title: Evaluation of continuous positive airway pressure therapy on renin-angiotensin system activity in obstructive sleep apnea.
abstract: BACKGROUND
  Obstructive sleep apnea (OSA) has been associated with kidney function loss, which may be related to changes in the renin-angiotensin system (RAS).
  
  
  OBJECTIVE
  We sought to determine the effect of continuous positive airway pressure (CPAP) of patients with OSA on renal hemodynamics at baseline and in response to angiotensin II (AngII), which reflects RAS activity.
  
  
  METHODS
  Twenty normotensive, nondiabetic, newly diagnosed OSA subjects (15 men, 5 women, 50 ± 2 yr, respiratory disturbance index [RDI] > 15 h(-1)) with nocturnal hypoxemia (SaO2 < 90% for >12% of the night) were studied in high-salt balance pre- and post-CPAP therapy (>4 h CPAP use/night for 1 mo). Glomerular filtration rate (GFR), renal plasma flow (RPF), and filtration fraction (FF) (a surrogate marker for intraglomerular pressure) were measured pre- and post-CPAP using inulin and para-aminohippurate clearance techniques at baseline and in response to graded AngII infusion (3 ng/kg/min × 30 min and 6 ng/kg/min × 30 min, respectively).
  
  
  RESULTS
  CPAP corrected OSA and hypoxemia (RDI: 42 ± 4 vs. 4 ± 1 h(-1), P < 0.001; duration SaO2 < 90%: 36% ± 5% vs. 6 ± 2%, P < 0.001). CPAP reduced GFR (124 ± 8 ml/min vs. 110 ± 6 ml/min, P = 0.014), increased RPF (692 ± 36 ml/min vs. 749 ± 40 ml/min, P = 0.059), and reduced baseline FF (18.9 ± 1.6% vs. 15.3 ± 1.0%, P = 0.004). Post-CPAP demonstrated a blunted GFR response (-9 ± 3 ml/min vs. -2 ± 2 ml/min, P = 0.033) and augmented RPF response (-182 ± 22 ml/min vs. -219 ± 25 ml/min, P = 0.024) to AngII. FF response was maintained (P = 0.4). CPAP reduced baseline mean arterial pressure (94 ± 2 vs. 89 ± 2 mm Hg, P = 0.002), plasma aldosterone (149 ± 18 vs. 109 ± 10 pmol/L, P = 0.003), and urinary protein excretion (61 [39-341] mg/day vs. 56 [22-204] mg/d, P = 0.003).
  
  
  CONCLUSIONS
  CPAP therapy was associated with improved renal hemodynamics and down-regulation of renal RAS activity, suggesting a potential therapeutic benefit for kidney function.
authors.affiliation: 1 Department of Medicine.
authors.forename: David D M
authors.initials: DD
authors.lastname: Nicholl
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Hanly
authors.forename: Marc J
authors.initials: MJ
authors.lastname: Poulin
authors.forename: George B
authors.initials: GB
authors.lastname: Handley
authors.forename: Brenda R
authors.initials: BR
authors.lastname: Hemmelgarn
authors.forename: Darlene Y
authors.initials: DY
authors.lastname: Sola
authors.forename: Sofia B
authors.initials: SB
authors.lastname: Ahmed
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D045422:Continuous Positive Airway Pressure; D005260:Female; D006801:Humans; D007668:Kidney / Q000503:physiopathology; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D012084:Renin-Angiotensin System / Q000502:physiology*; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology / Q000628:therapy*; D016896:Treatment Outcome; D055815:Young Adult
keywords: continuous positive airway pressure; nocturnal hypoxemia; obstructive sleep apnea; renal hemodynamics; renin–angiotensin system