title: Cerebral blood flow during supine rest and the first minute of head-up tilt in patients with orthostatic intolerance.
abstract: OBJECTIVE
  To assess the cerebral blood flow velocity during the first minute of head-up tilt in patients with postural tachycardia syndrome (POTS) or neurally-mediated reflex syncope compared with patients with dizziness.
  
  
  METHODS
  We evaluated 120 patients selected from 470 patients who underwent head-up tilt testing: 40 with POTS, 40 with typical neurally-mediated reflex syncope and 40 who complained of dizziness with no history of loss of consciousness and a negative head-up tilt test (with and without isosorbide). Transcranial Doppler sonography of the middle cerebral artery, heart rate and brachial blood pressure were recorded during a 70 degrees head-up tilt test.
  
  
  RESULTS
  During both baseline in supine position and the first minute of upright tilt, patients with postural tachycardia syndrome showed higher heart rate and cerebral blood flow velocity than patients with dizziness and patients with neurally-mediated reflex syncope (P < 0.05, ANOVA), but no significant difference was observed on the Gosling's pulsatility index.
  
  
  CONCLUSIONS
  Patients with POTS have an autonomic dysfunction that is not triggered by upright posture but is accentuated by it.
authors.affiliation: Unidad de Investigación Médica, HG CMN La Raza IMSS, México.
authors.forename: K
authors.initials: K
authors.lastname: Jáuregui-Renaud
authors.forename: J A G
authors.initials: JA
authors.lastname: Hermosillo
authors.forename: J L
authors.initials: JL
authors.lastname: Jardón
authors.forename: M F
authors.initials: MF
authors.lastname: Márquez
authors.forename: A
authors.initials: A
authors.lastname: Kostine
authors.forename: M A
authors.initials: MA
authors.lastname: Silva
authors.forename: M
authors.initials: M
authors.lastname: Cárdenas
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001783:Blood Flow Velocity / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D016683:Supine Position; D019462:Syncope, Vasovagal / Q000503:physiopathology*; D013610:Tachycardia / Q000503:physiopathology*; D018667:Tilt-Table Test; D017585:Ultrasonography, Doppler, Transcranial