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Summary: VOLUME 87, NUMBER 16 P H Y S I C A L R E V I E W L E T T E R S 15 OCTOBER 2001
Scale Invariance in the Nonstationarity of Human Heart Rate
Pedro Bernaola-Galván,1,2 Plamen Ch. Ivanov,1,3 Luís A. Nunes Amaral,1,3 and H. Eugene Stanley1
1
Center for Polymer Studies and Department of Physics, Boston University, Boston, Massachusetts 02215
2
Departamento de Física Aplicada II, Universidad de Málaga, E-29071, Spain
3
Cardiovascular Division, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215
(Received 17 May 2000; published 2 October 2001)
We introduce a segmentation algorithm to probe the temporal organization of heterogeneities in human
heartbeat interval time series. We find that the lengths of segments with different local mean heart rates
follow a power-law distribution and show that this scale-invariant structure is not a simple consequence of
the long-range correlations present in the data. The differences in mean heart rates between consecutive
segments display a common functional form, but with different parameters for healthy individuals and for
heart-failure patients. These findings suggest that there is relevant physiological information hidden in the
heterogeneities of the heartbeat time series.
DOI: 10.1103/PhysRevLett.87.168105 PACS numbers: 87.19.Hh, 05.40.a, 87.80.Vt, 89.75.Da
A time series is stationary if the mean, standard devia-
tion, and all higher moments, as well as the correlation
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