AJP - Heart and Circulatory Physiology, Vol 253, Issue 1 184-H193, Copyright © 1987 by American Physiological Society
Validity of microsphere depositions for regional myocardial flows
J. B. Bassingthwaighte, M. A. Malone, T. C. Moffett, R. B. King, S. E. Little, J. M. Link and K. A. Krohn
Due to the particulate nature of microspheres, their deposition in
small-tissue regions may not be strictly flow dependent. To evaluate the
importance of rheological and geometric factors and random error, their
deposition densities in small regions of rabbit hearts were examined in
comparison with those of a new "molecular microsphere,"
2-iododesmethylimipramine (IDMI), whose high lipid solubility allows it to
be delivered into tissue in proportion to flow, and whose binding in tissue
prevents rapid washout. 141Ce- and 103Ru-labeled 16.5-micron spheres in one
syringe and [125I]- and [131I]DMI in another syringe were injected
simultaneously into the left atrium of open-chest rabbits, while obtaining
reference blood samples from the femoral artery. Hearts were removed 1 min
after injection, cut into approximately 100 pieces averaging 54 mg, and the
regional deposition densities calculated for each tracer from the isotopic
counts. Correlations between the differently labeled microspheres were r
greater than 0.95 and for the two IDMIs were greater than 0.98. Scatter
plots of sphere densities vs. IDMI densities showed that differences
between microspheres and IDMI had substantial scatter, 0.87 less than r
less than 0.96 and were not random. Microsphere depositions tended to be
lower than IDMI depositions at low flows and higher at high flows. The
tendency for spheres to be deposited preferentially in high-flow regions
may be explained by a bias at bifurcations toward entering the branch with
higher flow and secondarily toward entering those branches that are
straighter. We conclude that microspheres are generally adequate for
estimating regional flows but suffer systematic error when the regions of
interest are supplied via arteries of diameters only a few times those of
the microspheres.
