Biorheology - Volume 26, issue 2

Authors: Alonso, C. | Pries, A.R. | Gaehtgens, P.

Article Type: Research Article

Abstract: Magnitude and time-dependence of the effects of red cell aggregation and sedimentation on the rheology of human blood were studied during low shear (τ W 2.5 to 92 mPa) flow through horizontal tubes (ID 25 to 105 μ m). Immediately following reduction of perfusion pressure to a low value the red cell concentration near the tube walls decreases as a result of red cell aggregation. This is associated with a transient increase of centerline velocity. Simultaneously, sedimentation begins to occur and eventually leads to the formation of a cell-free supernatant plasma layer. Time-course and extent of this sedimentation process …are strongly affected by wall shear stress variation, particularly in the larger tubes. At the lower shear stresses, centerline velocity decreases (flow resistance increases) with time following the initial acceleration period, due to sedimentation of red cells. This is followed by a further increase of resistance caused by the elevation of hematocrit occurring because of the reduction of cell/plasma velocity ratio. The time dependence of blood rheological behaviour under these flow conditions is interpreted to reflect the net effect of the partially counteracting phenomena of sedimentation and red cell aggregation. Show more

Keywords: sedimentation, red cell aggregation, blood rheology, horizontal tube, low shear flow, plasma layer

DOI: 10.3233/BIR-1989-26210

Citation: Biorheology, vol. 26, no. 2, pp. 229-246, 1989

Authors: Murata, T. | Secomb, T.W.

Article Type: Research Article

Abstract: The flow properties of aggregating red cell suspensions flowing at low rates through vertical tubes with diameters from 30 μ m to 150 μ m are analyzed using a theoretical model. unidirectional flow is assumed, and the distributions of velocity and red cell concentration are assumed to be axisymmetric. A three-layer approximation is used for the distribution of red cells, with a cylindrical central core of aggregated red cells moving with uniform velocity, a cell-free marginal layer near the tube wall, and an annular region located between the core and the marginal layer containing suspended non-aggregating red cells. This suspension …is assumed to behave approximately as a Newtonian fluid whose viscosity increases exponentially with red cell concentration. Physical arguments concerning the mechanics of red cell attachment to, and detachment from the aggregated core lead to a kinetic equation for core formation. From this kinetic equation and the equation for conservation of red cell volume flux, a relationship between core radius and pressure gradient is obtained. Then the relative viscosity is calculated as a function of pseudo-shear rate. At low flow rates, it is shown that the relative viscosity decreases with decreasing flow and that the dependence of relative viscosity on shear rates is more pronounced in larger tubes. It is also found that the relative viscosity decreases with increasing aggregation tendency of suspension. These theoretical predictions are in good qualitative and quantitative agreement with experimental results. Show more

Keywords: blood viscosity, narrow tube flow, cell-free layer, Fahraeus-Lindqvist effect, red cell aggregation, rouleaux

DOI: 10.3233/BIR-1989-26211

Citation: Biorheology, vol. 26, no. 2, pp. 247-259, 1989

Authors: Sugihara-Seki, Masako | Skalak, Richard

Article Type: Research Article

Abstract: Single rows or two rows of identical circular cylinders spaced regularly in a narrow channel flow have been shown to be capable of steady flow provided the cylinders are located at equal lateral positions and with equal spacings in the flow direction. The stability of such steady flows of circular cylinders is studied for periodic perturbations of the particle positions, assuming that every other cylinder is equally perturbed in lateral position and spacing along the channel. This results in two rows which are not symmetrically placed. The suspending fluid is assumed to be an incompressible Newtonian fluid. It is assumed …that no external forces or moments act on the cylinders and the effects of inertia forces on the motion of the fluid and the cylinders are negligible. The velocity field of the suspending fluid and the instantaneous velocities of the cylinders are computed by the finite element method. The translational velocities of the cylinders are obtained for a large number of particle positions, from which the trajectories of their relative motion are determined for various initial positions near the regular single-file and two-file arrangements. It is shown that when the initial arrangements of the cylinders are slightly perturbed from the regular (alternating) two-file flows, the trajectories of their relative motions become small closed loops around the regular two-file arrangements. In contrast, such small closed trajectories are not obtained when they start from the arrangements near the regular single-file flows or regular (symmetric) double-file flows, suggesting that these flows are unstable under the conditions examined. Show more

Keywords: channel flow, circular cylinders, stability of particle motions

DOI: 10.3233/BIR-1989-26212

Citation: Biorheology, vol. 26, no. 2, pp. 261-277, 1989

Authors: Fung, Y.C.

Article Type: Research Article

Abstract: The width and curvature of the collagen and elastin fiber bundles in the human pulmonary interalveolar septa and alveolar mouths are measured. The data, together with the known mechanical properties of collagen and elastin fibers, are used to derive the incremental elastic moduli of the lung tissue. The constitutive equation for small incremental stress and strain superposed on a homeostatic inflated lung is linear and isotropic, and characterized by two material constants.

Keywords: Microrheology, Alveolar duct, Elasticity, Incremental Moduli, Pulmonary ductal tree, Constitutive equation

DOI: 10.3233/BIR-1989-26213

Citation: Biorheology, vol. 26, no. 2, pp. 279-289, 1989

Authors: Silberberg, A.

Article Type: Research Article

Abstract: In order to induce and maintain a pressure gradient in a fluid mixture in steady state, the fluid has to pass through a solid-like matrix capable of generating and carrying an extra stress gradient. Frictional interactions between fluid components and the matrix then produce separations. Matrix deformation occurs and the implication of this is discussed. A general solution for multi component systems is given and then specialised to the case of three components - a deformable gel matrix component, a solvent and a macromolecular solute. A method is given for solving the system of equations and is applied in the …steady state. Applications involving transendothelial flow and self-regulated selectivity are stressed in particular. The calculations are based on the Flory-Huggins equation, on the Flory gel deformation model and on ad hoc, very crude approximations to the concentration dependence of the three, pairwise defined friction coefficients between the three components involved. Show more

Keywords: Deformable, porous matrixes, Transport, Separation, Permeability, Selectivity, Delivered concentration, Flow induced selectivity, Transendothelial transport, Friction coefficients

DOI: 10.3233/BIR-1989-26214

Citation: Biorheology, vol. 26, no. 2, pp. 291-313, 1989

Authors: Puchelle, E. | Zahm, J.M. | Jacquot, J. | Pierrot, D.

Article Type: Research Article

Abstract: The effect of varying the inspired air humidity on a rheological property (spinability) and transport capacity of airway mucus has been analyzed in 10 mongrel dogs. Tracheal mucus was collected in anesthetized dogs inspiring through an endotracheal tube the air of a climate chamber maintained at constant temperature (T°: 20°C). In one test, the dogs inspired air at an absolute humidity (AH) of 9 g water/m3 air directly through the endotracheal tube. In the other test, the dogs inspired through an artificial nose connected to the endotracheal tube giving a AH of 30 g water/m3 air. Tracheal mucus …was collected at the external distal end of the endotracheal tube. The spinability (Sp) or thread-forming properties of mucus was measured. The relative mucociliary transport rate (TR) of mucus was analyzed on a frog palate epithelium preparation. The transport rate was significantly (p < 0.01) lower (range: 0.59–0.80) when the AH of the inspired air was low in comparison to that obtained with high AH (range: 0.70–1.13). The variations in mucus Sp due to changing AH were positively and significantly correlated (r = 0.80, p < 0.01) with the corresponding variations in TR. These results suggest that lowering the AH of air induces a decrease in the transport capacity which appears to be dependent on the change of spinability that occurs in the mucus. Show more

Keywords: airway secretions, mucus hydration, mucociliary transport, spinability

DOI: 10.3233/BIR-1989-26215

Citation: Biorheology, vol. 26, no. 2, pp. 315-322, 1989

Authors: Muller, S. | Masson, V. | Droesch, S. | Donner, M. | Stoltz, J.F.

Article Type: Research Article

Abstract: The uptake of particles by phagocytic cells involves an increase in the membrane fluidity determined by steady-state fluorescence polarization. Binding and endocytosis of target particles is in vivo enhanced by humoral factors called opsonins. In this work, fluorescence polarization was used to detect in vitro the opsonic activity of a plasma protein: fibronectin. The assay is based on the analysis of membrane fluidity variations following the uptake of gelatinized latex beads by phagocytic cells in the presence or in the absence of fibronectin. Using TMA-DPH as fluorescent probe, it was observed that the increase in membrane fluidity was enhanced in …presence of fibronectin and depended upon the concentration of opsonin. It was also recorded that the level of opsonic activity was related to the integrity of the molecule. Using this method, the opsonic activity of various plasmas could be also determined. Show more

Keywords: opsonization, fibronectin, fluorescence polarization

DOI: 10.3233/BIR-1989-26216

Citation: Biorheology, vol. 26, no. 2, pp. 323-330, 1989

Authors: Schmid-Schönbein, Geert W. | Chien, Shu

Article Type: Research Article

Keywords: Stereology, leukocytes, granules, pseudopods

DOI: 10.3233/BIR-1989-26217

Citation: Biorheology, vol. 26, no. 2, pp. 331-343, 1989

Authors: Levesque, Murina J. | Nerem, Robert M.

Article Type: Research Article

Abstract: A number of cell culture studies have been reported on the influence of shear stress on vascular endothelial cells. Although through such studies much has been learned about the effect of an endothelial cell’s hydrodynamic environment on its structure and function, the reports indicate significant differences in methodology. Using cell shape as an indicator of differences that might result from differing methodologies, an investigation of the influence of selected variables has been carried out. The results presented indicate that not only are such variables as the level of shear stress and the duration of exposure important, but also substrate, media …composition, characteristics of the cell itself, and the nature of the flow, e.g. whether it is steady state or pulsatile. Show more

Keywords: vascular endothelial cells, shear stress, cell culture, rheological effects

DOI: 10.3233/BIR-1989-26218

Citation: Biorheology, vol. 26, no. 2, pp. 345-357, 1989

Authors: Xia, Z. | Woo, L. | van de Ven, T.G.M.

Article Type: Research Article

Abstract: The adhesion of both live and fixed bacteria (Escherichia coli ) on glass has been studied under well-defined hydrodynamic conditions, created in an impinging jet apparatus. With this technique one can accurately measure the initial deposition rate j0 on the surface, the average lifetime of a bacterium on the surface, τ esc and the surface area blocked per deposited bacterium, normalized by its projected area, γ . The experimental results are compared to theoretical results for equivalent spheres. It is found that near the stagnation point the deposition rate j0 is mainly controlled by convective diffusive transport …which, for rod-shaped Escherichia coli , with an axis ratio of about 2, is found to be equal to that for spheres. No differences in j0 and τ esc were found between live and fixed bacteria at low flow rates. At high flow rates fixed bacteria adhered to the surface at a slower rate. In both systems j0 was found to decrease suddenly at a distance of about 150 μ m from the stagnation point, in contrast to systems of spherical particles for which j0 is uniform over the surface. Most likely this is due to the rotation of the rod-shaped particles, which vary their distance to the surface periodically with time. The main difference between live and fixed bacteria, besides different deposition rates in strong flows, is that γ is about 30% larger for fixed bacteria than for live ones, resulting in a much lower final coverage for fixed bacteria. These results imply a larger repulsion between fixed bacteria than between living ones. From detachment experiments we can conclude that not all bacteria stick to the surface with the same bond strength. The variation in the bond strength is due to the aging of the bonds between the bacteria and the surface. The average bond strength corresponds to an energy of about 13-15 kT. Show more

Keywords: Bacterial adhesion, Escherichia coli, shear, aging

DOI: 10.3233/BIR-1989-26219

Citation: Biorheology, vol. 26, no. 2, pp. 359-375, 1989