Biorheology

The effect of pH on the velocity of aggregation of human erythrocytes was quantitatively examined with a rheoscope combined with a video-camera, an image analyzer and a computer, in relation to the morphological changes of erythrocytes and their aggregates. (i) With increasing pH of the medium, the velocity of erythrocyte aggregation increased. (ii) The rouleaux formed at high pH were longer in shape and more stable against the increase of shear rate than those formed at low pH. (iii) With increasing pH, t.he diameter of erythrocyte increased, the (maximum) thickness decreased, and the cell volume decreased. The pH dependency of erythrocyte aggregation may be mainly due to the morphological change of erythrocytes, and partly due to the changes of erythrocyte deformability and of interaction with macromolecules.

An electrochemical surface shear stress measurement was applied to a model of very thin unilateral arterial stenosis (height of 1/8 of the model pipe diameter with very smooth surface). Three dimensional wall shear stress distribution was measured under steady flow field from a relatively low Reynolds number, Re=270, to a high Reynolds number, Re=1200. There was a characteristic high and low wall shear distribution pattern around the stenosis. There were also remarkable high shear stress areas on the opposite wall and both side walls of the stenosis. It was clearly shown that three dimensional structure of the flow field, hence, the wall shear stress distribution, is affected by a minimal change on the arterial wall.

In order to describe a possible effect of smooth muscle cell (SMC) activation on arterial wall distensibility, the present study derived a mathematical equation applicable to relaxed and contracted arterial walls. Pressure(P)-diameter(D) relationship of dog renal arteries was investigated in vitro under a cyclic loading and unloading process in the pressure range of 5–180 mmHg. Smooth muscle cells were activated by 10⁻⁵M norepinephrine. On the basis of the P-D curves obtained with fully contracted arteries, the vessel wall compliance dD/dP was assumed to be given by a second order polynomial of D, dD dP = − ( D − D max ) ( D − D min ) E ( D max − D min ) The equation, including three parameters, D_min, D_max, and E, is integrated to yield the solution similar to the logistic curve as follows D = D min + D max − D min 1 − M ( 0 ) exp ( − P / E ) where D ( 0 ) = ( D max − D ( 0 ) ) / ( D ( 0 ) − D min ) , and D(0) is the diameter at the point P=0 The constant, E, has the same dimension as the modulus of elasticity. The calculated P-D relationships coincided well with the experimental data for contracted and relaxed arteries. The most significant change due to wall contraction took place in the magnitude of M. This result, therefore, suggests that the parameter M is a good index of the degree of SMC contraction.

The red cell deformation under oscillatory shear stress was studied. Shear stress was sinusoidally modulated between 8 and 32 dyn/cm², thus, the extent of cellular deformation altered sinusoidally. At a low modulation frequency (less than 1.8 Hz), intact red cells perfectly responded to the shear stress applied on cells, and they could deform as much as the deformation in stationary shear flow.

Above 2 Hz, the cellular deformation could not follow changes in shear stress along up-phase in the shear stress cycle. As decreasing the intracelluar hemoglobin concentration, the cellular response to oscillatory shear stress became better. Treatment of cells with low concentrations of diamide impaired the response of intact cells to oscillatory shear stress, but unaffected the response of partially hemolyzed cells.

These data suggest that the cellular response to oscillatory shear stress is determined by the cytoskeletal structure and the intracellular viscosity.

The whole blood RBC aggregometer head reported previously for measuring the degree of RBC aggregation in whole blood was tested for its usefulness as a flowmeter of blood vessels in situ. Modifications to its construction were made so that ir-became readily attachable and detachable without damage to the vessels. In ex vivo experiments employing a transparent vinyl tube and freshly drawn heparinized human whole blood, the RBC aggregometer head was applicable for evaluating semiquantitative flow changes within a limited flow range based on the degree of RBC aggregation. A linear relationship was observed between the logarithm of blood flow in a low shear range (below approximately 180/s) and changes in the light transmission of the flowing blood. The RBC aggregometer head with or without an electromagnetic flowmeter (EMF) was applied to the jugular vein and femoral vein in cats. A stop-flow change of whole blood in the jugular vein was detected by the RBC aggregometer head as a dramatic change in light transmission (LT). The aggregometer head recorded a similar LT change consistently, whereas the EMF was found to be rather discrepant, indicating the occurrence of anomalous flow. It is concluded that the RBC aggregometer head can be used as an semiquantitative flowmeter for relative changes in blood flow in veins in situ.

Experiment on STS 51-C in January 1985, carried out on blood samples obtained from patients with heart disease, diabetes, hyperlipidaemia and cancer showed that, under zero gravity, the morphology of red cell aggregates aggregates was normal, in contradistinction to the parallel and simultaneous observations under 1 g, which showed large and unorientated clumps of red cells. As such clumps could be considered of disadvantage in the microcirculation and tissue perfusion, the zero gravity observations were significant in a number of ways. In particular, a preliminary deduction (subject to further zero g experimentation) was that cell-cell interaction and adhesion are affected by zero gravity, and that most likely the microarchitecture of the cell membrane is modified; and that probably the receptors, their position and/or activity, are affected by zero gravity. Of particular interest could be a possible change in the properties of the discrete surface areas which respond preferentially to specific macromolecules (or ligands).

There is a dissonance between these in vitro results and theoretical deductions on flow in the microcirculations by Oka, and as well of deductions on space sickness by Dintenfass, both assuming a disabling effect of zero g on the in vivo microcirculation. This dissonance should be explored, as effect of zero g might be different on blood flow in vivo and in vitro.

However, the data available from the in vitro experiment suggest that studies in immunology and oncology might be enriched by zero gravity findings; and that studies under zero gravity might open a new avenue of research In these important fields.

We have used hydroelastic waves to treat the closed trauma of the soft tissue. The Shu Huo Jiu (S.H.J.) which is the Chinese traditional medicine alcohol, was used as the fluid medium for generating the pressure waves.

The biomechanical model was established and analysed. Both animal and human tests have been made. A practical system was designed, constructed and clinically tested to treat the closed trauma, such as the bruise, contusion, sprain etc.. This system was found to be effective.

In order to obtain a better understanding of the erythrocyte sedimentation rate (ESR), several models are presented. The first directs attention to the importance of geometrical models to represent the structure of mixtures. Here it is our intention to understand the effect of the structure on the packing of red blood cells. In this part of the study, “Cheerios” (trademark General Mills) are used as a macroscopic model. It is interesting that a random sampling of “Cheerios” has the same volume distribution curve that is found for erythrocytes with a Coulter Sizing Apparatus. In order to examine the effect of rouleaux formation, the “Cheerios” are stacked one on top of another and then glued. Rouleaux of 2, 3, 4, 5, 7 and 10 discs were used. In order to examine a more realistic biological model, the experiments of Dintenfass were used. These investigations were performed in a split-capillary photo viscometer using whole blood from patients with a variety of diseases. The novel part of this research is the fact that the work was performed at 1g and at near zero gravity in the space shuttle “Discovery.” The size of the aggregates and/or rouleaux clearly showed a dependence upon the gravity of the experiment. The purpose of this model was to examine the condition of self-similarity and fractal behavior. Calculations are reported which clearly indicate that there is general agreement in the magnitude of the fractal dimension from the “Cheerios” model, the “Discovery” experiment with those determined with the automatic sedimentimeter. The final aspect of this work examines the surface texture of the sedimention tube. A series of tubes were designed with “roughened” interiors. A comparison of the sedimentation rates clearly indicates a more rapid settling in “roughened” tubes than in ones with a smooth interior surface.

A non-linear elastic model taking into account the microscopic structure of biological soft tissues is briefly presented and extended to quasi linear viscoelasticity. The modelling of the rheological behavior for near zero stress values is then discussed.

Viscosity measurements were made using a coaxial rotating cylinder viscometer for blood having various volume fractions of red cells. A method is described for analyzing non Newtonian blood viscosity in low shear rates by taking account of an increase or a decrease in size of red cell aggregates induced by shear.

Our results are compared with empirical formulae presented by Scott Blair. Weaver Evans Walder and Thurston.

A kinetic equation for rouleau formation in a simple shear flow is derived, based on several assumptions. These are (a) colliding rouleaux stick to one another with a certain probability to form a single rouleau; (b) simultaneous collisions between more than two rouleaux are negligible; (c) rouleaux are broken by a viscous force exerted by the suspending fluid on the surfaces of rouleaux; (d) when a rouleau is broken by viscous forces, only two fragments are formed. Based on a simple mathematical model, collision rate, sticking probability and degradation rate are obtained as functions of applied shear rate. From the solution of the kinetic equation, the average size of rouleaux is obtained as a function of time with shear rate as a parameter. It is shown that the average size of rouleaux increases monotonically with increasing time and tends to an equilibrium size. The average size of rouleaux in a dynamical equilibrium decreases monotonically with increasing shear rate and tends to one cell as shear rate approaches infinity. It is also found that the initial rate of rouleau formation increases with increasing shear rate at very low shear rate, but this trend is reversed at higher shear rates. The theoretical results are compared quantitatively with experimental data.

To consider the effects of the viscoelasticity of cytoplasm on the relaxation phenomenon of red blood cell suspensions, we calculate the complex intrinsic viscosity [ η ∗ ] = lim c → 0 ( η ∗ − η ) / η c of the disperse system of spherical cells as a function of the frequency, where η ∗ is the complex viscosity in suspensions, η the medium viscosity and c the volume concentration of the cells. The cell consists of a viscoelastic membrane and a viscoelastic cytoplasm. The viscoelasticity of the membrane is described by the Voigt model, while the viscoelasticity of the cytoplasmic region is described either by the Maxwell model or by the Voigt model. The interfacial tension is taken into account on both the interfaces of the membrane. The results of [ η ∗ ] are compared with the ones in the case in which the cytoplasmic region is purely viscous liquid.

The Brownian motion of a spherical particle in a generalized viscoelastic medium is discussed to obtain the complex viscosity coefficient from the photocurrent correlation function of fluorescent light radiated from the particle. This method makes it possible to measure the viscoelastic properties of a small amount of solution sample.

Sudden increase of viscosity in former times indicated the start of coagulation. Yet its measurement destroyed the structure of coagulum. By the precursor method of thrombelastography the author 1944 found elasticity to be the essential physiological property of coagulum. In the production of elastic fibrin structure its early phase is the most efficient in this respect. The speed of prime structure formation is extremely fast in presence of enough phospholipid as well as of plasma factor XIII. Even high amounts of thrombin cannot replace one or both of these substances indispensable to grow rapidly a perfect fibrin web. This phase yet does not become effective if it is not accompanied by the orbital micro-flow of the new orbitometry method. Its shear is comparable to that in a coronary artery. The special resonance effect of the method in combination with the early phase of fibrin production is generating some kind of a physiological feed back: increasing fibrin will strengthen shear stress as long as less platelets are entangled which will reduce the elastic flexibility of fibrin web. Some kind of a “coagulation spin effect” in optimal combination of shear stress, phospholipid and factor XIII, will extremely fast originate a firm fibrin structure, a mechanism which may be of significance for a fast occlusion of arterial stenoses.

The tension-strain, stress-strain and stress relaxation curves of longitudinal and circumferential strips of proximal thoracic aortas in normal and WHHL rabbits of different ages were determined using a tensile testing instrument. Wall distensibility of longitudinal and circumferential strips was the greatest in the normal aorta and decreased with advancing age in the atherosclerotic aorta. The wall thickness of the atherosclerotic aorta was positively related to age with a correlation coefficient of 0.66 (p<0.01). The incremental elastic moduli calculated from the stress-strain curves increased with advancing age in the atherosclerotic aorta. Accordingly, the decreased distensibility of the atherosclerotic wall may be due to the increased wall thickness caused by the intimal thickening as well as to the increase in wall stiffness caused by the increased elastic modulus. The viscoelasticity of the atherosclerotic aorta was larger than that of the normal aorta. This reflects the mechanical effect of atherosclerotic changes that occurred in the thickened intima.

We have measured the sedimentation curves of swine erythrocytes in a physiological saline solution in inclined glass tubes. The curves are well fitted to the exponential type equation ı = a [ 1 − exp ( − bt ) ] for the tilt angle θ in the range of θ < 80° and hematocrits from 10 to 50 %, where ı and t are the medium length along the tube and the elapsed time from the sample injection, respectively. The coefficient a increases with θ and b is proportional to sin θ . The erythrocyte sedimentation rate ESR(θ) = (dı/dt)_{t → 0} determined from the above empirical equation increases with the increase in sin θ roughly linearly. The experimental results are discussed with reference to the Ponder-Nakamura-Kuroda theory and some recent theories.

The stress-strain curves of the vena cava have been measured of vena cava superior, and the intrathoracic and abdominal portions of vena cava inferior excised from dogs. The stress σ is expressed by the exponential function of the strain γ as follows: σ = σ 0 [ exp ( γ / γ 0 ) − 1 ] in the longitudinal direction, and σ = σ 1 [ exp ( γ / γ 1 ) − 1 ] + σ 2 [ exp ( γ / γ 2 ) − 1 ] in the circumferential one for all the three kinds of veins. The constants σ 0 , γ 0 , σ 1 , γ 1 , σ 2 and γ 2 are determined by a nonlinear least squares method.

Dynamic viscoelastic properties of 13 bronchorrhoea sputum samples from asthmatics with bronchorrhoea, defined as the production of watery sputum of 100 ml or more per day during asthmatic attacks, were examined and then compared with 7 saliva and 12 mucoid sputum samples obtained from patients during remission. Dynamic viscosity ( η ′ ) and elasticity (G′) of bronchorrhoea sputum increased rapidly with time up to 2 hours after collection and slowly thereafter, whereas η ′ and G′ of saliva and mucoid sputum remained unchanged up to 6 hours after collection. Then, η ′ and G′ of saliva, bronchorrhoea and mucoid sputum samples were measured between 2 to 4 hours after expectoration. Bronchorrhoea sputum samples showed significantly larger values at frequencies of both 0.1 and 1.0 rad/sec than did saliva samples and also significantly smaller values than did mucoid sputum samples. Thus, bronchorrhoea sputum differed in dynamic viscoelastic properties from saliva, indicating that it does not result from hypersalivation. Based on data of viscoelastic changes with time, it can be assumed that the viscoelasticity of bronchorrhoea sputum in the airways is considerably less than the optimal range reported previously for mucociliary velocity, suggesting the possibility of impaired mucociliary transport.

The hydrodynamic interaction of a red blood cell and a white blood cell in microvessels is studied, by use of a two-dimensional numerical model. The red blood cell, modeled as a small rigid circular cylinder, and the white blood cell, modeled as a larger rigid circular cylinder, are immersed in an incompressible Newtonian fluid in a two-dimensional channel. It is assumed that no external force or moment acts on the model cells, and the effect of inertia forces on the motion of the fluid and the cells is neglected. The velocity field of the suspending fluid and the instantaneous velocities of the two model cells are computed by the finite element method. Using the translational velocities of the model cells obtained, the trajectories of their relative motion arc determined, for various initial positions. It is shown that the cells may or may not pass each other or separate, depending on the initial positions. The present results compare well to the experimental results.

Flow of Latex suspension with high concentration between plate glasses was observed through an optical microscope. Size of aggregates of Latex particles was estimated by measuring area of a region without particles behind an obstacle in the flow region (this technique had been developed by one of the authors). At the same time, viscosity and elasticity of the suspension were measured by a cone-plate viscometer, and relations between the aggregate size and these properties were obtained. A simple model based on the Stokes law of resistance and the Maxwell model for viscoelastic materials is proposed to explain these relations. The theoretical results agree with the present experiment.

Mathematical models for blood flow in cone-plate viscometer have been considered, by assuming blood as a Casson/Herschel-Bulkley fluid. Three different cases have been analyzed (i) when there is no shearing, (ii) partial shearing and (iii) full shearing. The relationships between the angular velocity and torque have been obtained for the above three cases. By assuming total shearing, the analytical expression for apparent viscosity has been obtained. Variation of apparent viscosity with yield stress, angular velocity, Casson co-efficient of viscosity, consistency index and flow behaviour index has been computed. It is observed that as the angular velocity increases, the apparent viscosity decreases for both fluids. Further, it is found that as the cone angle increases, the apparent viscosity increases. This behaviour of apparent viscosity in cone-plate viscometer is interesting and unexpected and is being reported first time.

The dependence on hematocrit of whole blood viscoelasticity must be considered in order to compare pathological blood samples to normal ones. If one wants to calculate the measured values to a standard hematocrit value, the hematocrit dependence for the pathological sample must be available. As the latter however is unknown, the same dependence is assumed for both normal and pathological blood samples. To prove the validity of this assumption, hematocrit dependence of random blood samples from different diseases (cerebral and coronary vascular and myocardial disorders) were investigated. A statistical analysis showed the assumption as invalid. Therefore, it will be recommended to evaluate pathological blood samples at the measured hematocrit.

Lymphatic microvessels were microscopically observed on the surface of frog lungs. Magnified images of lymphatic microvessels were recorded on video tapes. The lymphatic microcirculation was studied on a TV monitor at the magnification of 1500 times. 1) valves were observed in lymphatic microvessels, whose diameter was 15 μm, in frog lungs, 2) the valves were incompetent, 3) contained particles repeatedly flowed backwards and forwards in each lymphatic section, 4) after repetition of the movements, particles passed through the outlet valve, 5) particles seldom flowed back through the inlet valve into the preceding section of the lymphatic, 6) the peak flow velocity of particles attained 0.5 mm/sec, and 7) the mean flow velocity was II ± 4 μm on an average and ± SD, 8) the diameter of a localized portion of the lymphatic rilicrovessels changed periodically.

To obtain a smaller sample volume and a suitable sample position for the measurement of blood velocity, we fabricated a laser Doppler velocimeter (LDV) with a dual-fiber pickup. The two fibers (clad: 62.5 μm and core: 50 μm) were placed side by side. An He-Ne laser was introduced into the blood through one fiber and the backscattered light was collected by the other fiber. The Doppler signal was analyzed by a spectrum analyzer. The spectrum of the Doppler shift frequency showed a sharp peaked pattern for both forward and reverse flows and exhibited an excellent correlation with the known blood velocity. The blood velocity in the poststenotic portion of canine coronary artery was successfully measured by the dual-fiber LDV. These results indicate that the dual-fiber LDV is useful for measuring blood velocity accurately with a small sample volume even in disturbed flow fields.

The mechanism of erythrocyte aggregation has been studied in normal plasma, dextran 40 and dextran 70 suspensions in presence and absence of magnetic field at a concentration of 5 percent by laser light scattering. The inhomogeneous magnetic field enhances the aggregating tendency of normal erythrocytes. The growth of aggregates due to dextran 70 is enhanced in presence Of magnetic field. On the other hand the disaggregating effect of dextran 40 is reduced due to this field. The induced changes due to magnetic field during the development of erythrocyte aggregates in these media are determined.

The separation process of blood and RBC suspensions in a hematocrit range between 0.3 – 0.7 was investigated with a centrifuge allowed to run at low accelerations (100 xg – 1000 xg). The position of the interface between the supernatant of plasma and the RBC column was continuously recorded by a new optoelectronic measuring system. The separation process could be mathematically described by an exponential decrease of the cell column approaching a final packing. At a given centrifugal acceleration the time constant is influenced by hematocrit, aggregation, deformation and plasma viscosity. The final packing depends linearly on the starting hematocrit (0.3 – 0.7) and can be used as a measure of deformability.

The absolute value of the viscosity in membrane lipid bilayers, which is different from the microviscosity advocated by Shinitzky, could be calculated from steady-state fluorescence depolarization of a hydrocarbon fluorophore, 1,6-diphenyl-1,3,5-hexatriene (DPH). This method was based on the theory of time-resolved fluorescence anisotropy and empirical relationships between fluorescence life time and the anisotropy parameters such as half cone angle in wobbling motion and wobbling diffusion rate of the fluorescent probe. Obtained viscosity values of various membranes from this method were consistent with those from time resolved method within experimental error.

The connection between microrheology and the constitutive equation of soft tissue is illustrated by an example of the incremental bulk modulus of the lung. It is shown that the following pieces of information are needed in order to make the connection: The detailed structure of the tissue embodied in a mathematical model, the morphometric data on the structural elements, the rheologic data of the materials, and the configuration at zero-stress state, or equivalently, the stress and strain at a homeostatic state. In the case of the lung, we have information on the first three items, but not the last one. Hence hypotheses have to be introduced concerning the homeostatic condition, the most important of which are the uniform fiber stress and the “optimal design” assumptions. We have shown that these data and hypotheses lead to theoretical results that are in good agreement with experimental observations.

The effects of fluid shear stress on the function and structure of the vascular system are outlined, based on the findings obtained in our laboratory or of our colleagues. First, it is pointed out that the adaptive response of the vascular wall to flow changes which we observed the internal diameter to keep the wall shear stress constant (1), can attain the optimum vascular branching structure as predicted in the minimum work model by Murray (2). Electron-microscopic studies of similarly shunted arteries revealing various morphological changes in the endothelial cells have suggested that the shear stress initially affects the endothelium (3,4,5). The in vitro experiments using cultured endothelial cells as well have exhibited that the mitotic activity of the cells significantly increases by applying fluid shear stress (6). From these findings, it is concluded that the adaptive response of the endothelium to the fluid shear stress is an inherent and key process locally regulating the vascular system to be in the most functional state.

Ten channels’ dual-sensor method newly developed was applied to the measurement of velocity profiles in arterioles and venules in the rat mesentery. In some experiments, red blood cells (RBC), labelled in vitro with a fluorescein isothiocyanate (FITC), were injected to compare the velocity profiles obtained by the RBC visualization technique with those measured by the dual-sensor method. It was found that the velocity profile of the FITC labelled RBC in straight microvessels was blunt as compared to a parabola. The centerline velocity measured by the dual-sensor method was smaller than that of the FITC labelled RBC by about 20 %. The velocity profiles were also measured at the curved arterioles and venules as well as at the bifurcation and the confluence. It was found that the velocities were higher along the inner wall at the curved portion and along the outer wall at the bifurcation of arterioles.

The behavior of a newly developed damped oscillation type rheometer was analyzed for fibrinogen solution and blood during coagulation. This rheometer consists of a cylindrical tube suspended from a torsion wire, that is filled with liquid to be tested. The logarithmic damping factor (LDF) during coagulation for blood and fibrinogen solution was obtained by this rheometer, which was closely related to the changes of viscosity and/or viscoelasticity of the blood sample. The slight increase of LDF prior to the rapid decrease was observed for blood. The increase of LDF would be reflected in the formation of the aggregation structure of red blood cells (rouleaux network) prior to the formation of fibrin network. The value of LDF for fibrinogen solution sharply increased and then decreased through a maximum value with the progress of coagulation, although the change of LDF was remarkably dependent on the fibrinogen concentration. The initial increase in LDF for fibrinogen solution was considered to be due to the formation of small clots in the solution. The decrease in LDF after attaining a maximum value is ascribed to the formation of fully developed fibrin network. The maximum value of LDF during coagulation for fibrinogen solution is higher than that for blood. The behavior was compared with that for non-biological fluids such as viscosity standard liquids and polyvinyl alcohol solution. From those data, it was concluded that the higher value of LDF than that for Newtonian liquids was due to the formation of aggregation structure or inhomogeneous fine clots in the liquid, which was accompanied with the appearance of the elasticity.

An optically active polymer, poly-β-hydroxybutyrate(PHB), is produced in cytoplasm of various bacteria. The bending piezoelectric effect was observed in oriented films of PHB. The coefficient between the electrical polarization and the stress gradient was found to be in the order of 10⁻¹⁸ Cm/N, which was similar to the value reported for bone. Anisotropy in the value of the coefficient was also observed.

Since the work of Bundgaard it is known that the interendothelial cell cleft is a narrow, but open, sometimes highly convoluted gap linking the blood vessel lumen with the subendothelial space. A remarkable feature of this cleft is its constant width. It is here suggested that electrostatic repulsions, and the presence of a system of posts between the walls act to maintain cleft width. Contrary to intuition the presence of posts would not constitute an intolerable increase in hydrodynamic resistance, since no massive posts are necessary. Links between the walls involving only a single macromolecular chain each, which would be very difficult to detect ultrastructurally, would, nevertheless, particularly when charged, act as extremely stiff springs of essentially fixed length. A detailed calculation is presented to show how this idea could work and it is proposed that similar such posts support the subendothelial layers. Recent ultrastructural evidence in support of single chain links is quoted.

The changes of viscosity, optical reflection and electrical resistivity of blood due to flow are dependent on the orientation and deformation of red cells. From electrical point of view, it can be assumed that blood is suspension of small insulating particles (red cells) in conductive fluid (plasma) when the frequency of supplied voltage is lower than several hundreds KHz. When blood flows, red cells deform and orient in flow direction. Therefore, flowing blood shows anisotropic electrical and optical properties. In steady flow, blood resistivity longitudinal to flow decrease with flow rate, and transverse one increases. Blood flow in living body is not steady but pulsatile. We measured both longitudinal and transverse resistivity changes, optical reflection change and viscosity change of sinusoidally flowing blood in a rectangular conduit. The results are 1) during one period of sinusoidal flow the longitudinal resistivity change is opposite to that of transverse one, 2) the waveform of reflection light change is similar to that of resistance change, and 3) minimum points of both longitudinal resistivity and viscosity changes do not appear at the moment when flow is zero but are delayed. When the amplitude of sinusoidal flow is small and oscillation frequency is high, the phase difference between the zero crossing period of flow and the period of minimum change in resistivity, increases up to 90°. Viscosity of blood decreases with increase of amplitude and frequency of sinusoidal flow.

In normal male rabbits loaded dietary cholesterol, intravital-microscopy revealed a marked acceleration of intravascular adhesiveness of white blood cells and aggregability of red blood cells and a swarming of lipid-laden macrophages in connective tissue space concurrently with a systemic hyperlipidemia and anemia. Possible roles of the microcirculatory changes in the atherogenesis were discussed.

Velocities of the red blood cell (RBC) and the suspending medium in glass capillaries of 9 to 20 μm were measured under microscopic observation. The effects of physical factors such as driving pressure, capillary diameter, hematocrits and RBC deformability on flow velocities were studied using freshly drawn blood of the rat resuspended in phosphate buffered saline solution in the hematocrit range between 5 and 12.5 %. These RBC suspensions were made to flow through the test glass capillaries under known negative driving pressures. Ratios of capillary hematocrit to feed hematocrit taken as measures of the Fahraeus effect showed almost constant value of about 0.74. While, ratios of capillary hematocrit to discharge hematocrit showed a characteristic dependence on capillary diameter, showing minimal values at about 13 μm in capillary diameter. The same hematocrit ratios were found to be well correlated with values of wall shear rates estimated from the relative RBC velocities.

Plasmatic proteins, namely fibrinogen and globulins, play a major role in red blood cell (RBC) aggregation which is accountable for the three-dimensional structure of blood. Consequently, blood rheological properties linked to this structure must be modified when the protein plasma content changes. This paper gives results and related comments on thixotropic properties of RBC suspensions (0.45 hematocrit) in isotonic solutions containing various amount of fibrinogen to which albumin is added. Thixotropic behavior of these RBC suspensions is studied with a low inertia coaxial cylinders viscometer at a shear rate step of γ ˙ = 1 s − 1 Rheograms are interpreted in term of thixotropy coefficient. The main conclusion is that albumin improves RBC disaggregability of whole blood, resulting probably from a competitive effect between fibrinogen and albumin in the RBC aggregation process.

Red cell aggregate sedimentation under gravitation produces pronounced and rapid “phase separation effects” culminating in “compaction stasis” (CS), i.e. almost complete stuffing of microvessels by RBC. This can be readily observed and monitored in microvessels of vertically placed mesentery preparations by a horizontally aimed intravital microscope as shown by (Göbel et al. Virchow’s Arch., 1988,). “Layered flow”, floatational plasma skimming and progressive increase in local tube hematocrit (HT) up to 100% (“compaction stasis”) occurs during induced low flow states in vivo (here preferentially in postcapillary venules), as well as in vitro (non-permeable artificial micro tube networks). Quantitative densitometry and velocimetry in vertically placed microvessels demonstrates that the process of RCA sedimentation results in progressive vertical skewing of the velocity profile, culminating in standstill of the RBC-sediment in the dependent vessel half, with superfluent plasma and small aggregates in the upper vessel half. The theory of compaction stasis is developed: in striking contrast to the situation under high shear conditions, red cells travel on slower trajectories than plasma: due to “red cell undervelocity” the average residence times of RBC in a venule is much higher than that of plasma. Consequently, CS can be explained as the result of a Fahraeus effect reversal since the principle of mass conservation requires that HT » HD. Network aspects and hemodynamic consequences are also incorporated into the theory.

Erythro-aggregometer is a Couette viscometer which was developed to measure aggregation parameters of red blood cells. The system is based on the analysis of the light intensity backscattered by a blood suspension. It allows to approach aggregation phenomenon in terms of kinetics, structural and rheological parameters. The measurement system designed for use with a microcomputer is suitable for both research and clinical investigations.