AJP - Gastrointestinal and Liver Physiology, Vol 254, Issue 2 275-G279, Copyright © 1988 by American Physiological Society
Microsphere estimates of blood flow: methodological considerations
C. von Ritter, R. A. Hinder, W. Womack, P. Bauerfeind, C. J. Fimmel, P. R. Kvietys, D. N. Granger and A. L. Blum
Department of Surgery, University of Witwatersrand, Johannesburg, South Africa.
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 Replacement of the withdrawn blood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.
