Burykin, A and Costa, MD and Citi, L and Goldberger, AL (2014) 'Dynamical density delay maps: simple, new method for visualising the behaviour of complex systems.' BMC Medical Informatics and Decision Making, 14 (6). 6. ISSN 14726947

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Abstract
Background. Physiologic signals, such as cardiac interbeat intervals, exhibit complex fluctuations. However, capturing important dynamical properties, including nonstationarities may not be feasible from conventional time series graphical representations. Methods. We introduce a simpletoimplement visualisation method, termed dynamical density delay mapping (``D3Map'' technique) that provides an animated representation of a system's dynamics. The method is based on a generalization of conventional twodimensional (2D) Poincar� plots, which are scatter plots where each data point, x(n), in a time series is plotted against the adjacent one, x(n+1). First, we divide the original time series, x(n) (n=1,..., N), into a sequence of segments (windows). Next, for each segment, a threedimensional (3D) Poincar� surface plot of x(n), x(n+1), hx(n),x(n+1) is generated, in which the third dimension, h, represents the relative frequency of occurrence of each (x(n),x(n+1)) point. This 3D Poincar\'e surface is then chromatised by mapping the relative frequency h values onto a colour scheme. We also generate a colourised 2D contour plot from each time series segment using the same colourmap scheme as for the 3D Poincar\'e surface. Finally, the original time series graph, the colourised 3D Poincar\'e surface plot, and its projection as a colourised 2D contour map for each segment, are animated to create the full ``D3Map.'' Results. We first exemplify the D3Map method using the cardiac interbeat interval time series from a healthy subject during sleeping hours. The animations uncover complex dynamical changes, such as transitions between states, and the relative amount of time the system spends in each state. We also illustrate the utility of the method in detecting hidden temporal patterns in the heart rate dynamics of a patient with atrial fibrillation. The videos, as well as the source code, are made publicly available. Conclusions. Animations based on density delay maps provide a new way of visualising dynamical properties of complex systems not apparent in time series graphs or standard Poincar\'e plot representations. Trainees in a variety of fields may find the animations useful as illustrations of fundamental but challenging concepts, such as nonstationarity and multistability. For investigators, the method may facilitate data exploration.
Item Type:  Article 

Additional Information:  See http://www.biomedcentral.com/14726947/14/6/additional for additional data files 
Uncontrolled Keywords:  Atrial fibrillation; Delay map; Heart rate variability; Nonlinear dynamics; Poincare plot; Sleep; Time series; Visualisation 
Subjects:  Q Science > QA Mathematics > QA75 Electronic computers. Computer science 
Divisions:  Faculty of Science and Health Faculty of Science and Health > Computer Science and Electronic Engineering, School of 
SWORD Depositor:  Elements 
Depositing User:  Elements 
Date Deposited:  13 Mar 2014 10:19 
Last Modified:  15 Jan 2022 00:21 
URI:  http://repository.essex.ac.uk/id/eprint/8776 
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