Hrv software version 3

Cardiac autonomic modulationThe series of RR intervals was subjected to digital filtering using the Polar Precision Performance SW software (version 4.01.029), followed by manual filtering performed through the Excel software, to eliminate ectopic premature and artifact beats. Only series with more than 95% sinus beats were included in the study²⁶. Cardiac autonomic modulation was analyzed using 1000 consecutive RR intervals, obtained from the most stable part of the series²⁶. The Kubios HRV software, version 3.1, was used to calculate the HRV indices²⁷.
To analyze HRV in the time domain, the indices Mean RR, rMSSD, SDNN and pNN50 were used. Mean RR represents the mean value of the RR intervals. rMSSD is the root mean square of differences between adjacent normal RR intervals in a time interval, expressed in ms⁷. SDNN is the standard deviation of all normal RR intervals, expressed in ms. pNN50 is the percentage of adjacent RR intervals with a difference in duration > 50 ms⁷.
For analysis on the frequency domain, the spectral components of low frequency (LF; 0.04 to 0.15 Hertz) and high frequency (HF; 0.15 to 0.4 Hertz), expressed in milliseconds squared (ms²) and normalized units, and the LF/HF ratio, were calculated using a fast Fourier transform algorithm⁷.

Before and after the experiment, the subjects wore the Polar Team2 (Finland), and the height, weight, date of birth, and other information of subjects were input into the computer, then collect the heart rate of subjects for 10 minutes when the subjects rest for 5 minutes in the supine position with eyes closed (10 subjects for each test). Finally, time domain and frequency domain index of HRV were calculated by Kubios HRV software version 3.1 (Kuopio, Finland).
The following spectral HRV parameters were obtained for analysis: Time domain indicators include heart rate (HR, beats/min), RR interval (ms), and RMSSD (square root of the squared difference between adjacent RR intervals and the mean, ms). Frequency-domain indicators of HRV include total power (TP, 0.00-0.40 Hz), low-frequency power (LF, 0.04-0.15 Hz; sympathetic activity indicator), and high-frequency power (HF, 0.15-0.40 Hz; vagal activity level indicator). Since HF and LF are affected by TP, their values are normalized and then compared. LFn (the normalized low‐frequency power) = LF/TP∗100%; HFn (the normalized high‐frequency power) = HF/TP∗100%; the LF/HF ratio is used as the index of sympathetic-vagal balance. The final statistical parameters include LFn, HFn, and LF/HF ratio.