Measurement of flow in perfused organs, using microsphere techniques.

Abstract

ABSTRACT Injection of radionuclide labelled microspheres into the circulation of animals can be used to measure the proportion of blood flow to any organ, or the regional distribution of blood flow within any organ. The use of this technique depends on the fact that these microspheres are distributed according to the blood flow and that they are completely trapped within the organ. It is important that they are adequately mixed within the flowing stream and also evenly distributed at branching sites. It has been shown that for the assessment of the regional distribution within an organ, microspheres of small diameter (10–15 μm) are preferable since they more accurately reflect true flow to all segments of the organ. The accurate measurement of the distribution of flow is also dependent on the absolute number of microspheres present in any organ or segment of organ under study. Studies of regional distribution of flow during cardio-pulmonary bypass in rhesus monkeys have shown that the proportion of cardiac output distributed to the kidneys falls, while that to the gut increases. The haematocrit of the perfusing blood may modify the distribution of flow to organs; thus, cerebral blood flow was maintained while using blood of low haematocrit whereas with normal haematocrit it fell during perfusion. The regional distribution of the blood flow within the kidney has been shown to change markedly with artificial perfusion in situ with a striking increase in flow to the medulla and inner cortex during perfusion as compared to normal.