title: Unexpected reductions in regional cerebral perfusion during prolonged hypoxia.
abstract: Cognitive performance is impaired by hypoxia despite global cerebral oxygen delivery and metabolism being maintained. Using arterial spin labelled (ASL) magnetic resonance imaging, this is the first study to show regional reductions in cerebral blood flow (CBF) in response to decreased oxygen supply (hypoxia) at 2 h that increased in area and became more pronounced at 10 h. Reductions in CBF were seen in brain regions typically associated with the 'default mode' or 'task negative' network. Regional reductions in CBF, and associated vasoconstriction, within the default mode network in hypoxia is supported by increased vasodilatation in these regions to a subsequent hypercapnic (5% CO2) challenge. These results suggest an anatomical mechanism through which hypoxia may cause previously reported deficits in cognitive performance.
  
  
  
  Hypoxia causes an increase in global cerebral blood flow, which maintains global cerebral oxygen delivery and metabolism. However, neurological deficits are abundant under hypoxic conditions. We investigated regional cerebral microvascular responses to acute (2 h) and prolonged (10 h) poikilocapnic normobaric hypoxia. We found that 2 h of hypoxia caused an expected increase in frontal cortical grey matter perfusion but unexpected perfusion decreases in regions of the brain normally associated with the 'default mode' or 'task negative' network. After 10 h in hypoxia, decreased blood flow to the major nodes of the default mode network became more pronounced and widespread. The use of a hypercapnic challenge (5% CO2) confirmed that these reductions in cerebral blood flow from hypoxia were related to vasoconstriction. Our findings demonstrate steady-state deactivation of the default network under acute hypoxia, which become more pronounced over time. Moreover, these data provide a unique insight into the nuanced localized cerebrovascular response to hypoxia that is not attainable through traditional methods. The observation of reduced perfusion in the posterior cingulate and cuneal cortex, which are regions assumed to play a role in declarative and procedural memory, provides an anatomical mechanism through which hypoxia may cause deficits in working memory.
authors: Extremes Research Group, School of Sport, Health and Exercise Sciences, Bangor University, Gwynedd, UK.|Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas, TX, USA.
authors: Justin S
authors: JS
authors: Lawley
authors: Extremes Research Group, School of Sport, Health and Exercise Sciences, Bangor University, Gwynedd, UK.
authors: Jamie H
authors: JH
authors: Macdonald
authors: Extremes Research Group, School of Sport, Health and Exercise Sciences, Bangor University, Gwynedd, UK.
authors: Samuel J
authors: 0000-0002-9971-9546
authors: SJ
authors: Oliver
authors: Bangor Imaging Centre, School of Psychology, Bangor University, Gwynedd, UK.
authors: Paul G
authors: 0000-0002-1339-6361
authors: PG
authors: Mullins
mesh_terms: D000328:Adult; D001921:Brain / Q000000981:diagnostic imaging / Q000503:physiopathology*; D002560:Cerebrovascular Circulation; D006801:Humans; D000860:Hypoxia / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology; D055815:Young Adult
keywords: ASL; Arterial Spin Label; CBF; DMN; cerebral blood flow; cerebral perfusion; default mode; hypoxia