J Am Coll Cardiol, 2007; 49:450-458, doi:10.1016/j.jacc.2006.08.059 © 2007 by the American College of Cardiology Foundation

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CLINICAL RESEARCH: HEART FAILURE

The Effects of Continuous Positive Airway Pressure on Myocardial Energetics in Patients With Heart Failure and Obstructive Sleep Apnea

Keiichiro Yoshinaga, MD, PhD^_*,1, Ian G. Burwash, MD, FRCPC^_*, Judith A. Leech, MD, FRCP(C), Haissam Haddad, MD, FRCPC, FACC^_*, Chris B. Johnson, MD, FRCPC^_*, Robert A. deKemp, PhD^_*, Linda Garrard, RN, BScN^_*, Li Chen, MSc^_*, Kathryn Williams, MS^_*, Jean N. DaSilva, PhD^_* and Rob S.B. Beanlands, MD, FRCPC, FACC^_*,2,_*

^_* Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Canada
Ottawa Hospital Sleep Medicine Centre, Ottawa, Canada.

Manuscript received May 23, 2006; revised manuscript received August 14, 2006, accepted August 28, 2006.

^_* Reprint requests and correspondence: Dr. Rob S. B. Beanlands, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, Ontario K1Y 4W7, Canada. (Email: rbeanlands{at}ottawaheart.ca).

OBJECTIVES: We sought to examine the short-term and longer term (6-week) effects of continuous positive airway pressure (CPAP) on myocardial energetics.

BACKGROUND: Obstructive sleep apnea (OSA) and heart failure (HF) are both states of increased afterload and metabolic demand. Treatment with CPAP may initially reduce stroke volume but subsequently improves left ventricular function. However, it is not clear whether CPAP therapy favorably affects myocardial energetics and hence improves cardiac efficiency.

METHODS: Twelve patients with HF were divided into two groups: 7 patients with OSA were treated with CPAP (group I), and 5 patients without OSA served as a control group (group II). Oxidative metabolism was measured using the mono-exponential fit of the myocardial [¹¹C] acetate positron emission tomography time-activity curve (k-mono). Myocardial efficiency was derived using the work metabolic index (WMI = [heart rate x stroke volume index x systolic blood pressure]/k-mono) measured at baseline, during short-term CPAP, and after 6 ± 3 weeks of CPAP.

RESULTS: In group I, short-term CPAP tended to reduce SVI (p = 0.063) and reduced oxidative metabolism (p = 0.031). Work metabolic index did not change. However, longer term CPAP improved left ventricular ejection fraction (38.4 ± 3.3% to 43.4 ± 4.8%, p = 0.031), tended to reduce oxidative metabolism (0.047 ± 0.012 to 0.040 ± 0.008 min^–1, p = 0.078), and improved WMI (7.13 ± 2.82 x 10⁶ to 8.17 ± 3.06 x 10⁶ mm Hg·ml/m², p = 0.031). In group II (control), these parameters did not change.

CONCLUSIONS: In this cohort of patients with HF and OSA, short-term CPAP decreased oxidative metabolism and tended to decrease SVI, but did not alter cardiac efficiency. Longer term CPAP improved cardiac efficiency, indicating an energy-sparing effect. These effects may contribute to the benefits of CPAP therapy.

Abbreviations and Acronyms   AHI = apnea/hypopnea index   CPAP = continuous positive airway pressure   HF = heart failure   LV = left ventricle/ventricular   LVEF = left ventricular ejection fraction   MVO 2 = myocardial oxygen consumption   OSA = obstructive sleep apnea   PET = positron emission tomography   SVI = stroke volume index   WMI = work metabolic index

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