title: Umbilical vein and middle cerebral artery blood flow response to partial occlusion by external compression of the umbilical vein (pressure test).
abstract: OBJECTIVE
  We studied the responses of flow in the umbilical vein and of the circulation in the proximal segment of the middle cerebral artery (MCA) during partial external compression of the umbilical vein.
  
  
  METHODS
  Partial occlusion of the umbilical vein was achieved by the pressure test, consisting of applying external pressure on the maternal abdominal wall for 1-2 s.
  
  
  RESULTS
  During 60 pressure tests in 45 fetuses with nuchal cords, we observed complete cessation of the umbilical vein flow, while blood flow in the umbilical arteries was preserved, and proximal MCA flow was moderately or markedly decreased. Blood flow in other segments of the MCA was unchanged. This effect, which was more pronounced before the 32nd week of gestation, was also observed in association with spontaneous fetal movements.
  
  
  CONCLUSIONS
  The pressure test decreases flow in the proximal MCA, and interrupts umbilical vein blood flow. Further analysis of this response suggested the presence of associated vasoconstriction of the proximal MCA.
authors.affiliation: Unit of Prenatal Diagnosis, Xeral Hospital, Vigo, Pontevedra, Spain.
authors.forename: C L
authors.initials: CL
authors.lastname: Ramón y Cajal
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D005260:Female; D005333:Fetus / Q000098:blood supply*; D005865:Gestational Age; D006801:Humans; D020768:Middle Cerebral Artery / Q000502:physiology*; D009333:Neck / Q000196:embryology; D011247:Pregnancy / Q000502:physiology*; D011263:Pregnancy Trimester, Third / Q000502:physiology; D016216:Ultrasonography, Prenatal; D014471:Umbilical Veins / Q000502:physiology*; D014599:Uterus / Q000098:blood supply*