Viscosity of mixtures of sickle and normal red cells at varying hematocrit levels

Abstract

Viscosity (eta) in a blood suspension is affected by the total hematocrit (HT) as well as by the deformability of the cells. The impact of these combined factors on the rheologic behavior of sickle cell suspensions and on guidelines for transfusion has not been explored fully. Therefore, the eta of mixtures of washed normal (AA) and sickle (SS) red cells was determined in a rotational viscosimeter as a function of the hematocrit level of SS cells (HS), HT, oxygen tension (PO2), and shear rate. The ratio HT:eta can be taken as an index of potential oxygen delivery. The optimal HT (for maximum HT:eta) became progressively higher as the HS or the HS:HT ratio was lowered: at a given HT, HT:eta rose with a decrease in HS, especially at low HS values. These data support the concept that simple transfusion alone is not as beneficial to the patient as exchange transfusion and that substantial benefit can be obtained by bringing the patient to very low HS levels. The finding that eta rose with HT more steeply when the HS:HT ratio rather than HS was held constant suggested that the absolute level of HS may be more useful than the HS:HT ratio as a guide for a transfusion regimen.

Red blood cell aggregation, aggregate strength and oxygen transport potential of blood are abnormal in both homozygous sickle cell anemia and sickle-hemoglobin C disease

“…For example, Schmalzer et al, 30 and more recently Alexy et al, 8 reported that the determination of an optimal Hct might be useful for transfusion therapy in SCA, and our viscosity results allowed determination of this optimal value. The present study also suggests an inverse relation between shear rate and the calculated Optimal Hct in SCA patients, whereas it was not shear rate dependent for the AA, AS and SCC groups (Table 4).…”

Red Cell Exchange in Sickle Cell Disease

“…1,2 Blood from an untransfused patient with sickle cell anemia has a significantly higher viscosity than normal blood at the same hemoglobin level. 3 Deoxygenated sickle blood has nearly a 10-fold greater viscosity than oxygenated sickle blood at the same hemoglobin level, with the effect being greatest at low shear forces. 3,4 Increased viscosity dramatically promotes the physiology of sickling.…”

“…3 Deoxygenated sickle blood has nearly a 10-fold greater viscosity than oxygenated sickle blood at the same hemoglobin level, with the effect being greatest at low shear forces. 3,4 Increased viscosity dramatically promotes the physiology of sickling. Looking at the Poiseuille equation above, flow will be slowest in vessels of small radius (capillaries, arterioles and venules) and under lower pressures (venules).…”

“…2 The viscosity effects in sickle cell anemia shift the curve dramatically to the left resulting in a Hb max of 10-11 g/dL. 3 The effect is greatest with more than 60% sickle red cells and decreases but is not eliminated even when more than 40% of the cells are normal red cells.…”

“…While there are few data, red cell exchange may also be useful in limiting the effects of stroke in adults. Curve adapted from references [1][2][3] . Oxygen transport increases with increasing hemoglobin until viscosity effects reduce flow and transport.…”