Polar s810i

Blood pressure was measured indirectly using a stethoscope (Littman, Saint Paul, USA) and an aneroid sphygmomanometer (Welch Allyn, New York, USA) on the left arm of the children, following the criteria established by the VI Brazilian Guidelines on Arterial Hypertension [24 ]. HR was captured by means of a frequency meter, Polar S810i (Polar Electro, Kempele, Finland), previously validated for capture of RR intervals, as well as for HRV analysis using the interval series obtained [25 (link),26 (link)].

The volunteers were evaluated in a room with a temperature between 21 and 23°C and humidity between 40 and 60%. All children were instructed not to drink ANS stimulants, such as coffee, tea and chocolate drinks, for a period of 12 hours prior to the evaluation, and not to perform intense physical activity on the day of the assessments. Before the autonomic assessment the children were instructed to remain silent and awake, spontaneously breathing at rest for 30 minutes in the supine position.
Before the start of the experimental procedure the children were identified by collecting the following information: age, sex, ethnicity, possible symptoms and associated pathologies.
After identification, weight, height, blood pressure, heart rate (HR), body fat percentage and casual blood glucose glycemia were measured. Next, a capture strap was placed at the distal third of the sternum and a heart rate receiver Polar S810i (Polar, Finland) on the wrist, to capture the heart rate beat-to-beat, with the child at rest, breathing spontaneously for 30 minutes in the supine position on a mattress. After the capture of HR at rest, the children performed the active orthostatic test and were then released.

For autonomic assessment, a capture strap was positioned at the distal third of the sternum of the children and the heart rate receiver, Polar S810i (Polar^®, Finland), on the wrist [25 (link),29 (link)] and HR beat-to-beat was recorded throughout the experimental protocol with a sampling rate of 1000 Hz.
The series of RR intervals was subjected to digital filtering complemented by manual to eliminate premature ectopic beats and RR artifacts and only series with more than 95% sinus beats were included in the study [29 (link),30 ]. HRV indices in the time and frequency domains were calculated using the software Kubios HRV (version 2.0) [31 (link)].
In the time domain, the SDNN and rMSSD indices were calculated. The SDNN index represents the standard deviation of all RR intervals [7 (link)] and the rMSSD the root mean square of the successive differences between adjacent normal RR intervals [7 (link)]. For the HRV analysis in the frequency domain the high frequency (HF, 0.15 to 0.4 Hz) and low frequency (LF, 0.04 to 0.15 Hz) spectral components were analyzed in ms² and normalized units, and the ratio of these components (LF/HF ratio). Spectral analysis was calculated using the Fourier Transform algorithm [7 (link)].
For analysis of the HRV indices at rest and during the test, a five minute recorded interval was used and verified to contain a minimum of 256 beats.

The EEG was recorded by using the Micromed Brainquick amplifier (SD-LTM-32) and Micromed Brainspy software (Micromed, Venice, Italy). Recordings were made from Fp1, Fp2, F3, F7, Fz, F4, F8, C3, Cz, C4, T3, T4, P3, P7, Pz, P4, P8, O1, O2 placed according to the Int. 10–20 system with reference to the nose. All electrode impedances were kept at 5 kΩ or below. The EEG signals were continuously recorded and digitized at a sampling rate of 256 Hz. The EEG signal was amplified with a time constant of 0.3 s with a second order high-pass filter at 0.5 Hz and a low-pass filter at 120 Hz (frequency range: 0.5–120 Hz). Electrooculography (EOG) was monitored placed at the medial upper and lateral orbital rim of the right eye (time constant: 0.3 s; high pass filter: 0.1 Hz; low pass filter: 120 Hz; frequency range: 0.5–120 Hz). Two electrodes placed on the neck and on the shoulder recorded muscle activity. Heart rate (Polar S810i, Polar Electro, Buettelborn, Germany) was assessed continuously to control exercise intensity.