title: Test-retest reliability of heart rate variability and respiration rate at rest and during light physical activity in normal subjects.
abstract: BACKGROUND
  A variable that remains stable over repeated measurements (in stable conditions) is ideal for tracking modifications of the clinical state. The aim of the present study is to examine test-retest reliability of time-domain heart rate variability and respiration rate measurements using a portable device on normal subjects during rest and light physical activity.
  
  
  METHODS
  Twenty-six normal subjects [18 females and 8 males aged 28 +/- 6 years and 34 +/- 12 years (mean +/- SD), respectively] underwent two measurements for time-domain heart rate variability (SDNN and RMSSD) and respiration rate, with 7 days in between. Measurements took place under three conditions: lying down in a laboratory, cycling in a laboratory and sleeping in an ambulatory surrounding. Reliability was assessed statistically by calculating intra-class correlation coefficients (ICC).
  
  
  RESULTS
  Reliability was found to be good to excellent for both time-domain heart rate variability (SDNN: ICC values between 0.74 and 0.85, RMSSD: ICC values between 0.75 and 0.98) and for respiration rate (ICC values between 0.77 and 0.96).
  
  
  CONCLUSIONS
  Both time-domain heart rate variability and respiration rate can be reliably assessed. However, we advise reliability research in a clinical setting before using the device for tracking modifications in a clinical state.
authors.affiliation: Coronel Institute of Occupational Health, Academic Medical Center, Universiteit van Amsterdam, Amsterdam, The Netherlands.
authors.forename: Alida M
authors.initials: AM
authors.lastname: Guijt
authors.forename: Judith K
authors.initials: JK
authors.lastname: Sluiter
authors.forename: Monique H W
authors.initials: MH
authors.lastname: Frings-Dresen
mesh_terms: D000328:Adult; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D012146:Rest / Q000502:physiology*