Hemorheology and vascular control mechanisms

Blood rheology is a well-known determinant of tissue perfusion and, according to the Poiseuille relation, hemodynamic resistance in a constant-geometry vascular network is directly proportional to blood viscosity. However, this direct relationship cannot be observed in all in vivo studies. Further, there are several reports indicating marked differences between the in vivo and ex vivo flow properties of blood. These differences can be explained, in large part, by considering special hemorheological mechanisms (e.g., Fahraeus-Lindqvist effect, axial migration) that are of importance in the microcirculation. Additionally, the influence of altered rheological properties of blood and its components on vascular control mechanisms requires consideration: (1) There is an indirect relation between blood rheology and microvascular tone that is mediated by tissue oxygenation, with a compensatory vasodilation occurring if tissue perfusion is impaired due to hemorheological deterioration; (2) Blood rheology may influence vascular tone through alterations of wall shear stress, which in turn determines endothelial generation of vasoactive substances (e.g., nitric oxide). This latter point is of particular relevance to the field of clinical hemorheology, since enhanced red blood cell aggregation has been shown to affect nitric oxide synthesis and thus control of vascular smooth muscle tone. Such multiple pathways by which hemorheological changes can affect vascular resistance help to explain the continuing difficulty of predicting correlations between in vivo and ex vivo hemorheological behavior; they also suggest the need for continued experimental studies in this area.     

Hemorheological mechanisms in Alzheimer's disease

OBJECTIVE: The aim of the present study was to elucidate the underlying mechanisms responsible for hemorheological abnormalities in elderly patients with Alzheimer's disease (AD). SUBJECTS AND METHODS: Twenty-one patients with AD and twenty-three age-matched healthy controls (CON) were studied. We used a controlled-shear rate rheometer generating various flow fields in vitro for simulating blood flow in vivo. The applied experimental techniques provided valid and quantitative data for the analysis of hemorheological abnormalities associated with AD. Principal blood biochemical parameters and hemorheological parameters, including blood viscosity, erythrocyte deformability, erythrocyte aggregation and oxygen transport efficiency of blood were assessed. RESULTS: The results show no statistically significant difference in most of the blood biochemical parameters between the AD patients and the CON, except that fibrinogen concentration and mean corpuscular cell volume level of erythrocytes (MCV) were significantly higher in the AD patients. Hemorheological parameters including blood viscosity, plasma viscosity, and blood viscoelasticity in the AD patients were considerably higher than the respective factors in the CON. Owing to the MDA levels of the AD patients being significantly higher than that of the CON, the AD patients also showed a decrease in erythrocyte deformability and an increase in blood flow resistance despite the lack of any significant difference in erythrocyte rigidity. In addition, the erythrocyte aggregation of AD patients was higher than that of the CON and reduced oxygen transport efficiency of blood was observed in the AD patients. CONCLUSIONS: The hemorheological abnormalities found in AD patients may be explained by the parallel findings of oxidative damage on erythrocyte membranes that could result in a decrease of erythrocyte deformability. Furthermore, the oxidative stress-induced elevation of fibrinogen concentration could lead to accelerated erythrocyte aggregation as a consequence of a rise in blood viscosity and blood viscoelasticity. Taken together, these factors may impair the oxygen transport efficiency of blood in AD patients.     

Blood hyperviscosity syndrome in type I diabetes mellitus

Blood rheological properties and oxygen metabolism were investigated in 50 patients with type I insulin dependent diabetes mellitus. Metabolic and morphological phases of the blood hyperviscosity syndrome were defined in relation to the nature of hemorheological disturbances. Oxygen metabolic disturbances were of unidirectional type manifesting themselves in a decrease in tissue oxygenation and the development of tissue hypoxia. Such disturbances of rheological properties and oxygen metabolism caused the development and progression of diabetic microangiopathies. Therefore pharmacological correction of hemorheological disturbances is a reserve method of therapy of patients with diabetes mellitus.     

About spread of local cerebral hemorheological disorders to whole body in critical care patients

PURPOSE: The aim of the present pathophysiological studies was elucidation of the feasible mechanism of spread of the blood rheological disorders from the cerebral to systemic circulation, and vice versa. METHODS: The investigation was carried out in the critical care patients with the brain tissue damage related to stroke (cerebral ischemic infarcts as well as parenchymatous and subarachnoid hemorrhages). The applied diagnostic techniques provided us with valid and quantitative data revealing the degree of the red blood cell aggregability, the value of local hematocrit, and the blood plasma viscosity in the cerebral and systemic circulation. In addition, rabbits experiments were carried out for analysis of the hemorheological disorders associated with the brain damage. RESULTS: Despite the local character of the patients primary brain damage, the hemorheological disorders were found regularly spread not only over the cerebral hemispheres, but even also the systemic circulation. Under such conditions they might cause the generalized brain tissue damage and play significant role in the subsequent damage-cascade of the whole brain. In addition, the rabbits experiments demonstrated pronounced hemorheological disorders in the cerebral cortex capillaries: increase of their numbers with RBC enhanced aggregation and blood stasis, as well as with lowering of the RBC deformability in the narrow capillary lumina. These changes befell simultaneously with increase of water contents in the cerebral tissue evidencing for edema development in the brain. CONCLUSION: Local cerebral hemorheological disorders might spread over the whole brain via the systemic circulation, thus promoting a generalized brain damage and being responsible for the critical state of the patients.     

Cardiovascular risk factors and hemorheology. Physical fitness, stress and obesity

To date there is little information about hemorheological data in the presence of secondary risk factors. Inter- and intraindividual comparisons of hemorheological parameters show that fitness has a significant influence on blood fluidity as quantified by ex vivo measurements of blood and plasma viscosity, red cell filterability and red cell aggregation. In fitter individuals blood is more fluid. Similar observations can be made with stress. Prolonged psychoemotional stress leads to a loss in blood fluidity and red cell filterability. Finally a comparison between excessively obese patients and healthy controls reveals a deterioration in hemorheological parameters in the obese group. These results, together with reports from the literature suggest that all accepted cardiovascular risk factors are associated with abnormalities in the flow properties of blood. It is proposed that partly the same phenomena are involved in the genesis of atherosclerotic lesions and influence rheological properties of blood.     

Blood rheology and aging

The flow properties of blood play significant roles in tissue perfusion by contributing to hydrodynamic resistance in blood vessels. These properties are influenced by pathophysiological processes, thereby increasing the clinical relevance of blood rheology information. There is well-established clinical evidence for impaired blood fluidity in humans of advanced age, including enhanced plasma and whole blood viscosity, impaired red blood cell (RBC) deformability and enhanced RBC aggregation. Increased plasma fibrinogen concentration is a common finding in many studies owing to the pro-inflammatory condition of aged individuals; this finding of increased fibrinogen concen-tration explains the higher plasma viscosity and RBC aggregation in elderly subjects. Enhanced oxidant stress in advanced age is also known to contribute to altered blood fluidity, with RBC deformability being an important determinant of blood viscosity. Several studies have shown that physical activity may improve the hemorheological picture in elderly subjects, yet well-designed observational and mechanistic studies are required to determine the specific effects of regular exercise on hemorheological parameters in healthy and older individuals.     

Blood rheology as a marker of venous hypertension in patients with venous disease

During chronic venous insufficiency (CVI), several microvascular functional abnormalities, due to venous hypertension, develop. To look for blood rheological consequences of venous hypertension "VH", whole blood viscosity and its main determinants were measured in 11 normal controls and 36 patients with CVI exposed to a short-term experimental VH. Patients were subdivided into 2 groups according to the severity of their disease. Blood was taken from a foot vein before and after VH, which was induced by appling a pneumatic tourniquet to 100 mmHg for 15 minutes. Whole blood viscosity at low and high shear rates, red blood cell (RBC) aggregation, RBC rigidity, plasma viscosity and proteins as well as red and white blood cell (WBC) counts were recorded. Patients at baseline, i.e., before application of the tourniquet, showed several hemorheological abnormalities such as an increased RBC aggregation, increased low shear rate viscosity, and a significant elevation in plasma fibrinogen level. Patients with more severe CVI had more marked hemorheological changes. The short term VH in patients led to further aggravation of these changes. There were also at baseline lower values, however not significantly, of hematocrit and RBC count, suggesting that hemoconcentration is not a feature of CVI. These same parameters were slightly, however not significantly, increased after VH, indicating a fluid escape into the extravascular space. A significant fall in WBC count was also observed after VH, in keeping with the white cell trapping hypothesis. In conclusion, even a short-term VH is able to induce several hemorheological impairments, which are probably involved in the failure of the microcirculation and hence the initiation of tissue damage in patients with CVI.     

Microcirculatory Stasis Induced by Hemorheological Disorders: Further Evidence

Objective : Reinvestigate the microcirculatory alterations immediately responsible for blood rheological disorders and blood stases, which are related to red blood cell (RBC) aggregation in capillaries. Methods : Blood rheological disorders were produced by significantly intensified intravascular red blood cell aggregation in the intestinal mesentery of Wistar rats and in the cerebral cortex of Chinchilla rabbits, either systemically (by intravascular administration of high molecular-weight dextran) or locally (by increase of high-molecular compounds in blood plasma inside individual or groups of capillaries). Results : Under conditions where the microvascular lumina were not decreased and the arteriolovenular pressure gradients got even higher, the significantly enhanced intravascular RBC aggregation resulted in the slowing down of blood flow in the microvessels to a full stop. Conclusion : A significant increase in microvascular RBC aggregation results in local hemorheological disorders, which is, in all probability, related to derangement of the blood-flow structuring in microvessels.     

Hemorheological disorders during ischemic brain infarcts in patients with and without diabetes mellitus

The aim of the present study was the comparative analysis of the role of specific hemorheological derangements in the pathogenesis of ischemic brain infarcts with and without diabetes mellitus. Blood plasma viscosity, as well as red blood cells (RBC) aggregability were quantitatively investigated in all patients during the study. Both of the above mentioned indices of hemorheological disorders were significantly higher in the patients with brain infarcts and diabetes mellitus as compared to the control and the group of ischemic brain infarcts without diabetes. During the ischemic stroke, blood plasma viscosity was increased by a mean of 9.2 per cent in the first and by a mean of 17.6 per cent in the second group of patients. As to the erythrocyte aggregability index, it was changed considerably more - by a mean of 113.8 per cent during stroke without diabetes, while in the diabetic patients the RBC aggregability index was found to be increased by a mean of 147.3 per cent. Ischemic brain infarcts in patients with diabetes mellitus were associated with a significant increase of the patients' blood rheological disorders in all the investigated cases.     

Hemorheological abnormalities in stable angina and acute coronary syndromes

The pathophysiological abnormalities of stable angina (SA) and acute coronary syndromes (ACS) may, in part, be promoted by fluid forces associated with local blood flow and hence by the rheological properties of blood. This study evaluated several hemorheological parameters in 16 healthy controls and in 16 SA, 18 unstable angina (UA) and 19 acute myocardial infarct (AMI) patients; all patients underwent diagnostic angiography following blood sampling. Rheological measurements included whole blood viscosity, plasma viscosity and RBC aggregation via erythrocyte sedimentation rate (ESR) and Myrenne aggregometer indices. Compared to controls, RBC aggregation was significantly elevated in all patient groups (p<0.001), with the rank being AMI>UA>SA. RBC aggregability as tested in 70 kDa dextran exceeded control in all patients. Blood viscosity values calculated at 40% Hct, plasma viscosity and yield shear stress values followed the same pattern (AMI>UA>SA>control); increases of inflammatory markers (i.e., WBC count, hs-CRP) were elevated in all patient groups in the order AMI>UA>SA. Our study thus indicates an association between hemorheological abnormalities and the severity of coronary artery disease, and suggests the merit of evaluating whether therapeutic interventions that normalize blood rheology may reduce the incidence and/or progression of coronary artery disease.     

Influence of plasmatic lipids on the hemorheological profile in healthy adults

Some hemorheological parameters constitute risk factors for ischemic cardiovascular events. Most of these hemorheological factors are determined by the erythrocyte intrinsic properties and the high molecular weight plasmatic proteins, especially fibrinogen. The contribution of the plasmatic lipids to hemorheological factors is not well established. With this aim we determined hemorheological parameters in 112 healthy volunteers (62 males, 50 females) aged 35+/-10 years, range 19-54 years, members of our hospital staff. A complete set of rheological test was performed. Blood viscosity (BV) 230 sec(-1), plasma viscosity (PV), erythrocyte aggregation index (EAI), erythrocyte elongation index (EEI), hematocrit and fibrinogen. We also determined plasmatic lipids including total cholesterol (T-Ch) and its fractions (HDL-Ch, LDL-Ch, VLDL-Ch), triglycerides, lipoproteins (Apo B, Apo A(1), B/A(1)). Exclusion criteria were concomitant cardiovascular risk factors or any other associated pathology. Our results show a positive correlation between BV 230 sec(-1) and triglycerides (r=0.335) and negative with HDL-Ch (r=-0.451) (p=0.01), respectively; PV shows a positive correlation with T-Ch (r=0.297), LDL-Ch (r=0.298) and Apo B/A (r=0.290) (p=0.01). The EEI was negatively correlated with TG (p=0.05). Of all the rheological parameters evaluated, EAI is the factor which shows the highest significant correlation with plasmatic lipids: T-Ch (r=0.515), TG (r=0.303), LDL-Ch (r=0.507) and Apo B/A ratio (r=0.403); (p=0.01). These results suggest that plasmatic lipids contribute to modulate the blood rheological properties, slowing blood flow, favouring the development of atherothrombotics events, especially in stenotic areas or bifurcations in the vascular tree.     

Capillary rarefaction and abnormal cardiovascular reactivity in hypertension

OBJECTIVE: To determine the effects of capillary rarefaction on cardiovascular reactivity and microcirculatory functioning in essential hypertension. DESIGN: Hypertension is associated with abnormal cardiovascular reactivity and increased vasoconstriction. Capillary rarefaction amplifies these abnormalities, which modify microcirculatory hemodynamics. Hence this study of the hemorheological pattern and the veno-arteriolar reflex in hypertensive patients and normotensive control subjects. METHODS: Sixty-one men with never-treated essential hypertension and capillary rarefaction (< 80 capillaries per field) and 20 age-matched and sex-matched controls underwent a strenuous cycle ergometer test to monitor, during exercise and recovery, the blood pressure profile and the hemorheological pattern: blood viscosity at low shear, hematocrit and leukocyte counts, soluble P-selectin levels, and red and white blood cell filterability rates. The veno-arteriolar reflex was determined by laser-Doppler flowmetry before exercise and at recovery.RESULTS Hypertensive men with < or = 72 capillaries per field had an abnormal hemorheological profile before exercise. The physiological response to exercise was observed only in the controls and in hypertensives with > or = 73 capillaries per field. Abnormal responses to exercise worsened as capillaries were more rarefied. At recovery, hemorheological parameters in hypertensives with 65-72 capillaries per field returned to baseline, remaining significantly (P < 0.05) different to control values. Variations in the hemorheological pattern in hypertensives with < 64 capillary per field persisted at recovery. The veno-arteriolar reflex followed the same pattern. CONCLUSION: A reduced microvascular network may contribute to abnormal cardiovascular reactivity and to exercise-induced rheological abnormalities in hypertension.     

Potential of Rheopheresis for the Treatment of Acute Ischemic Stroke When Initiated Between 6 and 12 Hours

Abstract: Improvement of hemorheology is one of the most important approaches in the treatment of acute ischemic stroke. We investigated the influence of extracorporal rheopheresis (ER) on cerebral blood flow in patients with acute ischemic stroke and evaluated its therapeutic effect. Thirty‐three patients (rheopheresis group, 17; control group, 16; mean age 64 ± 10 years) with acute ischemic stroke were included in our prospective randomized trial. The first treatment was started within 12 h after onset of symptoms, and treatment was repeated 3 times at an interval of 24 h. Hemorheological parameters were measured before and after each session. The cerebral blood flow was analyzed using ^99mTc‐ECD‐SPECT. The functional and neurological outcomes were determined by follow‐up investigations after 3 months. The hemorheological parameters were significantly different between the rheopheresis group (18% decrease of plasma viscosity, 55% decrease of red blood cell aggregation) and the control group (no decrease of both parameters). The single photon emission computed tomography (SPECT) analysis showed early reperfusion in 35% of the patients treated with rheopheresis and in 37% of the control group (NS). There were no differences in the neurological outcomes between the 2 groups. Extracorporal rheopheresis is practicable and safe. It rapidly and consistently improved the hemorheological parameters. Although this did not impact on cerebral perfusion or clinical outcome in patients with acute ischemic stroke in this report, we propose that ER deserves to be further evaluated by initiating the first treatment within 6 h post‐insult.     

Existe-t-il un mécanisme physique d'hémolyse chez les patients porteurs d'une anémie hémolytique autoimmune?

In autoimmune hemolytic anemia, the presence of antibodies on the erythrocyte membrane results in hemolysis through an immune process, but does it not alter the rheological properties of RBC, thus mechanically contributing to hemolysis? This study was designed to study the rheological properties of erythrocytes sensitized with IgG-type antibodies.The study involved 20 patients with anemia and positive direct antiglobulin test, including 12 with straightforward hemolysis, 10 samples sensitized in vitro, and 20 controls.The following hemorheological parameters were studied: erythrocyte filtration, blood and plasma viscosities, titration of ATP and 2–3 DPG, erythrocyte morphology under scanning electron microscopy.The results showed increased erythrocyte rigidity (p<0.025) as well as higher blood viscosity compared to controls with similar hematocrit values, and unaltered ATP and 2–3 DPG (consistently with SEM observations). These hemorheological disorders were more noticeable in patients with a clear-cut hemolysis, and there was a correlation between the increase in erythrocyte rigidity indices and the hemolytic parameters, especially haptoglobin (p<0.001). The in vitro study confirmed the results obtained ex vivo.To conclude, the mechanical properties of antibody-coated erythrocytes are impaired, which may add up to the immunological mechanism to favor hemolysis in the spleen.     

Improving effects of epigallocatechin-3-gallate on hemorheological abnormalities of aging Guinea pigs.

BACKGROUND: Epigallocatechin-3-gallate (EGCG) is the most potent antioxidant of all the green tea catechins. The objective of the present study was to find out whether it improved the age-induced hemorheological abnormalities or not. METHODS AND RESULTS: Twenty-four-month-old aging guinea pigs were used to test the effects of EGCG on hemorheological properties. Orally feeding EGCG at 30 mg x kg(-1) x day (-1) for 28 days resulted in a decrease in erythrocyte membrane malondialdehyde, and further improved erythrocyte deformability and blood viscosity at high and middle shear rates. In addition, it also significantly reduced erythrocyte aggregation, and improved blood viscosity at low shear rates and viscoelasticity at oscillatory flow. Consequently, efficiency of blood oxygen transport in aged guinea pigs increased after administration with EGCG. CONCLUSIONS: Orally feeding EGCG 30 mg x kg(-1) x day(-1) for 28 days significantly improves the abnormal hemorheological parameters. These results suggest that EGCG has considerable potential as a substantial component for the development of new drugs or functional foods in improving the age-induced hemorheological abnormalities.     

Hemorheological parameters in correlation with the risk factors for carotid atherosclerosis

The study aimed to follow the relationship between some hemorheological variables and the main risk factors (RF) for carotid atherosclerosis (CA). Carotid atherosclerosis was evaluated by color duplex sonography of the carotid arteries in 18 patients with RF for CA, 31 patients with transient ischemic attacks (TIAs), 21 patients with chronic unilateral cerebral infarctions (UCI) and 11 healthy subjects without RF for CA. The examined hemorheological variables were whole blood and plasma viscosity, hematocrit and fibrinogen. They were correlated with intima-media thickness (IMT) of the common carotid and the internal carotid arteries and with other main RF for CA: hypertension, diabetes mellitus, coronary heart disease, and hyperlipidemia. The hemorheological investigation showed an increase in blood and plasma viscosity at different shear rates and it was more expressed in the group with UCI. The neurosonographic investigation revealed an increase in the IMT and carotid artery stenoses in the patients' groups with CVD. These were also more frequent in the patients with UCI. Different correlations were established between the hemorheological parameters, the IMT of the carotid arteries and other RF for CA. In the group with UCI, the hematocrit and the whole blood viscosity correlated significantly with the IMT, arterial blood pressure and cholesterol values. These data confirm the influence of the hemorheological parameters on carotid blood vessel walls and on blood flow in patients with CVD.     

Hemorheological disturbances and cognitive function in patients with cerebrovascular disease

The aim of the study was to follow the relationship of the hemorheological variables with the cognitive functions in patients with ischemic cerebrovascular disease (CVD). The patient material comprised 117 patients with CVD, distributed in two main groups: 44 with transient ischemic attacks (TIAs) and 73 with chronic cerebral infarctions (CCI), 48 of them being unilateral (UCI) and 25 bilateral (BCI). Additional relative distribution according to the mean arterial blood pressure (MABP) values or to the presence of pathological asymmetries of the hemispheric cerebral blood flow (CBF) was made. The main hemorheological variables: hematocrit (Ht), fibrinogen (Fib) and plasma viscosity (PV) were examined. The cognitive functions were assessed with a psychological test battery for evaluation of the general cognitive state, the nonverbal intellect, the episodic memory, the selective attention and the executive functions. The hemorheological investigation revealed predominant increase of PV. The results of all neuropsychological tests showed significant impairment in the patients with CCI in comparison to TIAs. Fibrinogen correlated best with the psychological parameters. Its increase was associated with disturbance of the nonverbal intellect and the general cognitive capacity in the patients with CCI and BCI. In the presence of lower MABP or lack of pathological asymmetries the correlations of Fib and PV with the psychological scores predominated. The results of our study reveal distinct association between the blood rheological properties and the cognitive functions in the patients with ischemic CVD, which is probably based not only on vascular but also on other nonvascular mechanisms.     

An in vitro hyperbaric oxygen system for evaluation of free radical damage and protection by catechins on hemorheological parameters

Free radicals play a critical role in causing hemorheologic abnormality which is highly correlated with cardiovascular disease and stroke. In this study, we established an in vitro model to evaluate the influence of free radical attacks on hemorheological parameters. A well-sealed chamber with hyperbaric oxygen was used to simulate an environment of free radical attacks. Hemorheological parameters, including whole blood viscosity, erythrocyte membrane lipid peroxidation, and erythrocyte deformability, were investigated. We then used the in vitro model to evaluate the anti-free radical effects of some well-known catechin antioxidants, such as epigallocatechin gallate (EGCG), (-)-epicatechin 3-gallate (ECG), and (-)-epigallocatechin (EGC) on abnormal hemorheological parameters induced by hyperbaric oxygen. The results show that an increase in oxygen partial pressure (1.0, 1.5, 2.0 and 2.5 atm) and exposure time (4, 8, 12 and 16 h) resulted in elevated free radical formation and viscosity of whole blood, enhanced lipid peroxidation in erythrocyte membranes, but decreased erythrocyte deformability. In addition, EGCG, ECG, and EGC (0.1, 0.5 and 1.0 μM) effectively ameliorated hemorheologic abnormality and enhanced erythrocyte deformability. Therefore, this study has provided an in vitro hyperbaric oxygen model to rapidly screen or assess the efficacy of functional foods and drugs in the prevention or improvement of hemorheologic abnormality.     

Blood fluidity and thermography in patients with diabetes mellitus and coronary artery disease in comparison to healthy subjects

The study aimed at initial determination and analysis of selected rheological parameters of blood in the group of diabetics and patients after myocardial infarction and compare the results to the symptoms observed in thermographical studies. The parameters studied were: whole blood viscosity, plasma viscosity, relative blood viscosity and hematocrit value. A group of 60 subjects took part in the study. The control group (20 persons) included the healthy subjects who had never suffered from any circulatory system disorders and who did not receive any drugs affecting the hemorheological parameters. The group of diabetics included 18 patients and the group after myocardial infarction included 20 patients. Blood viscosity measurements were performed by means of a rotary-oscillatory reometer Contraves LS 40 at the decreasing shear rate ranging from 100-0.01 s(-1) during a period of 5 minutes. For each blood sample the hematocrit value was measured using the standard method. The plasma viscosity was calculated from the linear regression of the shear rate dependence of the shear stress measured by means of the Contraves LS 40 reometer.     

Improvement of hemorheologic parameters in hemodialyzed patients treated with human recombinant erythropoietin

Recombinant human erythropoietin (rhu EPO) is the choice treatment of dialytic anemia; however, this therapy has side effects due to the increased number of blood components involved. It seemed to us worth assessing, by hemorheological study, the impact of such a treatment on blood flow properties, already impaired in this type of patients. This study was designed to measure the evolution of hemorheological parameters in 16 hemodialysed patients before and after 2.3 and 6 months of treatment with rhu EPO. Hemorheological work-ups included: erythrocyte filtration with a hemorheometer; blood and plasma viscosities (LS30), ATP and 2.3 DPG, RBC aggregation (Sefam erythroaggregameter), RBC morphology under a scanning electron microscope; blood counts and full biochemical work-ups were performed to explore renal function. The results showed, besides a significant increase in hemoglobin: normalized rigidity index, reflecting the better deformability of erythrocytes; a moderate increase in blood viscosity with uncorrected hematocrit, becoming significant after 6 months of treatment. This increase however did not reach the values that could be expected with the increased hematocrit (it was probably balanced by improved erythrocyte deformability, which is confirmed by the fact that with corrected hematocrit, blood viscosity decreases during treatment). Studying erythrocyte aggregation in hemodialysed patients reveals, in the absence of any treatment, a decrease in aggregation time and a higher dissociation threshold, which reflects a tendency to erythrocyte hyperaggregation enhanced by erythropoietin.(ABSTRACT TRUNCATED AT 250 WORDS)