title: Effects of continuous positive airway pressure on cerebral vascular response to hypoxia in patients with obstructive sleep apnea.
abstract: BACKGROUND
  The mechanism leading to increased risk of stroke in patients with obstructive sleep apnea (OSA) is unknown. It may occur through alteration in the regulation of cerebral blood flow, reflected in part by the response of the cerebral vasculature to hypoxia. We hypothesized that the cerebrovascular response to hypoxia is reduced in patients with OSA.
  
  
  OBJECTIVE
  To determine the cerebral blood flow response to hypoxia in patients with OSA.
  
  
  METHODS
  The cerebral blood flow response to 20 minutes of isocapnic hypoxia was measured in eight male patients with OSA before and after 4 to 6 weeks of continuous positive airway pressure (CPAP) therapy and in 10 matched healthy control subjects.
  
  
  RESULTS
  The cerebral blood flow response to hypoxia was significantly lower in patients with OSA compared with control subjects (0.56 +/- 0.10 vs. 0.97 +/- 0.09% [mean +/- SE] change in blood flow velocity per % desaturation; p=0.007). After CPAP therapy, the cerebral blood flow response to hypoxia was similar between patients with OSA and control subjects (1.08 +/- 0.15 vs. 0.92 +/- 0.13% change in blood flow velocity per % desaturation; p=0.4). Moderately strong correlations were found between the cerebral blood flow response to hypoxia and the apnea-hypopnea index (r=-0.57; p=0.04) and nocturnal oxyhemoglobin saturation (r=0.48; p=0.01).
  
  
  CONCLUSIONS
  The cerebral blood flow response to hypoxia is significantly reduced in patients with OSA. Treatment of OSA with CPAP increases the cerebral blood flow response to hypoxia to normal levels. An attenuated cerebrovascular response to hypoxia in patients with OSA may contribute to their elevated risk of stroke.
authors.affiliation: Department of Physiology and Biophysics, Faculty of Medicine, University of Calgary, Calgary, AB T2N 4N1, Canada.
authors.forename: Glen E
authors.initials: GE
authors.lastname: Foster
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Hanly
authors.forename: Michele
authors.initials: M
authors.lastname: Ostrowski
authors.forename: Marc J
authors.initials: MJ
authors.lastname: Poulin
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D045422:Continuous Positive Airway Pressure; D005500:Follow-Up Studies; D006801:Humans; D000860:Hypoxia / Q000209:etiology / Q000503:physiopathology* / Q000628:therapy; D008297:Male; D012129:Respiratory Function Tests; D020181:Sleep Apnea, Obstructive / Q000150:complications / Q000503:physiopathology* / Q000628:therapy*; D014851:Wakefulness / Q000502:physiology