Autonomic modulation in adolescent obesity - Obesity - Author Abstract

Nutrition Research Newsletter, May, 2003

Hypertension and obesity are well-known risk factors for coronary heart disease in adults. Although the association between obesity and hypertension is firmly established, the mechanisms underlying the development of hypertension have not been identified. Pediatric obesity represents an attractive model to study the mechanisms of obesity and obesity-induced hypertension because weight gain in children is essentially related to increased caloric intake and there have not been interfering periods of dieting, as is often the case in adults.

Recent research has applied methods for quantifying sympathetic nervous pathophysiology in obesity-related hypertension. However, there is controversial data on this subject. A recent study published in Obesity Research investigated the cardiovascular autonomic modulation in children with different durations of obesity, by using standard time domain, spectral heart rate variability (HRV), and nonlinear methods.

Fifty obese children were compared with 12 lean subjects. Obese children were classified as recent (ROB, <4 years), intermediate obese (IOB, 4 to 7 years) and long-term obese (OB, >7 years). A clinical examination, 12 hr fasting wide-range of laboratory tests (including glucose, insulin, lipid profile, and urinary sodium), simultaneous 24 hr ECG Holter, and ambulatory BP monitoring (ABPM) were conducted. The spectral power was quantified in total power, very low-frequency (LF) power, high-frequency (HF) power, and LF to HF ratio. Total, long-term, and short-term time domain HRV were calculated. Time domain (TD) is a general measure of autonomic nervous system balance.

All obese groups had higher casual and ambulatory BP and higher glucose, homeostasis model assessment, and triglyceride levels. All parameters reflecting parasympathetic tone were significantly and persistently reduced in all obese groups in comparison with lean controls. LF normalized units, LF/HF, and cardiac acceleration, reflecting sympathetic activation, were significantly increased in the ROB group. In IOB and OB groups, LF, but not nonlinear, measures were similar to lean controls, suggesting biphasic behavior of sympathetic tone. The nonlinear analysis showed a decreasing trend with the duration of obesity. Long-term HRV measures were significantly reduced in ROB and IOB groups.

The major findings were that children with a shorter history of obesity showed a marked sympathovagal imbalance, characterized by a reduced tonic cardiac vagal outflow and an increase in the indexes of sympathetic hyperactivity. From these results, Rabbia et al. hypothesize that autonomic nervous system changes are already dependent in childhood on the duration of obesity. Therefore, the prevention of obesity in childhood and the effective treatment of overweight children are essential.

Franco Rabbia, Bernard Silke, Andrea Conterno, Tiziana Grosso, et al. Assessment of cardiac autonomic modulation during adolescent obesity. Obesity Research 11(4): 541-548 (April 2003) [Address correspondence to Dr. Franco Rabbia, Hypertension Unit, S. Vito Hospital, University of Turin, Str. San Vito Revigliasco 34, 10133 Turin, Italy. E-mail: franco.rabbia@libero.it]