title: Brain Perfusion and Arterial Blood Flow Velocity During Prolonged Body Tilting.
abstract: BACKGROUND
  It remains unknown whether brain perfusion is preserved and mirrored by middle cerebral blood flow velocity (MCA BFV) during prolonged changes in body posture. Herein, we examined the impact of sustained (180 min) 30° head-up (HUT) and head-down (HDT) tilt on brain perfusion, as determined by MCA BFV and blood flow in the extracranial arteries.
  
  
  METHODS
  In 10 healthy male subjects, arterial diameters, BFVs, and blood flows were determined in the left internal carotid (ICA) and vertebral (VA) arteries using duplex Doppler ultrasound in supine rest, and 5, 20, 60, 120, and 180 min following 30° HUT and HDT. MCA BFV was recorded throughout with transcranial Doppler ultrasound.
  
  
  RESULTS
  ICA as well as VA diameters and blood flows were unaltered during HUT. Likewise, brain blood flow and MCA BFV were preserved with HUT. In the HDT protocol, ICA and VA diameters were gradually increased, although ICA, VA, and brain blood flows were preserved. MCA BFV was progressively reduced during HDT. In addition, MCA BFV was positively associated with ICA BFV (β = 0.9) and negatively associated with ICA diameter (β = -125.5). MCA BFV was positively associated with brain blood flow during HUT (β = 0.2) but not HDT.
  
  
  CONCLUSIONS
  Brain perfusion is preserved whereas MCA BFV is progressively decreased and associated with extracranial arterial BFV during sustained 30° HDT. Therefore, MCA BFV may not be a surrogate of brain perfusion in conditions including prolonged HDT. Montero D, Rauber S. Brain perfusion and arterial blood flow velocity during prolonged body tilting. Aerosp Med Hum Perform. 2016; 87(8):682-687.
authors.affiliation: Zurich Center for Integrative Human Physiology (ZIHP), Institute of Physiology, University of Zurich, Zurich, Switzerland.
authors.forename: David
authors.initials: D
authors.lastname: Montero
authors.forename: Sven
authors.initials: S
authors.lastname: Rauber
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D002343:Carotid Artery, Internal / Q000000981:diagnostic imaging / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D018475:Head-Down Tilt / Q000502:physiology; D006801:Humans; D008297:Male; D020768:Middle Cerebral Artery / Q000502:physiology; D011187:Posture / Q000502:physiology*; D013997:Time Factors; D017585:Ultrasonography, Doppler, Transcranial; D014711:Vertebral Artery / Q000000981:diagnostic imaging / Q000502:physiology; D055815:Young Adult