Biorheology - Volume 33, issue 3

Authors: Sharp, M.K. | Thurston, G.B. | Moore Jr., J.E.

Article Type: Research Article

Abstract: An analytical solution for pulsatile flow of a generalized Maxwell fluid in straight rigid tubes, with and without axial vessel motion, has been used to calculate the effect of blood viscoelasticity on velocity profiles and shear stress in flows representative of those in the large arteries. Measured bulk flow rate Q waveforms were used as starting points in the calculations for the aorta and femoral arteries, from which axial pressure gradient ∇ P waves were derived that would reproduce the starting Q waves for viscoelastic flow. The ∇ P waves were then used to …calculate velocity profiles for both viscoelastic and purely viscous flow. For the coronary artery, published ∇ P and axial vessel acceleration waveforms were used in a similar procedure to determine the separate and combined influences of viscoelasticity and vessel motion. Differences in local velocities, comparing viscous flow to viscoelastic flow, were in all cases less than about 2% of the peak local velocity. Differences in peak wall shear stress were less than about 3%. In the coronary artery, wall shear stress differences between viscous and viscoelastic flow were small, regardless of whether axial vessel motion was included. The shape of the wall shear stress waveform and its difference, however, changed dramatically between the stationary and moving vessel cases. The peaks in wall shear stress difference corresponded with large temporal gradients in the combined driving force for the flow. Show more

Keywords: Blood, viscoelastic, Maxwell, pulsatile flow, acceleration

DOI: 10.3233/BIR-1996-33301

Citation: Biorheology, vol. 33, no. 3, pp. 185-208, 1996

Authors: Wagner, C.T. | Kroll, M.H. | Chow, T.W. | Hellums, J.D. | Schafer, A.I.

Article Type: Research Article

Abstract: Elevated shear stress levels in pathologically stenosed vessels induce platelet activation and aggregation, and may play a role in the pathogenesis of arterial disease. Increased plasma catecholamine concentrations have also been implicated in the onset of acute coronary ischemic syndromes. This study was designed to examine the synergistic interaction of shear stress and epinephrine in the activation of platelets. Platelets (in PRP) sheared at 60 dyn/cm2 showed little or no aggregation unless pretreated with epinephrine. Pretreatment with 250 nM epinephrine followed by shear at 60 dyn/cm2 induced >60% platelet aggregation. The specific α 2 …-adrenergic receptor antagonist yohimbine inhibited the synergistic aggregation, as did the ADP scavenging system phosphocreatine/creatine phosphokinase, indicating a three-way synergism with ADP. Chemical or monoclonal antibody blockade of von Wille brand factor (vWF) interactions with either platelet glycoprotein (Gp) Ib or Gp IIb/IIIa completely inhibited platelet aggregation induced by activating levels of shear stress alone. However, the combination of epinephrine and shear stress induced platelet aggregation that was blocked by 10E5, a monoclonal antibody that inhibits vWF binding to Gp IIb/IIIa, but not by aurin tricarboxylic acid or the monoclonal antibody 6D1, both of which inhibit vWF binding to Gp lb. Synergistic platelet aggregation in response to epinephrine and shear stress was observed in washed platelets, platelet-rich plasma and whole blood in vitro, and also ex vivo following exercise to elevate endogenous levels of catecholamines. These results indicate that epinephrine synergizes with shear stress to induce platelet aggregation. This synergistic response requires functional Gp IIb/IIIa complexes, but is at least partially independent of vWF-Gp Ib interactions. Show more

Keywords: Ephedrine, shear stress, platelet, glycoprotein, exercise

DOI: 10.3233/BIR-1996-33302

Citation: Biorheology, vol. 33, no. 3, pp. 209-229, 1996

Authors: Ebrahimzadeh, P.R. | Bazargani, F. | Afzal, F. | Högfors, C. | Braide, M.

Article Type: Research Article

Abstract: Leukocyte migration in vitro has been studied extensively during many years without providing satisfactory theoretical models for the different migratory behaviors (chemotaxis and chemokinesis) of leukocyte populations. The present study utilized the fluid gradient chamber, which is a new method to study leukocyte migration in filters. Human neutrophils were applied between two stacked filters and migrated in all directions under the influence of constant concentrations or chemotactic gradients of f-MLP, maintained in fluid phase density gradients. The distributions of the granulocytes over filter depth were fitted to theoretical functions composed by 1–3 Gaussian distributions, representing subpopulations. The results showed that …the neutrophils migrated as two discrete subpopulations during chemokinetic stimulation (a constant concentration of f-MLP). One of the subpopulations showed less active and passive (slow sedimentation under the influence of gravity) translocation. The most mobile subpopulation was divided into two new subpopulations when exposed to chemotactic stimulation (concentration gradient of f-MLP), one of which responded chemotactically and one of which migrated in random directions. The properties of the different subpopulations where characterized in terms of diffusion coefficient (random migration), convection velocity (chemotactic migration) and sedimentation coefficient (passive translocation). Show more

Keywords: Cell movement, chemotaxis, neutrophils, n-formylmethionine-leucyl-phenylalanine, subpopulations

DOI: 10.3233/BIR-1996-33303

Citation: Biorheology, vol. 33, no. 3, pp. 231-250, 1996

Authors: Artmann, G.M. | Li, A. | Ziemer, J. | Schneider, G. | Sahm, U.

Article Type: Research Article

Abstract: In this paper, a photometric method was introduced to quantify biochemically-induced red blood cell (RBC) shape changes when no shear force was acting on the cells. To obtain the photometric RBC shape parameter (RF1), a monolayer of point-attached RBCs was prepared on the floor of a flat flow chamber and the transmission of light perpendicular to the monolayer plane was measured: 1) in phosphate buffered saline with 0.1 % bovine serum albumin (PBS+ ) and 2) in PBS+ , containing a shape changing compound (in both, the RBCs were not deformed due to shear flow). To normalize the data, a …third transmission value at a shear stress of 3 Pa was measured in PBS+ from the same RBC monolayer. To validate the photometric data, RF1 of RBCs exposed to shape changing agents was correlated by linear regression analysis with 1) data obtained with the tangent-counting technique (TC) and 2) the morphological index (MI). The coefficient of correlation was calculated at 0.95 for the TC data and 0.94 for the MI data, respectively. The sensitivity of the photometric method was tested with stomatocytogenic chlorpromazine (CP) and echinocytogenic sodium salicylate (SA). CP (2.5 µM) induced a significant decrease of RF1 to -0.045 (N = 6 donors, p < 0.01), whereas SA (2.5 mM) increased RF1 to +0.027 significantly (N = 6, donors, p < 0.01). Both the CP-induced and the SA-induced shape changes appeared less than 2 min after application of the shape changing agents, and changed gradually within another 30 min when the agent was present in PBS+ , partly disappearing within about 2 min after reincubation of the shape transformed RBCs in PBS+ not containing the agent. Show more

Keywords: Erythrocyte shape, lipid bilayer, membrane, method, drug

DOI: 10.3233/BIR-1996-33304

Citation: Biorheology, vol. 33, no. 3, pp. 251-265, 1996

Authors: Murata, T.

Article Type: Research Article

Abstract: The flow properties of aggregating red cell suspensions flowing at low flow rates through horizontal tubes are analyzed using a theoretical model. The effects of sedimentation of small aggregates, which will be formed at comparatively high flow rates, on the relative apparent viscosity are considered. In the case in which a large number of small aggregates are formed in a suspension flowing through a horizontal tube, it seems that red cells are transported as a concentrated suspension through the bottom part of the tube because of sedimentation of aggregates. A two-layer flow model is used for the distribution of red …cells. It consists of plasma in the upper part and a concentrated red cell suspension in the bottom part of the tube divided by a smooth and horizontal interface. It is assumed that the suspension is a Newtonian fluid whose viscosity increases exponentially with hematocrit. The velocity distribution, the relative apparent viscosity and the flux of red cells are calculated as functions of width of plasma layer for a different discharge hematocrit. The theoretical results are compared with the results obtained from experimental data. The relative apparent viscosity increases rapidly with an increasing degree of sedimentation over a wide range of plasma layer widths. Show more

Keywords: Red cell aggregation, sedimentation of aggregates, microcirculation, flow resistance, blood viscosity

DOI: 10.3233/BIR-1996-33305

Citation: Biorheology, vol. 33, no. 3, pp. 267-283, 1996

Article Type: Correction

DOI: 10.3233/BIR-1996-33306

Citation: Biorheology, vol. 33, no. 3, pp. 285-285, 1996

Article Type: Other

DOI: 10.3233/BIR-1996-33307

Citation: Biorheology, vol. 33, no. 3, pp. 287-287, 1996