Changes in the guanylate cyclase activity of human thrombocytes during ADP-inducible aggregation]

Activity of guanylate cyclase (GC) and its capacity for sodium nitroprusside (SNP) activation were determined in platelets with different state of aggregation. The development of ADP-induced reversible aggregation was accompanied by a decrease in the basal GC activity and by an increase in the SNP activation of GC. It was shown that elevation of GC sensitivity to SNP during the aggregation might be due to the decrease in the state of enzyme blood deficiency. Preincubation of platelets with SNP before ADP adding markedly diminished or even prevented aggregation, depending on SNP concentration. GC parameters in platelets with prevented aggregation were just the same as in control. It is suggested that the regulatory role of cGMP system in platelet aggregation may be seen in the increase in GC sensitivity to endogenous activator, presumably to NO.     

Relationships between Platelets and Blood Cells in Postprandial Glycemia in Healthy Individuals

The relationships between platelet aggregation and blood cell amount were studied in healthy subjects after fasting and after a standard carbohydrate breakfast. Positive relationships were revealed between certain parameters of platelet aggregation and the amounts of monocytes and eosinophils. Negative relationships were revealed between most parameters of platelet aggregation and the amount of platelets. Along with the well-known food leukocytosis and increased fibrinogen, postprandial conditions were characterized by an increase in certain parameters of platelet aggregation, destruction of the relationship between the fibrinogen concentration and platelet aggregation, impairment of the inverse relationship between the amount and aggregation of platelets, and moderate direct or inverse relationships between certain parameters of the first and the second stages of platelet aggregation and the erythrocyte parameters. As a disturbing factor, postprandial conditions activated platelet hemostasis by modulating the initial stages of aggregation and substantially changed the interrelations between blood cells.     

Evaluation of a method to assess red blood cell aggregation

Reversible aggregation of red blood cells (RBC) plays an important role in determining the flow properties of blood. To study different factors affecting RBC aggregation we used a new commercially available erythro-aggregameter (SEFAM, Nancy, France). The method allows the photometric quantitation of the kinetics of RBC aggregation and the estimation of the shear resistance of the aggregates. Modification of the hematocrit acts mostly on the determination of the disaggregation shear rate, while plasma composition strongly affects all measurements. Anticoagulants per se do no influence the aggregation process, but can alter the value of the parameters through a plasma dilution effect. Presence of white blood cells and platelets in the sample did not modify the data. Study on the effects of low concentration of heparin and low molecular weight heparin showed that at therapeutical doses these drugs did not alter the values of the aggregation parameters. Provided that precise guidelines are followed for the processing of blood samples, this method may serve to investigate RBC aggregation in various diseases and to search for adequate hemorheologic treatment.     

The clinical rheological laboratory

To quantify the fluidity of blood it is not suitable to measure whole blood viscosity as blood is no Newton's fluid. For this reason, it is necessary to measure characteristic blood flow parameters direct. This study presents methods of measurement for plasma viscosity, haematocrit, thrombocyte aggregation, erythrocyte rigidity, erythrocyte aggregation and leukocyte adhesivity.     

Blood rheology of Weddell seals and bowhead whales

Red blood cell (RBC) aggregation and blood viscosity are important determinants of in vivo blood flow dynamics and, in marine mammals, these parameters may impact diving physiology by altering blood oxygen delivery during the diving response. Weddell seals are superb divers and exhibit age-related patterns in blood oxygen chemistry and diving ability. By contrast, bowhead whales are not long duration divers, and little is known of their blood properties relative to diving. The present study was designed to compare rheological characteristics of blood from Weddell seal pups, Weddell seal adults, and from adult bowhead whales: blood viscosity and RBC aggregation in plasma and in polymer solutions (i.e., RBC "aggregability") were measured. Salient findings included: (1) significant 4- to 8-fold greater aggregation in blood from adult seals compared with pups and human subjects; (2) 2-to 8-fold greater aggregation in bowhead whale blood compared with human blood; (3) compared to human red cells, enhanced RBC aggregability of RBC from adult seals and whales as determined by their greater aggregation in polymer solutions; (4) increasing RBC aggregation and aggregability of seal pup blood over a seven day period following birth; (5) significantly greater blood viscosity for adult seals compared with pups at both native and standardized hematocrits. These results indicate that, for both species, hemorheological parameters differ markedly from those of humans, and suggest progressive changes with seal age; the physiological implications of these differences have yet to be fully defined.     

Effect of ethyl alcohol on selected parameters of the hemostasis system in vitro]

Alcohol produces several disorders in all components of hemostasis system. However, its mechanism of action is not clear. Therefore, an effect of ethyl alcohol on the selected parameters of both platelet and plasma hemostasis has been examined in vitro. Blood aggregation induced by ADP and PAF and platelet-leucocytic aggregates have been determined in vitro in the group of 45 healthy volunteers. Out of plasma parameters the selected factors of blood coagulation and fibrinolysis have been examined. Results suggest that the examined concentrations of ethyl alcohol mainly affect platelet function decreasing platelet aggregation. Alcohol does not affect significantly blood coagulation and fibrinolysis occurring in vitro.     

The determination of blood viscoelasticity in clinical hemorheology

A brief outline of the background of viscoelasticity of blood is given in order to derive for blood relevant parameters. In this context, especially one method, the sinusoidal oscillating capillary rheometry, is discussed. The determination of different parameters to characterize blood samples, e.g. the viscoelastic phase angle, an aggregation index, a flexibility index, hematocrit and plasma viscosity is described. Most of these parameters show increased values in disease; however they can be influenced by drug treatment.     

Influence of malaria parasite (P. vivax) on erythrocyte aggregation: a study based on dynamic imaging and analysis

Malaria due to P. vivax (PV) is prevalent in many countries. The present work is aimed to determine the cell-cell interaction through formation of aggregates under dynamic conditions. Blood samples are obtained from patients (n=11) suffering from PV malaria, and the normal subjects (n=10) in test tubes containing citrate phosphate dextrose (10:1.4), as an anticoagulant. The signature analysis of infected erythrocytes shows significant alterations in their shape and membrane. For aggregation analysis, erythrocyte suspension in plasma at hematocrit 5%, was placed in a glass chamber and mounted vertically on the stage of the video-microscope system. The aggregate images thus acquired show erythrocytes adhering with each other to form mash-like structures. With increase in parasitaemia, the erythrocytes show hyper-aggregation compared to that of normal cells. By processing of the sequence of recorded images during sedimentation, the various aggregation parameters are obtained. These parameters show that the formed aggregates are compact which produce distinct changes in sedimentation pattern with significantly higher sedimentation velocity compared to that in healthy blood samples. These changes in malaria could partly be responsible for alteration in blood flow through microcirculatory system.     

Risk factors evaluation in some cardiovascular diseases

Cardiovascular risk factors are associated with limitations of blood fluidity. Rheological behaviour of blood in transient flow may result from the internal organization, which in turn depends upon many parameters, which may be considered as possible elements of a profiling algorithm for diagnostic and prognostic values in various pathophysiological states. This study was designed to investigate haemorheological parameters in patients being treated for hypertension, coronary heart disease and myocardial infarct. On the basis of plasma viscosity, whole blood viscosity, haematocrit, red cell aggregation and red cell deformation, the risk was evaluated. In cases of hypertension there was a significant rise in plasma viscosity, whole blood viscosity, red cell aggregation and a fall in red cell deformability. In cases of coronary disease, plasma viscosity and red cell aggregation was increased, while in patients with myocardial infarcts, where the degree of severity is greater it was found that there was a significant rise in both plasma and whole blood viscosity. Haematocrit values were unaffected in all three groups.     

Parameters of red blood cell aggregation as correlates of the inflammatory state

To identify clinically relevant parameters of red blood cell (RBC) aggregation, we examined correlations of aggregation parameters with C-reactive protein and fibrinogen in unstable angina (UA), acute myocardial infarction (AMI), and bacterial infection (BI). Aggregation parameters were derived from the distribution of RBC population into aggregate sizes (cells per aggregate) and changing of the distribution by flow-derived shear stress. Increased aggregation was observed in the following order: UA, AMI, and BI. The best correlation was obtained by integration of large aggregate fraction as a function of shear stress. To differentiate plasmatic from cellular factors in RBC aggregation, we determined the aggregation in the presence and absence of plasma and formulated a "plasma factor" (PF) ranging from 0 to 1. In AMI the enhanced aggregation was entirely due to PF (PF = 1), whereas in UA and BI it was due to both plasmatic and cellular factors (0 < or = PF < or = 1). It is proposed that clinically relevant parameters of RBC aggregation should express both RBC aggregate size distribution and aggregate resistance to disaggregation and distinguish between plasmatic and cellular factors.     

Hematocrit,viscosity and velocity distributions of aggregating and non-aggregating blood in a bifurcating microchannel

Microscale blood flow is characterised by heterogeneous distributions of hematocrit, viscosity and velocity. In microvascular bifurcations, cells are unevenly distributed between the branches, and this effect can be amplified in subsequent branches depending on a number of parameters. We propose an approach to infer hematocrit profiles of human blood flowing through a bifurcating microchannel. The influence of aggregation, induced by the addition of Dextran 2000 to the samples, is also considered. Averaged values indicate plasma skimming, particularly in the presence of red blood cell (RBC) aggregation. Using an empirical model, the hematocrit profiles are used to estimate local relative viscosity distributions. Simulations are used to predict how the non-uniform viscosity influences the velocity profiles. Comparing these data to velocity profiles of RBCs measured using particle image velocimetry provides validation of the model. It is observed that aggregation blunts velocity profiles after a long straight section of channel. Downstream of the bifurcation, skewing of the velocity profiles is detected, which is enhanced by aggregation. The proposed methodology is capable of providing hitherto unreported information on important aspects of microscale blood rheology.     

Effect of soluble fibrin on the blood coagulation process and platelets aggregation

The accumulation of soluble fibrin (SF) in the blood plasma causes acceleration of the final stage of blood coagulation. It increases functional activity of a hemostasis system platelet link, that is the precondition of thrombotic complication. Accumulation of SF in the blood plasma is accompanied by proportional reduction of coagulation time in ancistron and thrombin time tests, and also the intensification of platelets aggregation process. A conclusion was drawn that for early diagnostics of the DIC-syndrom it is expedient to carry out complex estimation of the hemostasis system with obligatory definition of the blood SF content, performance of ancistron and thrombin time tests, and also study of platelets aggregation.     

Aggregation behavior of red blood cells in shear flow. A theoretical interpretation of simultaneous rheo-optical and viscometric measurements

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.     

Importance of the functional activity of thrombocytes and the antiaggregation activity of the vascular walls in regulating blood aggregation

It was established in dog experiments that aggregation activity of platelets and the rate of aggregation were higher in arterial than in venous blood, with the platelet content being identical. Antiaggregation activity of vascular walls of the arterial system. The data obtained indicate the presence of the arteriovenous difference of the function of the vascular-platelet hemostasis, which is of a role in the processes of regulating the state of blood aggregation in the body.     

The flow properties of blood and their characterization by hemorheologic methods

In a number of supply disturbances the flow behaviour of blood plays an increasing role in modern therapy concepts. The present paper deals with representing factors, such as haematocrit, aggregation, deformation, which exercise an influence on the complex flow properties of blood under variable conditions. By referring to the example of deformability it is shown how and to what extent different mechanical parameters of individual erythrocytes participate in static or dynamic whole cell deformation. Starting from fundamental quality demands (sensitivity, specificity, value of prediction) to diagnostic measuring technique, haemorheological methods for determining complex flow properties, aggregation and deformation as single phenomena and mechanical properties of individual erythrocytes are presented. Selected examples of application for normal blood, cells altered in vitro or pathological changes measured ex vivo are referred to.     

Erythrocytes sedimentation profiles under gravitational field as determined by He-Ne laser. VII. Influence of dextrans, albumin and saline on cellular aggregation and sedimentation rate

The erythrocytes sedimentation profiles (ESP) of normal blood and of blood mixed with saline, albumin (7%), and various molecular weight dextrans of different concentrations, at various height and widths of the sample holder are determined. These observations show that the sedimentation characteristics of the erythrocytes depend on the influence of these substitutes on the plasma and cellular constituents. The normalised aggregation and the sedimentation rate, as determined from these profiles, show that the dextran 40 and dextran 70 retard the erythrocytes sedimentation, for high molecular weight it is similar to that of normal blood and is the maximum for saline. This change for high molecular weight dextrans could be attributed to the enhanced aggregation tendency of erythrocytes and for saline to the enhanced sedimentation due to decrease in the viscosity and density of suspending medium. The influence of the various concentrations of dextrans on these parameters has been determined.     

Mechanism of the biological impact of weak electromagnetic fields and the in vitro effects of blood degassing

The physical validity of the mechanism proposed by the author is discussed. According to the theory, prolonged exposure to weak electromagnetic fields leads to enlargement of microbubbles and degassing of bioliquid. Degassing alters the physical and chemical properties of bioliquid that affect some medical and biological indicators. The following changes in some blood parameters during degassing in vitro were analyzed: decrease in the glucose concentration, abnormal activation of blood clotting, increase in the rate of blood cell aggregation, decrease in the effectiveness of aspirin as an inhibitor of platelet aggregation and the slowing of indirect anticoagulants. All this is evidence of possible connection between environmental electromagnetic pollution and the risk of cardiovascular disease.     

Effect of enhanced red blood cell aggregation on blood flow resistance in an isolated-perfused guinea pig heart preparation

The role of red blood cell (RBC) aggregation as a determinant of in vivo blood flow is still unclear. This study was designed to investigate the influence of a well-controlled enhancement of RBC aggregation on blood flow resistance in an isolated-perfused heart preparation. Guinea pig hearts were perfused through a catheter inserted into the root of the aorta using a pressure servo-controlled pump system that maintained perfusion pressures of 30 to 100 mmHg. The hearts were beating at their intrinsic rates and pumping against the perfusion pressure. RBC aggregation was increased by Pluronic (F98) coating of RBC at a concentration 0.025 mg/ml, corresponding to about a 100% increment in RBC aggregation as measured by erythrocyte sedimentation rate. Isolated heart preparations were perfused with 0.40 l/l hematocrit unmodified guinea pig blood and with Pluronic-coated RBC suspensions in autologous plasma. At high perfusion pressures there were no significant differences between the flow resistance values for the two perfusates, with differences in flow resistance only becoming significant at lower perfusion pressures. These results can be interpreted to reflect the shear dependence of RBC aggregation: higher shear forces associated with higher perfusion pressures should have dispersed RBC aggregates resulting in blood flow resistances similar to control values. Experiments repeated in preparations in which the smooth muscle tone was inhibited by pre-treatment with papaverine indicated that significant effects of enhanced RBC aggregation could be detected at higher perfusion pressures, underlining the compensatory role of vasomotor control mechanisms.     

The role of aggregation kinetics in the sedimentation of erythtocytes

The well-known S-shaped settling curves are obtained as solutions of an autonomic dynamical system deduced mathematically from the generalized Stokes formula, the blood volume conservation law, and the Smoluchowski theory of particle coagulation. Numerical computations and parametric analysis of the deduced two nonlinear differential equations for the plasma zone thickness and aggregate size are given. It is shown that the model presented makes it possible, on the basis of experimentally recorded sedimentation curves and aggregate size growth, to identify quantitatively the values of the essential physical parameters of the coupled processes of erythrocyte aggregation and sedimentation. This method of identification could be used as a diagnostic test in hematological laboratories.     

Preparation of human platelets without the use of anticoagulants and study of the effect of Catt on aggregation]

A method for the preparation of human blood platelets is presented which substitutes the use of anticoagulants by a gelfiltration for the removal of plasma calcium from native blood. In a second step the platelets are separated from the gel filtered blood by a centrifugation on a Ficoll density gradient. The anticoagulant-free platelets reveal an intact morphological feature and a normal aggregation behaviour in response to different aggregation inducers. It was found that in ADP-induced aggregation monophasic aggregation is shifted to a biphasic one by increasing concentrations of extracellular calcium.