BOSTON -- Using information hidden in the beat-to-beat changes of theheart's electrical signals, researchers at Beth Israel DeaconessMedical Center (BIDMC) have developed an inexpensive method to assessthe stability and quality of sleep, which could be used to helpunderstand the mechanisms of sleep control and diagnose sleepdisorders, as well as to test the efficacy of sleep aids and othermedications.
Known as a "sleep spectrogram," the novel graph is based on dataobtained solely from a simple electrocardiogram (ECG). The spectrogramis described in a study in the Sept. 1 issue of the medical journal Sleep, which currently appears on-line.
"This new ECG-based approach is important because it promises toprovide an affordable and readily achievable way to monitor sleepstability in a wide range of conditions, including sleep apnea,depression, fibromyalgia, heart failure and stress," explainscardiologist Ary Goldberger, MD, Director of the Margret & H.A. ReyInstitute for Nonlinear Dynamics in Medicine and the study's seniorauthor.
The new study, led by sleep researcher Robert Thomas, MD, ofBIDMC's Division of Pulmonary, Critical Care and Sleep Medicine,identified two distinct types of behavior exhibited throughout thecourse of a person's sleep, the first being stable and restful, thesecond being unstable and aroused. The results show that conventionalapproaches to categorize non-REM (non-rapid-eye-movement) sleep intogrades of depth do not capture this potentially important dimension.
"Among healthy adults, physiological behaviors will showrelatively abrupt shifts -- a occurring over minutes -- between bothstable and unstable sleep, but the stable stage clearly dominates,"explains Goldberger, who is also a Professor of Medicine at HarvardMedical School. "But," he adds, "in a variety of disease states, thespectrogram shows that an unstable sleep pattern is predominant, andamong patients with severe cases of sleep apnea, virtually all of thepatient's non-REM sleep is unstable."
The creation of the spectrogram could serve as an importantcomplement to traditional sleep staging, which shows cycles of rapideye movement (REM) and non-REM sleep and is obtained throughpolysomnography, a series of measurements that require the use anelectroencephalogram (EEG) to record patients' brain waves.
"Spectrograms can uncover information that is not provided bytraditional sleep scoring," notes Thomas. "Polysomnograms are bothexpensive and time-consuming. The spectrogram, therefore, could providea new way of looking at sleep and offer doctors an alternative to theREM/non-REM sleep scoring system.
Furthermore, we have more recent data showing that thepatterns in humans and rodents are remarkably similar, and suggestingthat what we may be observing is a fundamental and conserved sleepmechanism."
In addition to Goldberger and Thomas, study coauthors includeBIDMC engineer Joseph Mietus and C.K. Peng, PhD, of BIDMC'sCardiovascular Division.
This study was supported by the National Institutes of Health, theG. Harold and Leila Y. Mathers Foundation and the James S. McDonnellFoundation.
Beth Israel Deaconess Medical Center is a patient care,teaching and research affiliate of Harvard Medical School, and ranksthird in National Institutes of Health funding among independenthospitals nationwide. BIDMC is clinically affiliated with the JoslinDiabetes Center and is a research partner of Dana-Farber/Harvard CancerCenter.
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