title: Effects of continuous positive airway pressure on obstructive sleep apnea and left ventricular afterload in patients with heart failure.
abstract: BACKGROUND
  The objectives of this study were to determine the effects of continuous positive airway pressure (CPAP) on blood pressure (BP) and systolic left ventricular transmural pressure (LVPtm) during sleep in congestive heart failure (CHF) patients with obstructive sleep apnea (OSA). In CHF patients with OSA, chronic nightly CPAP treatment abolishes OSA and improves left ventricular (LV) ejection fraction. We hypothesized that one mechanism whereby CPAP improves cardiac function in CHF patients with OSA is by lowering LV afterload during sleep.
  
  
  RESULTS
  Eight pharmacologically treated CHF patients with OSA were studied during overnight polysomnography. BP and esophageal pressure (Pes) (ie, intrathoracic pressure) were recorded before the onset of sleep and during stage 2 non-rapid eye movement sleep before, during, and after CPAP application. OSA was associated with an increase in systolic BP (from 120.4+/-7.8 to 131.8+/-10.6 mm Hg, P<0.05) and systolic LVPtm (from 124.4+/-7.7 to 137.2+/-10.8 mm Hg, P<0.05) from wakefulness to stage 2 sleep. CPAP alleviated OSA, improved oxyhemoglobin saturation, and reduced systolic BP in stage 2 sleep to 115.4+/-8.5 mm Hg (P<0.01), systolic LVPtm to 117.4+/-8.5 mm Hg (P<0.01), heart rate, Pes amplitude, and respiratory rate.
  
  
  CONCLUSIONS
  In CHF patients with OSA, LV afterload increases from wakefulness to stage 2 sleep. By alleviating OSA, CPAP reduces LV afterload and heart rate, unloads inspiratory muscles, and improves arterial oxygenation during stage 2 sleep. CPAP is a nonpharmacological means of further reducing afterload and heart rate during sleep in pharmacologically treated CHF patients with OSA.
authors.affiliation: Sleep Research Laboratories of the Rehabilitation Institute of Toronto and Mount Sinai Hospital and the Department of Medicine of the University of Toronto, Toronto, Ontario, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Tkacova
authors.forename: F
authors.initials: F
authors.lastname: Rankin
authors.forename: F S
authors.initials: FS
authors.lastname: Fitzgerald
authors.forename: J S
authors.initials: JS
authors.lastname: Floras
authors.forename: T D
authors.initials: TD
authors.lastname: Bradley
mesh_terms: D000328:Adult; D006333:Heart Failure / Q000150:complications / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D012891:Sleep Apnea Syndromes / Q000150:complications / Q000503:physiopathology / Q000628:therapy*; D012894:Sleep Stages; D013318:Stroke Volume; D016277:Ventricular Function, Left; D014851:Wakefulness