Table 1.

Characteristics of heart rate, QT interval duration, and variability in sleep stages.

Variables	Awake	NREM	REM
NN (ms)	962.4 ± 126.3	1032.0 ± 117.5	973.6 ± 109.1
QT mean (ms)	374.6 ± 24.6	389.5 ± 23.1	382.1 ± 23.8
Tp-e (ms)	72.4 ± 7.2	75.9 ± 6.6	74.3 ± 6.4
QTVI	−1.0 ± 0.3	−1.1 ± 0.3	−1.2 ± 0.3

Data are expressed as means ± SD; NREM: nonrapid eye movement sleep stage; REM: rapid eye movement sleep stage; NN: Normal-to-Normal interval; QT: QT interval; Tp-e: T-wave peak to T-wave end interval; QTVI: QT variability index.