BACKGROUND: Heart rate variability refers to the beat-to-beat alteration in heart rate. It is usually a slight periodic variation of R-R intervals. Much information of autonomic nerve system balance can be obtained by measuring the heart rate variability of patients. It remains to be shown whether heart rate variability can be used as an index for determining the severity of insomnia and cerebral infarction. OBJECTIVE: This study aimed to analyze the correlation for each frequency spectrum parameter of heart rate variability with an insomnia index, as well as the degree of neurological defects in patients with simple cerebral infarction and cerebral infarction complicated by insomnia. The goal was to verify the feasibility of frequency spectrum parameters for heart rate variability as a marker for insomnia and cerebral infarction. DESIGN: A case-control observation. SETTING: Department of Neurology, First Hospital Affiliated to China Medical University. PARTICIPANTS: Sixty inpatients, and/or outpatients, with cerebral infarction were admitted to the 202 Hospital of Chinese PLA between December 2005 and October 2006, confirmed by CT, and recruited to the study. According to the insomnia condition (insomnia is defined by a Pittsburgh Sleep Quality Index score > 7), the patients were assigned to a simple cerebral infarction group and a cerebral infarction complicated by insomnia group, with 30 subjects in each group. Thirty additional subjects, who concurrently received ex-aminations and were confirmed to not suffer from cerebral infarction and insomnia, were recruited into the control group. Written informed consent was obtained from each subject for laboratory specimens. The pro-tocol was approved by the Hospitals Ethics Committee. METHODS: Following admission, each subjects neurological impairment was assessed with the National Institutes of Health Stroke Scale and Pittsburgh Sleep Quality Index. Heart rate variability of each subject was measured with an autonomic nerve analyzer (Weijin Science and Technology Co., Ltd., Taiwan). Each frequency spectrum parameter of heart rate variability was obtained, including very low frequency, low fre-quency, high frequency, total power, R-R interval, and its mean square. In addition, percentage of low fre-quency, high frequency, and ratio of low frequency to high frequency were calculated. For each heart rate frequency spectrum parameter, the difference between groups was analyzed. Moreover, correlations of each frequency spectrum parameter with insomnia and disease condition were analyzed. Data from each index, which were not normally distributed, were processed by logarithmic transformation. The t-test was used for the comparison of intergroup differences. Single-factor linear regression analysis and t-test were used for the analysis of factor-factor correlation and coefficient of correlation, respectively. MAIN OUTCOME MEASURES: ①Differences of scores in the National Institutes of Health Stroke Scale and Pittsburgh Sleep Quality Index between the simple cerebral infarction group and the cerebral in-farction complicated by insomnia group. ② Differences of heart rate variability parameters between the simple cerebral infarction group and the control group. ③ Correlation of heart rate variability parameters, the Pittsburgh Sleep Quality Index score, and the neurological impairment score.RESULTS: Sixty patients and thirty healthy controls were included in the final analysis. ① The scores of the Pittsburgh Sleep Quality Index and the neurological impairment were significantly higher in the cerebral infarction complicated by insomnia group compared to the simple cerebral infarction group (P < 0.05–0.01). ② R-R interval was significantly longer in the simple cerebral infarction group than in the control group, while R-R interval variance and high-frequency band were significantly lower in the simple cerebral infarc-tion group compared to the control group (P < 0.05). ③ For cerebral infarction patients with insomnia, the Pittsburgh Sleep Quality Index score was significantly positively correlated with neurological impairment (r = 0.54, P < 0.01). The low-frequency band, very low-frequency band, high-frequency band, R-R interval variance, total power, R-R interval, and the percentage of high-frequency were significantly negatively cor-related with the National Institutes of Health Stroke Scale score (r =–0.45 to –0.90, P < 0.05–0.01) and with the Pittsburgh Sleep Quality Index scores (r = –0.56 to –0.36, P < 0.05–0.01). CONCLUSION: Each heart rate variability parameter can be used as an index for assessing dyssomnia and neurologic impairment (r =–0.56 to –0.36, P < 0.05–0.01).