The aggregation and disaggregation behaviors of red blood cells were investigated in 17 nonnotensive 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< 0.001) and disaggregation shear rate (20%, p<0.01) and shear stress (18%, p<0.01) were observed in hypertensive subjects when compared with nonnotensive 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. 1 The aggregation of RBC is a reversible phenomenon that occurs with macromolecules bridging the membranes of adjacent cells, and it is influenced by 1) the shearing force of blood, 2) the properties of erythrocytes (concentration, deformability, surface charge, and shape), and 3) the bridging force of high molecular weight plasma proteins.2 " 4 This phenomenon represents an equilibrium between adhesive forces (macromolecules bridging force), repulsive forces (electrical charges on RBC surface), 5 and mechanical forces (shear stress). -6 When the adhesive force is increased in pathological conditions, the shear stress required to break up RBC aggregates would become elevated.In hypertension, increases of red blood cell aggregation were largely extrapolated from blood viscosity measurements at low shear rates. 7 -11 In contrast, few studies have used direct quantitative methods to evaluate red blood cell aggregation in hypertension.12 Relatively little data are available on the shear stress needed to break up the aggregated RBC in normal and patho- A preliminary report of this work was presented at the 64th Scientific Sessions of the American Heart Association, Anaheim, Calif., November 11-14, 1991, and was published in abstract form (Razavian SM, Levenson J, Del-Pino M, Simon A: The shear stress for disaggregating red blood cells is increased in hypertension. Circulation 1991;84:II-53).Supported by grants from the Institut National de la Santi et de la Recherche Medicale and the Institut Jean Merlen.Address for reprints: Dr. Jaime Levenson, Centre de M6decine Preventive Cardiovasculaire, H6pital Broussais, 96 Rue Didot, 75674 Paris CEDEX 14, France.Received May 7,1991; accepted in revised form April 13, 1992. logical cond...
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 (yt) as determined by laser reflectometry, plasma fibrinogen, total serum protein, and hematocrit. The lipoprotein variables included total cholesterol, triglycerides, highdensity lipoprotein (HDL) cholesterol and its subfractions HDL 2 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 yt) were elevated in this hypercholesterolemic population. Univariate analysis showed that both T he fluidity of blood plays an important role in the physiological behavior of the circulation, and its alteration might promote cardiovascular complications in situations associated with low-flow states. 1In this condition red blood cells (RBCs) aggregate due to the increase in the bridging force of high-molecularweight plasma proteins.12 Among these proteins, some are considered to be cardiovascular risk markers (eg, lipoproteins, fibrinogen) and are associated with increased plasma and whole-blood viscosity.313 Associations between rheology and components of lipoproteins in human blood are reported. Studies in patients with various forms of hyperlipoproteinemia show a concentration-dependent increase in plasma viscosity for lowdensity lipoprotein cholesterol (LDL-C) and chylomicrons and hence, for total triglycerides. 9 ' 10 These earlier studies are in line with the positive linear correlation of plasma viscosity with total cholesterol and apolipoprotein (apo) A-II and apoB observed in a recent study. 11Moreover, both blood viscosity 11 and erythrocyte aggregation 12 are negatively related to high-density lipoprotein cholesterol (HDL-C) concentration, which is known to be inversely correlated with coronary heart disease risk. 14 Furthermore, HDL may also be separated according to apolipoprotein composition, leading to at least two species of particles: LpA-I, which contains apoA-I without apoA-II, and LpA-I/A-II, which contains both apoA-I and apoA-II. 15 These heterogeneous HDL subfractions seem to have distinct metabolic roles, but the specific effect of one or another particle on the atherosclerotic process remains unclear. 1621 In the present study we investigated the relation of lipoprotein components, and especially HDL subfractions, to the aggregation and disaggregation of RBCs in a population of asymptomatic, hypercholesterolemic, normotriglyceridemic, normotensive subjects. Methods Selection of Su...
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