title: Heart rate variability and cardiovascular risk factors in adolescent boys.
abstract: OBJECTIVE
  To establish reference values of heart rate variability (HRV) measures in a cohort of adolescent boys and to determine the relationship between HRV and the clustering of risk factors (RFs) for cardiovascular disease.
  
  
  METHODS
  This cross-sectional study included 1152 adolescent boys (age: 16.6 ± 1.2 years old). Demographic data, health-related habits, obesity indicators, and blood pressure were evaluated. HRV measures of time (SD of all RR intervals, root mean square of the squared differences between adjacent normal RR intervals, and the percentage of adjacent intervals over 50 ms) and frequency domains were assessed (low [LF] and high [HF] frequency).
  
  
  RESULTS
  The components of HRV were RR interval (827 ± 128 ms), SD of all RR intervals (61.9 ± 23.5 ms), root mean square of the squared differences between adjacent normal RR intervals (54.5 ± 29.4 ms), percentage of adjacent intervals over 50 ms (29.4 ± 20.4%), LF (53 ± 16 nu), HF (47 ± 16), and LF/HF (1.44 ± 1.08). Greater sympathetic and lower parasympathetic modulation at rest were associated with higher adiposity, higher blood pressure and physical inactivity. Adolescents with 2 or more RFs also presented lower HRV than subjects with no RFs (P < .001).
  
  
  CONCLUSIONS
  The study has provided descriptive indicators that help the interpretation of HRV results in adolescents. Lower HRV measures are associated with the clustering of cardiovascular RFs.
authors.affiliation: Associate Graduate Program in Physical Education, University of Pernambuco, Recife, PE, Brazil.
authors.forename: Breno Q
authors.initials: BQ
authors.lastname: Farah
authors.affiliation: Associate Graduate Program in Physical Education, University of Pernambuco, Recife, PE, Brazil.
authors.forename: Mauro V G
authors.initials: MV
authors.lastname: Barros
authors.affiliation: Nemours Children's Clinic and Mayo Clinic College of Medicine, Jacksonville, FL.
authors.forename: Babu
authors.initials: B
authors.lastname: Balagopal
authors.affiliation: Associate Graduate Program in Physical Education, University of Pernambuco, Recife, PE, Brazil. Electronic address: raphaelritti@gmail.com.
authors.forename: Raphael M
authors.initials: RM
authors.lastname: Ritti-Dias
mesh_terms: D000293:Adolescent; D001794:Blood Pressure; D001938:Brazil; D002318:Cardiovascular Diseases / Q000503:physiopathology*; D003430:Cross-Sectional Studies; D004562:Electrocardiography; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D012044:Regression Analysis; D012307:Risk Factors