title: Changes in umbilical arterial blood flow by an intraamniotic distilled water infusion.
abstract: OBJECTIVE
  The purpose is to investigate how umbilical arterial blood flow changes by an intraamniotic distilled water infusion and to determine whether the changes in umbilical circulation have any relationship with fetal cardiovascular status and osmolality in amniotic fluid and fetal plasma.
  
  
  METHODS
  Eleven chronically catheterized pregnant sheep were used in this study. After a 1-hour control period, 1.5 L of warmed sterile distilled water was injected over 10 minutes into the amniotic cavity. Fetal heart rate and carotid arterial pressure, blood flow of the umbilical and fetal carotid arteries were continuously measured. Fetal arterial blood sampled twice during the control period and then at 30, 60, 90, 120, 180, 240, 300, and 360 minutes after the start of the infusion, was analyzed for blood gases, pH, plasma electrolytes, and osmolality.
  
  
  RESULTS
  Data obtained from seven sheep with normoxemic fetuses were studied statistically. Umbilical arterial blood flow decreased significantly from 229.5 +/- 3.83 mL/min in the control to 167.4 +/- 11.1 mL/min at 30 minutes after water infusion (P < .001). Umbilical arterial vascular resistance increased rapidly and reached its peak at approximately 60 minutes after infusion and then showed a gradual recovery to the control level (P < .001). Amniotic fluid osmolality had a high degree of correlation with umbilical arterial blood flow and vascular resistance, while fetal arterial blood pressure and heart rate had only little correlation with umbilical blood flow.
  
  
  CONCLUSIONS
  A distilled water infusion into the amniotic cavity in near-term pregnant sheep led to an acute drop in umbilical arterial blood flow. The changes in umbilical flow were closely correlated with those in amniotic fluid osmolality. Hemolysis in the capillary networks in the fetal membranes seems to be one of the main causes of umbilical vasoconstriction. It is speculated that the fetal membranes, including capillary networks, intramembranous pathway, and amnion epithelial cells, sense the changes in amniotic fluid osmolality, which leads to a fetal adaptation to the hypotonic environment.
authors.affiliation: Department of Obstetrics and Gynecology, University of Tokyo, Tokyo, Japan. atsukoma@yahoo.cp.jp
authors.forename: Atsushi
authors.initials: A
authors.lastname: Komatsu
authors.forename: Shiro
authors.initials: S
authors.lastname: Kozuma
authors.forename: Hiroe
authors.initials: H
authors.lastname: Hyodo
authors.forename: Tsuguhiro
authors.initials: T
authors.lastname: Horikoshi
authors.forename: Ken
authors.initials: K
authors.lastname: Sakamaki
authors.forename: Akihiko
authors.initials: A
authors.lastname: Kikuchi
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Kamei
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Fujii
authors.forename: Yuji
authors.initials: Y
authors.lastname: Taketani
mesh_terms: D000653:Amniotic Fluid / Q000378:metabolism; D000818:Animals; D001158:Arteries / Q000502:physiology; D005260:Female; D005333:Fetus / Q000098:blood supply* / Q000502:physiology; D006461:Hemolysis; D008431:Maternal-Fetal Exchange; D009994:Osmolar Concentration; D011247:Pregnancy; D012039:Regional Blood Flow; D012756:Sheep; D014470:Umbilical Cord / Q000098:blood supply*; D014661:Vasoconstriction / Q000502:physiology; D014867:Water / Q000008:administration & dosage
chemical_list: D014867:Water