Fig. 1

Comparison of the HRV time-domain parameters among the participants. Values are shown as mean ± SEM of a mean of RR intervals (mean RR), b standard deviation of all R–R intervals (SDNN), c root mean square of successive RR intervals differences (RMSSD), and d the mean number of times in an hour in which the change in successive normal sinus R–R intervals exceeds 50 ms (pNN50). Significance level is indicated above the horizontal line in each chart