title: Association between obesity and heart rate variability indices: an intuition toward cardiac autonomic alteration - a risk of CVD.
abstract: BACKGROUND
  Obese people have a higher prevalence of cardiovascular disease, which is supposed to be due to autonomic dysfunction and/or metabolic disorder. The alterations in cardiac autonomic functions bring out the changes in the heart rate variability (HRV) indicators, an assessing tool for cardiac autonomic conditions.
  
  
  OBJECTIVE
  To compare the cardiac autonomic activity between obese and normal weight adults and find out the highest association between the indices of HRV and obesity.
  
  
  METHODS
  The study was conducted in 30 adult obese persons (body mass index [BMI] >30 kg/m2) and 29 healthy normal weight controls (BMI 18-24 kg/m2). Short-term HRV variables were assessed using standard protocol. Data were compared between groups using Mann-WhitneyUtest. Obesity indices such as waist circumference, hip circumference, waist-hip ratio (WHR), and BMI were measured and calculated, and they were correlated with HRV indices using Spearman's correlation analysis.
  
  
  RESULTS
  In the obese group, there was a significant increase in the mean heart rate, whereas the HRV parasympathetic indicators were less (eg, root mean square of differences of successive RR intervals [28.75 {16.72-38.35} vs 41.55 {30.6-56.75} ms,p=0.018], number of RR intervals that differ by >50 ms, that is, NN50 [15.5 {2-39} vs 83.5 {32.75-116.25},p=0.010], etc) and the sympathetic indicator low frequency (LF)/high frequency (HF) ratio (1.2 [0.65-2.20] vs 0.79 [0.5-1.02],p=0.045) was more than that of the normal weight group. Spearman's correlation between HRV and obesity indices showed significant positive correlation of WHR with LF in normalized unit (r=0.478,p<0.01) and LF/HF ratio (r=0.479,p<0.01), whereas it had significant negative correlation with high frequency power ms2(r=-0.374,p<0.05) and HF in normalized unit (r=-0.478,p<0.01). There was a nonsignificant correlation of BMI with HRV variables in obese individuals.
  
  
  CONCLUSIONS
  Increased WHR, by far an indicator of visceral adiposity, was strongly associated with reduced cardiac parasympathetic and increased sympathetic activity in obese individuals defined by BMI. However, BMI itself has a weak relationship with HRV cardiac autonomic markers. Thus, even with a slight increase in WHR in an individual, there could be a greater risk of cardiovascular morbidity and mortality brought about by cardiac autonomic alterations.
authors.affiliation: Department of Physiology.
authors.forename: Ram Lochan
authors.initials: RL
authors.lastname: Yadav
authors.affiliation: Department of Physiology.
authors.forename: Prakash Kumar
authors.initials: PK
authors.lastname: Yadav
authors.affiliation: Department of Microbiology, Chitwan Medical College, Bharatpur.
authors.forename: Laxmi Kumari
authors.initials: LK
authors.lastname: Yadav
authors.affiliation: Department of Physiology, BP Koirala Institute of Health Sciences, Dharan.
authors.forename: Kopila
authors.initials: K
authors.lastname: Agrawal
authors.affiliation: Department of Biochemistry, Janaki Medical College, Janakpur, Nepal.
authors.forename: Santosh Kumar
authors.initials: SK
authors.lastname: Sah
authors.affiliation: Department of Physiology.
authors.forename: Md Nazrul
authors.initials: MN
authors.lastname: Islam
keywords: BMI; HRV; WHR; body mass index; cardiac autonomic regulation; heart rate variability; obesity; waist–hip ratio