AJP - Heart and Circulatory Physiology, Vol 244, Issue 2 308-H311, Copyright © 1983 by American Physiological Society
Precautions for measuring blood flow during anemia with the microsphere technique
A. A. Rosenberg, M. D. Jones Jr, R. C. Koehler, R. J. Traystman and G. Lister
Preliminary data from a study of the effects of anemia on organ blood flow
showed large discrepancies between cardiac output measured with the
microsphere technique and simultaneous values calculated by the Fick
principle. The most likely explanation was that the reference sample drawn
according to our standard procedure underestimated the microsphere
concentration in arterial blood, resulting in erroneously high blood flow
values. In the present experiments we compared our usual reference sample,
from a small catheter advanced from a peripheral artery into the
brachiocephalic artery (withdrawal rate 1.3 ml/min), with a simultaneous
sample from a larger catheter withdrawn at the much higher rate (7.89
ml/min). At hematocrits above 32%, microsphere concentrations from the two
catheters were similar, but below 32% the concentration of microspheres in
blood from the larger catheter was 30-50% more than from the smaller. The
discrepancy was not altered by changing the injection site from left
ventricle to left atrium and thus was probably not the result of poor
mixing within the heart. It may have been the result of nonhomogeneous
distribution of microspheres within larger vessels, perhaps as a
consequence of laminar flow and axial streaming of both red blood cells and
microspheres during anemia. Whatever the cause, it was possible to
eliminate the difference by withdrawing from the smaller catheter at a more
rapid rate (2.46 ml/min).
