Association of heart rate variability index with depressive symptoms and lung function in chronic obstructive pulmonary disease

Table 3 Comparison of relevant indexes of heart rate variability of subjects in each group, mean ± SD

Variable	Without depression (n = 77)	Depression (n = 43)	Control (n = 60)	P value
SDNN (ms)	108.32 ± 17.68	83.21 ± 14.26	148.27 ± 34.73	< 0.001
SDANN (ms)	101.17 ± 13.82	84.54 ± 11.24	136.38 ± 24.12	< 0.001
rMSSD (ms)	32.47 ± 10.23	23.62 ± 8.21	42.72 ± 11.24	< 0.001
PNN50 (%)	13.68 ± 4.91	7.41 ± 2.03	23.85 ± 7.43	< 0.001
HF (ms)	2689.21 ± 841.38	1037.64 ± 302.54	6983.62 ± 1096.37	< 0.001
LF (ms)	963.81 ± 164.82	547.92 ± 110.04	1182.73 ± 287.41	< 0.001

SDNN: Standard deviation of normal-to-normal intervals; SDANN: Standard deviation of the average of normal-to-normal intervals; rMSSD: Root mean square of successive differences of normal-to-normal intervals; PNN50: Percent of pairs of successive normal intervals that differ by more than 50 ms; HF: High frequency; LF: Low frequency.