Association Between Nocturnal Vagal Tone and Sleep Depth, Sleep Quality, and Fatigue in Alcohol Dependence

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Abstract
Background: This study examined whether nocturnal vagal tone as indexed by the high-frequency (HF) power component of heart rate variability is related to measures of sleep depth and daytime perceptions of sleep quality, sleepiness, and fatigue in alcohol dependence. Methods: Abstinent alcohol-dependent patients (n = 14) and comparison control subjects (n = 14) underwent all-night polysomnography along with assessment of heart rate variability during an awake period before sleep and during sleep. Sleep-quality perceptions, along with self-reported sleepiness and levels of energy and fatigue, were obtained in the morning. Results: As compared with control subjects, alcohol-dependent persons showed marked decreases in delta sleep along with impairments of sleep quality and daytime energy. In addition, alcoholics showed a decrease of the HF power component of heart rate variability during the awake period before sleep and during nocturnal sleep as compared with control subjects. HF power during the awake period before sleep correlated with electroencephalographic delta sleep and delta power observed during the subsequent sleep period. HF power during the awake period before sleep also correlated with morning reports of sleep quality, sleepiness, and fatigue. Conclusions: Alcohol dependence compromises vagal output measured before sleep onset, which correlates with loss of delta sleep and with morning reports of sleep impairments. Testing of interventions that target sympathovagal balance might identify new strategies for partial amelioration of the sleep disturbances and impairments in daytime functioning observed in persons with alcohol dependence. ANOVA = analysis of variance; BMI = body mass index; DSM-IV = Diagnostic and Statistical Manual–IV; EKG = electrocardiogram; EEG = electroencephalogram; EMG = electromyography; EOG = electrooculography; h = hours; HF = high frequency; Hz = hertz; LF = low frequency; NREM = nonrapid eye movement; POMS = Profile of Mood States; PSG = polysomnography; PSQI = Pittsburgh Sleep Quality Index; REM = rapid eye movement.