Table 2.

HR and HRV at baseline and during hypoxia.

		Baseline	Hypoxia	$p$	$df$	$t$	ES
RR	Mean	972	849	0.001**	14.00	4.12	0.74
	S.D.	159	133	—	—	—	—
SDRR	Mean	151	144	0.955	14.00	0.26	0.07
	S.D.	191	185	—	—	—	—
HR	MEAN	65	74	0.000***	14.00	−21.97	0.99
	S.D.	9	9	—	—	—	—
RMSSD	Mean	134	123	0.256	14.00	0.25	0.07
	S.D.	208	209	—	—	—	—
pRR50	Mean	0.33	0.27	0.023*	14.00	2.56	0.56
	S.D.	0.19	0.23	—	—	—	—
VLF (${\mathrm{ms}}^2$)	Mean	4,534	2,785	0.955	14.00	1.05	0.27
	S.D.	7,751	3,145	—	—	—	—
LF (${\mathrm{ms}}^2$)	Mean	8,304	4,745	0.820	14.00	1.04	0.27
	S.D.	15,825	7,663	—	—	—	—
HF (${\mathrm{ms}}^2$)	Mean	50,029	39,955	0.532	14.00	0.64	0.17
	S.D.	113,363	100,374	—	—	—	—
VLF (%)	Mean	27	30	0.479	14.00	−0.73	0.27
	S.D.	19	21	—	—	—	—
LF (%)	Mean	26	28	0.659	14.00	−0.45	0.27
	S.D.	12	17	—	—	—	—
HF (%)	Mean	43	38	0.233	14.00	1.25	0.17
	S.D.	23	26	—	—	—	—
LF/HF	Mean	1.03	1.99	0.115	14.00	−1.68	0.41
	S.D.	0.90	2.73	—	—	—	—

Values are presented as mean and SD. Effects of hypoxia on most parameters of HRV were analyzed using Student’s $t$-test; the exceptions were SDRR and LF/HF, which were analyzed using Wilcoxon’s signed rank test in accordance with the results of normality. Asterisks indicate significant difference between baseline and hypoxia at *$P<0.05$, **$P<0.01$, and ***$P<0.001$, respectively.

Abbreviations: SD, standard deviation; R–R, R–R interval; SDRR, standard deviation of R–R interval; HR, heart rate; HRV, heart rate variability; RMSSD, root mean square of successive differences; pRR50, percentage of adjacent R–R intervals that varied by $>50\mathrm{ms}$; VLF, very-low-frequency spectral power; LF, low-frequency spectral power; HF, high-frequency spectral power; ${\mathrm{ms}}^2$, absolute power; %, relative power; LF/HF, low-frequency to high-frequency ratio.