ABSTRACT
OBJECTIVES: It is well established that primary insomnia affects the activity of autonomic nervous system. We tried to know how the activity of autonomic nervous system during night sleep changes by analyzing correlation between heart rate variability (HRV) index and the variables related with sleep structure in primary insomnia. METHODS: Thirty three subjects (mean age:36.2+/-14.2 years, male:female=15:18) who were diagnosed with primary insomnia were selected for the study. Nocturnal polysomnography (NPSG) was carried out on each subject and correlation was analyzed between high frequency/low frequency ratio (LF/HF ratio), one of HRV indices and the variables related with sleep structure which were calculated from NPSG. RESULTS: When age and sex were controlled, LF/HF ratio showed negative correlations with slow wave sleep and stage 2 sleep, respectively (r(p)=-0.43, p=0.01;r(p)=-0.37, p=0.04). On the other hands LF/HF ratio showed a positive correlation with arousal index (r(p)=0.65, p<0.001). The activity of autonomic nervous system responded differentially depending on the change of sleep structure in primary insomnia. Especially the increase of arousal index and the decrease of slow wave sleep and stage 2 sleep which are the components of non-REM sleep provoked hyperactivity of sympathetic nervous system. CONCLUSION: This study suggests that the typical change of sleep structure in primary insomnia can negatively impact on cardiovascular system.