Biorheology - Volume 27, issue 5

Article Type: Editorial

DOI: 10.3233/BIR-1990-27518

Citation: Biorheology, vol. 27, no. 5, pp. I-III, 1990

Authors: Chaturani, P. | Palanisamy, V.

Article Type: Research Article

Abstract: Pulsatile flow of a Casson fluid under the influence of a periodic body acceleration has been studied in this paper. An implicit finite difference numerical procedure has been used to analyze the flow. Applicability of this method has been checked by comparing the obtained results with the analytical solution for Newtonian flow and explicit scheme solution. The agreement between the implicit and explicit scheme solutions and the analytical solution is good (error less than 1 %). Flow variables have been computed at three lo ations in cardiovascular system (wide (femoral) and narrow (arteriole and coronary) tubes). Effects of yield stress, tube …radius and pressure gradient combined, body acceleration amplitude and frequency etc., on flow have been studied. The following observations have been made: (i) Initial transient time It changes with yield stress in narrow tubes are insignificant, whereas in wide tubes It decreases with yield stress; (ii) The axial velocity and fluid acceleration variations with yield stress are uniform (changes only quantitatively, profiles shape remain same) in narrow tubes, whereas in wide tubes these variations are non-uniform (profiles change qualitatively as well as quantitatively); (iii) Yield stress effects on wall shear amplitude are insignificant in narrow tubes (≃ 0.3 % in arteriole and ≃ 6 % in femoral); and (iv) For Newtonian fluid, mean flow rate does not change with body acceleration amplitude a0 and frequency fb but it increases (decreases) with a0 (fb ) for Casson fluid. Show more

Keywords: Pulsatile flow, Casson fluid, Blood flow, Body acceleration

DOI: 10.3233/BIR-1990-27501

Citation: Biorheology, vol. 27, no. 5, pp. 619-630, 1990

Authors: Ertepinar, H. | Süzen, B. | Özoran, A. | Özoran, Y. | Ceylan, S. | Yeḡinoḡlu, G. | Üremek, G.

Article Type: Research Article

Abstract: In order to determine the effect of drag reducing polymers on the occurrence of atherosclerosis, the Guinea pigs were used as the experimental animals. The inhibitory effect of a drag reducing polymer (polyacrylamide) on atherosclerosis in the aortas of Guinea pigs on a high cholesterol diet (2%) was investigated over a period of 6 months. The aortas, livers, kidneys and lungs of the animals, which were separated into four experimental groups (control, polymer, cholesterol and cholesterol + polymer) were also investigated both macroscopically and light microscopically. The selected physiological parameters such as, plasma cholesterol levels, plasma hemoglobin, hematocrit and total …lipid values were determined at regular intervals for each group. The results indicate that the atherosclerosis in aorta of the animals receiving the polymer injection is suppressed significantly and the drag reducing water soluble polymers may be effectively applied against atherosclerosis. Show more

Keywords: Drag reduction, atherosclerosis, semiflexible polymers

DOI: 10.3233/BIR-1990-27502

Citation: Biorheology, vol. 27, no. 5, pp. 631-644, 1990

Authors: Bell, David R. | Sabbah, Hani N. | Stein, Paul D.

Article Type: Research Article

Abstract: The influence of altered local hemodynamics on fatty streak development in rabbits fed high cholesterol diets was investigated. An aortic coarctation was created in the abdominal aorta of nine rabbits by placing a partially constricting gold or silver band (1.7 mm × 10 mm) around the aorta between the renal arteries and aortic bifurcation. Controls were 20 rabbits; seven sham operated and 13 unoperated rabbits. The abdominal aorta 1–2 cm proximal to the coarctation showed lipid deposition involving 45 ± 8% (mean ± SEM) of the luminal surface which was more than occurred within or distal to the obstruction (p …< 0.05) and also more than in controls (p < 0.05). within the coarctation, 4 ± 2% of the luminal surface showed lipid deposition which was less than either proximally or distally (p < 0.01) and also less than in comparable regions in controls (p < 0.05). The aorta 1–2 cm distal to the coarctation showed lipid deposition involving 18 ± 4% of the surface which was similar to control rabbits. Lipid deposition in corresponding regions of the control rabbits was involved in 17 ± 4%, 19 ± 5% and 19 ± 4% of the luminal surface, respectively. Fatty streak development, therefore, appeared to be inhibited within the coarctation and enhanced proximal to it. The results suggest that some early step in the process of lipid accumulation may be affected by local fluid dynamics or modification of the wall of the vessel. Show more

Keywords: Fatty streaks, Coarctation, Shear, Hypercholesterolemia

DOI: 10.3233/BIR-1990-27503

Citation: Biorheology, vol. 27, no. 5, pp. 645-657, 1990

Authors: Safari, M. | Bjelle, A. | Gudmundsson, M. | Högfors, C. | Granhed, H.

Article Type: Research Article

Abstract: For the first time it is clearly exhibited that synovial fluid (SF) is thixotropic. Although rio hysteresis loops were observed for SF, not even at high shear rates, thixotropy may be exhibited by measuring the rate of recovery after extensive shearing. The rebuilding of the structure in a small-amplitude oscillatory state following the high-shear-rate state reveals the thixotropic behaviour. Five different viscoelastic parameters for various synovial fluids (SF) were obtained using oscillatory rheometry. It was also shown that for SF in the low frequency range, corresponding to a knee joint almost at rest, the shear loss modulus G″ is greater …than the shear storage modulus G′, since the system is allowed to dissipate energy at rest. However, with movement, G′ increases and eventually becomes greater than G″ at a characteristic frequency above which the system has insufficient time to dissipate energy and hence responds as an elastic body. This functional behaviour, characteristic for normal SF, broke down in the SF of rheumatoid arthritis. It was also absent in the SF of knee joints with meniscus lesions and ligament defects. Show more

Keywords: synovial fluid, thixotropy, rheumatic disease, zero shear viscosity, relaxation time, phase lag, dynamic moduli, meniscus lesion, linear viscoelastic behaviour

DOI: 10.3233/BIR-1990-27504

Citation: Biorheology, vol. 27, no. 5, pp. 659-674, 1990

Authors: Ando, J. | Komatsuda, T. | Ishikawa, C. | Kamiya, A.

Article Type: Research Article

Abstract: We have previously observed a stimulatory effect of fluid shear stress on the regeneration of cultured endothelial cell layers after mechanical denudation. In this study we examined how fluid shear stress affects endothelial cell DNA synthesis during regeneration. Following mechanical denudation of narrow linear areas, monolayers of bovine aortic endothelial cells cultured on plastic dishes were subjected to shear stress of 1.3–4.1 dynes/cm2 for 24–48 hours in a specially designed apparatus. After the application of shear stress, cells were stained with propidium iodide, and its fluorescence intensity, reflecting cellular DNA content, was measured using photometric fluorescence microscopy. The DNA …content of cells exposed to shear stress increased significantly more than that of paired, static control cells (p < 0.005 to p < 0.001). The DNA histogram showed that cells exposed to shear stress contained a relatively high proportion of cells located in the S, G2 , and M phases of the cell cycle as compared with the static control. These data suggest that fluid shear stress enhances endothelial cell DNA synthesis during the repair of mechanical denudation. Show more

Keywords: vascular endothelial cell, hemodynamic force, DNA histogram, propidium iodide, cell growth

DOI: 10.3233/BIR-1990-27505

Citation: Biorheology, vol. 27, no. 5, pp. 675-684, 1990

Authors: Thurston, George B.

Article Type: Research Article

Abstract: Measurements were made of the intensity of light transmitted through various thicknesses of normal human blood confined between two parallel plane surfaces, one fixed and the other oscillating in its own plane. When the light propagation direction is perpendicular to the direction of shear flow the transmitted intensity contains a steady component and a dominant second harmonic of the oscillation frequency. For a thin layer of blood, the steady intensity is a minimum value when the oscillation amplitude produces unit strain. The second harmonic is very small at small strains, but increases rapidly near unit strain where it is approximately …in phase with the strain. For thicker layers, the effects of viscoelastic shear waves reduce the size of the second harmonic and modify its phase. Changes in light transmission are interpreted by relating the optical density of the blood to the total amount of contact between red cells. In oscillatory flow at low strains (<1) cell-to-cell contact is reduced by disaggregation of cell groups, and light transmission decreases. Near unit strain, disaggregation becomes complete, cell alignment occurs, and light transmission is minimized. At higher strains cell-to-cell contact is increased by formation of aligned layers of compacted cells separated by parallel plasma layers, and light transmission increases. Show more

Keywords: Blood, light transmission, oscillatory blood flow, optical density, cell layering

DOI: 10.3233/BIR-1990-27506

Citation: Biorheology, vol. 27, no. 5, pp. 685-700, 1990

Authors: Zaiss, S.

Article Type: Research Article

Abstract: Experiments were carried out to determine the importance of extra- and intracellular calcium for the deformability of granulocytes during filtration tests. At low calcium concentration (0.1 mM), granulocytes are more deformable than at the physiological free-calcium concentration of 1.25 mM. Increasing calcium concentrations up to 10 mM do not further impair the deformability. Parallel measurements of the intracellular calcium concentration by means of the fura fluorescence method were performed to explain this. Extracellular calcium concentrations between 1.25 mM and 10 mM had no influence on the intracellular calcium level. A lower extracellular calcium concentration (0.1 mM), however, decreased the intracellular …calcium level. Therefore, the measurements of the intracellular calcium concentrations are consistent with the deformability results Studies with the calcium entry blocker nifedipine suggested that a low intracellular calcium improves the deformability of granulocytes. It is concluded; (i) the physiological calcium concentration of 1.25 mM is stressful for isolated granulocytes, and (ii) the intracellular calcium level plays a crucial role in granulocyte deformability, i.e the lower the intracellular calcium concentration the greater the deformability. Show more

Keywords: Calcium, Deformability, Granulocytes

DOI: 10.3233/BIR-1990-27507

Citation: Biorheology, vol. 27, no. 5, pp. 701-709, 1990

Authors: Mann, David E. | Tarbell, John M.

Article Type: Research Article

Abstract: The influence of non-Newtonian rheology on wall shear rate in steady and oscillatory flow through rigid curved and straight artery models was studied experimentally . Wall shear rates measured by flush mounted hot film anemometry under nearly identical flow conditions are reported for the following four fluids: aqueous glycerin (Newtonian), aqueous polyacrylamide (shear thinning, highly elastic), aqueous Xanthan gum (shear thinning, moderately elastic), and bovine blood. For steady flow conditions there was little difference at any measurement site in the wall shear rate levels measured for the four fluids. However, large differences were apparent for oscillatory flows, particularly at the …inner curvature 180 degrees from the entrance of the curved artery model. At that position the peak wall shear rate for polyacrylamide was 5–6 times higher than for glycerin and 2–3 times higher than for bovine blood. It is concluded that polyacrylamide is too elastic to provide a good model of blood flow under oscillatory conditions, particularly when there is wall shear reversal. Xanthan gum and glycerin are better analog fluids, but neither is entirely satisfactory. Show more

Keywords: Wall shear stress, blood rheology, atherosclerosis, physiological flow, bovine blood, polyacrylamide

DOI: 10.3233/BIR-1990-27508

Citation: Biorheology, vol. 27, no. 5, pp. 711-733, 1990

Authors: Grebe, R. | Zuckermann, M.J.

Article Type: Research Article

Abstract: In a recent paper we examined the morphology of erythrocytes in terms of the mean mean curvature (MMC) of their cell membranes. A computer simulation of these shapes based on the different geometries showed that the MMC increased from the sphero–stomatocyte to the sphero–echinocyte via the discocyte. In this work we extend this analysis by using a numerical optimization method based on importance sampling and the principle of adiabatic cooling. The erythrocyte membrane is treated as a single closed fluid lamina exhibiting viscoelastic characteristics. The energy function of the lamina includes the following terms: (i) Curvature-elastic energy terms which depend …on both local and global curvature. (ii) A term describing the compression elasticity of the lamina. (iii) A term which depends on the volume of the cell and which is related to the osmotic pressure across the membrane. In the simulation the cell is assumed to have axial symmetry and it can therefore be described by a finite set of conic sections. So far we have been able to obtain an energy minimum corresponding to a discocyte shape using a sphere as the initial configuration. Our results therefore imply that the well-known sequence of erythrocyte shapes could solely be governed by the above mentioned properties of an ideal fluid forming a closed singly connected lamina. Show more

Keywords: Erythrocyte, morphology, membrane, curvature, viscoelasticity, fluid lamina, optimization

DOI: 10.3233/BIR-1990-27509

Citation: Biorheology, vol. 27, no. 5, pp. 735-746, 1990