Summary. Limited normovolemic hemodilution has been performed in splenectemized dogs during pentobarbital anesthesia and controlled ventilation. The hematoerit has been decreased by exchanging arterial blood against dextran 60 until 200/0 was reached. Cardiac output, myocardial contractility, local muscle blood flow and local tissue P02 were investigated in relation to progressive decrease in red cell concentration. Limited normovolemic hemodilution was associated with a significant increase of total and local blood flow; local tissue hypoxia did not develop despite the decrease in oxygen capacity of the blood as proved by the measurements of spatial P02 in liver, kidney, pancreas, small intestine and skeletal muscle. It is concluded that flow improvement in limited normovolemic hemodilution is the key mechanism in maintaining the oxygen supply to the tissues, a fact which favors the concept of normovolemic hemodilution as a therapeutic tool in microcirculatory disorders.Key words: Local tissue POz --Hemodilution --Dextran --Myocardial contractility.L i m i t e d normovolemic hemodilution as induced b y colloidal solutions has been recognized as a causative a p p r o a c h to the impaired microcirculation m a i n l y d e t e r m i n e d b y alterations of the flow properties of blood. N u m e r o u s experiments have shown t h a t the acute reduction of the whole blood viscosity b y dilution will increase the cardiac o u t p u t and the t o t a l organ flow rate [5,20,23,25]. More recently it has been p r o v e d t h a t the increase in cardiac o u t p u t is followed b y an increase in nutritional flow too as suggested from findings obtained in skeletal muscle [19,26]. Since the linear fall of the oxygen c a p a c i t y is associated * Dedicated to Prof. Dr. Dr. R. Zenker on his 70th anniversary. ** Supported in part by grant from Landesamt fiir Forschung of NordrheinWestfalen.Abbreviations. CO = cardiac output, hot = hematocrit, HR = heart rate, M'BF = skeletal muscle blood flow, MCI = myocardial contractility index, RAP = right atrial pressure.

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