. 2015 Mar;106:79–85. doi: 10.1016/j.biopsycho.2015.02.004

Table 2.

Descriptive statistics and correlations for HF-HRV_sleep during each sleep stage separately with primary indices of sleep quality.

Variables	M	SD	HF-HRV N1	HF-HRV N2	HF-HRV N3	HF-HRV REM
HF-HRV N1 (ms²)^a	8.73	0.97	–
HF-HRV N2 (ms²)^a	8.57	0.92	.85^**	–
HF-HRV N3 (ms²)^a	8.37	1.01	.79^**	.93^**	–
HF-HRV REM (ms²)^a	8.53	0.97	.81^**	.83^**	.69^**	–
PSQI (sum score)^b	4.10	1.37	−.23	−.37^*	−.38^*	−.26
Sleep latency (min)^b	25.71	19.06	−.22	−.17	−.10	−.13
Total sleep time (min)^b	445.81	22.97	−.10	−.11	−.01	−.23
Sleep efficiency (%)^b	92.86	4.70	−.10	−.12	−.04	−.23
Wake after sleep onset (min)^b	13.50	15.81	.29	.20	−.01	.36⁺
Awakenings (N)^a	10.03	6.29	.25	.21	.09	.37^*
Arousals (N)^a	177.62	67.47	−.15	−.13	−.16	.00

Note: N = 29. For HF-HRV N1 N = 28, because no N1 segment was longer than 2 min in one participant.

HF-HRV = high-frequency heart rate variability; PSQI = Pittsburgh Sleep Quality Index, with lower values indicating better sleep quality; HF-HRV N1/N2/N3/REM: HF-HRV during different sleep stages.

Correlation between: HF-HRV N2 &PSQI: p = .035; HF-HRV N3 & PSQI: p = .029; HF-HRV REM & Wake after sleep onset: p = .055; HF-HRV REM & Awakenings: p = .049.

Pearson correlations.

Spearman rho correlations.

p < .05.

^**

p < .01.

⁺

p < .10.