[Cardiac autonomic responses to head-up tilt in obese adolescents]

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.

to compare cardiac autonomic responses to the head-up tilt maneuver between obese and non-obese adolescents by analyzing heart rate variability.

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 70 masculine 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.

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).

Obese adolescents have an abnormal cardiac autonomic response to the head-up tilt maneuver, characterized principally by a decreased parasympathetic response.