Some sources of error in measuring regional blood flow with radioactive microspheres.

BUCKBERG, GERALD D., JOHN C. LUCK, D. BRUCE PAYNE, JULIEN I. E. HOFFMAN, JOSEPH P. ARCHIE, AND DAVID E. FIXLER. Some sources of error in measuring regional blood flow with radioactive microspheres. J. Appl. Physiol. 3 l(4) : 538-604. 197 1 .-Radioactive microspheres (8-50 p diameter) distribute in proportion to regional blood flow so that their concentrations in all arteries should be similar but for random variation. Varying numbers of microspheres were injected into the left atrium and ventricles of lambs, sheep, and dogs, and microsphere concentrations were measured in samples drawn simultaneously from two or more arteries (femoral, carotid, or aorta), in the free walls of the left and right ventricles and both kidneys. Coronary and renal blood flows were measured with microspheres (using peripheral reference samples) and by independent methods. Despite some nonrandomness (poor mixing) errors were usually under 20% for all injection and sampling sites in both species as long as each sample had over 400 microspheres; lesser numbers caused errors up to 1 13y0. Variability was less in dogs than sheep, less for left atria1 injections, but equivalent in all arteries. Coronary and renal flows by microspheres were usually within 20y0 and 6%, respectively, of measured flow. The greatest precision occurs on injection of the largest number of microspheres consistent with no physiological changes.