Erythrocyte rheology and oxygen transfer in microcirculatory system

The molecular investigation on the structure-function relationship of hemoglobin carried out in the Postgraduate School of Nara Medical College has been systematically and fortunately developed to those on the oxygen delivery from blood to peripheral tissues in microcirculatory system in Medical School, Ehime University. Microcirculatory system contributes to the delivery of essential substrates such as oxygen and nutrients to tissues, and to the removal of by-products accumulated in the tissues, mainly through capillaries with the surface area of more than 6,000 m2. Therefore, the function of microcirculation is critical for all organs in living body. Particularly, rheological properties of blood are fundamentally important for understanding the function of the microcirculation. The International Society of Biorheology and the Japanese Society of Biorheology have played an important role in the fields of microcirculation and hemorheology. The activity of the International Society of Biorheology has been universally introduced together that of the International Society of Clinical Hemorheology [O’Rear E, et al: The International Society of Biorheology. Rheology Bulletin. 73: 9–11, 2004]. The microcirculation is particularly influenced by the flow behavior of erythrocytes, because the cells occupy nearly half of blood volume [1, 2]. I have exhaustively analyzed rheological properties of erythrocytes in micro-to macro level for understanding the relationship between blood flow in microcirculatory system and oxygen transport from erythrocytes to tissues [3, 4]. The erythrocytes deform under high shear force to reduce their flow resistance by lessening their hydrodynamic effective volume. On the other hand, the erythrocytes aggregate under low shear force, and increase the flow resistance in the microcirculatory system. Thus the flow behavior of erythrocytes and their aggregates in microcirculatory system seems to affect the oxygen transport. Under strong gravitational field, flow of erythrocytes in a blood vessel occasionally deviates from the central axis to the wall, and the cells accumulate. In this essay, I describe mainly about the effect of erythrocyte aggregation/accumulation on the flow behavior of the cells and the oxygen release from the cells, because such conditions seem to be more commonly encountered in clinical medicine and under various physical circumstances.