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Computational and Mathematical Methods in Medicine
Volume 2012, Article ID 578785, 6 pages
http://dx.doi.org/10.1155/2012/578785
Research Article

An Efficient Time-Varying Filter for Detrending and Bandwidth Limiting the Heart Rate Variability Tachogram without Resampling: MATLAB Open-Source Code and Internet Web-Based Implementation

1Department of Medical Physics & Clinical Engineering, Royal Liverpool & Broadgreen University Hospital, Liverpool L7 8XP, UK
2National Refractory Angina Centre, Royal Liverpool & Broadgreen University Hospital, Liverpool L7 8XP, UK
3Department of Neonatal Medicine, Liverpool Women’s Hospital, Liverpool L8 7SS, UK

Received 13 May 2011; Revised 3 November 2011; Accepted 21 November 2011

Academic Editor: Quan Long

Copyright © 2012 A. Eleuteri et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The heart rate variability (HRV) signal derived from the ECG is a beat-to-beat record of RR intervals and is, as a time series, irregularly sampled. It is common engineering practice to resample this record, typically at 4 Hz, onto a regular time axis for analysis in advance of time domain filtering and spectral analysis based on the DFT. However, it is recognised that resampling introduces noise and frequency bias. The present work describes the implementation of a time-varying filter using a smoothing priors approach based on a Gaussian process model, which does not require data to be regular in time. Its output is directly compatible with the Lomb-Scargle algorithm for power density estimation. A web-based demonstration is available over the Internet for exemplar data. The MATLAB (MathWorks Inc.) code can be downloaded as open source.