Cognitive deficit is correlated with sleep stability in insomnia: A cardiopulmonary coupling study

OBJECTIVES: To assess the correlation of cognitive function with sleep stability and depressive‐anxious symptoms in insomnia patients. METHODS: Twenty‐two insomnia patients with cognitive impairment (insomnia‐CI), 21 insomnia patients with normal cognition (insomnia‐CN), and 15 matched healthy control subjects (HCs) were enrolled and completed neuropsychological tests, the Hamilton Depression and Anxiety Scales (HAMD and HAMA), the Epworth Sleepiness Scale, the Pittsburgh Sleep Quality Index (PSQI),the Insomnia Severity Index (ISI), and the cardiopulmonary coupling (CPC) examination. Ratios of high‐frequency coupling (HFC), low‐frequency coupling (LFC), and very low‐frequency coupling (VLFC) measured by CPC analysis represent stable sleep, unstable sleep, and wake/rapid eye movement (REM) sleep, respectively. RESULTS: The HAMD, HAMA, PSQI, and ISI scores were higher in the insomnia‐CN patients than in the HCs (all p < .01). However, no differences were found in the HFC, LFC, and VLFC ratio between the HCs and insomnia‐CN groups. Compared with the insomnia‐CN patients, insomnia‐CI patients exhibited higher scores on the HAMD, HAMA (all p < .01), and PSQI (p < .05), performed worse on the Auditory Verbal Learning Test, Trial Making Test B, and Stroop Test B (all p < .01), had a lower HFC ratio, and had a higher LFC ratio in the CPC analysis (all p < .01). Furthermore, in the insomnia patients, poorer cognition was correlated with a decreased HFC ratio and an increased VLFC ratio (r = .356, p = .019; r = −.339, p =.026, respectively) and increased HAMD and HAMA scores (r = −.507, p < .001; r = −.561, p < .001, respectively); a higher VLFC ratio was correlated with an increased ISI score (r = .346, p = .023). CONCLUSIONS: Cognitive deterioration in insomnia patients was associated with a decreased stable sleep ratio, an increased wake/REM sleep ratio and more severe symptoms of depression and anxiety. CPC analysis can reflect the severity of insomnia.