Biorheology - Volume 31, issue 1

Authors: Sugihara-Seki, M.

Article Type: Research Article

Abstract: The motion of a doublet consisting of two rigidly connected circular cylinders freely suspended in an incompressible Newtonian fluid in a narrow channel bounded by two parallel planes is studied numerically at zero Reynolds number. The Stokes equations are solved by a finite element method for various positions and orientations of the particle, and the trajectories of the particle are determined for a number of initial configurations. A doublet of equal-sized cylinders is found either to tumble or oscillate in rotation, while a doublet of unequal-sized cylinders possesses a stable, steady equilibrium configuration, at which the particle is located close …to the channel centerline with a constant angle of inclination. Thus, doublets of unequal diameters tumble, oscillate in rotation or approach the equilibrium configuration asymptotically, depending on the radius ratio of cylinders, particle size-channel width ratio and initial conditions. Show more

Keywords: Stokes flow, particle motion, tumbling motion, oscillation, stability

DOI: 10.3233/BIR-1994-31101

Citation: Biorheology, vol. 31, no. 1, pp. 1-10, 1994

Authors: Agarwal, M. | King, M. | Shukla, J.B.

Article Type: Research Article

Abstract: Under some conditions, such as inhalation injury, an array of longitudinal channels without cilia may be formed on the epithelial surface, affecting mucus transport in the lung during coughing. Moreover, in certain cases of the diseased state of the lung, immotile cilia remain embedded in the serous fluid and may form channels in the direction of air motion during coughing, providing a resistance-free pathway for serous layer fluid and assist in mucus clearance. To understand this phenomenon, we have conducted experiments with mucous gel simulants (MGS) in a simulated cough machine (SCM) using soap solution as a serous layer simulant …(SLS). The channel structure of the airway surface was modeled by introducing bottom plates with longitudinal grooves about 10 cm long having different depths, widths and number of grooves. It was shown that mucous gel transport increases as the cross-sectional area occupied by channel grooves increases. The effects of sinusoidal constriction and mucous gel filance were also investigated in this model system. It was found that mucous gel transport increases in the constricted case (minimum gap, 3 mm, and maximum gap, 9 mm) in comparison with that in the parallel case (constriction gap of 9 mm). The effect of increasing the mucous gel filance was to decrease the transport as reported in previous studies. Show more

Keywords: Cough clearance, mucus, cilia, serous fluid, primary ciliary dyskinesia

DOI: 10.3233/BIR-1994-31102

Citation: Biorheology, vol. 31, no. 1, pp. 11-19, 1994

Authors: Hsu, S. | Jamieson, A.M. | Blackwell, J.

Article Type: Research Article

Abstract: We describe an in vitro test of the hypothesis that viscoelastic properties of the collagen fiber network of skin are influenced by interactions between the macromolecular components in the extracellular matrix. Native type I collagen gels were investigated as a mechanical analog for connective tissue. A series of gels were formed under physiological conditions via fibril precipitation in the presence of selected matrix macromolecules, including dermatan sulfate (DS), hyaluronic acid (HA), dermatan sulfate proteoglycan (DSPG), fibronectin (FN) and elastin. Viscoelastic measurements and transmission electron microscopy were performed to explore the relationship between mechanical strength and fibril morphology. The results …demonstrate that associative interactions of DSPG and HA with collagen fibrils, as well as variations in collagen fibril size distribution and the amount of elastin, can modify the viscoelastic behavior of the model collagen gels. Addition of DSPG, DS and HA increases both storage and loss moduli, G′ and G″; morphological examination shows adhesive binding of these species to the collagen fibrils. At 37°C, elastin increases G′ by forming elastic coacervate particles. FN has no effect on the gel viscoelasticity. The observed effects are discussed in terms of current clinical observations on age-related changes in the mechanical properties of skin. Show more

Keywords: Native collagen gels, viscoelasticity, extracellular matrix

DOI: 10.3233/BIR-1994-31103

Citation: Biorheology, vol. 31, no. 1, pp. 21-36, 1994

Authors: Reihsner, R. | Menzel, E.J.

Article Type: Research Article

Abstract: Rat tail tendons from 54-day-old and 900-day-old animals were incubated with different concentrations of the dibasic amino acids, lysine and arginine. We observed a significant incorporation of these amino acids into the tendons. Uniaxial tension tests and relaxation experiments were performed at strain levels within the linear portion of the stress-strain relationship. The incorporation of the amino acids resulted in a decrease of ultimate stress and maximum Young’s modulus and, after separation of the elastic and viscous stress components, in a decrease of the elastic fraction. The incorporation of amino acids and the resulting mechanical alterations were more pronounced in …the young animals. The reversibility of the effects induced by the amino acids was tested. After the glycosaminoglycan chains were digested with chondroitinase ABC, we showed that the dibasic amino acids bind predominantly to the proteoglycan matrix. A possible analogy to the effects of amino acid incorporation on biomechanics and swelling with a monovalent cation such as Na+ is discussed. Show more

Keywords: Biomechanical properties, rat tail tendon, dibasic amino acids, age

DOI: 10.3233/BIR-1994-31104

Citation: Biorheology, vol. 31, no. 1, pp. 37-55, 1994

Authors: Ando, J. | Ohtsuka, A. | Katayama, Y. | Korenaga, R. | Ishikawa, C. | Kamiya, A.

Article Type: Research Article

Abstract: We studied the responses of cultured endothelial cells to mechanical shearing force directly applied to those cells in vitro to determine changes in the concentration of intracellular calcium ion (Ca++ ), one of the factors that transfers information within the cell. Cultured bovine fetal aortic endothelial cells containing the Ca++ fluorescence indicator, Fura-2, were rubbed with a latex balloon in a specially designed system, and changes in the fluorescence of Fura-2 caused by this shear stimulation were determined by photometric fluorescence microscopy. Immediately after shear stimulation, the concentration of Ca++ in the cells was increased and reached …a peak (511 ± 165 nM, n = 12) within 15 seconds after stimulation. After the peak, the concentration was gradually restored to the resting level (55 ± 17 nM, n = 12). The magnitude of the Ca++ response was dependent on the intensity of the shear force applied. Analysis of fluorescence images of Fura-2 revealed that the cells showed this Ca++ reaction without being injured or desquamated, although there were slight differences in the degree and duration of reaction among cells. This reaction appeared even when the cells were placed in the air with no contact with the fluid. This result suggests that neither the fluid flow associated with the balloon movement nor chemical substances in the fluid are involved in the reaction, but that pure physical force alone is responsible for the Ca++ reaction. Further, it suggests that endothelial cells have the ability to perceive such physical stimulation as shear force and to transfer this information to the interior of the cell via changes in the intracellular Ca++ concentration. Show more

Keywords: Shear stress, endothelial cell, intracellular calcium, mechanical stress

DOI: 10.3233/BIR-1994-31105

Citation: Biorheology, vol. 31, no. 1, pp. 57-68, 1994

Authors: Dao, K.M. | O’Rear, E.A. | Johnson, A.E. | Peitersen, S.E.

Article Type: Research Article

Abstract: Exposure of human erythrocytes to subhemolytic shear stress is known to cause lipid loss and ion fluxes across the red cell membrane and to result in decreased filterability of suspensions of these cells. Damage to the lipid bilayer of traumatized erythrocytes has been examined by fluorescence anisotropy using the probe 1,6-diphenylhexatriene. Because literature methods for the introduction of the probe damaged the cells, a gentler method was developed using liposomes. Significant disruption of the lipid bilayer following subhemolytic trauma was detected by a decreased anisotropy of the membrane-bound fluorescent probe after stress.

Keywords: Fluidity, erythrocyte, mechanical trauma, deformability

DOI: 10.3233/BIR-1994-31106

Citation: Biorheology, vol. 31, no. 1, pp. 69-76, 1994

Authors: Kuo, C.-D. | Bai, J.-J. | Chien, S.

Article Type: Research Article

Abstract: The erythrocyte sedimentation test is a useful tool for studying the biophysical properties of red blood cells (RBCs) and the interactions between RBCs and bridging macromolecules in the suspending fluid. In our previous model of erythrocyte sedimentation formulated on the basis of a logistic growth equation of population dynamics (Kuo et al. , 1989), the sedimentation rate constant, r, was assumed to be an intrinsic constant characteristic of the interaction between RBCs and bridging macromolecules in the suspending fluid. By analyzing the time dependence of r in that model, however, it was found that r depends on the sedimentation time, …t . There is a power law relation between r(t ) and t ; the rate “constant” is therefore an effective kinetic rate constant rather than a true constant. The realization that r is an effective kinetic rate constant allowed the introduction of a power law function r(t ) into the formalism of erythrocyte sedimentation. Doing so yielded a new model with the following capacities: (a) The skew-symmetric sedimentation curves can be modeled; (b) the experimental data can be fitted better with the new sedimentation equations; (c) a fractal dimension, D, and a new rate constant, k, can be defined; (d) the tendency for a certain amount of plasma to be trapped inside the rouleau network, ξ , can be accounted for. The D, k, ξ , and other parameters can be used in the analysis of RBC interactions mediated by bridging macromolecules. Show more

Keywords: Blood sedimentation, ESR, erythrocyte, fractals, rheology

DOI: 10.3233/BIR-1994-31107

Citation: Biorheology, vol. 31, no. 1, pp. 77-89, 1994

Authors: Kaniewski, W.S. | Hakim, T.S. | Freedman, J.C.

Article Type: Research Article

Abstract: The deformability of red blood cells is important in the microcirculation where capillary diameters are often smaller than those of the red blood cells. In the present study, ektacytometry was used to examine the effect of hypoxia on the deformability of red blood cells from five mammalian species: Human, cat, rat, rabbit, and dog. Deformability was characterized in both normoxic (PO2 = 129 ± 6 mm Hg) and hypoxic (PO2 = 47 ± 6 mm Hg) conditions in two different ways. First, we used the Elongation Index (EI) which quantitates the extent of elongation of red blood cells …in response to increasing fluid shear stress; second, we used the Elongation Constant (EC), which quantitates the exponential dependence of the fraction of maximal elongation on the varying shear stress. The EI was measured at high shear stresses (150–250 dyn/cm2 ), as well as at lower shear stresses (15, 32 and 64 dyn/cm2 ) that occur in the microcirculation. In response to hypoxia at high shear stresses, the EI of the rat red blood cells decreased by 9.3% (P < 0.05), but was not altered in the other four species studied. Moreover, in all five species, the EC and EI at the lower shear stresses were unaltered in response to hypoxia. These ektacytometry experiments indicate that (1) the elongation constant is a new and useful parameter for characterizing the deformability of red blood cells and (2), the deformability of human, cat, dog, and rabbit red blood cells is unaltered by hypoxia. The results constrain the possible mechanisms that could account for the observation that hypoxia decreases the filterability of certain species of red blood cells, which was reported previously. Show more

Keywords: Red blood cell deformability, ektacytometer, laser diffractometry, hypoxia

DOI: 10.3233/BIR-1994-31108

Citation: Biorheology, vol. 31, no. 1, pp. 91-101, 1994

Authors: Chen, D. | Kaul, D.K.

Article Type: Research Article

Abstract: The present study compares hematologic, rheologic and hemodynamic characteristics of red cells from mouse, rat and human. Red cells in these species are biconcave discs that show significant differences in diameter and mean corpuscular volume (MCV). However, differences in mean corpuscular hemoglobin concentration (MCHC) are not significant. Viscosity measurement of washed red cell suspensions (in each case the medium osmolarity adjusted to match plasma osmolarity) showed significant interspecies differences at shear rates of 37.5 and 750 sec−1 as follows: Human > rat > mouse. Hemodynamic and microcirculatory behavior of these red cells was investigated in the artificially perfused ex …vivo mesocecum vasculature of the rat. Hemodynamic measurements in the whole ex vivo mesocecum preparation revealed maximal increase in the peripheral resistance unit (PRU) for the human red cells followed by the rat and mouse red cells, respectively, at a hematocrit (Hct) of 40%. Further, measurements of red cell velocities (Vrbc) in single arterioles of the mesocecum vasculature, during sustained perfusion with washed red cell suspensions, showed that at any given perfusion pressure (Pa), Vrbc for both mouse and rat red cells was higher than that for human red cells, while Vrbc for mouse red cells was higher than that for the rat. These results demonstrate that the microvascular flow behavior of these red cells is likely to be influenced by both physical and rheologic characteristics. Show more

Keywords: Mammalian red cells, rheology, hemodynamics, ex vivo vasculature, peripheral resistance (PRU), red cell velocity (Vrbc)

DOI: 10.3233/BIR-1994-31109

Citation: Biorheology, vol. 31, no. 1, pp. 103-113, 1994

Authors: Shehada, R.E.N. | Cobbold, R.S.C. | Mo, L.Y.-L.

Article Type: Research Article

Abstract: Ultrasound B-mode imaging (7 MHz) was used to measure blood echogenicity and velocity profiles simultaneously as they developed with axial distance for a steady flow of 28% hematocrit whole blood flowing in a long (> 60 D) large diameter (D = 2.54 cm) tube. At selected sites along the flow axis, velocity profiles were measured using block matching (cross correlation) between successive digitized images with a known time separation; from these shear rate profiles were calculated. The corresponding echogenicity profiles were also determined by averaging the digitized images. It was found that over a range of low shear rates, the …echogenicity is enhanced in a manner similar to the previously reported influence on aggregation. Evidence is presented confirming the important role of aggregation in controlling the echogenicity. The transient effects of abrupt flow stoppage were studied and shown to provide useful insights into aggregation kinetics. Based on the above results, a detailed explanation is provided of the echogenicity variations seen in B-mode ultrasound images of slow-moving blood. Show more

Keywords: Ultrasound, blood echogenicity, erythrocyte aggregation, shear rate

DOI: 10.3233/BIR-1994-31110

Citation: Biorheology, vol. 31, no. 1, pp. 115-135, 1994