Table 2.

Characteristics of heart rate variability parameters from deep breathing test (N = 101).

HRV Parameters	Median [IQR]
SDNN (ms)	47.3 [26.5–69.4]
CV	5.3 [3.1–7.7]
RMSSD (ms)	27.5 [17.5–51.1]
PNN50	7.3 [1.2–26.7]
SD1	19.4 [12.4–36.2]
SD2	63.8 [34.7–90.4]

SDNN, standard deviation of all normal RR intervals; CV, coefficient of variation of RR intervals; RMSSD, root-mean square of differences between adjacent normal RR intervals; PNN50, the proportion of NN50 divided by total number of RRs, where NN50 represents the number of pairs of successive RRs that differ by more than 50 ms.; SD1, dispersion of points perpendicular to the axis of line-of-identity; SD2, dispersion of points along the line of identity; SD1/SD2, ratio of SD1 to SD2.