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. 2021 Jan 13;94(5):855–866. doi: 10.1007/s00420-020-01632-4

Table 4.

Descriptive statistics for heart rate variability variables

Differential stress inventory groups
Total sample Normal Overstressed Stress resistant Low stress/high coping High stress/high coping DSI groups’ differences
(n = 119) (n = 58) (n = 11) (n = 21) (n = 17) (n = 12)
Time domain
SDNN (ms)
 Mean ± SD 60.74 ± 16.38 61.88 ± 15.35 54.17 ± 21.20 57.28 ± 14.47 63.14 ± 20.26 63.93 ± 13.28 F = 0.95,
 CI (57.80, 63.69) (57.93, 65.83) (41.64, 66.70) (51.10, 63.47) (53.51, 72.77) (56.41, 71.44) p = .437
 Median 60,31 61,44 47,16 52,20 61,82 63,98
 Minimum 28,30 28,30 30,43 37,69 35,22 43,54
 Maximum 118,26 102,96 104,12 87,29 118,26 87,49
RMSSD (ms)
 Mean ± SD 35.27 ± 15.53 37.54 ± 16.45 28.34 ± 13.44 31.54 ± 13.99 37.17 ± 15.92 34.49 ± 13.68 F = 1.24,
 CI (32.48, 38.06) (33.30, 41.77) (20.40, 36.28) (25.55, 37.52) (29.60, 44.73) (26.75, 42.23) p = .297
 Median 31,97 35,40 23,15 31,34 30,76 33,36
 Minimum 10,97 10,97 14,60 15,78 13,61 14,74
 Maximum 82,75 82,75 52,36 69,23 69,29 63,87
PNN50 (%)
 Mean ± SD 11.00 ± 9.27 12.18 ± 9.60 7.83 ± 9.37 7.87 ± 6.54 12.72 ± 10.93 11.20 ± 8.48 F = 1.32,
 CI (9.33, 12.66) (9.71, 14.65) (2.29, 13.37) (5.08, 10.67) (7.53, 17.91) (6.41, 16.00) p = .268
 Median 9,44 10,02 3,39 8,89 8,66 11,38
 Minimum 0,19 0,19 0,58 1,16 0,28 0,67
 Maximum 41,47 41,47 26,41 20,77 36,68 29,54
Frequency domain
Total power (ms2)
 Mean ± SD 1,439.21 ± 953.56 1,510.71 ± 950.76 1,087.42 ± 822.14 1,238.51 ± 833.41 1,568.94 ± 1,143.54 1,583.51 ± 1,007.11 F = 0.83,
 CI (1,267.88, 1,610.53) (1,266.03, 1,755.40) (601.58, 1,573.26) (882.06, 1,594.96) (1,025.34, 2,112.53) (1,013.69, 2,153.33) p = .508
 Median 1225,55 1236,46 719,24 907,89 1405,51 1421,77
 Minimum 235,93 235,93 286,84 355,02 381,89 522,81
 Maximum 4815,85 4815,85 2639,94 3084,05 4540,96 4195,91
LF (n.u.)
 Mean ± SD 69.35 ± 11.69 68.06 ± 11.38 71.97 ± 7.49 72.58 ± 12.46 67.50 ± 14.93 70.18 ± 9.81 F = 0.83,
 CI (67.25, 71.45) (65.13, 70.99) (67.54, 76.40) (67.26, 77.91) (60.40, 74.59) (64.63, 75.73) p = .506
 Median 71,96 71,70 70,59 77,59 72,66 69,55
 Minimum 31,36 36,28 58,14 46,04 31,36 54,04
 Maximum 88,32 84,91 83,19 88,32 86,55 85,10
HF (n.u.)
 Mean ± SD 30.53 ± 11.64 31.81 ± 11.34 27.93 ± 7.45 27.30 ± 12.40 32.37 ± 14.83 29.74 ± 9.78 F = 0.83,
 CI (28.44, 32.62) (28.90, 34.73) (23.53, 32.33) (22.00, 32.61) (25.32, 39.42) (24.21, 35.27) p = .507
 Median 27,95 28,12 29,27 22,33 27,27 30,32
 Minimum 11,64 15,06 16,78 11,64 13,42 14,86
 Maximum 68,19 63,61 41,64 53,84 68,19 45,91
LF/HF ratio
 Mean ± SD 2.75 ± 1.40 2.53 ± 1.22 2.85 ± 1.16 3.33 ± 1.71 2.74 ± 1.68 2.74 ± 1.34 F = 1.28,
 CI (2.50, 3.01) (2.22, 2.85) (2.16, 3.53) (2.60, 4.07) (1.94, 3.54) (1.98, 3.50) p = .283
 Median 2,57 2,55 2,41 3,48 2,66 2,30
 Minimum 0,46 0,57 1,40 0,85 0,46 1,18
 Maximum 7,59 5,64 4,96 7,59 6,45 5,73
LF peak (Hz)
 Mean ± SD 0.06 ± 0.02 0.06 ± 0.02 0.05 ± 0.01 0.06 ± 0.02 0.06 ± 0.02 0.06 ± 0.03 F = 1.04,
 CI (0.06, 0.06) (0.05, 0.06) (0.05, 0.06) (0.05, 0.07) (0.06, 0.07) (0.05, 0.08) p = .389
 Median 0,05 0,05 0,05 0,05 0,06 0,05
 Minimum 0,04 0,04 0,04 0,04 0,04 0,04
 Maximum 0,12 0,10 0,08 0,10 0,09 0,12
HF peak (Hz)
 Mean ± SD 0.20 ± 0.06 0.21 ± 0.07 0.20 ± 0.06 0.18 ± 0.05 0.19 ± 0.06 0.19 ± 0.06 F = 1.29,
 CI (0.19, 0.21) (0.19, 0.23) (0.17, 0.24) (0.16, 0.20) (0.16, 0.22) (0.16, 0.22) p = .278
 Median 0,15 0,20 0,19 0,15 0,15 0,15
 Minimum 0,15 0,15 0,15 0,15 0,15 0,15
 Maximum 0,35 0,35 0,32 0,31 0,32 0,30
Non-linear
SD1 (ms)
 Mean ± SD 24.94 ± 10.98 26.54 ± 11.63 20.04 ± 9.50 22.30 ± 9.89 26.28 ± 11.25 24.39 ± 9.67 F = 1.24,
 CI (22.97, 26.91) (23.55, 29.54) (14.43, 25.65) (18.07, 26.53) (20.93, 31.63) (18.91, 29.86) p = .297
 Median 22,61 25,03 16,37 22,16 21,75 23,59
 Minimum 7,76 7,76 10,32 11,16 9,62 10,43
 Maximum 58,52 58,52 37,02 48,95 49,00 45,16
SD2 (ms)
 Mean ± SD 47.44 ± 14.26 48.52 ± 13.61 41.16 ± 13.89 44.66 ± 14.98 49.20 ± 15.79 50.29 ± 14.14 F = 1.00,
 CI (44.87, 50.00) (45.02, 52.03) (32.95, 49.37) (38.25, 51.07) (41.69, 56.70) (42.29, 58.29) p = .410
 Median 45,91 46,32 35,88 39,07 47,07 48,02
 Minimum 21,19 21,19 22,99 24,72 24,07 31,77
 Maximum 81,44 81,44 65,73 74,22 80,47 81,31
α1
 Mean ± SD 1.20 ± 0.16 1.18 ± 0.14 1.24 ± 0.14 1.25 ± 0.17 1.17 ± 0.23 1.22 ± 0.15 F = 0.99,
 CI (1.17, 1.23) (1.14, 1.22) (1.16, 1.32) (1.17, 1.32) (1.06, 1.28) (1.13, 1.30) p = .418
 Median 1,23 1,21 1,23 1,30 1,24 1,20
 Minimum 0,66 0,77 0,98 0,80 0,66 0,92
 Maximum 1,53 1,48 1,48 1,49 1,53 1,46
α2
 Mean ± SD 0.49 ± 0.06 0.49 ± 0.06 0.50 ± 0.07 0.50 ± 0.06 0.48 ± 0.07 0.49 ± 0.08 F = 0.26,
 CI (0.48, 0.50) (0.47, 0.50) (0.46, 0.54) (0.47, 0.52) (0.45, 0.51) (0.44, 0.54) p = .906
 Median 0,49 0,49 0,49 0,50 0,47 0,46
 Minimum 0,36 0,36 0,41 0,36 0,36 0,38
 Maximum 0,66 0,65 0,64 0,60 0,62 0,66
Indices
PNS index
 Mean ± SD − 0.76 ± 0.74 − 0.66 ± 0.74 − 0.96 ± 0.86 − 0.88 ± 0.56 − 0.76 ± 0.89 -0.82 ± 0.75 F = 0.61,
 CI (− 0.89, − 0.62) (− 0.85, − 0.47) (− 1.47, − 0.45) (− 1.12, − 0.64) (− 1.19, − 0.34) (− 1.24, -0.39) p = .658
 Median − 0,85 − 0,79 − 1,22 − 0,99 − 0,96 − 0,65 –
 Minimum − 2,28 − 2,28 − 2,19 − 2,04 − 1,96 − 1,95 –
 Maximum 1, 58 1, 47 0,81 0,13 1,58 0,15 –
SNS index
 Mean ± SD 0.43 ± 0.79 0.35 ± 0.76 0.60 ± 1.02 0.47 ± 0.66 0.52 ± 0.86 0.46 ± 0.87 F = 0.34,
 CI (0.29, 0.57) (0.16, 0.55) (− 0.00, 1.20) (0.19, 0.76) (0.11, 0.93) (− 0.03, 0.95) p = .853
 Median 0,40 0,31 0,68 0,41 0,67 0,18 –
 Minimum − 1,62 − 1,43 − 1,16 − 0,75 − 1,62 − 0,41 –
 Maximum 2, 56 2, 56 2, 47 2, 13 1, 91 2, 21 –
Stress index
 Mean ± SD 7.75 ± 1.79 7.54 ± 1.74 8.56 ± 2.26 7.98 ± 1.66 7.72 ± 1.82 7.65 ± 1.80 F = 0.85,
 CI (7.43, 8.07) (7.09, 7.99) (7.22, 9.90) (7.27, 8.69) (6.86, 8.59) (6.63, 8.67) p = .497
 Median 7, 77 7,59 9, 16 8, 15 8, 09 7, 22 –
 Minimum 3, 86 3, 86 5, 24 5, 03 3, 86 4, 91 –
 Maximum 12, 39 12, 39 12, 16 11, 41 11, 64 10, 95 –
Stress zones
 Low 46 (38.7%) 24 (41.4%) 4 (36.4%) 6 (28.6%) 7 (41.2%) 5 (41.7%) p = .873
 Normal 72 (60.5%) 33 (56.9%) 7 (63.6%) 15 (71.4%) 10 (58.8%) 7 (58.3%) –
 Elevated 1 (0.8%) 1 (1.7%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) –

For continuous variables, mean, standard deviation, 95% confidence interval, median, minimum, and maximum values are reported, along with results from ANOVA. For categorical variables, n and % are reported, along with results from Fisher's exact test

LF  low frequency, HF  high frequency, n.u.  normalised units, SDNN standard deviation of RR intervals, RMSSD  square root of the mean squared differences between successive RR intervals. PNN50  % of successive RR interval pairs that differ more than 50 ms. α1   short-term fluctuations of detrended fluctuation analysis, α2  long-term fluctuations of detrended fluctuation analysis, PNS  parasympathetic nervous system, SNS  sympathetic nervous system, Stress index  square root of Baevsky’s stress index. Heart rate variability was recorded over 24 h