title: The effects of continuous positive airway pressure on myocardial energetics in patients with heart failure and obstructive sleep apnea.
abstract: OBJECTIVE
  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 [(11)C] 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 10(6) to 8.17 +/- 3.06 x 10(6) mm Hg.ml/m(2), 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.
authors.affiliation: Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Canada.
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Yoshinaga
authors.forename: Ian G
authors.initials: IG
authors.lastname: Burwash
authors.forename: Judith A
authors.initials: JA
authors.lastname: Leech
authors.forename: Haissam
authors.initials: H
authors.lastname: Haddad
authors.forename: Chris B
authors.initials: CB
authors.lastname: Johnson
authors.forename: Robert A
authors.initials: RA
authors.lastname: deKemp
authors.forename: Linda
authors.initials: L
authors.lastname: Garrard
authors.forename: Li
authors.initials: L
authors.lastname: Chen
authors.forename: Kathryn
authors.initials: K
authors.lastname: Williams
authors.forename: Jean N
authors.initials: JN
authors.lastname: DaSilva
authors.forename: Rob S B
authors.initials: RS
authors.lastname: Beanlands
mesh_terms: D000368:Aged; D045422:Continuous Positive Airway Pressure; D005260:Female; D006333:Heart Failure / Q000150:complications / Q000000981:diagnostic imaging / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000378:metabolism*; D049268:Positron-Emission Tomography; D011446:Prospective Studies; D020181:Sleep Apnea, Obstructive / Q000150:complications / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000628:therapy*; D013997:Time Factors