Biorheology - Volume 35, issue 2

Authors: Chen, Chih‐Tung | Malkus, David S. | Vanderby Jr., Ray

Article Type: Research Article

Abstract: Collagen fibrils in ligaments and tendons are highly organized into parallel arrays which influence interstitial fluid transport. Finite element (FE) models were developed analogous to the fibrillar arrays in ligaments and tendons to investigate interstitial fluid flow and tissue permeability as a function of interfibrillar spacing and fluid properties. Collagen fibrils were assumed to be a periodic square array of impermeable cylinders. A two‐dimensional FE model was used to study transverse fluid flow and a three‐dimensional model was used to study flow parallel to the collagen fibrils. Parametric FE analysis provided data to formulate empirical expressions for permeability (\kappa …) as a function of porosity (\phi ). Results show that longitudinal permeability (\kappa=1.1\cdot 10^{-15} \phi^{2.5}[1-\phi]^{-0.333} ) can be up to 50 times higher than transverse permeability (\kappa=1.2\cdot 10^{-15} \phi^{0.5}[\phi-\phi_{\min}]^{2.5} ) in a compact array. Maximum fluid shear stresses occur at the narrowest zones of adjacent fibrils (1.21 Pa or 12.1 dyn/cm^{2} at 10 \mu m/s of average transverse influx). If interstitial fluid is highly non‐Newtonian, the permeability should be considered as flow (shear)‐dependent. The computational results suggest that tissue permeability in ligaments and tendons is highly anisotropic, porosity‐dependent, and can be estimated by analytic expressions. Show more

Keywords: Finite element analysis, ligaments and tendons, interstitial fluid, tissue permeability, non‐Newtonian fluid

Citation: Biorheology, vol. 35, no. 2, pp. 103-118, 1998

Authors: Cook, A.M. | Evans, S.‐A. | Jones, J.G.

Article Type: Research Article

Abstract: A filtrometer is described for measuring the flow of fluids through microfilters. The flow of Newtonian fluids through the filters can be predicted from the diameter, length and number of pores. There are no physical artefacts such as turbulent flow or a significant lag period before steady‐state flow is achieved. The instrument has been used as a viscometer and has been used to record and analyse the flow of undiluted blood through 5 \mu m polycarbonate filters. The calculated viscosity of Newtonian fluids agrees well with those measured by a more conventional viscometer (Ostwald). Flow profiles of blood have …been analysed to give both the numbers and the flow properties of a small population of slow leukocytes which equate numerically with the monocytes. They are subdivided into three distinct sub‐populations, according to their rheological properties, and these are termed \mathit{SL}_{1} , \mathit{SL}_{2} and \mathit{PB} . The concentration of these cells, in blood, are 0.12\pm0.02 \times 10^{6} ml^{-1} , 0.11\pm0.02 \times 10^{6} ml^{-1} , 0.09\pm0.02 \times 10^{6} ml^{-1} in young females aged about 25 years. The transit time of these cells, through 5 \mu m pores, is 34.8\pm1.4 s, 147.5\pm2.5 s and > 300 s, respectively. Analysis of blood from older men (53–79 years) gives essentially the same results although the concentration of SL_{1} is slightly higher at 0.19\pm0.09 \times 10^{6} ml^{-1} . Show more

Keywords: Leukocytes, monocytes, filterability, filtrometer

Citation: Biorheology, vol. 35, no. 2, pp. 119-130, 1998

Authors: Lindmark, Krister | Engström, K. Gunnar

Article Type: Research Article

Abstract: We tested a new routine to eliminate leukocytes for blood rheology measurements using commercial leukocyte absorbing filters (here PALL RC400). These filters were punched out and fitted in smaller chambers through which blood was filtered under controlled suction pressure (<30 mm Hg). This technique resulted in a very effective leukocyte elimination to 0.0022% but also a platelet reduction to 0.2%. The process causes a small but significant hemolysis with free hemoglobin, of the order of 0.06% of the filtered erythrocytes. A small fraction of the erythrocytes were retained in the filter, versus plasma, to reduce the hematocrit on …the order of 1.4%. The leukocyte filtration did not cause any detectable functional trauma to the erythrocytes, measured as micro‐pore filterability of normal and glutaraldehyde (GA) hardened erythrocytes. However, when 10% of the erythrocytes were hardened with GA, which caused an increase in pore clogging slope (p<0.05 ), the additional passage through the leukocyte elimination filter removed this measured change in clogging. This observation suggests that the leukocyte elimination filter may selectively remove, not only leukocytes and platelets, but also hardened erythrocytes. Reticulocyte counting did not reveal any selective removal of young erythrocytes. In general, we find the presented method reproducible, efficient and easy for eliminating leukocytes for blood rheology research although the risk of removing undeformable erythrocytes must be considered. Show more

Keywords: RBC, filtration, WBC removal, rheology

Citation: Biorheology, vol. 35, no. 2, pp. 131-140, 1998

Authors: Lisovskaya, I.L. | Shurkhina, E.S. | Nesterenko, V.M. | Rozenberg, J.M. | Ataullakhanov, F.I.

Article Type: Research Article

Abstract: The results of most filtration assays for deformability of erythrocytes do not distinguish whether the entire population or only its small fraction exhibits abnormal rheological properties. We developed a simple filtration method for determination of the percentage of nonfilterable cells in erythrocyte suspension using membrane filters with mean pore diameter of 3.1 \mu m. This method makes it possible to detect even minor abnormal subpopulations in erythrocyte suspensions. The flow rate of buffer depends on the number of free pores of a filter. The plot of the number of pores clogged by nonfilterable cells vs the total number of …erythrocytes that were allowed to pass through the filter had a linear portion, with a slope representing the relative content, Z %, of nonfilterable cells in the suspension. We determined Z % for various medium osmolalities u and used the data to derive the distribution of erythrocytes in u_{\mathrm{cr}} (u_{\mathrm{cr}} is the maximum value of u at which an erythrocyte cannot pass through a pore of a given filter because of geometric limitations). The distribution of u_{\mathrm{cr}} in suspension of normal erythrocytes has a maximum of about 200 mOsm/kg and a half‐width of about 20 mOsm/kg. The distributions of u_{\mathrm{cr}} are altered in normal erythrocyte suspensions at decreased pH values, in cryopreserved and ATP‐depleted erythrocyte suspensions and in erythrocytes from a xerocytosis patient. Show more

Keywords: Erythrocyte, erythrocyte filterability, erythrocyte sub‐populations

Citation: Biorheology, vol. 35, no. 2, pp. 141-153, 1998

Authors: Suzuki, Y. | Tateishi, N. | Maeda, N.

Article Type: Research Article

Abstract: Electrostatic repulsion among erythrocytes in flow was evaluated through measurement of the thickness of the marginal cell‐free layer in narrow glass tubes of 20–50 \mu m in inner diameter. To reduce the electrostatic repulsive force, due mainly to sialic acid of the membrane glycoproteins, human erythrocytes were treated with neuraminidase. The surface negative charge of the erythrocytes, as determined from the electrophoretic mobility using free‐flow electrophoresis, was found to be proportional to the sialic acid content. When erythrocytes with decreased sialic acid content flowed through narrow tubes, the thickness of cell‐free layer determined using an image processor increased even …in the absence of erythrocyte aggregation in the suspension. The effect was more pronounced at acidic pH. The addition of Dextran T‐70 (70,400 Mol. Wt.) further increased the cell‐free layer thickness due to erythrocyte aggregation. Thus, reducing the negative charge density on the erythrocyte surface by itself accelerates the axial accumulation of erythrocytes in flow due to the decreased electrostatic repulsive force between the cells, even in the absence of erythrocyte aggregation. Show more

Keywords: Marginal cell‐free layer, sialic acid, electrostatic repulsion, human erythrocytes, erythrocyte aggregation

Citation: Biorheology, vol. 35, no. 2, pp. 155-170, 1998