Factors Affecting the Determination of Uterine Blood Flow in Vivo

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Abstract
When 4-aminoantipyrine (4AA) was injected into pregnant goats, the time curves of blood concentration could be determined easily and accurately when the injection was carried out over about seven minutes' time. The arterial-and uterine venous-blood concentration curves came together after 15 minutes, and afterward the arteriovenous difference remained negligible. The blood concentration of 4AA gave an accurate estimate of concentrations in the tissue water of the uterus, placenta, and fetus after disappearance of the arteriovenous difference. At the time interval of 15 to 20 minutes, 4AA concentrations in amniotic and allantoic fluids were so low that they could be regarded as negligible. There fore, when 4AA was used as the diffusing substance, the major factors affecting the determination of uterine blood flow by diffusion-equilibration methods were favorable for an estimate of the rate of blood flow per unit weight of metabolically active tissue.