Cardiac Autonomic Nervous System Activity in Obese and Never-Obese Young Men

ARONNE, LOUIS J, RONALD MACKINTOSH, MICHAEL ROSENBAUM, RUDOLPH L LEIBEL, JULES HIRSCH. Cardiac autonomic nervous system activity in obese and never-obese young men. Autonomic nervous system (ANS) activity in age-matched, weight-stable, free-living, ad libitumfed, obese (OB) and never-obese (NO) young men (body mass index means [SD], 38.5 [3.9] and 22.0 [1.7], respectively) was evaluated by sequential blockade of cardiac autonomic innervation with weight-adjusted doses of parasympathetic (atropine) and sympathetic (esmolol) blockers so as to produce maximal effects on heart rate. Change in heart period (interbeat interval) from baseline, induced by atropine, defined parasympathetic control (PC), and the subsequent change, after esmolol administration, defined sympathetic control (SC). The heart period, after PC and SC blockade, defined intrinsic heart period (I). In the OB group, baseline heart period and PC were lower, and SC and I were higher, than in the NO group. The results in the OB, relative to the NO subjects, are similar to those reported in a previous study of NO subjects who had undergone a 10% weight gain by overfeeding. These findings suggest that the ANS of individuals with obesity is chronically altered in a way that would tend to oppose their excessive adiposity, and that these autonomic changes are more likely to be responses to other forces that induce obesity, rather than being primary agents in the production of the disease.     

Autonomic Nervous System Activity and the State and Development of Obesity in Japanese School Children

Objective: The autonomic nervous system (ANS) plays an important role in regulating energy expenditure and body fat content; however, the extent to which the ANS contributes to pediatric obesity remains inconclusive. The aim of this study was to evaluate whether sympathetic and/or the parasympathetic nerve activities were altered in an obese pediatric population. We further examined a physiological association between the duration of obesity and the sympatho‐vagal activities to scrutinize the nature of ANS alteration as a possible etiologic factor of childhood obesity. Research Methods and Procedures: Forty‐two obese and 42 non‐obese healthy sedentary school children were carefully selected from 1080 participants initially recruited to this study. The two groups were matched in age, gender, and height. The clinical records of physical characteristics and development of the obese children were retrospectively reviewed to investigate the onset and progression of obesity. The ANS activities were assessed during a resting condition by means of heart rate variability power spectral analysis, which enables us to identify separate frequency components, i.e., total power (TP), low‐frequency (LF) power, and high‐frequency (HF) power. The spectral powers were then logarithmically transformed for statistical testing. Results: The obese children demonstrated a significantly lower TP (6.77 ± 0.12 vs. 7.11 ± 0.04 ln ms², p < 0.05), LF power (6.16 ± 0.12 vs. 6.42 ± 0.05 ln ms², p < 0.05), and HF power (5.84 ± 0.15 vs. 6.34 ± 0.07 ln ms², p < 0.01) compared with the non‐obese children. A partial correlation analysis revealed that the LF and HF powers among 42 obese children were negatively associated with the duration of obesity independent of age (LF: partial r = ?0.55, p < 0.001; HF: partial r = ?0.40, p < 0.01). The obese children were further subdivided into two groups based on the length of their obesity. All three spectral powers were significantly reduced in the obese group with obesity of >3 years (n = 18) compared to the group with obesity of <3 years. Discussion: Our data indicate that obese children possess reduced sympathetic as well as parasympathetic nerve activities. Such autonomic depression, which is associated with the duration of obesity, could be a physiological factor promoting the state and development of obesity. These findings further imply that preventing and treating obesity beginning in the childhood years could be an urgent and crucial pediatric public health issue.