Heart Autonomic Modulation in the Obese Children: Evaluation using linear and nonlinear methods

Background: Functional alterations of the Autonomic Nervous System (ANS) may be due to obesity, but may be identified by the analysis of heart rate variability (HRV). Better understanding of organic systems complexity enables an extension to more sophisticated analysis of HRV, those related to Chaos Theory included, and might be used in the investigation of obese children ANS. Aim: Investigation of autonomic heart modulation in obese children (OC). Methods: The sample consisted of 12 OC (BMI > p97) and 12 eutrophic children (BMI < p85), aged from 6 to 13 years old. Heart rate was collected with a Polar device, during a 20 minutes rest in a supine position. HRV was analysed linearly by the square root of mean squared differences of successive NN intervals (RMSSD) and the division of the number of interval differences of successive NN intervals greater than 50 ms by number of NN intervals (pNN50), and nonlinearly by recurrence percentage (%REC), Trapping Time and Entropy, along with components of symbolic analysis (%0 V, %1 V, %2LV, %2UV), and Shannon Entropy. Differences between the groups was evaluated by Student t test for independent samples (α = 5%). Results: Differences with statistical significance (p < 0.05) were found in all but one of the parameters, being RMSSD the sole exception (p = 0.074). Conclusions: Autonomic heart modulation within an OC population is somewhat endangered when compared to non-obese subjects. Thus, complex and interconnected mechanisms involving cardiovascular regulation, and nonlinear parameters related to Chaos Theory may bring additional evidence when compared to linear methods.