A new approach to sleep study: does heart tell us a lot?

Abstract

Introduction It has been proven that ECG-derived respiration signal is highly correlated with the actual respiration waveforms. Cardiopulmonary coupling (CPC) analysis is derived from an estimation of the coupling between the autonomic and respiratory drives, using heart rate and respiratory modulation of QRS amplitude, respectively. This dual information can be extracted from a single channel of ECG, and is highly correlated with the actual respiration waveforms. High frequency coupling (HFC) is the marker of stable sleep, and low-frequency coupling (LFC) is the marker of unstable sleep. Fragmented sleep is characterized by coupled low-frequency behaviors across numerous sleep based physiological stream. There have been an increasing number of papers evaluating CPC or using CPC as a clinical measurement. Materials and methods The literature search was performed via the internet using the PubMed, the Cochrane database and Sleep abstract supplements. The search included papers only in English, published up to June 2013. The key words which were searched in the titles and abstracts were the terms “cardiopulmonary”, “coupling”, “CPC”, “ECG-derived” “Electrocardiogram-based spectrogram” in combination with the name of all types of sleep disorders (e.g. “insomnia”). Results 46 relevant English articles were found, 29 (63%) was cardiopulmonary coupling. 9 (19.6%) articles explain mechanism, 30 (65.2%) articles are studies on SDB, and 7 (15.2%) articles relate to other sleep disorders or comorbidities. The methods of CPC analysis as a measurement of sleep evaluation has been compared with conventional PSG or PTT. While most of the articles are about sleep apnea, sleep quality, detecting central and obstructive, and evaluating effects of PAP therapies, studies have covered sleep quality study in sleep apnea, insomnia, hypertension, chronic heart failure, diabetics, fibromyalgia, as well as healthy subjects. Conclusion Using data derived from ECG can be used as clinical screen or post-treatment follow-up. This review confirmed the association between sleep physiology and sleep spectrums analyzed by cardiopulmonary coupling. As sleep problems are of growing concern, easier access of overnight ECG data can be used broadly when sleep monitor is necessary. With the techniques of cardiopulmonary analysis, a portable monitor for sleep can be effective by collecting enough data for sleep analysis, meanwhile be more convenient and cost-effective. Furthermore, adding actigraphy and/or oximetry will be recommended for clinical applications. Acknowledgements I would like to thank Professor C.K. Peng (Division of Interdisciplinary Medicine & Biotechnology in BIDMC) for his help in organizing a project and mentoring me with the Cardiopulmonary Coupling techniques. I would also like to thank Dr. Robert Thomas (Sleep specialist in BIDMC, affiliated Hospital of Harvard Medical School) for his mentoring me with sleep clinic observation.