A three electrode (left shoulder, right shoulder and abdomen) electrocardiogram (ECG) will be recorded at a sampling rate of 2048 Hz. Artifacts and heartbeats that will not be generated by sinus node depolarization will be manually edited by an ECG expert who is blinded about the study aims, protocol, and experimental paradigm. Inter beat intervals (IBI) will be automatically calculated from recurrence rate (RR) intervals. Spectral analysis will be carried out using a fast Fourier transform to generate the heart period power spectrum. The heart rate (HR) parameters used were automatically elaborated and included the following: Heart rate (HR); High frequency band (0.15-0.4 Hz, HF n.u.); Low frequency band (0.04-0.15 Hz, LF n.u.); LF/HF ratio, Root Mean Square Standard Deviation (RMSSD); Percentage of the normal sinus-initiates IBI (pNN50); Determinism (DET); and RR.