title: Cerebral syncope: insights from Valsalva maneuver.
abstract: OBJECTIVE
  Cerebral syncope refers to a loss of consciousness associated with cerebral vasoconstriction in the absence of systemic hypotension. The diagnosis of cerebral syncope could be established by the head-up tilt test (HUT) and transcranial Doppler ultrasonography. Valsalva maneuver (VM) permitted assessment of cerebral autoregulatory function by provoking blood pressure (BP) changes. To develop a path-physiological approach for vasomotor reactivity of cerebral syncope, the authors combined these maneuvers (HUT/transcranial Doppler/VM).
  
  
  METHODS
  Using transcranial Doppler ultrasonography, we simultaneously recorded systemic arterial BP in the radial artery and flow velocities in both middle cerebral arteries (MCAFV) in 10 cerebral syncope patients (4 males and 6 females, 35.24 +/- 4.5 years old) during the Valsalva maneuver.
  
  
  RESULTS
  The characteristic changes in BP (phases I-IV) were seen in all subjects, accompanying distinct changes in cerebral blood flow velocity. The BP/heart rate responding to VM was within normal limit in all subjects. There was no orthostatic hypotension. Instead, BP increased during the tilting test in 2 subjects (20.00%). The MCAFV dropped 25.4 +/- 2.3% from baseline. Abnormal flattening of MCAFV during late phase II (IIb), the paradoxical drop of flow velocity despite restoration of BP, was noted in 9 subjects (90.00%).
  
  
  CONCLUSIONS
  During VM there are complex changes in relevant cardiovascular and cerebrovascular variables within a short time span. The paradoxical drop of MCAFV during phase IIb was the result of complex parameters. Among them, a failure in cerebrovascular resistance reduction and even paradoxical vasoconstriction might further compromise cerebral perfusion pressure and lead to syncope.
authors.affiliation: Department of Neurology, Keelung General Hospital, Taiwan, Republic of China. eric.tpe@yahoo.com.tw
authors.forename: Yu-Ming
authors.initials: YM
authors.lastname: Chuang
authors.forename: Han-Haw
authors.initials: HH
authors.lastname: Hu
authors.forename: Po-Jung
authors.initials: PJ
authors.lastname: Pan
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D001794:Blood Pressure; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D020768:Middle Cerebral Artery / Q000502:physiology*; D017534:Radial Artery / Q000502:physiology; D019462:Syncope, Vasovagal / Q000175:diagnosis* / Q000503:physiopathology; D018667:Tilt-Table Test; D017585:Ultrasonography, Doppler, Transcranial; D014636:Valsalva Maneuver; D014655:Vascular Resistance; D014661:Vasoconstriction