title: Multifractality and heart rate variability.
abstract: In this paper, we participate to the discussion set forth by the editor of Chaos for the controversy, "Is the normal heart rate chaotic?" Our objective was to debate the question, "Is there some more appropriate term to characterize the heart rate variability (HRV) fluctuations?" We focused on the approximately 24 h RR series prepared for this topic and tried to verify with two different techniques, generalized structure functions and wavelet transform modulus maxima, if they might be described as being multifractal. For normal and congestive heart failure subjects, the h(q) exponents showed to be decreasing for increasing q with both methods, as it should be for multifractal signals. We then built 40 surrogate series to further verify such hypothesis. For most of the series (approximately 75%-80% of cases) multifractality stood the test of the surrogate data employed. On the other hand, series coming from patients in atrial fibrillation showed a small, if any, degree of multifractality. The population analyzed is too small for definite conclusions, but the study supports the use of multifractal series to model HRV. Also it suggests that the regulatory action of autonomous nervous system might play a role in the observed multifractality.
authors: Dipartimento di Tecnologie dell'Informazione, Universita degli studi di Milano, via Bramante 65, 26013 Crema, Italy. roberto.sassi@unimi.it
authors: Roberto
authors: R
authors: Sassi
authors: Maria Gabriella
authors: MG
authors: Signorini
authors: Sergio
authors: S
authors: Cerutti
mesh_terms: D001281:Atrial Fibrillation / Q000503:physiopathology; D001341:Autonomic Nervous System / Q000502:physiology / Q000503:physiopathology; D004562:Electrocardiography / Q000706:statistics & numerical data; D017709:Fractals; D006333:Heart Failure / Q000503:physiopathology; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008955:Models, Cardiovascular; D017711:Nonlinear Dynamics; D012016:Reference Values