Biorheology - Volume 13, issue 5

Authors: Gaffin, Stephen L.

Article Type: Research Article

DOI: 10.3233/BIR-1976-13501

Citation: Biorheology, vol. 13, no. 5, pp. 273-280, 1976

Authors: Copley, Alfred L. | King, Robert G. | Huang, Ching-Rong

Article Type: Research Article

Abstract: Findings are reported on the erythrocyte sedimentation of blood subjected to varying shear rates. The blood was obtained from healthy adult human subjects. Whole blood, anticoagulated with EDTA, was exposed to shear rates from 0.0001 to 10 sec−1 with readings taken at zero shear as control. From zero to 0.01 sec−1 no change in the sedimentation rate was observed. However, from 0.01 sec−1 the sedimentation rate increased, reaching a maximum at 0.1 sec−1 . From 0.1 to 10 sec−1 the rate decreased progressively to zero, Individual differences found between donors were not significant. Tentative explanations for …the above findings in relation to the various shear rates are discussed. They include the balance and relationships between electrostatic forces and the diffusivity of erythrocytes. Our findings may mirror flow properties in certain parts of the the microcirculation, since erythrocyte sedimentation changes with varying shear rates. It is emphasized that increased erythrocyte sedimentation is not necessarily a sign of disease but can be a physiological occurrence in certain parts of the circulation which may well be one of the prerequisites for maintaining certain functions of the blood. Copley’s hypothesis on blood cellular clumping, proposed in 1958, which brings together the views of Fåhraeus and Knisely, is discussed in connection with the erythrocyte sedimentation, According to his view, intravascular clumping is identical with either rouleau formation, which he considers as reversible aggregation of erythrocytes, or with their agglutination, which is an irreversible process of clumping. It is pointed out that erythrocyte agglutinates may well be an important factor in increased sedimentation rates and be mainly responsible for these in pathological conditions, a problem which is in need of experimental study. In an Appendix to the paper, a mathematical interpretation of the parameters affecting erythrocyte sedimentation is given by S. Oka.1 1 With an Appendix compiled by Syoten Oka. Kyorin University School of Medicine, Mitaka, Tokyo, Japan. With an Appendix compiled by Syoten Oka. Kyorin University School of Medicine, Mitaka, Tokyo, Japan. Show more

DOI: 10.3233/BIR-1976-13502

Citation: Biorheology, vol. 13, no. 5, pp. 281-285, 1976

Authors: Oka, Syoten

Article Type: Other

DOI: 10.3233/BIR-1976-13503

Citation: Biorheology, vol. 13, no. 5, pp. 285-286, 1976

Authors: Murata, Tadayoshi

Article Type: Research Article

Abstract: Non-Newtonian behavior of blood in which red cells aggregate to form rouleaux at very low shear rate are theoretically considered. The theory of coagulation in colloids is applied to the process of rouleaux formation. The expression of the average size of rouleaux in a dynamical equilibrium is obtained. It is shown that the average size of rouleaux decreases monotonously with increase in shear rate and is reduced to that given by Casson on some assumptions. The apparent viscosity and the shear stress–shear rate relationship for a dilute red cell suspension are also obtained. It is shown that the plots of …square root of shear rate vs square root of shear stress lie on the curve whose asymptote is given by Casson’s equation. On some assumptions the relationship between shear stress and shear rate for a quasi-concentrated red cell suspension is obtained. Show more

DOI: 10.3233/BIR-1976-13504

Citation: Biorheology, vol. 13, no. 5, pp. 287-296, 1976

Authors: Deutsch, S. | Phillips, W.M. | Heist, J.

Article Type: Research Article

Abstract: It is commonly observed that blood shear stress when measured in an instantaneously started Couette viscometer, at low steady state strain rates, initially overshoots its steady state value. The extent of the overshoot and the strain rate range at which the overshoot occurs are evidently strongly dependent on the specific device used for the measurement. The phenomenon is usually explained by recourse to a non-continuum argument which postulates the formation of a cell free plasma skimming layer. It is shown herein that the phenomenon can be qualitatively predicted, in a continuum manner, by accounting for the viscoelastic nature of the …fluid. To this end a four constant Oldroyd model equation is solved for the instantaneous start up. The model exhibits both shear thinning and a positive Weissenberg effect. The method of solution is by finite difference approximation. A forward time differencing, centered space differencing technique is applied. It is shown that fluid elasticity is responsible for the initial overshoot, while the increase in the viscous time scale, due to shear thinning, is responsible for the decay and eventual disappearance of the phenomenon with increasing strain rate. Increased shear thinning is shown to heighten the phenomen. The results are shown to be in general agreement with the hypothesis that the stress overshoot is associated with the breakdown with time of shearing of aggregates of red cells. Show more

DOI: 10.3233/BIR-1976-13505

Citation: Biorheology, vol. 13, no. 5, pp. 297-307, 1976

Authors: Sabbah, Hani N. | Stein, Paul D.

Article Type: Research Article

Abstract: The effect of erythrocytic deformability upon turbulent blood flow was studied in vitro , Fresh blood and blood composed of hardened cells from four healthy volunteers was caused to flow through a precision orifice at rates sufficient to produce turbulence. Flow was steady, with a duration of 0.5–2.5 sec. The random fluctuations of velocity indicative of turbulent flow were measured with a hot-film probe. Normal erythrocytes diminished the tendency of blood to flow in a turbulent fashion, in comparison to blood composed of hardened cells, At all Reynolds numbers studied, suspensions of normally deformable cells consistently showed lower relative intensities …of turbulence than suspensions of cells made non-deformable by glutaraldehyde. The viscoelastic properties of the membranes of normal erythrocytes appeared to cause the red cells to act as an energy sink by absorbing some of the kinetic energy generated by turbulent flow. The results of this study may be of clinical significance in view of the possible pathophysiological effects of turbulent blood flow. Show more

DOI: 10.3233/BIR-1976-13506

Citation: Biorheology, vol. 13, no. 5, pp. 309-314, 1976

Authors: Utterback, N.G. | McMillan, D.E.

Article Type: Research Article

DOI: 10.3233/BIR-1976-13507

Citation: Biorheology, vol. 13, no. 5, pp. 315-316, 1976

Article Type: Abstract

DOI: 10.3233/BIR-1976-13508

Citation: Biorheology, vol. 13, no. 5, pp. 317-323, 1976