Biorheology - Volume 13, issue 3

Authors: Kopp, Ch. | Eichhorn, J.L. | Obrecht, B.

Article Type: Research Article

DOI: 10.3233/BIR-1976-13301

Citation: Biorheology, vol. 13, no. 3, pp. 151-159, 1976

Authors: Dormandy, John | Hoare, Edmund | Postlethwaite, John

Article Type: Research Article

DOI: 10.3233/BIR-1976-13302

Citation: Biorheology, vol. 13, no. 3, pp. 161-164, 1976

Authors: Leichtberg, Sam | Weinbaum, Sheldon | Pfeffer, Robert

Article Type: Research Article

Abstract: The tendency of red cells to stack axially and form aggregates, or rouleaux, in their passage through the microcirculation is a well documented phenomenon. The mechanism for the formation of rouleaux is commonly attributed to London–Van der Waals attractive forces and to intercellular bridging by macromolecular monolayers. While these short range forces and other assumed mechanisms are unquestionably important for red cells that are almost touching, they do not explain the mechanism by which the red cells achieve their nearly touching configuration. The paper describes a simplified theoretical model for the time-dependent behavior of a closely spaced, neutrally-buoyant chain …of identical red cells in Poiseuille flow. The results of this model predict a new hydrodynamical mechanism for the formation of rouleaux in the microcirculation which is of comparable importance to the statistical variation in size of the red cells. This model suggests that the long range forces responsible for the red cell aggregation may be hydrodynamic in origin and due to unequal multi-particle Stokes flow interaction effects. Toward that end, the interaction theory developed by the authors for gravity-driven Stokes flow is extended to the time-dependent, axisymmetric motion of finite chains of neutrally-buoyant spheres in unbounded Poiseuille flow at low Reynolds number. This theory predicts that individual particles in a finite chain of identical cells travel at different velocities due to particle interactions and that these effects are most pronounced for 16–80μ diameter arterioles and venules. Show more

DOI: 10.3233/BIR-1976-13303

Citation: Biorheology, vol. 13, no. 3, pp. 165-179, 1976

Authors: Richardson, Peter D.

Article Type: Research Article

Abstract: If a steady flow rate of a Newtonian liquid is established in a capillary device (having many equal-sized capillaries in parallel) and then the liquid entering the device is changed to blood, with the flow rate kept constant, the pressure drop across the device rises to a peak which exceeds the ultimate steady pressure drop associated with blood flow. The effect has been observed in bundles of parallel capillaries ranging in diameter from 200 to 1000 μ m, lengths 3–200 mm and numbers of capillaries from 14 to ca . 50,000, in experiments using fresh anti-coagulated blood with hematocrits ranging …from 20 to 72%. The strength of the effect varies with conditions. The cumulative flow of blood required to reach the pressure peak can be several times the priming volume of the capillary device, and decreases with increase in flow rate. Show more

DOI: 10.3233/BIR-1976-13304

Citation: Biorheology, vol. 13, no. 3, pp. 181-183, 1976

Authors: Říha, Pavel

Article Type: Research Article

Abstract: The effect of red cells on the heat-conduction in blood is studied by describing the thermomechanical constitution of blood using the micro continuum theory, Solutions to the system of governing equations are given for the case of the steady heat-conduction in blood trapped between two heated parallel plates. The influence of hematocrit on the obtained thermodynamic fields and on the theoretical expression for the thermal conductivity of blood is examined. The predicted thermal conductivity values are found to agree closely with the experimental data.

DOI: 10.3233/BIR-1976-13305

Citation: Biorheology, vol. 13, no. 3, pp. 185-189, 1976

Authors: Thurston, George B.

Article Type: Research Article

Abstract: The theory for oscillatory flow of a linear viscoelastic fluid in rigid circular tubes is reviewed. It differs from that for a viscous fluid in that the Newtonian viscosity is replaced by the complex coefficient of viscosity η ∗ = η ′ − i η ″ . The theory reduces to Newtonian case for η ″ = 0. The theory for the tube impedance is compared with measurements over the frequency range from 0.2 to 200 Hz in tubes having radii, a , from 0.02 to 0.35 cm. This …is done for a glycerol solution and for human blood (H = 46%). The shear rate in the blood is kept in the lower range where the viscoelasticity is linear. When the dispersion of η * with frequency is taken into account, the agreement with theory is excellent. At low frequencies the tube reactance is negative (spring-like) and changes to positive (mass-like) when the radian frequency ω 0 = 6 η ″ / π a 2 , a condition for resonance. The glycerol, being Newtonian and purely viscous, does not exhibit the viscoelastic resonance. Show more

DOI: 10.3233/BIR-1976-13306

Citation: Biorheology, vol. 13, no. 3, pp. 191-199, 1976

Authors: Walburn, Frederick J. | Schneck, Daniel J.

Article Type: Research Article

Abstract: A constitutive equation for whole human blood was developed using a power law functional form containing two parameters, a consistency index and a non-Newtonian index. These two parameters were determined by a multiple regression technique performed on viscometric data obtained from anticoagulated blood samples of known hematocrit and chemical composition. An initial constitutive model depending only on shear rate was found to be lacking any substantial degree of significance. When hematocrit was included as an independent variable, there was a considerable increase in the fit of experimental data with the analytic model. This fit became even better when fibrinogen and …globulin concentrations were further taken into account. The best constitutive model ultimately included a dependence of shear stress on shear rate hematocrit and the sum of fibrinogen and globulin concentrations. Plasma lipids and the protein albumin were found to contribute little to the rheologic behavior of blood. Show more

DOI: 10.3233/BIR-1976-13307

Citation: Biorheology, vol. 13, no. 3, pp. 201-210, 1976

Authors: Chen, T.M. | Dulfano, M.J.

Article Type: Research Article

Abstract: The viscoelasticity of reconstituted sputum was found to vary as a function of the solid concentration, pH, ionic strength and temperature. At a given solid concentration, the highest viscosity and elastic modulus occurred at pH = 6.0 and decreased with higher or lower pH. This effect is theorized to be mainly the result of electrostatic interactions. The addition of sodium chloride acted to shorten the Newtonian viscosity area. Both the elastic modulus and viscosity were increased with increasing solid concentration. A slight, 4°C increase in experimental temperature reduced the elastic modulus by 19.3% and the Newtonian viscosity by 80.3% at …pH 7.9. Whenever rheological changes occurred, both viscosity and elastic modulus changed in the same direction: an increase in viscosity correlated with a decrease in elastic recoil (increased modulus) and vice versa. Show more

DOI: 10.3233/BIR-1976-13308

Citation: Biorheology, vol. 13, no. 3, pp. 211-218, 1976

Authors: Fung, Y.C.

Article Type: Book Review

DOI: 10.3233/BIR-1976-13309

Citation: Biorheology, vol. 13, no. 3, pp. 219-219, 1976