High-frequency cardiopulmonary coupling during sleep correlates with memory in depressed patients: A pilot study

It has been demonstrated that a reduction in the amount of high-frequency cardiopulmonary coupling (CPC) is indicative of unstable sleep in unmedicated patients with major depressive disorder (MDD). Considering the close relationship between sleep quality and memory consolidation, this study sought to investigate the potential of high-frequency CPC as a novel biomarker for objective evaluation of memory impairment in MDD. A total of 64 depressed patients and 35 healthy controls were included in this cross-sectional study. High-frequency coupling (HFC) was assessed by electrocardiogram-based CPC analysis using a portable sleep-respiration monitor during sleep for one night. The next day, subjects completed the cognition assessment with the Assessment of Neuropsychological Status (RBANS). The 17-Item Hamilton Depression Rating Scale (HAMD17) and the Hamilton Rating Scales for Anxiety (HAMA) were used to evaluate the severity of depression and anxiety in each patient, respectively. There was no significant difference in the proportion of HFC between depressed patients and healthy controls. In patients with low HFC proportion (<35%), severe anxiety could significantly decrease HFC proportion. The HFC proportion positively correlated with immediate and delayed memory in depressed patients. Further analysis showed that patients with low HFC proportion may have worse delayed memory. The lack of prior exposure to the monitoring equipment and procedure could have generated artefacts that would have disappeared after habituation. These results support a positive correlation between the HFC proportion and memory in depressed patients. Further research is required to explore the clinical implications of these findings.