title: Cerebral blood flow response to isocapnic hypoxia during slow-wave sleep and wakefulness.
abstract: Nocturnal hypoxia is a major pathological factor associated with cardiorespiratory disease. During wakefulness, a decrease in arterial O2 tension results in a decrease in cerebral vascular tone and a consequent increase in cerebral blood flow; however, the cerebral vascular response to hypoxia during sleep is unknown. In the present study, we determined the cerebral vascular reactivity to isocapnic hypoxia during wakefulness and during stage 3/4 non-rapid eye movement (NREM) sleep. In 13 healthy individuals, left middle cerebral artery velocity (MCAV) was measured with the use of transcranial Doppler ultrasound as an index of cerebral blood flow. During wakefulness, in response to isocapnic hypoxia (arterial O2 saturation -10%), the mean (+/-SE) MCAV increased by 12.9 +/- 2.2% (P < 0.001); during NREM sleep, isocapnic hypoxia was associated with a -7.4 +/- 1.6% reduction in MCAV (P <0.001). Mean arterial blood pressure was unaffected by isocapnic hypoxia (P >0.05); R-R interval decreased similarly in response to isocapnic hypoxia during wakefulness (-21.9 +/- 10.4%; P <0.001) and sleep (-20.5 +/- 8.5%; P <0.001). The failure of the cerebral vasculature to react to hypoxia during sleep suggests a major state-dependent vulnerability associated with the control of the cerebral circulation and may contribute to the pathophysiologies of stroke and sleep apnea.
authors.affiliation: Clinical and Academic Unit of Sleep and Breathing, National Heart and Lung Institute, Imperial College, London SW3 6LY, UK.
authors.forename: Guy E
authors.initials: GE
authors.lastname: Meadows
authors.forename: Denise M
authors.initials: DM
authors.lastname: O'Driscoll
authors.forename: Anita K
authors.initials: AK
authors.lastname: Simonds
authors.forename: Mary J
authors.initials: MJ
authors.lastname: Morrell
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Corfield
mesh_terms: D000328:Adult; D001921:Brain / Q000098:blood supply*; D002245:Carbon Dioxide / Q000097:blood*; D002560:Cerebrovascular Circulation; D006801:Humans; D006935:Hypercapnia / Q000150:complications / Q000000981:diagnostic imaging / Q000503:physiopathology*; D002534:Hypoxia, Brain / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology*; D012890:Sleep; D012891:Sleep Apnea Syndromes / Q000000981:diagnostic imaging / Q000209:etiology / Q000503:physiopathology; D014463:Ultrasonography; D014851:Wakefulness
chemical_list: D002245:Carbon Dioxide