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Figure 1. Comparison of the high-frequency (HF; 0.04–0.15 Hz) component of heart rate variability across the night and during awake before sleep, stage 2 sleep, and rapid eye movement (REM) sleep in alcohol-dependent subjects (n = 14) and matched comparison control subjects (n = 14). Data are mean ± standard error of mean. Repeated-measures analysis of variance showed a significant group effect with alcoholics having lower levels of the HF power component as compared with control subjects (F [1, 24] = 5.0, p < .05), a significant effect for sleep stage (F [2, 52] = 7.8, p < .001] but no group-by-sleep-stage interaction.
