Clinical Hemorheology and Microcirculation

Plasma proteins have a multiform effect on blood rheology and circulation. I. Plasma viscosity increases as the concentration or molecular weight of protein increases. When high molecular weight proteins are present, non-Newtonian rheology is evident. II. Rigidity/fluidity of the red cell is influenced by the ratio of the internal viscosity of the red cell to the viscosity of plasma; and may be affected by adsorption of proteins onto the red cell membrane. III. Aggregation of red cells greatly increases in the presence of paraproteins, and the morphology of aggregates may be affected by protein composition. IV. Viscosity of whole blood is affected by proteins via the blood subphases; actual determination of blood viscosity can be affected by flow instability which is also related to the proteins present. V. Thrombus formation is affected by plasma proteins through interference with platelet aggregation and polymerization of fibrinogen. VI. Coating of blood vessels by proteins (especially fibrinogen/fibrin) might influence flow rate. VII. Control of hyperviscosity can be carried out by plasmapheresis, etc.

Rheological and morphological measurements are performed on blood stored in liquid state as packed cells in CPD anticoagulant solution. Rheological data are obtained from viscometric measurements and processed by means of Quemada’s model of blood viscometry. Morphological data are obtained from electron microscopy and by cells counting. A relationship between a parameter of Quemada’s law and rate of functional cells is established and experimentaly confirmed. As a result we show that viscometry is able to give precise information on the quality of stored blood.

Red blood cells (RBC) deformability can be measured by a variety of methods of which bulk filtration through polycarbonate membranes is the most widely used. The aim of this paper is here to compare this last and viscometry on stored blood samples and on blood samples artificially modified by an echinocytic agent.

(i) viscometric experiments are performed with a servo-controlled Couette apparatus with coaxial cylinders. Viscometric data are analysed by means of Quemada’s rheological model from which is obtained an index of deformability D_v.

(ii) filtration measurements are made using an initial flow-rate gravity filtration instrument (Hanss’ hemorheometer). The results are given in term of Hanss’ index D_f.

Indices of deformability D_v and D_f are compared and interpreted according to morphological RBC changes controlled under microscope. We found:

- No correlation between D_f and D_v for stored blood.

- An exponential correlation between D_f and D_v when normal and artificially modified RBC are used.

The orientation rate of flowing erythrocytes was studied by electron spin resonance spectroscopy as a function of time on blood samples stored either in the classical anticoagulant solution CPD or in the new SAG resuspension medium. The maximum orientation rate decreases quickly and the critical shear rate increases strongly in CPD. These parameters are much more stable in SAG. These results indicate that the red blood cell deformability and rheological properties are well better preserved with the SAG storage procedure.

In order to investigate the parameters governing plasma separation by a microporous membrane, plasma filtration rates were measured in two single-channel filter press devices of 170 and 600 cm² membrane area with adjustable blood film thickness. The filtration rate reaches a maximum at a mean transmembrane pressure of 70 to 100 mm Hg. The maximum filtration rate is very well correlated with the inlet wall shear rate γ_w as γ_w^0.76. The maximum filtration rate is also found to decrease with increasing platelet concentration c_p as ℓn (1/c_p). These observations are consistant with the assumption that the plasma filtration rate is limited by platelet concentration polarization taking into account enhancement of platelet diffusivity by red blood cell motion. At low platelet concentrations the filtration rate decreases linearly with increasing hematocrit. The resulting model is used to predict the maximum filtration rates as a function of geometrical parameters of the filters.

In alcoholic liver disease patients, characteristic changes in erythrocyte membrane lipid composition are reported. Membrane cholesterol and cholesterol/phospholipid molar ratio are increased compared to controls.

Distribution of palmitic acid (C16:0 saturated) and polyunsaturated linoleic (C18:2 n-6) and arachidonic acid (C20:4 n-6) in the membrane phospholipids is abnormal in alcoholic liver disease. Furthermore positive correlations between this abnormal fatty acid distribution and red cell filterability is found.

We conclude that membrane filterability could be. influenced either by cholesterol content or the lenght and degree of unsaturation or its fatty acid composition.

Research has revealed that the rheological parameters undergo alterations during various pathological conditions. In this paper the authors present their rheological investigations during parodontopathic disorders. Two groups of patients were studied:

A group of 30 healthy control subjects.

The filtration of dilute erythrocyte suspension over 5 micron polycarbonate filters was examined as a measure of erythrocyte deformability in 20 insulin requiring diabetic patients and related to glycaemic control as assessed by fasting whole blood glucose and HbAlc. Twelve patients were reassessed after a period of improved glycaemic control. No relationship was found between filterability and whole blood glucose and HbAlc but there was a highly significant relationship p < 0.001 between the calculated residual leucocyte count of the erythrocyte suspensi on and filterability. The change in erythrocyte suspension filterability following a period of improved diabetic control was also dependent on the concentration of contaminating leucocytes present on each occasion p < 0.05, and bore no relationship to improvement in diabetic control. Gross alterations of the erythrocyte concentration did not affect this linear relationship between the leucocyte concentration and pressure generated on filtration in either a normal or a diabetic subject. In both normal and diabetic subjects the leucocyte appears to be the major determinant of filterability in this low pressure filtration system.