title: Cranial venous outflow under lower body positive and negative pressure conditions and head-up and -down tilts.
abstract: BACKGROUND
  Although there exists a large body of knowledge on the regulation of arterial cerebral hemodynamics, little is known about the cerebral venous outflow (CVO).
  
  
  METHODS
  In 19 healthy volunteers, the middle cerebral artery and the straight sinus were examined using transcranial Doppler sonography. Arterial and venous mean flow velocities (aFV(mean), vFV(mean), respectively) were registered continuously while applying lower body positive (LBPP) or negative (LBNP) pressure of 30 mmHg and performing head-down (-20 degrees , HDT) and -up (+30 degrees , HUT) tilt manoeuvres. The arterial blood pressure was registered simultaneously with a noninvasive finger blood pressure monitor. Relative changes in parameters compared to the proceeding no-pressure, no-tilt baseline were used for analysis.
  
  
  RESULTS
  While aFV(mean) did not change significantly, vFV(mean) inc reased during LBPP by 10.5 +/- 2.9% and decreased during LBNP by 15.1 +/- 3.5% (mean +/- standard error of mean [SEM], P < .01). HUT resulted in a decrease in vFV(mean) by 25.5 +/- 3.3% and HDT, in an increase by 7.8 +/- 3.2% (P < .01) without alteration in aFV(mean). This may imply a decrease of cerebral blood volume (CBV) during LBPP and HDT and an increase during LBNP and HUT.
  
  
  CONCLUSIONS
  CVO cannot be neglected when studying cerebral hemodynamics because it might affect the CBV.
authors.affiliation: Department of Neurology, Justus-Liebig-University, Giessen, Germany. erwin.stolz@neuro.med.uni-giessen.de
authors.forename: Erwin
authors.initials: E
authors.lastname: Stolz
authors.forename: Bettina C
authors.initials: BC
authors.lastname: Fox
authors.forename: Oskar
authors.initials: O
authors.lastname: Hoffmann
authors.forename: Tibo
authors.initials: T
authors.lastname: Gerriets
authors.forename: Franz
authors.initials: F
authors.lastname: Blaes
authors.forename: Jörg
authors.initials: J
authors.lastname: Kraus
authors.forename: Manfred
authors.initials: M
authors.lastname: Kaps
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology*; D001795:Blood Pressure Determination; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D018475:Head-Down Tilt; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D018709:Statistics, Nonparametric; D018667:Tilt-Table Test; D017585:Ultrasonography, Doppler, Transcranial; D014680:Veins / Q000000981:diagnostic imaging*