Biorheology - Volume 38, issue 1

Article Type: Other

Citation: Biorheology, vol. 38, no. 1, pp. 1-2, 2001

Authors: Sugihara‐Seki, Masako

Article Type: Research Article

Abstract: The flow around adherent cells in a parallel‐plate channel and that in a circular cylindrical tube are numerically analyzed, and their effects on the adherent cells are compared. The cells are modeled as rigid spherical particles and they are assumed to be attached to a wall of a 2D channel uniformly in a square array, or a wall of a circular tube regularly in a line along the tube axis. It is found that, when the size ratios of the particle‐to‐channel height and the particle‐to‐tube diameter are smaller than approximately 0.2, the distributions of the shear stress and the pressure …exerted on the surface of an adherent particle as well as the drag force and torque acting on it compare favorably in the 2D channel flow and tube flow. As the size ratios increase from 0.2, the differences between the 2D channel and the tube increase drastically, especially when separation distances between neighboring particles are large. Show more

Keywords: Adhesion, drag, leukocytes, numerical simulation, stress, torque

Citation: Biorheology, vol. 38, no. 1, pp. 3-13, 2001

Authors: Cao, Pei‐Jie | Paeng, Dong‐Guk | Shung, K.K.

Article Type: Research Article

Abstract: The “black hole” phenomenon was further investigated with porcine whole blood under pulsatile flow conditions in a straight rigid tube 120 cm long and of 0.95 cm diameter. A modified Aloka 280 commercial scanner with a 7.5 MHz linear array was used to collect the radio frequency (RF) signal of backscattering echoes from the blood inside the tube. The transducer was located downstream from the entrance and parallel to the longitudinal direction of the tube. The experimental results showed that higher hematocrits enhanced the black hole phenomenon, leading to a more apparent and larger diameter black hole. The black hole …was not apparent at hematocrits below 23%. The highest hematocrit used in the experiment was 60%. Beat rates of 20, 40 and 60 beats per minute (bpm) were used, and the black hole became weaker in amplitude and smaller in diameter when the peak flow velocity was increased at each beat rate. These results are consistent with the suggestion in previous work that the black hole arises from insufficient aggregation of red blood cells (RBCs) at the center of the tube because of the low shear rate. At 20 and 40 bpm, the peak flow velocity ranges were 10∼25 cm/s and 18∼27 cm/s, respectively. The black hole was very clear at the minimal peak flow velocity but almost disappeared at the maximal velocities for each beat rate. At 60 bpm, experiments were only performed at one peak flow velocity of 31 cm/s and the black hole was clear. The results showed that the black hole was more pronounced at higher beat rates when the peak velocity was the same. This phenomenon cannot be explained by previous hypotheses. Acceleration seems to be the only flow parameter that varies at different beat rates when peak velocities are the same. Therefore, the influence of acceleration on the structural organization and orientation of RBC rouleaux might be another factor involved in the formation of the black hole in addition to the shear rate. As the entrance length was changed from 110 to 15 diameters (D) in seven steps at the hematocrit of 60%, it was found that a position farther downstream yielded a black hole with a greater contrast relative to the surrounding region, while the backscattering power at the central hypoechoic zone did not increase with increasing entrance length. Show more

Keywords: RBC aggregation, ultrasonic backscatter, pulsatile flow

Citation: Biorheology, vol. 38, no. 1, pp. 15-26, 2001

Authors: Berli, Claudio L.A. | Quemada, Daniel

Article Type: Research Article

Abstract: A theoretical interpretation of simultaneous viscosity measurements and light backscattering experiments is carried out in the framework of the structural model for concentrated dispersions proposed previously by one of the authors. The work is mainly focused on erythrocyte aggregation, hence spherical as well as linear aggregates (rouleaux) were considered in the modeling. A connection between the structural parameters provided by each technique is established, in particular the characteristic shear rates for break up of aggregates. Theoretical predictions were then applied to experimental data of human blood collected from patients with different diseases in a hospital data bank. Finally, we conclude …that the structural modeling proposed permits a reasonably good correlation between experimental data of viscometry and light backscattering from blood samples, leading to new perspectives in the analysis of the red blood cell aggregation phenomena. Show more

Keywords: Erythrocyte aggregation, viscometry, light backscattering, structural model

Citation: Biorheology, vol. 38, no. 1, pp. 27-38, 2001

Authors: Bäumler, Hans | Neu, Björn | Mitlöhner, Rita | Georgieva, Radostina | Meiselman, Herbert J. | Kiesewetter, Holger

Article Type: Research Article

Abstract: The electrophoretic mobility of native and glutaraldehyde‐fixed bovine, human, and horse red blood cells (RBC) was investigated as a function of ionic strength (5–150 mM) and concentration of 464 kDa dextran (2 and 3 g/dl); RBC aggregation in autologous plasma and in dextran solutions was also measured. In agreement with previous observations, human and horse RBC form stable rouleaux whereas bovine RBC do not aggregate in either plasma or in dextran 464 kDa solutions. Electrophoretic measurements showed a species‐dependent adsorption and depletion of dextran that can be theoretically evaluated. Adsorption of polymer is not a prerequisite for RBC aggregation (bovine …RBC show the highest amount of adsorbed dextran yet do not aggregate). Aggregate formation thus occurs as long as the Gibbs free energy difference, given by the osmotic pressure difference between the bulk phase and the polymer‐depleted region between two RBC, is larger than the steric and electrostatic repulsive energy contributed by the macromolecules present on the RBC surface. With increasing bulk‐phase polymer concentration the depletion layer thickness decreases and the amount of adsorbed macromolecules increases, thereby resulting in an increase of the repulsive component of the interaction energy and decreased aggregation. We thus view electrophoretic measurements of RBC in various media as an important tool for understanding polymer behavior near the red cell surface and hence the mechanisms involved in RBC aggregation. Show more

Keywords: RBC aggregation, electrophoretic mobility, polymer adsorption, depletion layer, steric forces

Citation: Biorheology, vol. 38, no. 1, pp. 39-51, 2001

Authors: Neu, B. | Armstrong, J.K. | Fisher, T.C. | Meiselman, H.J.

Article Type: Research Article

Abstract: The present study was prompted by prior reports suggesting that small polymers can affect RBC aggregation induced by large macromolecules. Human RBC were washed and re‐suspended in isotonic buffer solutions containing 72.5 kDa dextran (DEX 70, 2 g/dl) or 35.0 kDa poly(ethylene glycol) (PEG 35, 0.35 g/dl), then tested for aggregation in these solutions with and without various concentrations of smaller dextrans (10.5 and 18.1 kDa) or PEGs (3.35, 7.5 and 10.0 kDa). RBC aggregation was measured at stasis and at low shear using a photometric cone‐plate system (Myrenne Aggregometer) and RBC electrophoretic mobility (EPM) in the various polymer solutions …via an automated system (E4, HaSoTec GmbH). Our results indicate: (1) a heterogeneous effect with greater reduction of aggregation for small PEGs added to DEX 70 or for small dextrans added to PEG 35 than for small polymers of the same species; (2) for cells in DEX 70, aggregation decreased with increasing molecular mass and concentration of the small dextrans or PEGs; (3) for cells in PEG 35, small dextrans decreased aggregation with increasing molecular mass and concentration, whereas small PEGs had minimal effects with a minor influence of concentration and an inverse association between molecular mass and inhibition of aggregation. RBC EPM results indicated the expected polymer depletion for cells in DEX 70 or PEG 35, and that small PEGs yielded greater EPM values than small dextrans for cells in PEG 35 whereas the opposite was true for cells in DEX 70. Interpretation of our results in terms of the depletion model for RBC aggregations appears appropriate, and our findings are consistent with the assumption that inhibition of aggregation occurs because of an increase of small molecules in the depletion region. Our results thus suggest the merit of further studies of red blood cell aggregation in binary polymer systems. Show more

Keywords: Dextran, poly(ethylene glycol), PEG, red blood cell, aggregation

Citation: Biorheology, vol. 38, no. 1, pp. 53-68, 2001