Eynon, Colin Andrew; (2001) The use of fluorescent microspheres to measure organ blood flows in low flow states. Doctoral thesis (M.D), UCL (University College London).

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Abstract

Organ perfusion can be measured using microspheres delivered into the blood stream. Blood flow is proportional to the number of microspheres entrapped in the tissue. The commonest method of quantitating the number of microspheres present in a sample is to measure levels of radioactivity from radiolabelled microspheres. The relative expense of radiolabels has led to alternative, non-radioactive, microsphere methods. The use of fluorescent labelled microspheres for measurement of regional organ perfusion has been validated in comparisons with radio labelled microspheres in conditions of normal or enhanced flow. In this work, limitations in the fluorescent microspheres technique were established in preliminary experiments. Inter- and intra-animal variability in organ blood flows in conditions of normal flow were studied in a rat model. Fluorescent microspheres were subsequently used to measure organ perfusion in established animal models of low blood flow states. Organ-specific recovery rates for fluorescent microspheres during the extraction process were also studied. The fluorescent microsphere technique produced high sensitivity with good spectral separation allowing at least four different fluorescent labels to be easily separated. The technique had excellent reproducibility in repeated measurements. Temporal variation in organ blood flows compared favourably with previous studies. Inter-animal variability was 22% for all tissues except the lungs and adrenals. Under conditions of low flow, the fluorescent microsphere technique appeared robust with organ blood flows following the patterns reported by other groups. Overall recovery of microspheres using KOH digestion and a negative pressure filtration technique was high. Fluorescent microspheres provide a new method of repeated measurement of regional perfusion over a wide range of organ blood flows. The accuracy of the technique appears superior to other non-radioactive microsphere methods. The principal limitation of the technique is that it is labour intensive. Automation of the process is likely to make the use of fluorescent microspheres more attractive.

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