title: Feeling lightheaded: the role of cerebral blood flow.
abstract: OBJECTIVE
  The main aims of this study were a) to investigate the relationship between lightheadedness and cerebral blood flow velocity (CBFv) during hyperventilation-induced hypocapnia, and b) to investigate whether and why the relationship between lightheadedness and CBFv may change after several episodes of this sensation.
  
  
  METHODS
  Three hypocapnic and three normocapnic overbreathing trials were administered in a semirandomized order to healthy participants (N = 33). Each type of breathing trial was consistently paired with one odor. Afterward, participants were presented each odor once in two spontaneous breathing and in two normocapnic overbreathing trials. CBFv in the right middle cerebral artery was measured by transcranial Doppler ultrasonography (TCD). Also breathing behavior and self-reported lightheadedness were measured continuously. Each trial was followed by a symptom checklist.
  
  
  RESULTS
  Self-reported lightheadedness was closely related to changes in CBFv in the hypocapnic overbreathing trials. During the subsequent normocapnic trials, however, participants experienced more lightheadedness and "feeling unreal" to the odor that had previously been paired with hyperventilation-induced hypocapnia. These complaints were not accompanied by changes in end-tidal CO(2) nor in CBFv.
  
  
  CONCLUSIONS
  The results show that lightheadedness is associated with changes in CBFv but that after a few episodes, the underlying mechanism for this symptom may shift to perceptual-cognitive processes. These findings may help to understand why lightheadedness occurs during emotional distress and panic. In addition, altered cerebral blood flow is unlikely to play a primary precipitating role in recurrent symptoms of lightheadedness.
authors.affiliation: Department of Psychology, University of Leuven, Leuven, Belgium.
authors.forename: Johan
authors.initials: J
authors.lastname: Bresseleers
authors.forename: Ilse
authors.initials: I
authors.lastname: Van Diest
authors.forename: Steven
authors.initials: S
authors.lastname: De Peuter
authors.forename: Peter
authors.initials: P
authors.lastname: Verhamme
authors.forename: Omer
authors.initials: O
authors.lastname: Van den Bergh
mesh_terms: D000293:Adolescent; D001783:Blood Flow Velocity / Q000502:physiology; D001921:Brain / Q000098:blood supply / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D057189:Checklist; D003214:Conditioning, Classical / Q000502:physiology; D004244:Dizziness / Q000000981:diagnostic imaging / Q000503:physiopathology*; D005260:Female; D006801:Humans; D006985:Hyperventilation / Q000000981:diagnostic imaging / Q000503:physiopathology*; D016857:Hypocapnia / Q000000981:diagnostic imaging / Q000503:physiopathology; D008297:Male; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000503:physiopathology; D009812:Odorants; D012039:Regional Blood Flow / Q000502:physiology; D011795:Surveys and Questionnaires; D017585:Ultrasonography, Doppler, Transcranial