title: Heart Rate Variability in Adolescents - Normative Data Stratified by Sex and Physical Activity.
abstract: BACKGROUND
  Heart rate variability (HRV) refers to the beat-to-beat fluctuations in the cardiac rhythm occurring due to modulation of the pacemaker (sinoatrial node) activity of the heart by the sympathetic and parasympathetic branches of the autonomic nervous system. Nowadays, cardiovascular diseases and their risk factors are increasingly occurring at a younger age (children and adolescents) and recording of HRV in them will help us to identify cardiovascular autonomic derangement earlier. However, to be used clinically, normative data has to be established in this age group considering other major factors that can influence HRV such as sex, physical activity, and BMI.
  
  
  METHODS
  Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology has provided the standards for measurement of heart rate variability and we have followed the same. In the present study, we have described the normative data for HRV in the adolescent in the age group of 12-17 years, stratified based on sex and physical activity.
  
  
  RESULTS
  Data given below are expressed as median with interquartile range (Median (IQR)) in the following order: non-athlete girls, non athlete boys, athlete girls and athlete boys. Time domain indices - SDNN - 66.35 (40.78), 63.20 (36.20), 113.00 (31.40) and 94.20 (35.55); RMSSD - 69.00 (50.55), 58.70 (43.40), 94.90 (42.10) and 100.30 (47.50); NN50 - 137.50 (100.25), 116.00 (90.50), 137.00 (81.00) and 156.00 (81.50). The frequency domain indices - LF power 1015.00 (1098.75), 945.00 (831.00), 1465 (642.25), and 1211.00 (811.37); HF power - 1324.00 (1707.00), 988.00 (1426.50), 2409.00 (1387.50), and 2219.00 (1752.00); Total power - 3374.50 (3094.25), 2757.00 (2641.00), 5202.00 (2501.50) and 5273.00 (3507.50); LFnu - 45.44 (16.61), 47.63 (29.98), 38.59 (11.81) and 37.10 (11.21); HFnu - 54.56 (16.61), 52.37 (29.98), 61.41 (11.81) and 62.90 (11.21).
  
  
  CONCLUSIONS
  We have given sex and physical activity stratified HRV normative data for adolescents in the age between 12-17 years.
authors.affiliation: Additional Professor, Department of Physiology, Jawaharlal Institute of Postgraduate Medical Education and Research , Puducherry, India .
authors.forename: Vivek Kumar
authors.initials: VK
authors.lastname: Sharma
authors.affiliation: Assistant Professor, Department of Physiology, ESIC Medical College and Hospital , Coimbatore, Tamilnadu, India .
authors.forename: Senthil Kumar
authors.initials: SK
authors.lastname: Subramanian
authors.affiliation: Principal, Jawahar Navodaya Vidyalaya , Kalapet, Puducherry, India .
authors.forename: Vinayathan
authors.initials: V
authors.lastname: Arunachalam
authors.affiliation: PhD scholar, Department of Physiology, Jawaharlal Institute of Postgraduate Medical Education and Research , Puducherry, India .
authors.forename: Rajathi
authors.initials: R
authors.lastname: Rajendran
keywords: Cardiac autonomic function; School children; Short term HRV; Spectral analysis; Time domain analysis