title: Effect of continuous positive airway pressure and placebo treatment on sympathetic nervous activity in patients with obstructive sleep apnea.
abstract: OBJECTIVE
  We studied the effect of continuous positive airway pressure (CPAP) treatment on sympathetic nervous activity in 38 patients with obstructive sleep apnea.
  
  
  METHODS
  Randomized, placebo-controlled trial.
  
  
  METHODS
  Patients underwent polysomnography on three occasions in a clinical research center, and had BP monitored over 24 h at home. All of the patients had sleep apnea with a respiratory disturbance index (RDI) > 15.
  
  
  METHODS
  The patients were randomized blindly to CPAP or placebo (CPAP at ineffective pressure) treatment.
  
  
  RESULTS
  Prior to therapy, the number of apneas and the severity of nocturnal hypoxia correlated significantly with daytime urinary norepinephrine (NE) levels, but not nighttime urinary NE levels. CPAP treatment lowered daytime BP from 99 +/- 2 mm Hg to 95 +/- 3 mm Hg (mean +/- SEM) and nighttime BP from 93 +/- 3 mm Hg to 88 +/- 3 mm Hg. Placebo CPAP treatment decreased both day and night mean BP only 2 mm Hg. CPAP, but not placebo, treatment lowered daytime plasma NE levels by 23%, daytime urine NE levels by 36%, daytime heart rate by 2.6 beats/min, and increased lymphocyte beta(2)-adrenergic receptor sensitivity (all p < 0.05). The effect of CPAP treatment on nighttime urine NE levels and heart rate did not differ from placebo treatment. There was a suggestion of an effect of placebo CPAP treatment on nighttime measures, but not on daytime measures.
  
  
  CONCLUSIONS
  We conclude that daytime sympathetic nervous activation is greater with more severe sleep apnea. CPAP treatment diminished the daytime sympathetic activation; the potential nighttime effect of CPAP treatment was obscured by a small placebo effect.
authors.affiliation: Department of Medicine, University of California San Diego, San Diego, CA 92103, USA. mziegler@ucsd.edu
authors.forename: M G
authors.initials: MG
authors.lastname: Ziegler
authors.forename: P J
authors.initials: PJ
authors.lastname: Mills
authors.forename: J S
authors.initials: JS
authors.lastname: Loredo
authors.forename: S
authors.initials: S
authors.lastname: Ancoli-Israel
authors.forename: J E
authors.initials: JE
authors.lastname: Dimsdale
mesh_terms: D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000652:urine; D017286:Polysomnography; D011175:Positive-Pressure Respiration; D011943:Receptors, Adrenergic, beta; D012891:Sleep Apnea Syndromes / Q000503:physiopathology* / Q000628:therapy*; D013564:Sympathetic Nervous System / Q000503:physiopathology*
chemical_list: D011943:Receptors, Adrenergic, beta; D009638:Norepinephrine