TABLE 5.

Heart rate variability of the participants before and immediately after 4‐7‐8 breathing control

Variables	Control group (n = 21)				SD group (n = 22)				p value (before vs. before)	p value (after vs. after)
	Before	After	% change	p value	Before	After	% change	p value
NN intervals (ms)	884.92 ± 86.94	1062.37 ± 95.48	10.55	<0.001*	849.40 ± 125.92	924.22 ± 60.56	13.14	<0.001*	0.515	0.333
SDNN (ms)	75.22 ± 29.12	66.81 ± 48.42	−13.04	0.018*	85.43 ± 49.88	66.13 ± 30.44	−13.29	0.022*	0.913	0.956
RMSSD (ms)	79.30 ± 52.28	79.47 ± 74.42	2.01	0.237	88.39 ± 59.21	66.85 ± 36.49	−7.93	0.041*	0.671	0.990
Total power (ms2)	6289.64 ± 5462.12	5972.90 ± 10049.70	−9.62	0.012*	7779.23 ± 8275.33	4746.41 ± 4503.15	−10.68	0.020*	0.990	0.836
VLF power (ms2)	1676.50 ± 1233.76	603.15 ± 700.30	−58.01	<0.001*	2921.39 ± 3825.24	1087.95 ± 1139.06	−30.78	0.003*	0.568	0.112
LF power (ms2)	1150.47 ± 956.52	807.84 ± 1296.65	−29.71	0.018*	1430.13 ± 1437.75	1091.07 ± 1374.48	−12.07	0.221	0.743	0.388
LFnu power	35.96 ± 15.86	23.12 ± 16.13	−33.54	0.001*	35.97 ± 16.72	30.89 ± 16.80	−5.18	0.155	0.997	0.130
HF power (ms2)	2588.12 ± 2736.36	2202.97 ± 2703.89	−2.50	0.154	3097.27 ± 3864.65	2294.81 ± 2610.88	−42.81	0.258	0.653	0.990
HFnu power	57.03 ± 17.41	65.80 ± 18.00	21.88	0.014*	54.54 ± 16.37	56.72 ± 16.91	11.51	0.519	0.725	0.096
LF/HF ratio	0.77 ± 0.72	0.49 ± 0.70	−26.53	0.002*	0.94 ± 1.22	0.64 ± 0.48	−4.23	0.119	0.836	0.067

Note: Data are presented as mean ± standard deviation.Abbreviations: HF, High‐frequency; HFnu, High‐frequency in normalized units; LF, Low‐frequency; LFnu, Low‐frequency in normalized units; NN, Normal‐to‐normal beat; RMSSD, Root mean square of successive R‐R interval differences; SD, Sleep deprivation; SDNN, Standard deviation of normal beat‐to‐normal beat intervals; VLF, Very low frequency.

^*Significant difference compared with before 4‐7‐8 breathing control (P < 0.05).