Precautions for measuring blood flow during anemia with the microsphere technique

Precautions for measuring blood flow during anemia with the microsphere technique. Am. J. Physiol. 244 (Heart Circ. Phys-iol. 13): H308-H311, 1983.-Preliminary data from a study of the effects of anemia on organ blood flow showed large discrep-ancies between cardiac output measured with the microsphere technique and simultaneous values calculated by the Fick prin-ciple. The most likely explanation was that the reference sample drawn according to our standard procedure underestimated the microsphere concentration in arterial blood, resulting in erro-neously 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artery into the brachiocephalic artery (withdrawal rate 1.3 ml/min), with a simultaneous sam-ple from a larger catheter withdrawn at the much higher rate (7.89 ml/mm). At hematocrits above 32%, microsphere concen