title: Relationship between delta power and the electrocardiogram-derived cardiopulmonary spectrogram: possible implications for assessing the effectiveness of sleep.
abstract: OBJECTIVE
  The physiologic relationship between slow-wave activity (SWA) (0-4 Hz) on the electroencephalogram (EEG) and high-frequency (0.1-0.4 Hz) cardiopulmonary coupling (CPC) derived from electrocardiogram (ECG) sleep spectrograms is not known. Because high-frequency CPC appears to be a biomarker of stable sleep, we tested the hypothesis that that slow-wave EEG power would show a relatively fixed-time relationship to periods of high-frequency CPC. Furthermore, we speculated that this correlation would be independent of conventional nonrapid eye movement (NREM) sleep stages.
  
  
  METHODS
  We analyzed selected datasets from an archived polysomnography (PSG) database, the Sleep Heart Health Study I (SHHS-I). We employed the cross-correlation technique to measure the degree of which 2 signals are correlated as a function of a time lag between them. Correlation analyses between high-frequency CPC and delta power (computed both as absolute and normalized values) from 3150 subjects with an apnea-hypopnea index (AHI) of ≤5 events per hour of sleep were performed.
  
  
  RESULTS
  The overall correlation (r) between delta power and high-frequency coupling (HFC) power was 0.40±0.18 (P=.001). Normalized delta power provided improved correlation relative to absolute delta power. Correlations were somewhat reduced in the second half relative to the first half of the night (r=0.45±0.20 vs r=0.34±0.23). Correlations were only affected by age in the eighth decade. There were no sex differences and only small racial or ethnic differences were noted.
  
  
  CONCLUSIONS
  These results support a tight temporal relationship between slow wave power, both within and outside conventional slow wave sleep periods, and high frequency cardiopulmonary coupling, an ECG-derived biomarker of "stable" sleep. These findings raise mechanistic questions regarding the cross-system integration of neural and cardiopulmonary control during sleep.
authors.affiliation: Division of Pulmonary, Critical Care and Sleep Medicine, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215, United States. Electronic address: rthomas1@bidmc.harvard.edu.
authors.forename: Robert Joseph
authors.initials: RJ
authors.lastname: Thomas
authors.affiliation: Division of Interdisciplinary Medicine and Biotechnology, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215, United States.
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Mietus
authors.affiliation: Division of Interdisciplinary Medicine and Biotechnology, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215, United States.
authors.forename: Chung-Kang
authors.initials: CK
authors.lastname: Peng
authors.affiliation: Sleep Disorders Center, Meitan General Hospital, Beijing, China.
authors.forename: Dan
authors.initials: D
authors.lastname: Guo
authors.affiliation: Department of Pediatrics, University of Chicago, 5721 S. Maryland Ave, MC 8000, Suite K-160, Chicago, IL 60637, United States.
authors.forename: David
authors.initials: D
authors.lastname: Gozal
authors.affiliation: Department of Psychology, West Virginia University, 53 Campus Dr., Morgantown, WV 26506, United States.
authors.forename: Hawley
authors.initials: H
authors.lastname: Montgomery-Downs
authors.affiliation: Veterans Affairs Health Care System, 1400 VFW Pkwy, West Roxbury, MA 02132, United States.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Gottlieb
authors.affiliation: Research Center for Adaptive Data Analysis, National Central University, Chungli, Taiwan.
authors.forename: Cheng-Yen
authors.initials: CY
authors.lastname: Wang
authors.affiliation: Division of Interdisciplinary Medicine and Biotechnology, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215, United States; Wyss Institute for Biologically Inspired Engineering at Harvard University, Boston, MA 02215, United States.
authors.forename: Ary L
authors.initials: AL
authors.lastname: Goldberger
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D016208:Databases, Factual; D004562:Electrocardiography / Q000379:methods*; D004569:Electroencephalography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017286:Polysomnography / Q000379:methods*; D044469:Racial Groups; D012737:Sex Factors; D012815:Signal Processing, Computer-Assisted; D020181:Sleep Apnea, Obstructive / Q000175:diagnosis / Q000503:physiopathology*; D012894:Sleep Stages / Q000502:physiology*
keywords: Correlation; Delta power; High frequency coupling; NREM slow oscillation; Sleep effectiveness; Sleep spectrogram