Biorheology - Volume 21, issue 4

Article Type: Editorial

DOI: 10.3233/BIR-1984-21424

Citation: Biorheology, vol. 21, no. 4, pp. I-III, 1984

Authors: Copley, Alfred L.

Article Type: Editorial

DOI: 10.3233/BIR-1984-21401

Citation: Biorheology, vol. 21, no. 4, pp. 419-419, 1984

Authors: Oka, Syoten

Article Type: Introduction

DOI: 10.3233/BIR-1984-21402

Citation: Biorheology, vol. 21, no. 4, pp. 421-422, 1984

Authors: Quemada, D.

Article Type: Research Article

Abstract: Biofluids as concentrated suspensions exibit (at fixed shear rate γ ˙ ) a steady shear viscosity η which critically depends on (i) the volume fraction of particles ϕ , and (ii) the ability the particles have to form more or less loose structural units (flocs, aggregates or parts of network). The latter can be quantified by some effective packing volume fraction ϕ p which reflects the actual compacity of structural units. A special η –ϕ relationships which involves such a packing fraction will be discussed. Changes of structural units as shear rate …γ ˙ (or shear stress σ ) varies lead to ϕ p = ϕ p ( γ ˙ ) i.e. to non-newtonian viscosity. This shear-thinning behaviour is believed to result from some dynamical equilibrium between formation and destruction of structural units, in the presence of both brownian motions of particles and the shear stresses the suspending fluid exerts on them. A (simple) rate equation (from reaction kinetics) gives a quantitative description of ϕ p -dependences in γ ˙ and time t. Under steady conditions, the present approach is capable not only to model shear-thinning behaviour but also plastic and shear thickening (dilatant) ones. Time variations under transient shear rate (i.e. thixotropy) can be described with ϕ p (t) deduced from the same rate equation. Extension to visco-elastic behaviour has been obtained using a Maxwell-model with instantaneous values of viscosity and elasticity which both are functionals of the structural variable ϕ p ( t , γ ˙ ) . Show more

Keywords: Blood viscosity, shear-thinning, shear-thickening, thixotropy, non-linear viscoelasticity

DOI: 10.3233/BIR-1984-21403

Citation: Biorheology, vol. 21, no. 4, pp. 423-436, 1984

Authors: Hennenberg, M. | Silberberg, A.

Article Type: Research Article

Abstract: The relationship between stress and strain is the rheological equation of state. In the case of sophisticated systems such as biological tissue, this is rarely a simple relationship. The relationship is seen to be even more complex when it is recalled that in most living tissues, the tissue is not in chemical equilibrium, but is at best in some controlled steady state. At worst, it is undergoing major fluctuations or transitions because the chemical reactions or fluxes are altering the system. It is shown, in particular, that in addition to the changes in composition, the effective rheological relaxation times of …the system are shortened due to contributions deriving from the reaction rate constants. These and other points are illustrated by considering a process of irreversible monomolecular degradation of a large macromolecular species. Show more

Keywords: Kinetorheology, Chemorheology, Chemical Change, Degradation, Aging

DOI: 10.3233/BIR-1984-21404

Citation: Biorheology, vol. 21, no. 4, pp. 437-443, 1984

Authors: Niimi, Hideyuki | Sugihara, Masako

Article Type: Research Article

Abstract: A mathematical model is developed to elucidate microhemorheological factors of the oxygen transport between blood and tissue. A two-fluids model is introduced for capillary blood flow, including the non-equilibrium and relative motion between red blood cell (RBC) and plasma. A capillary-tissue unit is devised to describe the oxygen supply to tissue from a couple of capillaries with symmetric antiparallel input and output. Non-equilibrium flows are examined numerically on the basis of the model for various geometrical and dynamical parameters such capillary hematocrit, RBC velocity and flux. It is found that both RBC flux and capillary hematocrit have important influences …on the oxygen transfer to tissue. Especially under low capillary hematocrit flow, the lowest oxygen pressure within tissue may appear at the maximal difusional distance from the capillary between arterial and venous side. Show more

Keywords: capillary blood flow, hematocrit, microhemorheology, oxygen supply, tissue oxygenation, two-fluids model

DOI: 10.3233/BIR-1984-21405

Citation: Biorheology, vol. 21, no. 4, pp. 445-461, 1984

Authors: Skalak, Richard

Article Type: Research Article

Abstract: The aggregation of red blood cells may be analyzed as an interaction of an adhesive surface energy and the elastic stored energy which results from deformation of the cell. The adhesive surface energy is the work required to separate a unit adhered area and is the resultant of adhesive forces due to the bridging molecules that bind the cells together and the electrostatic repulsion due to surface charge. The elastic strain energy in the case of the red blood is associated with the membrane elasticity only since the interior of the cell is liquid. The membrane elasticity is due both …to bending stiffness and shear. The area expansion is small and may be neglected. These assumptions allow realistic computation of red cell shapes in rouleaux. The disaggregation of rouleaux requires an external force which must overcome the adhesive energy and also supply additional elastic energy of deformation. Depending on the geometry, the initial effect of elastic energy may tend to aid disaggregation. In a shear flow, the stresses on a suspended rouleau alternately tend to compress and to disaggregate the cells if they are free to rotate. This introduces a time dependence so that viscous effects due to the viscosity of the cell membrane, the cell cytoplasm and the external fluid may play a role in determining whether disaggregation proceeds to completion or not. Show more

Keywords: Aggregation, Disaggregation, Rouleau, Erythrocyte adhesion

DOI: 10.3233/BIR-1984-21406

Citation: Biorheology, vol. 21, no. 4, pp. 463-476, 1984

Authors: Lerche, D.

Article Type: Research Article

Abstract: On the basis of a recently developed biophysical model of cell-cell interaction, including electrostatic, electrodynamic, steric and bonding/bridging interaction energies the influence of different fixed charge (dissociated groups of the glycocalyx) density distributions in red blood cell (REC) glycocalyces on the total free interaction energy was investigated. An analytical equation of electrostatic free energy on the basis of the linear Poisson-Boltzmann approach taking into account arbitrary distributions of fixed glycocalyx charges was obtained and corresponding free electrostatic energies of three example distributions were calculated. The electrodynamic, steric and bonding/bridging energies were computed as usual. It was shown that the free …energy as a function of interaction distances strongly depends on the charge distribution and, correspondingly, the “weight” of this energy term in the total free interaction energy balance equation. Generally, it can be stated that as more charges are assumed to be fixed in the outer layer of REC glycocalyx as more important becomes the electrostatic energy in contrast to the remaining three terms. Show more

Keywords: red blood cells, glycocalyx, surface structure, total interaction energy, aggregation

DOI: 10.3233/BIR-1984-21407

Citation: Biorheology, vol. 21, no. 4, pp. 477-492, 1984

Authors: Reinhold, H.S. | van den Berg-Blok, A.

Article Type: Research Article

Abstract: When experimental tumours are inoculated into a host animal, the tumour growth depends, among other things, on its vascular supply. This vascular supply has been shown to be initiated by substances released by the tumour tissue, and vascular sprouting towards implanted tumour substances has been extensively demonstrated in nonvascular tissue. Most tissues, however, already contain a vascular supply sufficient for their own needs. In such conditions, the host vascular system is probably incorporated into the tumour without much vascular sprouting. It is well known that, as a tumour grows larger, the center tends to become ischaemic and necrotic. It is …not clear why the tumour vascularity does not respond to this development with reactive vascular proliferation, but increased interstitial tissue pressure and impaired fluid transport may be implicated. Show more

Keywords: Neovascularization, microcirculation, experimental tumours, angiogenesis

DOI: 10.3233/BIR-1984-21408

Citation: Biorheology, vol. 21, no. 4, pp. 493-501, 1984

Authors: Peterson, H.-I. | Mattson, J.

Article Type: Research Article

Abstract: Different observations on the reactivity of tumor vessels to vasoactive drugs have suggested a decreased, a similar or an increased reactivity to vasoactive stimuli in the vascular bed of tumors as compared to normal tissues. No adrenergic innervation of newly developed tumor vessels has been found, while preexisting normal vessels incorporated during tumor growth may retain some innervation. In transplantable rat tumors, contractile cells, including smooth muscle cells, have been seen in tumor vessels. From recent experimental studies, it was concluded that the tumor’s vascular bed is probably in a state of maximal dilatation and therefore sensitive to vasoconstriction, but …less sensitive to pharmacological dilatation. These observations may correspond to regional tumor hypoxia and progressive development of tumor necrosis during tumor growth. The results of experimental tumor studies might question the reliability of diagnostic and therapeutic procedures in clinical oncology, which are based on differences in the reactivity to vasoactive drugs between normal and malignant tissues. Show more

Keywords: Neoplasm, Blood supply, Vasoactive drugs

DOI: 10.3233/BIR-1984-21409

Citation: Biorheology, vol. 21, no. 4, pp. 503-508, 1984