title: Normal values and reproducibility of the real-time index of vagal tone in healthy humans: a multi-center study.
abstract: BACKGROUND
  The parasympathetic nervous system has been implicated in the pathogenesis of a number of gastrointestinal disorders including irritable bowel syndrome. Within the field, cardiometric parameters of parasympathetic/vagal tone are most commonly derived from time, or frequency, domain analysis of heart rate variability (HRV), yet it has limited temporal resolution. Cardiac vagal tone (CVT) is a non-invasive beat-to-beat measure of brainstem efferent vagal activity that overcomes many of the temporal limitations of HRV parameters. However, its normal values and reproducibility in healthy subjects are not fully described. The aim of this study was to address these knowledge gaps.
  
  
  METHODS
  200 healthy subjects (106 males, median age 28 years, range 18-59 years) were evaluated across three study centers. After attachment of CVT recording equipment, 20 min of data (resting/no stimulation) was acquired. 30 subjects, selected at random, were restudied after 1 year.
  
  
  RESULTS
  The mean CVT was 9.5±4.16 linear vagal scale (LVS). Thus, the normal range (mean±2 standard deviations) for CVT based on this data was 1.9-17.8 LVS. CVT correlated negatively with heart rate (r=-0.6, P=0.001). CVT reproducibility over 1 year, as indexed by an intra-class correlational coefficient of 0.81 (95% confidence interval 0.64-0.91), was good.
  
  
  CONCLUSIONS
  In healthy subjects, the normal range for CVT should be considered to be 1.9-17.8 LVS and is reproducible over 1 year. Future research utilizing CVT should refer to these values although further study is warranted in patient groups.
authors.affiliation: Centre for Digestive Diseases, Blizard Institute, Wingate Institute of Neurogastroenterology, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, UK (Adam D. Farmer, Steven J. Coen, Michiko Kano, Claude Botha, Qasim Aziz).
authors.forename: Adam D
authors.initials: AD
authors.lastname: Farmer
authors.affiliation: Centre for Digestive Diseases, Blizard Institute, Wingate Institute of Neurogastroenterology, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, UK (Adam D. Farmer, Steven J. Coen, Michiko Kano, Claude Botha, Qasim Aziz).
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Coen
authors.affiliation: Centre for Digestive Diseases, Blizard Institute, Wingate Institute of Neurogastroenterology, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, UK (Adam D. Farmer, Steven J. Coen, Michiko Kano, Claude Botha, Qasim Aziz) ; Behavioural Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan (Michiko Kano).
authors.forename: Michiko
authors.initials: M
authors.lastname: Kano
authors.affiliation: Translational Research Centre for Gastrointestinal Disorders, University of Leuven, Belgium (Nathalie Weltens, Huynh Giao Ly, Lukas Van Oudenhove).
authors.forename: Nathalie
authors.initials: N
authors.lastname: Weltens
authors.affiliation: Translational Research Centre for Gastrointestinal Disorders, University of Leuven, Belgium (Nathalie Weltens, Huynh Giao Ly, Lukas Van Oudenhove).
authors.forename: Huynh Giao
authors.initials: HG
authors.lastname: Ly
authors.affiliation: Centre for Digestive Diseases, Blizard Institute, Wingate Institute of Neurogastroenterology, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, UK (Adam D. Farmer, Steven J. Coen, Michiko Kano, Claude Botha, Qasim Aziz).
authors.forename: Claude
authors.initials: C
authors.lastname: Botha
authors.affiliation: Salford Royal Foundation NHS Trust, UK (Peter A. Paine) ; Gastrointestinal Sciences, University of Manchester, UK (Peter A. Paine).
authors.forename: Peter A
authors.initials: PA
authors.lastname: Paine
authors.affiliation: Translational Research Centre for Gastrointestinal Disorders, University of Leuven, Belgium (Nathalie Weltens, Huynh Giao Ly, Lukas Van Oudenhove).
authors.forename: Lukas Van
authors.initials: LV
authors.lastname: Oudenhove
authors.affiliation: Centre for Digestive Diseases, Blizard Institute, Wingate Institute of Neurogastroenterology, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, UK (Adam D. Farmer, Steven J. Coen, Michiko Kano, Claude Botha, Qasim Aziz).
authors.forename: Qasim
authors.initials: Q
authors.lastname: Aziz
keywords: Autonomic nervous system; cardiac vagal tone; parasympathetic nervous system