Increase in erythrocyte disaggregation shear stress in hypertension.

The aggregation and disaggregation behaviors of red blood cells were investigated in 17 normotensive and 21 hypertensive subjects with a laser reflectometry technique, and simultaneous measurements were taken of blood viscosity with a coaxial viscometer. Increased red blood cell aggregation (26%, p less than 0.001) and disaggregation shear rate (20%, p less than 0.01) and shear stress (18%, p less than 0.01) were observed in hypertensive subjects when compared with normotensive subjects. Similar elevations in hypertensive subjects were found when the hematocrit was adjusted to 40%. Variation of red blood cell concentration caused the red blood cell disaggregation shear rate to change in an opposite direction but did not modify red blood cell aggregability and disaggregation shear stress. The increase of the reversible aggregation of red blood cells was associated with higher fibrinogen and plasma protein concentrations in hypertension. An increase in red blood cell aggregability and in the shear resistance of red blood cell aggregates may play a role in the development of the cardiovascular complication in hypertension. The quantification of red blood cell disaggregation shear stress, which represents the hydrodynamic force required to disperse the aggregates, may provide a useful parameter for clinical investigations.

Influence of sialic acid on erythrocyte aggregation in hypercholesterolemia.

The respective role of adhesive forces induced by fibrinogen and repulsive forces induced by erythrocyte sialic acid content on erythrocyte aggregation, was investigated in hypercholesterolemic and control subjects. Aggregation index (AI) and disaggregation shear rate threshold (gamma t) were determined in the presence of either autologous plasma or dextran. Compared with controls, fibrinogen (p < 0.001) and aggregation parameters (AI p < 0.01; gamma t p < 0.01) were higher in hypercholesterolemics while erythrocyte sialic acid content (p < 0.001) was lower; in addition total serum sialic acid was increased (p < 0.01). The aggregation properties of erythrocytes, independent of plasma environment using dextran as a bridging macromolecule, showed an enhanced disaggregation shear rate threshold and an inverse relationship with erythrocyte sialic acid content. We conclude that decreased erythrocyte sialic acid content may intensify the effect of fibrinogen on aggregation and disaggregation of erythrocytes and participate in the development of atherothrombotic complications.

Blood lipids and rheological modifications in glycogen storage disease.

OBJECTIVES: Hyperlipidemia is a feature of liver glycogen storage disease (GSD). Recent studies have suggested that rheological mechanisms such as elevated erythrocyte aggregation may be involved in the pathogenesis of ischemic syndromes associated with hyperlipidemia. DESIGN AND METHODS: We investigated erythrocyte aggregation, lipids, and circulatory proteins in the blood of 24 patients affected with GSD, aged from 1 to 23 years (mean = 8) and 26 controls aged from 1 to 28 years (mean = 9). RESULTS: The aggregation results were much higher in patients than controls. The lipid data showed a mixed hyperlipidemia with predominant hypertriglyceridemia, low HDL-C, apoA-I and LpA-I/A-II, and high apoB as compared with controls. However, the LpA-I was not significantly different from controls. CONCLUSIONS: In conclusion, patients with GSD presented hyperlipidemia and elevated erythrocyte aggregation such that they are at long-term risk of ischemic complications.

Decreased erythrocyte deformability in glycogen storage disease.

Liver glycogen storage diseases (GSD) are disorders associated with severe dyslipidaemia which can induce cell membrane alterations and possibly reduced cell deformability. Since decreased erythrocyte deformability is known to disturb blood flow in capillaries and may promote ischaemic diseases, this study was designed to investigate erythrocyte deformability using a new filtration system, the Cell Transit Analyser (CTA), and to examine lipid compounds in the blood of 23 patients affected with GSD, aged from 1 to 20 years and 18 controls aged from 1 to 17 years. The patients showed a mixed hyperlipidaemia with predominant hypertriglyceridaemia and an increase in erythrocytes mean transit times (TT) due to the presence of more rigid erythrocytes subpopulations when compared to controls. Thus the erythrocyte rigidity, in addition to the lipid abnormalities must be taken into account for long-term evolution of GSD patients. Moreover this cellular alteration may contribute to shortened erythrocyte survival.

Ultrasonic interferometry: study of particle sedimentation in liquid.

An ultrasonic interferometry method was designed to study sedimentation of particles in liquid. The method, based on A mode echography, measures the amplitude of ultrasonic waves reflected (echo E1) by a fixed interface I1 called "solid plate-sediment" interface formed when particles are sedimenting on a solid plate. The amplitude of the echo depends both on mechanical properties of the three media (solid plate, sediment and suspension) on the thickness of the sediment and on the presence of a second mobile interface I2 called "sediment-suspension" interface. In the first phase of sedimentation when the second interface is very close to the first, two reflected waves interfere. Then, in the second phase of sedimentation when the sediment is thick enough, the amplitude of the echo E1 depends only on the sediment and solid plate properties. The first phase will give information on the sedimentation rate of particles (SR). We have compared SR of particles determined by this method with SR measured in a cylindrical tube of the same geometry as the ultrasonic measurement cell and with theoretical values of the sedimentation rate given by theoretical models.

Quantification of erythrocyte aggregation by blood echogenicity: a preliminary study.

Many techniques were proposed to assess erythrocyte aggregation in clinical and experimental investigations in view of in vitro determination. However no methodology until now is available to measure erythrocyte aggregation in flowing blood in vivo. High resolution ultrasonography provides an original way to quantify erythrocyte aggregation using the echogenicity of blood. We have developed and A-mode ultrasound scanner coupled with an oscilloscope and a computer allowing the analysis of ultrasonic signals produced by erythrocytes. A closed measurement chamber connected to a calibrated roller-type blood pump where blood was perfused was used. The echogenicity of blood was determined at different shear rates. Dextran, fibrinogen and other high molecular weight substances were added to increase erythrocyte aggregation. Changes in red blood concentration was also tested. An increase in blood echogenicity rate was observed at low shear. At a given shear rate blood echogenicity increased when fibrinogen or dextran were added. Such determination of the echogenicity of flowing blood in vitro will provide an approach to the quantification of erythrocyte aggregation in vivo circulation, especially in the veins where low shear rates are observed.

Assessment of red blood cell aggregation with dextran by ultrasonic interferometry.

Aggregation of human red blood cells (RBCs) induced by dextrans of various molecular weight has been studied by using a new ultrasonic interferometry method. This method, based on A-mode echography, allowed for the measurement of the accumulation rate of particles on a solid plate which is related to their sedimentation rate (i.e., to their mean size). The initial aggregation process, the mean and the maximum sedimentation rate of aggregates and the packing of the sedimented RBCs have been investigated. Effects of hematocrit, molecular weight of dextrans and inhibition by dextran 40 on the RBC aggregation induced by dextran of higher molecular weight have been determined by analysing variations of the aggregate size. Results obtained confirm the aggregation effect of dextrans of molecular weights equal or higher than 70,000 dalton and disaggregation effect of dextran 40,000 dalton on aggregation by dextrans of higher molecular weight.

Determination of particle sedimentation rate by ultrasonic interferometry: role of particle size, density and volume fraction.

The sedimentation rate (SR) of non-aggregated spherical particles in suspension was determined using an ultrasonic interferometry technique (Echo-Cell); this method is based on A-mode echography and measures the rate of formation of a sediment on a solid plate during settling. The particle accumulation rate, which is related to SR, is obtained from the interference of two waves reflected by two interfaces: one between the plate and the sediment and the other between the sediment and the suspension. Studies were carried out at 25 degrees C using latex spheres of different diameters (7 to 20 micron) and densities (1.062 to 1.190 g/cm3) suspended in distilled water at various volume fractions (1% to 5%). As anticipated by the Stokes model, linear relations were found between SR and both particle density and the square of particle radius. Experimental SR values decreased with increasing suspension particle concentration; these concentration effects were in good agreement with those predicted by the Steinour model. Our results thus serve to validate the theoretical aspects of the Echo-Cell method and suggest its usefulness as a tool for studies of RBC interaction and RBC aggregation.

[Increase of erythrocyte disaggregation shear rate in arterial hypertension]. / Augmentation de la contrainte de cisaillement de désagrégation érythrocytaire dans l'hypertension artérielle.

Aggregation index and critical disaggregation shear rate (which represent the minimum shear rate necessary to break up the aggregates) have been measured for 21 hypertensive and 17 normotensive subjects by a laser technique (erythro-aggregameter SEFAM). A simultaneous measurement of blood viscosity by a Couette viscometer with coaxial cylinders at different shear rate allowed the calculation of critical disaggregation shear stress by the product of critical disaggregation shear rate and blood viscosity. The comparison of the results of normotensive and hypertensive subjects showed a higher aggregation index (22%, p less than 0.0001), critical disaggregation shear rate (19%, p less than 0.002) and critical disaggregation shear stress (29%, p less than 0.004) in hypertensive patients. These alterations might play an important role on development of cardiovascular complication in hypertensive subjects.

[Increase of erythrocyte aggregation in hypertensive men with dyslipidemia]. / Augmentation de l'agrégation érythrocytaire chez les hommes hypertendus dyslipidémiques.

We have already reported that erythrocyte aggregation (EA) is increased in hypertensive subjects. To study the influence of other risk factors in EA, we have measured aggregation index IA and disaggregation shear rate threshold (gamma c) by a laser technique and the biochemical parameters in 16 normotensive normocholesterolemic subjects (NT/NCT) and 45 hypertensive subjects where 17 were normocholesterolemic (HT/NCT), 18 were pure hypercholesterolemic (HT/HCTIIa) and 10 were hypercholesterolemic hypertriglyceridemic (HT/HCTIIb). The results show that IA and gamma c are more important in HT/NCT than NT/NCT patients and much more in patients with hypercholesterolemia and hypertriglyceridemia. The cumulative effects of hypertension and hyperlipidemia merit take into consideration in pathophysiology of cardiovascular complications and could help to new strategy therapeutic developments for treatment of these complications.

Influence of HDL subfractions on erythrocyte aggregation in hypercholesterolemic men. PCVMETRA Group.

Recent studies have suggested that rheological mechanisms may be involved in the pathogenesis of ischemic syndromes in hyperlipidemias. We investigated the association between erythrocyte aggregation and components of lipoproteins in the blood of 60 normotensive, hypercholesterolemic men aged 45 +/- 8 years. The rheological parameters assessed were aggregation index (AI) and disaggregation shear rate threshold (gamma t) as determined by laser reflectometry, plasma fibrinogen, total serum protein, and hematocrit. The lipoprotein variables included total cholesterol, triglycerides, high-density lipoprotein (HDL) cholesterol and its subfractions HDL2 cholesterol and HDL3 cholesterol, apolipoprotein (apo) B, apoA-I, HDL particles containing apoA-I without apoA-II (LpA-I), and HDL particles containing both apoA-I and apoA-II (LpA-I/A-II). Covariables considered for possible confounding effects were age, body mass index, and smoking behavior. Fibrinogen, total serum protein, and both aggregation parameters (AI and gamma t) were elevated in this hypercholesterolemic population. Univariate analysis showed that both AI and gamma t correlated positively with fibrinogen (P < .001) and total serum protein (P < .01) and negatively with HDL2 cholesterol (P < .01) and LpA-I (P < .01); gamma t also provided a positive correlation with LpA-I/A-II (P < .05). A multivariate model analysis demonstrated that HDL2 cholesterol, LpA-I, and LpA-I/A-II also emerged as significant factors influencing erythrocyte aggregation; 60% to 68% of the variance of AI and 47% to 64% of the variance of gamma t could be explained by these factors.(ABSTRACT TRUNCATED AT 250 WORDS)