Rheology of Leukocytes, Leukocyte Suspensions, and Blood in Leukemia POSSIBLE RELATIONSHIP TO CLINICAL MANIFESTATIONS

Abstract

Suspensions of leukemic lymphocytes and myeloblasts and blood of leukemic patients were studied to examine (a) the effect of leukemic cells on blood viscosity and (b) the ability of leukemic cells to traverse channels of capillary diameter. The viscosity of suspensions of leukemic cells was dependent logarithmically on (a) shear strain rate and (b) cytocrit, although, suspensions of small lymphocytes and of myeloblasts had a similar viscosity at equivalent shear rates and cytocrit. The minimum apparent viscosity (MAV) of leukemic cells and red blood cells, measured over shear rates of 2.3-230 s^-1 was dependent logarithmically on cytocrit. However, MAV was slightly greater for leukemic cells than for red cells at cytocrits up to 20%. At cytocrits above 20%. MAV of leukemic cells increased more rapidly than that of erythrocytes. For example, at a 15% cytocrit MAV_WBC (1.85 centipoise) was only slightly greater than MAV_RBC (1.59); whereas, at 45% cytocrit MAV_WBC (14.9) was markedly greater than MAV_RBC (3.81). The blood of subjects with leukemia with marked elevation of leukocyte concentration (leukocrits of 6-32%) had 24% higher mean MAV (3.72) than blood with a similar total cytocrit composed of red cells (3.00). A negative correlation was present between leukocrit and erythrocrit in chronic lymphocytic (r = - 0.82) and chronic granulocytic (r = - 0.81) leukemia. Therefore, the modest increase in whole blood MAV in leukemia can be explained by (a) the negative association of leukocrit and erythrocrit and (b) the rarity of leukocrits over 20% and total cytocrits over 45%. However, the MAV of blood of leukemic patients was 71% greater than expected on the basis of their packed red cell volume. Hence, the ratio of hemoglobin concentration (O₂ carrying capacity) to MAV was abnormally low in the subjects with leukemia studied. Individual leukemic leukocytes were nearly rigid. The mean deformability index (DI) of leukemic myeloblasts (1.22; 1.18) and lymphocytes (1.22; 1.40) as measured by filtration and elastometry, respectively, at 50 mm H₂O negative pressure, approached that of a rigid body (1.0) as compared to red cells studied by filtration (3.09) or elastometry (4.23). The ability of leukemic cells to traverse nucleopore filter or micropipette channels was related to cell diameter. The relevance of the rheology of leukemic cells to the interruption of blood flow and of tissue oxygen delivery and thereby to clinical manifestations of leukemia is considered.