title: Reliability of three commercially available heart rate variability instruments using short-term (5-min) recordings.
abstract: OBJECTIVE
  To assess the reliability of heart rate variability (HRV) measures made by three commercially available analysers in healthy subjects.
  
  
  METHODS
  Twenty-nine volunteers (20 males, mean age 35 +/- 13 years and nine females, mean age 29 +/- 11 years) underwent repeated HRV measures under three conditions: lying supine, standing, lying supine with controlled breathing. HRV was measured simultaneously by three instruments. Reliability was assessed statistically by calculating coefficient of variation (CV), intraclass correlation coefficient (ICC) and limits of agreement (LoA).
  
  
  RESULTS
  A wide range of values were found for CV (1-235%) and ICC (R = 0.16-0.99) dependent on the HRV measure assessed and the position in which the measurement was made. For the most part the analysers gave similar values in each condition. The values for CV and ICC were high but within the range reported in the literature. Values for LoA were also high and showed a wide range of values.
  
  
  CONCLUSIONS
  The similarity in measures between systems indicates that biological variation and experimental error play a major role in determining the repeatability of HRV measurements. It is therefore recommended that population-specific reliability coefficients should be published where possible and that authors should take into account the reliability of measures when making sample size calculations.
authors.affiliation: Research Centre for Health Studies, Buckinghamshire Chilterns University College, Chalfont St Giles, Buckinghamshire HP8 4AD, UK. gsande01@bcuc.ac.uk
authors.forename: G R H
authors.initials: GR
authors.lastname: Sandercock
authors.forename: P
authors.initials: P
authors.lastname: Bromley
authors.forename: D A
authors.initials: DA
authors.lastname: Brodie
mesh_terms: D000328:Adult; D015716:Electrocardiography, Ambulatory / Q000295:instrumentation* / Q000379:methods; D019544:Equipment Failure Analysis; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology*; D015203:Reproducibility of Results; D016192:Resting Phase, Cell Cycle / Q000502:physiology*; D012680:Sensitivity and Specificity