title: Microsphere estimates of blood flow: methodological considerations.
abstract: The microsphere technique is a standard method for measuring blood flow in experimental animals. Sporadic reports have appeared outlining the limitations of this method. In this study we have systematically assessed the effect of blood withdrawals for reference sampling, microsphere numbers, and anesthesia on blood flow estimates using radioactive microspheres in dogs. Experiments were performed on 18 conscious and 12 anesthetized dogs. Four blood flow estimates were performed over 120 min using 1 X 10(6) microspheres (15 microns) each time. The effects of excessive numbers of microspheres (13 million), pentobarbital sodium anesthesia (30 mg/kg), and replacement of volume loss for reference samples with dextran 70 were assessed. In both conscious and anesthetized dogs a progressive decrease in gastric mucosal blood flow and cardiac output was observed over 120 min. This was also observed in the pancreas in conscious dogs. The major factor responsible for these changes was the volume loss due to reference sample withdrawals. Replacement of the withdrawn blood with dextran 70 led to stable blood flows to all organs. The injection of excessive numbers of microspheres did not modify hemodynamics to a greater extent than did the injection of 4 million microspheres. Anesthesia exerted no influence on blood flow other than raising coronary flow. We conclude that although blood flow to the gastric mucosa and the pancreas is sensitive to the minor hemodynamic changes associated with the microsphere technique, replacement of volume loss for reference samples ensures stable blood flow to all organs over a 120-min period.
authors.affiliation: Department of Surgery, University of Witwatersrand, Johannesburg, South Africa.
authors.forename: C
authors.initials: C
authors.lastname: von Ritter
authors.forename: R A
authors.initials: RA
authors.lastname: Hinder
authors.forename: W
authors.initials: W
authors.lastname: Womack
authors.forename: P
authors.initials: P
authors.lastname: Bauerfeind
authors.forename: C J
authors.initials: CJ
authors.lastname: Fimmel
authors.forename: P R
authors.initials: PR
authors.lastname: Kvietys
authors.forename: D N
authors.initials: DN
authors.lastname: Granger
authors.forename: A L
authors.initials: AL
authors.lastname: Blum
mesh_terms: D000818:Animals; D001775:Blood Circulation; D004285:Dogs; D006439:Hemodynamics; D008863:Microspheres; D012039:Regional Blood Flow; D012212:Rheology / Q000379:methods*