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Enhancement of sleep stability with Tai Chi exercise in chronic heart failure: Preliminary findings using an ECG-based spectrogram methodIntroductionMethodsSubjects, recruitment, and interventionQuality of life, exercise capacity, and neurohormonal markersContinuous ambulatory ECG recordingsStandard heart rate variabilitySleep spectrogram techniqueStatistical analysisResultsSubject characteristicsSleep spectrogramsNeurohormones, exercise capacity, and quality of lifeCorrelations between sleep stability and neurohormones, exercise capacity, and quality of lifeStandard heart rate variability measuresDiscussionAcknowledgementsReferencesOriginal ArticleEnhancement of sleep stability with Tai Chi exercise in chronicheart failure: Preliminary findings using an ECG-basedspectrogram methodGloria Y. Yeha,b,*, Joseph E. Mietusd, Chung-Kang Pengd, Russell S. Phillipsa,b,Roger B. Davisb, Peter M. Waynea, Ary L. Goldbergerd, Robert J. ThomascaDivision for Research and Education in Complementary and Integrative Medical Therapies, Harvard Medical School, Boston, MA, USAbDivision of General Medicine and Primary Care, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USAcDivision of Pulmonary, Critical Care and Sleep Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USAdDivision of Interdisciplinary Medicine and Biotechnology, Beth Israel Deaconess Medical Center, Boston, MA, USAReceived 19 December 2006; received in revised form 7 June 2007; accepted 7 June 2007Available online 3 August 2007AbstractObjective: To assess the effects of a 12-week Tai Chi exercise program on sleep using the sleep spectrogram, a method based on asingle channel electrocardiogram (ECG)-derived estimation of cardiopulmonary coupling, previously shown to identify stable andunstable sleep states.Methods: We retrospectively analyzed 24-h continuous ECG data obtained in a clinical trial of Tai Chi exercise in patients withheart failure. Eighteen patients with chronic stable heart failure, left ventricular ejection fraction 640% (mean [±standard deviation]age, 59 ± 14 years, mean baseline ejection fraction 24% ± 8%, mean) were randomly assigned to receive usual care (N = 10), whichincluded pharmacological therapy and dietary and exercise counseling, or 12 weeks of Tai Chi training (N = 8) in addition to usualcare. Using the ECG-based sleep spectrogram, we compared intervention and control groups by evaluating baseline and 12-weekhigh (stable) and low (unstable) frequency coupling (HFC & LFC, respectively) as a percentage of estimated total sleep time (ETST).Results: At 12 weeks, those who participated in Tai Chi showed a significant increase in HFC (+0.05 ± 0.10 vs. 0.06 ± 0.09 %ETST, p = 0.04) and significant reduction in LFC (0.09 ± 0.09 vs. +0.13 ± 0.13 % ETST, p < 0.01), compared to patients inthe control group. Correlations were seen between improved sleep stability and better disease-specific quality of life.Conclusions: Tai Chi exercise may enhance sleep stability in patients with chronic heart failure. This sleep effect may have a ben-eficial impact on blood pressure, arrhythmogenesis and quality of life.Ó 2007 Elsevier B.V. All rights reserved.Keywords: Exercise; Heart failure; Heart rate variability; Mind-body; Sleep stability1. IntroductionSleep fragmentation is a well-known clinical featurein patients with heart failure. Standard polysomno-graphic categorization of sleep quality shows severalchanges, including reduced total sleep time, reducedsleep efficiency, frequen t stage shifts, increased stage 1non-rapid eye movement (NREM) sleep, reduced toabsent slow wave sleep, and a high microarousal index[1]. Insomnia is a common symptom in patients withheart failure. The mechanisms involved include sleep-disordered breathing, poor sleep hygiene, direct (e.g.,beta-blocker) and indirect (e.g., diuretic causing noctu-ria) medication effects, orthopnea/paroxysmal nocturnaldyspnea, and possibly neurohumoral activation itself.1389-9457/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.sleep.2007.06.003*Corresponding author. Address: Harvard Medical School, OsherInstitute, 401 Park Drive, Suite 22A, Boston, MA 02215, USA. Tel.:+1 617 384 8550; fax: +1 617 384 8555.E-mail address: [email protected] (G.Y. Yeh).www.elsevier.com/locate/sleepSleep Medicine 9 (2008) 527–536Recurrent arousals can severely fragment sleep, contrib-uting to impaired cognitive function and quality of life[2]. In addition , repeated episodes of apnea and hypo-pnea can have deleterious effects on cardiac physiolo gyand function , causing arterial oxyhemoglobin desatura-tions, nocturnal hypertensive surges amplified by arous-als, triggering of arrhythmias, and an amplification ofneurohumoral activation [3,4]. Improving sleep andsleep-breathing, therefore, is considered an importanttherapeutic target in the heart failure population.A relatively new and complementary approach toquantify sleep physiology is the domain of sleep stabil-ity. Originally described solely by the electroencephalo-graphic feature of cyclic alternating pattern (CAP andnon-CAP) NREM sleep [5], recent work has shown thatintegrated oscillations of multiple, linked, physiologicalsystems occur during sleep, and that sleep stabilitymay be better described using a more complex, multi-systems approach. For example, features of CAP onelectroencephalogram (EEG) are usually associated withtemporal instability of respiration, lack of nocturnalblood pressure ‘‘dipping,’’ cyclic bursts of sympatheticactivity, lower thresholds for arousals, and non-restor-ative sleep, a state referred to here as NREM unstablesleep. When the CAP features are absent on EEG (the‘‘non-CAP’’ state), blood pressure ‘‘dipping’’ occurs,respiration demonstrates temporal stability, and arousalthresholds are elevated, a state referred to here as stableNREM sleep [6].We developed a method to quantify sleep stabilityfrom a single channel electrocardiogram (ECG), mathe-matically combining heart rate variability (modulatedby the autonomic nervous system) and the amplitudemodulation of the R-wave associated with mechanicaleffects of respiration. This method that is based on car-diopulmonary coupling generates a ‘‘sleep spectrogram’’and provides a visual and numerical estimate of sleepstability and instability. We have previously shown thathigh-frequency cardiopulmonary coupling during sleepis a feature of


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