Red Cell Aggregation Research Articles

Aspectos estruturais da membrana eritrocitária

Este artigo descreve as estruturas e funções da membrana eritrocitária e sua importância na medicina transfusional. A membrana eritrocitária é uma das membranas mais conhecidas em termos de estrutura, função e genética. Como qualquer membrana plasmática, tem como função mediar transportes e, ainda, fornece ao eritrócito resistência e maleabilidade. De acordo com a International Society of Blood Transfusion (ISBT), são mais de 500 antígenos expressos na membrana das hemácias e, destes, cerca de 270 estão envolvidos nos casos de reação transfusional e doença hemolítica do feto e do recém-nascido. Na classificação feita pela ISBT, destaca-se a série de alta freqüência representada por antígenos presentes em mais de 99% dos indivíduos de uma população. Estes antígenos são conhecidos também como antígenos públicos e a maioria, quando ausente, determina problemas graves do ponto de vista transfusional. Como exemplo dessa problemática, uma gestante com ausência do antígeno P já sofreu seis abortos de repetição por insuficiência placentária devido ao anticorpo formado pela ausência do antígeno. Proteínas importantes são descritas nesta revisão como: banda 3, glicoforinas, espectrina e outras. A banda 3 é a mais abundante proteína integral da membrana do eritrócito e sua principal função é mediar a troca de cloro e ânions de bicarbonato através da membrana plasmática. A segunda proteína integral mais abundante é a sialoglicoproteína glicoforina A (GPA). Com um alto conteúdo de ácido siálico, a GPA contribui com a rede de carga negativa na superfície da membrana do eritrócito, minimizando, assim, a interação célula-célula e prevenindo sua agregação. Glicoforina C (GPC) é o receptor para PfEBP-2 (baebl, EBA-140), o mais novo local de ligação identificado para o Plasmodium falciparum.O complexo terciário - espectrina, actina e 4.1R - define a rede de citoesqueleto da membrana do eritrócito e é ainda responsável pela estabilidade sob mecanismos de estresse. Essa revisão da membrana eritrocitária é importante para um melhor entendimento das reações transfusionais, onde a formação de anticorpos contra antígenos de alta freqüência dificulta a transfusão compatível. O estudo da diversidade antigênica, a caracterização bioquímica de diferentes proteínas trará uma contribuição para o estabelecimento da saúde, assim como para o diagnóstico, desenvolvimento de tecnologias, como a produção de anticorpos monoclonais e conduta terapêutica para muitas enfermidades.

Leukocyte margination in a model microvessel

The physiological inflammation response depends upon the multibody interactions of blood cells in the microcirculation that bring leukocytes (white blood cells) to the vessel walls. We investigate the fluid mechanics of this using numerical simulations of 29 red blood cells and one leukocyte flowing in a two-dimensional microvessel, with the cells modeled as linearly elastic shell membranes. Despite its obvious simplifications, this model successfully reproduces the increasingly blunted velocity profiles and increased leukocyte margination observed at lower shear rates in actual microvessels. Red cell aggregation is shown to be unnecessary for margination. The relative stiffness of the red cells in our simulations is varied by over a factor of 10, but the margination is found to be much less correlated with this than it is to changes associated with the blunting of the mean velocity profile at lower shear rates. While velocity around the leukocyte when it is near the wall depends upon the red cell properties, it changes little for strongly versus weakly marginating cases. In the more strongly marginating cases, however, a red cell is frequently observed to be leaning on the upstream side of the leukocyte and appears to stabilize it, preventing other red cells from coming between it and the wall. A well-known feature of the microcirculation is a near-wall cell-free layer. In our simulations, it is observed that the leukocyte’s most probable position is at the edge of this layer. This wall stand-off distance increases with velocity following a scaling that would be expected for a lubrication mechanism, assuming that there were a nearly constant force pushing the cells toward the wall. The leukocyte’s near-wall position is observed to be less stable with increasing mean stand-off distance, but this distance would have potentially greater effect on adhesion since the range of the molecular binding is so short.

Correlation between the degree of hemolysis and acoustic impedance, speed of sound, and attenuation in flowing whole blood

The effect of increasing levels of mechanical hemolysis on the propagation of 15‐MHz ultrasound in flowing whole blood at 37 °C was investigated. An experimental setup was developed, which enabled the continuous measurement of attenuation, speed of sound, and acoustic impedance in porcine whole blood under conditions of laminar flow and mean shear rates well above the threshold for red cell aggregation. Starting with an initial hematocrit of 35%, an increasing volume fraction of the blood in the flow loop was hemolyzed by exposure to very high shear stresses. The attenuation coefficient at 15 MHz was found to vary between 1 dB/cm for 0% hemolysis (no red cell damage) to 5 dB/cm for 75% hemolysis, remaining approximately constant for higher hemolysis levels. Speed of sound decreases from 1561 m/s for healthy blood to 1545 m/s for 80% hemolysis. Finally, acoustic impedance was also found to vary from a minimum of 1575 Kg/m2 to 1589 Kg/m2 between 15% and 90% hemolysis. These results show great promise towards solving the inverse problem, namely developing a technique capable of deducing the degree of hemolysis noninvasively and in real time based on measured changes in ultrasound parameters.

A Computer‐Based Method for Determination of the Cell‐Free Layer Width in Microcirculation

The cell-free layer between the erythrocyte column and the vessel wall is an important determinant of hydrodynamic resistance in microcirculatory vessels. The authors report a method for continuous measurement of the width of this layer. The light intensity of a linear array of pixels perpendicular to the vessel axis is continuously determined from a video image of a microcirculatory vessel. A threshold level based on Otsu's method is used to establish the interface between the cell-free layer and the erythrocyte column. To test the method, video images at 750-4500 frames/s were obtained from venules and arterioles in rat spinotrapezius muscle at normal and reduced arterial pressures before and after induction of erythrocyte aggregation with Dextran 500. The current measurements were compared to manual measurements of the same images. Values obtained by the manual and the new methods were in agreement within the 95% confidence limit by the Bland-Altman analysis and within 90-95% range by the correlation coefficient (R2). The more frequent measurements reveal substantial, rapid variations in cell-free layer width and changes in mean values with alteration of arterial pressure and red cell aggregability. A new, computer-based technique has been developed that provides measurements of rapid, time-dependent variations in the width of the cell-free layer in the microcirculation.

C-Reactive Protein and Red Cell Aggregation Correlate With Late Venous Function After Acute Deep Venous Thrombosis

C-Reactive Protein and Red Cell Aggregation Correlate With Late Venous Function After Acute Deep Venous Thrombosis

Decreased wall shear stress in the common carotid artery of patients with peripheral arterial disease or abdominal aortic aneurysm: Relation to blood rheology, vascular risk factors, and intima-media thickness

Wall shear stress, a local risk factor of atherosclerosis, is decreased in the common carotid artery of patients with vascular risk factors. We evaluated wall shear stress in the common carotid artery of patients with symptomatic peripheral arterial occlusive disease (PAD) and abdominal aortic aneurysm (AAA). As blood viscosity is a determinant of wall shear stress, we further investigated the impact of rheologic variables on wall shear stress in relation to vascular risk factors and intima-media thickness. High-resolution ultrasonography scans were used to study intima-media thickness, internal diameter, and blood velocity in the common carotid artery of 31 patients with PAD, 36 patients with AAA, and 37 controls. Furthermore, major hemorheologic variables and vascular risk factors were evaluated, and wall shear stress was calculated. Wall shear stress was lower in patients with PAD (median [IQR], dynes/cm(2): 14.4 [10 to 19]) and with AAA (12.1 [9 to 15]) than in healthy controls (20.6 [17 to 24]; P < .0001). Wall shear stress was inversely related to red cell aggregation (P = .01), fibrinogen (P = .003), leucocyte count (P = .001), plasma viscosity (P = .04), and intima-media thickness (P < .0001). Furthermore, wall shear stress was negatively associated with age, smoking, and triglycerides, but positively correlated with high-density lipoprotein cholesterol (all P < .001). When the influence of all these predictors were simultaneously taken into account in a multiple regression model, only age (P < .0001), smoking (P = .005), and triglycerides (P = .003) remained significantly associated with wall shear stress. This is the first report, to our knowledge, showing that wall shear stress of the common carotid artery is decreased in patients with symptomatic PAD and in patients with AAA. Rheologic variables are less important in predicting wall shear stress than age, triglycerides, and smoking.

Blood viscosity in patients with bone fractures and long term bedrest.

Eighteen patients with bone fractures and without systemic disease were studied for blood rheology. Blood and plasma viscosities, haematocrit, red cell aggregation and filterability as well as plasma colloid oncotic pressure were measured. Results show that patients exhibit a substantial haemorheological deficit on admission. During bedrest this returns to normal, owing to marked 'autohaemodilution'. It is concluded that trauma causes increased viscosity of blood in these patients. This change could predispose to deep vein thrombosis. However, such a risk is reduced by 'autohaemodilution' which is most probably an effect of immobilization.

Influence of Phlebotomies on Arterial Hemodynamic Parameters in Polycythemia Vera Patients.

Thrombosis is the major complication of Polycythemia Vera (PV) and the main cause of morbidity and mortality. Hypercoagulability is principally secondary to hypervisosity of the whole blood. Blood viscosity is an exponential function of the hematocrit, and red cell aggregation increases in high hematocrit level, creating the potential for vascular stasis. PV is also associated with endothelial dysfunction that can predispose to arterial disease. Reduction of the red cell mass to a safe level by phlebotomy is the first principle of therapy in PV. Such an effective therapy may have some effect on the arterial compliance in PV patients; nevertheless, to the best of or knowledge, the influence of phlebotomies on arterial hemodynamic parameters has not be studied in PV patients. In this study we estimated the influence of phlebotomies on large arteries (C1) and small arteries compliance (C2) in PV patients by non invasive method. Hemodynamic parameters were studied by Pulse Wave Analysis using the HDI-Pulse Wave CR2000 (Minneapolis MN, USA) immediatly before and after venesection (300–500cc of blood) (short effect of phlebotomy) and repeated within 3 months, after the hematocrit has been reduced to below 45% in male and 42% in female (long effect). Seventen PV (10 males) patients diagnosed according to the PVSG criterias have been included. 37 phlebotomies were performed with analysis of short effect (for 3 patients phlebotomy was performed 5 times, for one patient- 4 times, for five-twice, and for eight- once). There were 10 mesurements of long time effect of the phlebotomy. The median age of the patients was 66 years (range 48–82). The median hematocrit level was 49.3% (range 46.5–62) before phlebotomy. 47 measurements of the arterial compliance were performed (two patients visited 6 times, one- five times, one-4 times, three- 3 times, seven- twicely, and 3 patients once). The mean large artery compliance (C1) before phlebotomy was 12.0 ml/mmHg x 10 (range 4.5–28.6), in 36 measurements these parameters were normal for gender and age adjustment, and in 11 they were borderline. Immediately after phlebotomy the mean large artery compliance was 12.6 ml/mmHg x 10 (range 5.2–20.1). The mean small artery compliance (C2) before and immediately after phlebotomy were 4.4 mg/mmHg x 10(range 1.2–14.3) and 5.5 mg/mmHg x 10 (range 1.2 – 15.6) respectively (delta C2 1.1- not statistically significant). In 47 measurements of C2 before phlebotomy, 22 were within normal range, 6 borderline, and 19 pathological.. In 37, C2 measurements after phlebotomy, 21 were within normal range, 4 borderline and 12 pathological. The long term effect analysis demonstrates that the mean C1 after hematocrit normalization was13.8 mg/mmHg x 10 (delta 1.8- not statistically significant). The mean C2 after hematocrit normalization was 4.76 mg/mmHg x 10 (delta 0.36- not significant). In conclusion, phlebotomy has no significantly short or long term influence on large and small artery compliance in PV patients.

Detection of blood coagulation and clot formation using quantitative ultrasonic parameters

The ultrasonic parameters of sound velocity, attenuation and integrated backscatter were applied to detect the process of coagulation and clot formation in porcine blood. Fresh porcine blood containing 15% anticoagulant solution was collected. Blood samples with a hematocrit of 45% were obtained by reconstituting the packed erythrocytes with the separated plasma for ultrasound measurements performed with a 10-MHz focused transducer. A 24-mL aliquot of blood was placed in a container and 12 mL of 0.2 mol/L CaCl 2 solution was added to induce clot formation. In each measurement, radio-frequency signals of the blood digitized at 100 MHz were collected for 50 min at a temporal resolution of 1 A-line per s. Results showed that all of the parameters increased within the initial 3 min and, then, immediately decreased dramatically as the CaCl 2 solution was added. Subsequently, the sound velocity gradually increased with time and the integrated backscatter and attenuation increased in accordance with blood coagulation until approximately 500 and 2600 s, respectively. The integrated backscatter, attenuation and sound velocity can be divided into different stages, including red cell aggregation, reduction in hematocrit, blood coagulation and clot formation, corresponding to variations in the physical and chemical properties of the blood. The integrated backscatter, attenuation and sound velocity increased because of the changes in blood properties during the process of coagulation and clot formation: by 8.2 dB, 0.65 dB/cm, and 0.6%, respectively. These results provide a feasibility for further applying ultrasonic parameters to in vivo monitor the progress of clotting and thrombosis research. (E-mail: shyhhau@cycu.edu.tw)

Haemorheology in Gaucher disease

In Gaucher disease, a deficiency of glucocerebrosidase results in the accumulation of glucocerebroside within the lysosomes of the monocyte-macrophage system. Prior to the availability of enzyme replacement therapy (ERT), splenectomy was often indicated for hypersplenism. Haemorheological abnormalities could be expected in view of the anaemia and abnormal lipid metabolism in these patients and the role of the spleen in controlling erythrocyte quality. To investigate the effect of Gaucher disease on blood and plasma viscosity, erythrocyte aggregation and erythrocyte deformability, and to determine whether observed rheological differences could be attributed to splenectomy. Haematological and haemorheological measurements were made on blood collected from 26 spleen-intact patients with Gaucher disease, 16 splenectomised patients with Gaucher disease, 6 otherwise healthy asplenic non-Gaucher disease subjects and 15 healthy controls. No haemorheological differences could be demonstrated between spleen-intact patients with Gaucher disease and the control group. Compared to controls, both asplenic Gaucher disease and asplenic non-Gaucher disease study groups had a reduced MCHC (P = 0.003 and 0.005, respectively) and increased whole blood viscosity at 45% haematocrit (Hct), relative viscosity and red cell aggregation index - all measured at low shear (P < 0.05 for all). Additionally, asplenic patients with Gaucher disease alone showed an increased MCV (P = 0.006), an increased whole blood viscosity at 45% Hct measured at high shear (P = 0.019), and a reduced relative filtration rate (P = 0.0001), compared to controls. These observations demonstrate a direct and measurable haemorheological abnormality in Gaucher disease only revealed when there is no functioning spleen to control erythrocyte quality.

Enhanced Erythrocyte Aggregation in Clinically Diagnosed Pelvic Inflammatory Disease

Enhanced erythrocyte aggregation, revealed using a simple bedside test, has been found recently in several inflammatory conditions. The diagnosis of pelvic inflammatory disease (PID) is at times difficult because of the vague symptoms and signs, but is crucial because even mild PID can have future reproductive consequences. Our objective was to determine the degree of erythrocyte aggregation in PID. The demonstration of an increase in aggregation could be of additive value in cases in which the diagnosis is difficult. A prospective case-control study was conducted. Fifteen consecutive women diagnosed clinically as having PID based on Centers for Disease Control and Prevention criteria, and 15 matched controls were enrolled. Blood samples were drawn for hematologic indices, C-reactive protein, fibrinogen levels, and red cell aggregation. We studied the degree of red cell aggregation using a simple slide test and image analysis. The variable measured was the erythrocyte percent (EP), equivalent to the slide area covered by erythrocytes. Erythrocyte percent was 59.6 +/- 4.2 and 80.0 +/- 3.6 for the study group and controls, respectively (P <0.001). A significant difference was noted also for the other hematologic and biochemical markers of inflammation between patients and the controls. We conclude that the degree of erythrocyte aggregation is increased in PID. Its simplicity, rapidity, and low cost should be further evaluated as a diagnostic tool in the context of this frequent disease.

Hémorrhéologie et cardiologie. Concept, physiopathologie, applications aux affections cardiologiques

The discovery that the blood and the vessel wall constitute a single organ, i.e., that the content definitely influences the container - which is the main object of the haemorrheology - is attributable to A.L. Copley (1910-1992). Due to driving forces, blood flow organizes itself as concentric layers (laminar flow) shearing over each other. Such a shear stress is stronger at the wall level than in the middle of the vessel, where layers are less distinct. Red cells deform and take the shape of layers, allowing blood to become fluid (low viscosity). In vascular areas with decreased pressure, thus lower shear stress, blood becomes more viscous due to the presence of huge red cell aggregates, in relation to fibrinogen level (thyxotropy, red cell aggregation), changing and decreasing the shearing at the wall level. Such a two-phase behaviour of the shear stress characterizes the blood flow reactivity toward the wall. As viscosity measurement consists of plasma and blood viscosity, time and threshold of erythrocyte aggregation appear more accurate determinants. The shear stress mechanotransduction involves endothelial membrane receptors (caveoli, ion channels, integrins), then MAP-kinases systems, and finally transcription factors able to bind specific areas in gene promoters. Over 10 000 shear-sensitive genes have been identified to date. In arteries the shear stress induces NO, which is vasoactive and inhibits platelets. The shearing power at the wall level or at branching zones is often poor, due to pulsations and picks, where subsequently NO production is low and shear-down-regulated functions can occur, mainly leukocyte adhesion and migration. In veins changes in shear are more frequent, particularly in valvulae. Microcirculation is implemented as functional units, exhibiting a vasoactive precapillary side, capillaries with diameters lower than those of red cells and a post-capillary venous side with low output and much decreased shear stress. Endothelial cells are here very active for leukocyte adhesion, inflammation and haemostasis as well. Atherosclerosis stems from zones where monocytes-macrophages are able to enter the wall, bearing large amounts of lipoproteins, the main plaque constituent. As risk factors increase fibrinogen, high red cell aggregates change the wall shear stress and then LDL-receptors can be activated allowing plaques to grow up and extend along the arterial trunks. The atherosclerosis plaque is submitted to high shear upwardly, that activates platelets, but exhibits a stagnant zone downward, where leucocytes adhere and migrate. Myocardial infarct is due to the rupture of a coronary plaque, but its size is related to the rheological factors (fibrinogen, viscosity). Occlusive arterial disease largely exhibits such rheological disorders, with subsequent actions on ischemia. Hemodilution is proposed during acute events, mainly in stroke. Flow restoration (bypass), prevention of risk factors, venous contention and venoactive drugs reduce the influence of rheological disorders in vascular diseases.

Microvascular Rheology and Hemodynamics

The goal of elucidating the biophysical and physiological basis of pressure-flow relations in the microcirculation has been a recurring theme since the first observations of capillary blood flow in living tissues. At the birth of the Microcirculatory Society, seminal observations on the heterogeneous distribution of blood cells in the microvasculature and the rheological properties of blood in small bore tubes raised many questions on the viscous properties of blood flow in the microcirculation that captured the attention of the Society's membership. It is now recognized that blood viscosity in small bore tubes may fall dramatically as shear rates are increased, and increase (dramatically with elevations in hematocrit. These relationships are strongly affected by blood cell deformability and concentration, red cell aggregation, and white cell interactions with the red cells anti endothelium. Increasing strength of red cell aggregation may result in sequestration of clumps of red cells with either reductions or increases in microvascular hematocrit dependent upon network topography. During red cell aggregation, resistance to flow may thus decrease with hematocrit reduction or increase due to redistribution of red cells. Blood cell adhesion to the microvessel wall may initiate flow reductions, as, for example, in the case of red cell adhesion to the endothelium in sickle cell disease, or leukocyte adhesion in inflammation. The endothelial glycocalyx has been shown to result from a balance of the biosynthesis of new glycans, and the enzymatic or shear-dependent alterations in its composition. Flow-dependent reductions in the endothelial surface layer may thus affect the resistance to flow and/or the adhesion of red cells and/or leukocytes to the endothelium. Thus, future studies aimed at the molecular rheology of the endothelial surface layer may provide new insights into determinants of the resistance to flow.

First trimester maternal blood rheology and pregnancy induced hypertension

SummaryThis study evaluates the relationship between the first trimester assessment of maternal rheology and the subsequent development of pregnancy induced hypertension. This is a prospective observational study based in the Glasgow Royal Maternity Hospital, Scotland. From an original population of 744 consecutive antenatal attendees a total of 579 women were booked at less than 14 weeks' gestation. The main study group is a further subset comprising 251 primigravid women booking with a singleton pregnancy without essential hypertension. Previously published data from a group of non-pregnant women of similar age drawn from the same local community was used for external comparison. Blood samples were collected at the booking visit, from which fibrinogen, red cell aggregation, haematocrit and plasma, whole blood, relative and corrected viscosities were recorded. Information was obtained from the case notes in retrospect starting approximately 1 year after the first patients had first been recruited into the trial. The overall outcome of the pregnancies was noted with particular reference to pregnancy induced hypertension (PIH), birth weight, antepartum haemorrhage, pre-term labour, perinatal death, condition at delivery and neonatal complication. Our results show PIH is associated with a significantly raised mean blood viscosity and fibrinogen at time of booking. All significance disappears after adjustment for smoking, diastolic blood pressure and age. Viscosity is, however, only marginally non-significant (p = 0.07). In conclusion, blood rheology, in particular blood viscosity and fibrinogen, may play a predictive role in the development of pregnancy-induced hypertension. When combined with measurement of smoking and diastolic blood pressure at booking, these measurements could be used to calculate a risk score for the development of PIH, allowing targeting of antenatal care. Further data is required.

Hémorhéologie clinique. Concept, physiopathologie et applications aux maladies vasculaires

The discovery that the blood and the vessel wall constitute a single organ, i.e, that the content definitely influences the container - which is the main object of the hoemorheology - is attributable to A.L. Copley (1910-1992). Due to driving forces, blood flow organizes itself as concentric layers (laminar flow) shearing over each other. Such a shear stress is stronger at the wall level than in the middle of the vessel, where layers are less distinct. Red cells deform and take the shape of layers, allowing blood to become fluid (low viscosity). In vascular areas with decreased pressure, thus lower shear stress, blood becomes more viscous due to the presence of huge red cell aggregates, in relation to fibrinogen level (thyxotropy, red cell aggregation), changing and decreasing the shearing at the wall level. Such a two-phase behaviour of the shear stress characterizes the blood flow reactivity toward the wall. As viscosity measurement consists of plasma and blood viscosity, time and threshold of erythrocyte aggregation appear more accurate determinants. The shear stress mechanotransduction involves endothelial membrane receptors (caveoli, ion channels, integrins), then MAP-kinases systems, and finally transcription factors able to bind specific areas in gene promoters. Over 10,000 shear-sensitive genes have been identified to date. In arteries the shear stress induces NO, which is vasoactive and inhibits platelets. The shearing power at the wall level or at branching zones is often poor, due to pulsations and picks, where subsequently NO production is low and shear-down-regulated functions can occur, mainly leukocyte adhesion and migration. In veins changes in shear are more frequent, particularly in valvulae. Microcirculation is implemented as functional units, exhibiting a vasoactive precapillary side, capillaries with diameters lower than those of red cells and a post capillary venous side with low output and very decreased shear stress. Endothelial cells are here very active for leukocyte adhesion, inflammation and haemostasis as well. Atherosclerosis stems from zones where monocytes-macrophages are able to enter the wall, bearing large amounts of lipoproteins, the main plaque constituent. As risk factors increase fibrinogen, high red cell aggregates change the wall shear stress and then LDL-receptors can be activated allowing plaques to grow up and extend along the arterial trunks. The occlusive arterial disease largely exhibits such rheological disorders, with subsequent actions on ischemia. The same is observed in diabetes, along with the addition of hyperglycemia picks, viscous HbA1c et glycation of red cells, adding worsened effect on retinopathy. Ischemic cerebral vascular accidents also exhibit high red cell aggregation making prognostic worse, mainly in elderly. Patients with lacunar CVA of Binswanger use to show a strong hyperviscosity. Haemorrhoeological disorders also worsen retinal vein occlusion, hearing loss, secondary forms of Raynaud’s disease. In chronic venous disease, they appear as contributory factors to the development of varicosities and ulcer genesis, for their facilitating action upon adhesion migration of leukocytes. Hemodilution is proposed during acute events, mainly in CVA. Flow restoration ( bypass), prevention of risk factors, venous contention and venoactive drugs, are the opposing treatments of rheological disorders in vascular diseases.

Rheology and Ultrasound Scattering from Aggregated Red Cell Suspensions in Shear Flow

The shear flow dynamics of reversible red cell aggregates in dense suspensions were investigated by ultrasound scattering, to study the shear disruption processes of Rayleigh clusters and examine the effective mean field approximation used in microrheological models. In a first section, a rheo-acoustical model, in the Rayleigh scattering regime, is proposed to describe the shear stress dependence of the low frequency scattered power in relation to structural parameters. The fractal scattering regime characterizing the anisotropic scattering from flocs of size larger than the ultrasound wavelength is further discussed. In the second section, we report flow-dependent changes in the low-frequency scattering coefficient in a plane-plane flow geometry to analyze the shear disruption processes of hardened or deformable red cell aggregates in neutral dextran polymer solution. Rheo-acoustical experiments are examined on the basis of the rheo-acoustical model and the effective medium approximation. The ability of ultrasound scattering technique to determine the critical disaggregation shear stress and to give quantitative information on particle surface adhesive energy is analyzed. Lastly, the shear-thinning behavior of weakly aggregated hardened or deformable red cells is described.

C-reactive protein and red cell aggregation correlate with late venous function after acute deep venous thrombosis

Risk factors leading to development and subsequent progression of chronic venous insufficiency after acute deep venous thrombosis (DVT) are only partially identified. Inflammation and rheologic abnormalities might have a causative role. The purpose of this study was to investigate C-reactive protein (CRP), D -dimer, and blood rheologic parameters in patients after acute DVT in relation to clinical outcome. Patients with a history of acute proved DVT underwent clinical examination and duplex ultrasound scanning of the veins, and Venous Clinical Severity Score (VCSS) and Venous Segmental Disease Score (VSDS) were calculated. Further, CRP, D -dimer, and several rheologic parameters were determined and related to outcome as assessed with venous scores. Forty-three patients were examined 28 (median) months after the index event. Patients had higher CRP ( P < .001), D -dimer ( P < .001), red blood cell aggregation ( P < .01), fibrinogen concentration ( P < .01), and leukocyte count ( P < .05) than did healthy control subjects. CRP and red blood cell aggregation were positively correlated with VCSS ( r = 0.42 and P < .01, and r = 0.30 and P < 0.05, respectively). Multivariate regression analysis showed that the relation between CRP and VCSS was independent of other laboratory and rheologic parameters and of age, total thrombus load, duration of compression therapy after the index event, recurrence, recanalization, and presence of comorbid conditions ( P < .05). CRP is independently related to the severity of venous dysfunction in patients after acute DVT. Chronic inflammation as well as changes in blood rheologic parameters may be causally involved in the development of chronic venous insufficiency occurring in the medium-term and long-term course after acute DVT.

Boundary element simulation of backscattering properties for red blood with high frequency ultrasonic transducers

High frequency ultrasonic imaging (e.g. >30 MHz) from blood is difficult due to its tenuous backscattered pressure and the interference from adjacent tissues as well. To increase the sensitivity focused transducer has to be used, thus raising the complexity of interpreting the received signals. A numerical simulation of the ultrasonic scattering property from erythrocyte and rouleaux based on boundary element method was performed with experimental results based on a modified substitution method. The results (proportional relationship between backscattered pressure and frequency and the frequency limit for Rayleigh scattering) closely coincide with experimental data for erythrocyte. Rouleaux model results also show the dependence of degree of red cell aggregation on backscattering properties. The boundary element method serves as a good means to calculate the acoustic scattering from blood cells under arbitrary incident waves.

Diffusion ultrasonore par des suspensions concentrées d'agrégats fractals de globules rouges dans un écoulement de cisaillement

Shear flow dynamics of reversible fractal clusters in dense suspensions were investigated by ultrasound scattering to study shear disruption processes of Rayleigh aggregates and further examine the effective mean field approximation used in the microrheological models. Within the framework of a fractal flocculation process, the concept of variance in local particle volume fraction is used to derive an original expression of the ultrasonic backscattering cross-section for a dense distribution of correlated Rayleigh fractal clusters. Considering the scaling laws for shear break-up of reversible aggregates in concentrated suspensions, a rheo-acoustical model in the Rayleigh scattering regime is proposed to describe the shear stress dependence of the low frequency backscattering coefficient with physical parameters. The anisotropic scattering effects from flocs of size larger than ultrasound wavelength are further discussed. In a second part, we report flow dependent changes of the ultrasonic backscattering coefficient in a plane–plane flow geometry to analyze shear break-up processes of hardened or deformable red cell aggregates in dextran solutions. Rheo-acoustical experiments were examined on the basis of the rheo-acoustial model and the effective medium approximation. The ability of ultrasound scattering to determine the critical shear stress and to give quantitative information on particle surface adhesive energy is analyzed.

Analysis of red blood cell aggregation in cardio-pulmonary bypass (CPB) surgery.

Not much is known about red cell aggregation during cardio-pulmonary bypass surgery (CPB). Blood samples from 19 patients undergoing CPB were anticoagulated with EDTA. Hematocrit was adjusted to 40%. A red blood cell aggregometer (LORCA) measured changes in light reflection from each blood sample after cessation of the rotation, and calculated an aggregation index (AI). Reflection measurements were stored. Because LORCA software failed for 87 of 171 samples, we developed new software, and applied it to the stored reflection measurements. This software failed only in 7 out of 171 cases and showed that all LORCA failures occurred for AI < 40%. The new calculations revealed that the aggregation index significantly decreased from 46.6 +/- 10.1 (mean +/- standard deviation) baseline to 22.8 +/- 8.3 at the end of CPB and recovered to 37.1 +/- 13.5 at day 1. It is concluded that the new software can be used to study decreased red cell aggregation during CPB.