz, Duffing, Rossler, Hennon and dissipative chaos system – Logistic map (Tab.1)

  • For long-term heart rate variability (HRV) records of MIT-BIH database for Normal Sinus Rhythm (NSR), Congestive Heart Failure (CHF) and Atrial Fibrillation (AF), we have compared values of z-score, which statistically defines the limit of irreversibility of time series, and values of HRV complexity indicators: entropy EnRE [18] and correlation dimension D2 [19]

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Summary

Introduction

The heart rate variability is based on measuring (time) intervals between R-peaks (of RRintervals) of an electrocardiogram and plotting a rhythmogram on their basis with its subsequent analysis by various mathematical methods. Time irreversibility is a fundamental parameter of a system, it defines justification and necessity of applying nonlinear methods for analysis of a system’s dynamics. The heart rate variability (HRV) is based on measuring (time) intervals between Rpeaks (of RR-intervals) of an electrocardiogram (ECG) and plotting a rhythmogram on their basis with its subsequent analysis by various mathematical methods that are classified as Time-Domain, Frequency-Domain and Nonlinear [1, 2]. Analysis of an HRV time series' irreversibility has been a popular and oft-discussed topic in scientific literature for the last 20 years [4,5,6,7,8,9]. In [12], effectiveness of TiROP algorithm for analysis of electroencephalographic (EEG) signals has been demonstrated, and it has been shown ‘that interictal EEG dynamics can be associate to a reversible linear process, whereas time irreversibility characterizes epileptic seizures’

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