Biorheology

Red blood cells were submitted to a bending stress by incubation in hyperosmolar media and their membrane molecular structure studied by a fatty acid paramagnetic label which probes its hydrophobic part. Measurement of the apparent rotation frequency of the label, and numerical analysis of the spectrum shapes indicate that a high fluidity phase appears in the stressed membrane. The physiological implications of this finding are discussed in the light of the rheological properties of the circulating red blood cell.

Poiseuille flow of a micropolar fluid has been reexamined from the point of view of its applications to blood flow. Couple stresses are assumed to be non-zero at the boundary, and a method has been proposed to determine such boundary conditions for a given suspension. Velocity profiles (both axial and rotational) as well as apparent viscosity have been computed for various values of s¯ (a boundary condition and concentration parameter). The results obtained have been compared with experimental values (for blood flow). It is found that they are in a reasonably good agreement. Some of the earlier workers have used solvent viscosity for the classical shear viscosity of the suspension and obtained infinite relative viscosity for a suspension concentration of 40 % which, according to experimental results, is not feasible. An appropriate expression for the classical shear viscosity has been used in the present analysis which removes the apparent viscosity anomaly, i.e., apparent viscosity tends to infinity as the concentration approaches 40 %, from the micropolar fluid theory. Finally, some biological applications of this theory have been discussed.

Water partition between the interstitial fluid in articular cartilage and an external bathing solution was found using a new in-situ method. This consisted of measuring the concentration of radioactive water allowed to diffuse through the articular surface of laterally constrained cartilage-subchondral bone plugs. Incubation times ranged from 15 minutes to 48 hours. Tracer solutions included: Hank’s Balanced Salt Solution with and without antibiotics and enzyme inhibitors, and distilled water. Bulk partition coefficients ranged from 0.305 to 0.811. Both the hydration and partition coefficients varied spatially with depth, while no association was found between them. The macromolecular structure of the collagen and proteoglycan components are believed responsible for these findings.

Red blood cells aggregate to form rouleaux and cause elevation of blood viscosity at low shear rates in the presence of plasma proteins and other macromolecules. Low molecular weight dextran with a molecular weight of 40,000 (Dx 40) has been postulated to cause disaggregation of RBCs in blood. Plasma proteins and dextran with a molecular weight of 63,000 (Dx 70) were used to induce RBC aggregation in the present investigation. Dx 40 was added to the suspensions at concentrations up to 10 g/dl to study the mechanisms of its disaggregation effect. The relative viscosity at a shear rate of 0.05 sec⁻¹ and a hematocrit value of 45 percent (n_r) was used to indicate the degree of RBC aggregation. Suspensions of normal RBCs in Dx 70-saline (in the absence of Dx 40) showed an increase in n_r as Dx 70 concentration was raised to 4 g/dl; further increases in Dx 70 concentration resulted in a progressive decrease in n_r. When Dx 40 was added to RBC suspensions in Dx 70-saline, a significant reduction of n_r was found. The surface potential (determined in a cell microelectrophoresis apparatus) of normal RBCs increased significantly when Dx 40 was added to Dx 70-saline. With the use of neuraminidase-treated RBCs, Dx 40 did not exhibit disaggregation effects on Dx 70-induced RBC aggregation. These results indicate that the disaggregation effect of Dx 40 on Dx 70-induced RBC aggregation is primarily due to the elevation of RBC surface potential by Dx 40. Addition of Dx 40 to plasma, besides causing an elevation of RBC surface potential, also resulted in a significant reduction of fibrinogen concentration. Analysis of the results indicates that the disaggregation effect of Dx 40 on RBCs in plasma is due to a combined effect of an increase in surface potential and the precipitation of fibrinogen by Dx 40.

The effect of two cationic drugs (chlorpromazine and isoxsuprine) 011 the suspension viscosity of human erythrocytes were examined, comparing with the effect of anionic drugs. (1)

As increasing the drug concentrations, the cationic drugs transformed the erythrocytes to stomatocytes, then to spherostomatocytes, while trinitrobenzene sulfonate, dehydroepiandrosterone sulfate and lysolecithin induced echinocytes, as well known.

Kinetics of red cells aggregation were studied by microphotography of blood contained between parallel-plates in a slit of 12.5 micrometers. Blood samples, anticoagulated with EDTA, were adjusted to haematocrit of 0.30 using native plasma. Blood was allowed to flow at shear rate of 2000 sec⁻¹, flow was stopped, and sequential photography carried out. Full development of aggregation required from 2 to 10 minutes, depending on the blood sample. Blood studied included normal donors and patients with polycythaemia, lymphoma, hyperparathyroidism, Waldenström’s macroglobulinaemia, influenza. The quantitative evaluation of colour slides was carried out on Microvideomat No.2 with Zeiss Interference Monochromator, using light wave length of 460 or 560 nanometers. The stereological parameters defined included d(Heyn), Lamda, and S*/V*. Linear regressions of stereological parameters against square root of stasis time showed correlation coefficients of 0.8 up to 0.99. Linear regressions for different blood samples were compared, and Significance of differences between slopes or between elevations was defined using F-distribution. Such differences were significant up to P<0.001. Rate of aggregation was much higher in macroglobulinaemia or lymphoma than in normals, and it was lowest in the hyperparathyroid disease.

The adsorption of protein on red cell surface was studied by the measurement of protein in plasma and incubation of blood with ¹³¹I-albumin. The protein concentration of the moderately hypertonic plasma clearly decreased by the addition of red cells. The decay counts of ¹³¹I-albumin increased in the centrifuged red cell segment as the ionic strength in the plasma increased. For the interpretation of these results it was assumed that the human red cells suspended in plasma are covered with albumin under the normal ionic strength and adsorb more albumin molecules when the ionic strength in the plasma is elevated by the addition of NaCl. A multilayer adsorption of albumin is suggested at the ionic strength of 450 mOsmol. The excess adsorption of albumin on red cells reduces the filtrability of red cells through the nuclepore filter.