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  Estonian Journal of Engineering

ISSN 1736-7522 (electronic)  ISSN 1736-6038  (print)

 An international scientific journal
Formerly: Proceedings of the Estonian Academy of Sciences Engineering
(ISSN 1406-0175)
Published since 1995

Estonian Journal of Engineering

ISSN 1736-7522 (electronic)  ISSN 1736-6038  (print)

 An international scientific journal
Formerly: Proceedings of the Estonian Academy of Sciences Engineering
(ISSN 1406-0175)
Published since 1995

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Bio-impedance signal decomposer: enhanced accuracy and reduced latency solution; pp. 201–219

(Full article in PDF format) doi: 10.3176/eng.2011.3.03


Authors

Andrei Krivoshei

Abstract

The paper presents an overview of the electrical bio-impedance (EBI) signal decomposi­tion into its cardiac and respiratory components. This problem mainly originates from the non­stationarity of the signal components and overlapping of their harmonic spectra. In the introductory part of the paper, an overview of the bio-impedance signal decomposer (BISD), as a solution of the problem, is accompanied with an introduction to a cardiac BI signal model, which is constructed from the components of the application-specific orthonormal basis. In the main part of the paper a semi-synchronous cardiac signal amplitude estimator, which is based on the cardiac signal model and on the proposed extrema searching algorithm, is proposed. After that, the cardiac signal lock-in detection algorithm is proposed. Finally, a conditioning of the estimated cardiac signal frequency is discussed. The proposed amplitude estimator, lock-in detector and frequency conditioning increase twice the reaction speed of the BISD to the input EBI signal. The proposed version of the BISD estimates the cardiac signal amplitude during only a few cardiac periods, even if very large difference between amplitudes exists in different conditions. As a result, the entire BISD becomes locked during 8 s (including 4 s of soft start). The proposed improvements allowed reducing the latency of the BISD from 2 to 1 s.

Keywords

bio-impedance, signal decomposition, heart rate monitoring, amplitude estimator, lock-in detector, model-based signal processing.

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