title: Enhancing coronary Wave Intensity Analysis robustness by high order central finite differences.
abstract: BACKGROUND
  Coronary Wave Intensity Analysis (cWIA) is a technique capable of separating the effects of proximal arterial haemodynamics from cardiac mechanics. Studies have identified WIA-derived indices that are closely correlated with several disease processes and predictive of functional recovery following myocardial infarction. The cWIA clinical application has, however, been limited by technical challenges including a lack of standardization across different studies and the derived indices' sensitivity to the processing parameters. Specifically, a critical step in WIA is the noise removal for evaluation of derivatives of the acquired signals, typically performed by applying a Savitzky-Golay filter, to reduce the high frequency acquisition noise.
  
  
  METHODS
  The impact of the filter parameter selection on cWIA output, and on the derived clinical metrics (integral areas and peaks of the major waves), is first analysed. The sensitivity analysis is performed either by using the filter as a differentiator to calculate the signals' time derivative or by applying the filter to smooth the ensemble-averaged waveforms. Furthermore, the power-spectrum of the ensemble-averaged waveforms contains little high-frequency components, which motivated us to propose an alternative approach to compute the time derivatives of the acquired waveforms using a central finite difference scheme.
  
  
  CONCLUSIONS
  The cWIA output and consequently the derived clinical metrics are significantly affected by the filter parameters, irrespective of its use as a smoothing filter or a differentiator. The proposed approach is parameter-free and, when applied to the 10 in-vivo human datasets and the 50 in-vivo animal datasets, enhances the cWIA robustness by significantly reducing the outcome variability (by 60%).
authors.affiliation: Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St. Thomas' Hospital, London SE1 7EH, UK.
authors.forename: Simone
authors.initials: S
authors.lastname: Rivolo
authors.affiliation: Cardiovascular Division, British Heart Foundation Centre of Research Excellence, King's College London, St. Thomas Hospital, London SE1 7EH, UK.
authors.forename: Kaleab N
authors.initials: KN
authors.lastname: Asrress
authors.affiliation: Division of Imaging Science and Biomedical Engineering, King's College London, King's Health Partner, St. Thomas Hospital, London SE1 7EH, UK.
authors.forename: Amedeo
authors.initials: A
authors.lastname: Chiribiri
authors.affiliation: Division of Imaging Science and Biomedical Engineering, King's College London, King's Health Partner, St. Thomas Hospital, London SE1 7EH, UK.
authors.forename: Eva
authors.initials: E
authors.lastname: Sammut
authors.affiliation: Division of Imaging Science and Biomedical Engineering, King's College London, King's Health Partner, St. Thomas Hospital, London SE1 7EH, UK.
authors.forename: Roman
authors.initials: R
authors.lastname: Wesolowski
authors.affiliation: Department of Cardiology, Aarhus University Hospital Skejby, Brendstrupgaardsvej 100, DK-8200 Aarhus N, Denmark.
authors.forename: Lars Ø
authors.initials: LO
authors.lastname: Bloch
authors.affiliation: Department of Cardiothoracic & Vascular Surgery, Aarhus University Hospital Skejby, Brendstrupgaardsvej 100, DK-8200 Aarhus N, Denmark.
authors.forename: Anne K
authors.initials: AK
authors.lastname: Grøndal
authors.affiliation: Department of Cardiothoracic & Vascular Surgery, Aarhus University Hospital Skejby, Brendstrupgaardsvej 100, DK-8200 Aarhus N, Denmark.
authors.forename: Jesper L
authors.initials: JL
authors.lastname: Hønge
authors.affiliation: Department of Cardiology, Aarhus University Hospital Skejby, Brendstrupgaardsvej 100, DK-8200 Aarhus N, Denmark.
authors.forename: Won Y
authors.initials: WY
authors.lastname: Kim
authors.affiliation: Cardiovascular Division, British Heart Foundation Centre of Research Excellence, King's College London, St. Thomas Hospital, London SE1 7EH, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Marber
authors.affiliation: Cardiovascular Division, British Heart Foundation Centre of Research Excellence, King's College London, St. Thomas Hospital, London SE1 7EH, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Redwood
authors.affiliation: Division of Imaging Science and Biomedical Engineering, King's College London, King's Health Partner, St. Thomas Hospital, London SE1 7EH, UK.
authors.forename: Eike
authors.initials: E
authors.lastname: Nagel
authors.affiliation: Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St. Thomas' Hospital, London SE1 7EH, UK.
authors.forename: Nicolas P
authors.initials: NP
authors.lastname: Smith
authors.affiliation: Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St. Thomas' Hospital, London SE1 7EH, UK.
authors.forename: Jack
authors.initials: J
authors.lastname: Lee
keywords: Coronary artery disease; Sensitivity analysis; Wave Intensity Analysis