July 2009 Archives

 

In June 2008, the editors of Chaos decided to institute a new section to appear from time to time that addresses timely and controversial topics related to nonlinear science. The first of these deals with the dynamical characterization of human heart rate variability. We asked authors to respond to the following questions: Is the normal heart rate chaotic? If the normal heart rate is not chaotic, is there some more appropriate term to characterize the fluctuations (e.g., scaling, fractal, multifractal)? How does the analysis of heart rate variability elucidate the underlying mechanisms controlling the heart rate? Do any analyses of heart rate variability provide clinical information that can be useful in medical assessment (e.g., in helping to assess the risk of sudden cardiac death)? If so, please indicate what additional clinical studies would be useful for measures of heart rate variability to be more broadly accepted by the medical community. In addition, as a challenge for analysis methods, PhysioNet [A. L. Goldberger et al., "PhysioBank, PhysioToolkit, and PhysioNet: Components of a new research resource for complex physiologic signals," Circulation 101, e215-e220 (2000)] provided data sets from 15 patients of whom five were normal, five had heart failure, and five had atrial fibrillation (http://www.physionet.org/challenge/chaos/). This introductory essay summarizes the main issues and introduces the essays that respond to these questions. ©2009 American Institute of Physics

Chaos 19, 028501 (2009)

DOI:10.1063/1.3156832 

Permalink:

http://link.aip.org/link/?CHAOEH/19/028501/1

Published 30 June 2009

 

This paper explores the possibility of applying statistical nonlinear physics methods to elucidate the underlying mechanisms controlling the heart rate. In particular, the presence of delays in RR interval dynamics is studied by using a lagged detrended fluctuation analysis. The results indicate that patients with congestive heart failure (CHF) have a prolonged time delay in the baroreflex response. Some implications of large delays for the functioning of autonomic control in subjects with CHF are discussed. ©2009 American Institute of Physics

 

Chaos 19, 028502 (2009)

DOI:10.1063/1.3152005

Permalink:

http://link.aip.org/link/?CHAOEH/19/028502/1

Published 30 June 2009

We present new evidence that normal heartbeat series are nonchaotic, nonlinear, and multifractal. In addition to considering the largest Lyapunov exponent and the correlation dimension, the results of the parametric and semiparametric estimation of the long memory parameter (long-range dependence) unambiguously reveal that the underlying process is nonstationary, multifractal, and has strong nonlinearity. ©2009 American Institute of Physics

Chaos 19, 028503 (2009)

DOI:10.1063/1.3152006

Permalink:

http://link.aip.org/link/?CHAOEH/19/028503/1

Published 30 June 2009

 

 

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. ©2009 American Institute of Physics 

Chaos 19, 028504 (2009)

DOI:10.1063/1.3152008

Permalink:

http://link.aip.org/link/?CHAOEH/19/028504/1

Published 30 June 2009  

Providing a conclusive answer to the question "is this dynamics chaotic?" remains very challenging when experimental data are investigated. We showed that such a task is actually a difficult problem in the case of heart rates. Nevertheless, an appropriate dynamical analysis can discriminate healthy subjects from patients. ©2009 American Institute of Physics 

Chaos 19, 028505 (2009)

DOI:10.1063/1.3139116

Permalink:

http://link.aip.org/link/?CHAOEH/19/028505/1

Published 30 June 2009