Revista da Associação Médica Brasileira
Print version ISSN 0104-4230
BRUNETTO, Antônio Fernando et al. Cardiac autonomic responses to head-up tilt in obese adolescents. Rev. Assoc. Med. Bras. [online]. 2005, vol.51, n.5, pp. 256-260. ISSN 0104-4230. http://dx.doi.org/10.1590/S0104-42302005000500015.
INTRODUCTION: Obesity is associated with alterations of the autonomic nervous system. Previous studies in adults have shown that obese individuals present a decreased cardiac autonomic response to postural challenges. However, little is known about the impact of overweight on autonomic responses to passive postural stress in adolescents. OBJECTIVE: to compare cardiac autonomic responses to the head-up tilt maneuver between obese and non-obese adolescents by analyzing heart rate variability. METHODS: Fourteen obese adolescents (15.5±1.6 years) were compared with twenty non-obese subjects (15.4±0.8 years). Cardiac autonomic modulation was studied by heart rate variability (HRV) analysis of 5 minute RR interval recordings before and after a 70º head-up tilt maneuver. HRV was analyzed according to the time domain (TD) and frequency-domain (FD) methods. The power spectral components were studied at low (LF) and high (HF) frequencies and as the LF/HF ratio. RESULTS: Obese adolescents demonstrated significantly lower HF normalized units (38.2±11.1 vs 53.9±15.5, p<0.05) and higher LF normalized units (60.7±11.3 vs 44.6±15.7, p<0.05) in the supine position. No difference was found in any HRV parameters after head-up tilt. When comparing differences between the orthostatic and supine positions, obese adolescents showed lesser changes of LF normalized units (22.4±12.6 vs 38±16.4, p<0.05) and HF normalized units (-21.9±12.4 vs -37.3±16.3, p<0.05). CONCLUSIONS: Obese adolescents have an abnormal cardiac autonomic response to the head-up tilt maneuver, characterized principally by a decreased parasympathetic response.
Keywords : Obesity; Adolescence; Autonomic Nervous System.