Effects of leucocyte depletion on rheologic properties of human CPDA-1 blood

BACKGROUND AND OBJECTIVES: Leucocyte depletion improves the quality of stored blood units. We have studied its role on blood viscosity. MATERIALS AND METHODS: Viscosity of CPDA-1 blood units was measured in a Couette viscometer at shear rates of 94.5 and 0.1 s(-1) prior to and following filtration with the Leukotrap((R)) A1 system on day 0 and after 21 days at +4 degrees C. RESULTS: On day 0, high but not low shear viscosity was significantly decreased. The red blood cell morphology was unaffected. On day 21, blood viscosity was increased similarly for unfiltered and filtered samples at both shear rates. The echinocytosis observed after storage correlated with the increase in viscosity. CONCLUSION: Leucocyte depletion is associated with a decrease in high shear viscosity. This effect is, however, completely lost after 21 days.     

Effect of shear rate variation on apparent viscosity of human blood in tubes of 29 to 94 microns diameter

In order to test the hypothesis that the increase of vascular resistance observed in vivo at low flow rates is due in part to blood rheological properties, the apparent viscosity of human blood was measured in small tubes in a range of shear rates. Pressure-flow relationships were obtained in vertical glass tubes (29 to 94 microns i.d.) perfused with blood at hematocrits between 0.13 and 0.65. Viscosity of blood and plasma was calculated using Poiseuille's law. With the exception of data obtained in the largest tube at a hematocrit of 0.6, relative blood viscosity was found to be independent of shear rate in the range between 1 and 120 s-1. Microscopic observation revealed pronounced red cell aggregation at low shear rates. Velocity profiles obtained by the use of fluorescence-labelled red cells showed increased blunting with decreasing shear rate. The Fahraeus-Lindqvist effect was evident in a reduction of viscosity with tube size at a given feed hematocrit. The observed constancy of apparent blood viscosity with decreasing shear is attributed to the opposing effects of a cell-depleted marginal layer and red cell aggregation or deformation in the cell core. The findings indicate that the increase of vascular resistance at low arterial pressure cannot be explained by shear-dependent changes of apparent blood viscosity observed in macroviscometers.     

Elevated blood viscosity in patients with borderline essential hypertension

In patients with borderline hypertension, total peripheral resistance (TPR) is either elevated or abnormally related to cardiac output. Since blood viscosity is one determinant of TPR, we compared various components of blood viscosity in 25 patients with borderline hypertension and 25 normal subjects. Under all experimental blood flow conditions examined, blood viscosity directly correlated with systolic and diastolic blood pressure (p less than 0.05 or better) and was greater in the hypertensive than in normal subjects. Venous hematocrit and plasma viscosity were higher in the hypertensive patients. These latter rheologic abnormalities accounted for the increased blood viscosity at higher shear rates. At lower shear rates, increased red cell aggregation, primarily mediated by elevated fibrinogen concentration, accounted for the higher blood viscosity in the hypertensive subjects. We conclude that even relatively small elevations in arterial pressure are associated with increased viscous resistance of blood to flow, and that the increased blood viscosity is a consequence of increased hematocrit, plasma viscosity, and red cell aggregation.     

Two-phase model for prediction of cell-free layer width in blood flow

This study aimed to develop a numerical model capable of predicting changes in the cell-free layer (CFL) width in narrow tubes with consideration of red blood cell aggregation effects. The model development integrates to empirical relations for relative viscosity (ratio of apparent viscosity to medium viscosity) and core viscosity measured on independent blood samples to create a continuum model that includes these two regions. The constitutive relations were derived from in vitro experiments performed with three different glass-capillary tubes (inner diameter = 30, 50 and 100 μm) over a wide range of pseudoshear rates (5–300 s^− 1). The aggregation tendency of the blood samples was also varied by adding Dextran 500 kDa. Our model predicted that the CFL width was strongly modulated by the relative viscosity function. Aggregation increased the width of CFL, and this effect became more pronounced at low shear rates. The CFL widths predicted in the present study at high shear conditions were in agreement with those reported in previous studies. However, unlike previous multi-particle models, our model did not require a high computing cost, and it was capable of reproducing results for a thicker CFL width at low shear conditions, depending on aggregating tendency of the blood.     

Failure of pentoxifylline or cilostazol to improve blood and plasma viscosity,fibrinogen, and erythrocyte deformability in claudication

Peripheral artery disease is associated with altered blood rheologic properties, including increased viscosity and decreased red blood cell (RBC) deformability. Pentoxifylline and cilostazol are available therapies for intermittent claudication. Improvement of blood viscosity and erythrocyte deformability have been cited as potential mechanisms of action for pentoxifylline. Cilostazol is a new drug with antiplatelet and vasodilating activity, but the mechanism by which it promotes an improvement in walking is not known. This study was performed to evaluate and compare the hemorheologic effects of pentoxifylline and cilostazol on viscosity, fibrinogen levels, and erythrocyte deformability when administered to adults with moderate to severe claudication. A double-blind, controlled study was conducted and included 59 patients (46 male, 13 female; mean age 65 yr) randomized to pentoxifylline 400 mg orally thrice daily (n=20), cilostazol 100 mg orally twice daily (n=19), or placebo (n=20); all subjects were observed for 24 weeks. Walking ability was assessed before, during, and at the conclusion of treatment by standard constant speed, variable grade treadmill testing. Erythrocyte deformability was measured by passage of washed RBCs, 10% hematocrit in phosphate buffered saline (PBS), through a polycarbonate membrane with 4.7 to 5.0 microm pores. Whole blood and plasma viscosity were measured using a cone/plate viscometer at variable shear rates (from 4.5 to 450 sec(-1)). Erythrocyte sedimentation rate was measured by a modified Westergren technique. Fibrinogen was assayed by a commercial reference laboratory. Plasma viscosities did not change significantly in any treatment group. Within-group comparisons demonstrated a significant (p<0.01) drop in whole blood viscosity (week 24 compared with week 0) for cilostazol-treated subjects (at shear rates of 45, 90, 225, and 450 sec(-1)), but these changes were not significantly different from those in the placebo group. There were no significant changes in whole blood viscosity for subjects treated with pentoxifylline or placebo. There were no significant changes in erythrocyte deformability, fibrinogen, or erythrocyte sedimentation rate. A trend toward improved walking distances was noted for both pentoxifylline and cilostazol in comparison with placebo. This trend was not correlated with changes in any underlying rheologic parameter. Ex vivo rheologic characteristics of blood from patients with intermittent claudication are not significantly affected by long-term administration of pentoxifylline or cilostazol. Pentoxifylline did not modulate viscosity or red cell deformability, a finding at variance with its putative mechanism of action. Pentoxifylline cannot be differentiated from cilostazol based on specific hemorheologic effects evaluated in this study. Different mechanisms of action for these medications should be considered.     

Effect of stasis of blood in varicose veins on erythrocyte fragility,with accompanying studies comparing red cells and other blood elements with cubital vein blood

1. Blood from varicose veins was compared with cubital vein blood in 20 patientsin order to determine whether or not the degree of stasis present in varicose veinswould increase red cell fragility. Corollary studies consisted of comparative determinations of red cells, hemoglobin, packed cell volume, white blood cells,platelets and serum proteins.

2. There was no increase in red cell fragility in the varicose vein specimen, indicating that the theory that minor degrees of intravascular erythrostasis contribute substantially to some of the hemolytic anemias is untenable.

3. There was a small but statistically significant elevation in red cells per cu.mm. in varicose vein blood as compared with blood from cubital veins. There wasa suggestive, but not significant, increase in packed cell volume and serum proteinin the varicose vein samples. The evidence indicates a mild degree of hemoconcentration.

4. White cells, platelets and hemoglobin determinations were found to have thesame values in varicose vein blood as in blood from the cubital vein.

     

The erythrocyte in aging

The whole blood viscosity was determined as a function of the shear rate for young and old subjects. The results of these studies indicate that a definite difference does exist in the viscosity of whole blood. This difference is related to the age, morphology, mean corpuscular volume and hemoglobin content of the red cell.     

Effect of contrast media products on the erythrocyte aggregation and deformability in vitro

It has been suggested that contrast media could interfere with red blood cell aggregation, hyperosmolar media leading to an inhibition of red blood cell aggregation whereas non ionic products might induce a sludge phenomenon. We present an in vitro study accompanying two contrast media: 1) Ioxitalamate of sodium and meglumin (ionic, hyperosmolar). 2) Iopaminol (non ionic). In their effect on hemorheological parameters of red blood cell aggregation. Blood samples have been obtained from 7 healthy donors. Contrast media have been tested at increased contrast media (O.1, 1, 2, 10, 100 mg/ml of Iodine in final concentration). The following parameters have been studied: hematocrit, fibrinogen level, erythrocyte aggregation using the Erythro-aggregometer*, whole blood viscosity at 3 different shear rates (0.87, 18.74, 118 sec.-1) using Low Shear 30*. Deformability of red blood cell was assessed by ektacytometry. Osmolarity was controlled in each sample. Results show an inhibition effect of both contrasts media on red blood cell aggregation. There is a concomitant decrease of blood viscosity at low shear rates. On the contrary, apparent viscosity increases at high shear rates in parallel with the contrast media concentration. This effect is more pronounced with ioxitalamate above a concentration of 10 mg/ml. Ektacytometric parameters are not modified by contrast media and this could indicate a complete reversibility of the media-induced alteration on red blood cell. In order to precise the prothrombotic effect on contrast media, hemorheological studies have to be completed by the assessment of their effect on hemostatic parameters.     

Plasma and whole blood viscosity in treated primary polycythaemia

Whole blood viscosity at a range of shear rates (230-0.77 s^_1) and plasma viscosity have been measured in 39 patients with treated primary polycythaemia (idiopathic erythrocytosis and primary proliferative polycythaemia) and 30 age-matched normal individuals. There was a wider range of plasma viscosity and whole blood viscosity values at the same haematocrit (0.46), particularly at the lower shear rates, in the‘polycythaemic’group than the normal group. Hypochromic microcytic red cell changes present in 14 patients in the‘polycythaemic’group did not have any noticeable influence on whole blood viscosity at a given haematocrit value, since plasma protein factors override any possible effect of these red cell changes. The range of observed whole blood viscosity results in the‘polycythaemic’patients at the same haematocrit (0.46) was equivalent to the effect on whole blood viscosity of a rise in haematocrit from 0.41 to 0.51. Since there is such a range of whole blood viscosity at the same haematocrit, the haematocrit alone does not necessarily give a precise assessment of the viscosity of a whole blood sample. Since there is evidence from other publications that blood flow in vivo may be critically influenced by whole blood viscosity, this lack of precision should be considered when treating patients at risk of vascular occlusive episodes.     

Red blood cell aggregation, aggregate strength and oxygen transport potential of blood are abnormal in both homozygous sickle cell anemia and sickle-hemoglobin C disease

Background

Recent evidence suggests that red blood cell aggregation and the ratio of hematocrit to blood viscosity (HVR), an index of the oxygen transport potential of blood, might considerably modulate blood flow dynamics in the microcirculation. It thus seems likely that these factors could play a role in sickle cell disease.

Design and Methods

We compared red blood cell aggregation characteristics, blood viscosity and HVR at different shear rates between sickle cell anemia and sickle cell hemoglobin C disease (SCC) patients, sickle cell trait carriers (AS) and control individuals (AA).

Results

Blood viscosity determined at high shear rate was lower in sickle cell anemia (n=21) than in AA (n=52), AS (n=33) or SCC (n=21), and was markedly increased in both SCC and AS. Despite differences in blood viscosity, both sickle cell anemia and SCC had similar low HVR values compared to both AA and AS. Sickle cell anemia (n=21) and SCC (n=19) subjects had a lower red blood cell aggregation index and longer time for red blood cell aggregates formation than AA (n=16) and AS (n=15), and a 2 to 3 fold greater shear rate required to disperse red blood cell aggregates.

Conclusions

The low HVR levels found in sickle cell anemia and SCC indicates a comparable low oxygen transport potential of blood in both genotypes. Red blood cell aggregation properties are likely to be involved in the pathophysiology of sickle cell disease: the increased shear forces needed to disperse red blood cell aggregates may disturb blood flow, especially at the microcirculatory level, since red blood cell are only able to pass through narrow capillaries as single cells rather than as aggregates.     

Microcirculatory dysfunction in cardiac syndrome X: role of abnormal blood rheology

Objective: Cardiac syndrome X (CSX) is of clinical interest, yet the underlying pathophysiological mechanisms have not been fully elucidated. It is well known that elevated blood viscosity and red blood cell (RBC) aggregation can adversely affect microcirculatory blood flow. The present study was designed to explore whether CSX is associated with abnormalities of blood rheology. Methods: Blood samples were obtained from 152 adult angina patients undergoing diagnostic coronary angiography; geometric and flow‐velocity data were obtained. Rheologic measurements were performed in a blinded manner; 21 subjects were later identified with CSX. Hemorheologic and clinical laboratory data were compared to 21 age‐ and gender‐matched healthy controls. Results: CSX patients had markedly abnormal blood rheology: (1) higher RBC aggregation and aggregability as judged by erythrocyte sedimentation rate and Myrenne indices at stasis and low shear (p < 0.001) and (2) elevated hematocrit‐corrected blood viscosity, plasma viscosity (p < 0.001), and yield stress (p < 0.01). White blood cell counts and high‐sensitivity C‐reactive protein levels were significantly elevated in CSX; coronary‐flow velocities were below normal. Conclusions: Abnormal hemorheologic parameters exist in subjects with CSX and may contribute to the pathophysiology of the disease, presumably via adversely affecting blood flow in the coronary microcirculation. Therapeutic measures aimed at normalizing blood rheology and hence microcirculatory flow should be explored.     

Studies on blood rheology in patients with primary pulmonary hypertension

The rheologic properties of blood were studied in 6 patients with primary pulmonary hypertension (PPH) and compared with those of a control group of 10 healthy subjects. Blood viscosity was studied with a rotational viscometer and blood cell deformability with a filtrometer giving values for clogging particles (CP) and red cell transit time (RCTT). Blood viscosity at varying shear rates was found to be increased both at natural (p less than 0.025-0.005) and standardized hematocrit, 45% (p less than 0.05 at 40 s-1) in patients with PPH. Red cell deformability was reduced as indicated by a significant increase of RCTT (p less than 0.01). Increased values for hematocrit (p less than 0.001), hemoglobin concentration (p less than 0.001), and erythrocyte count (p less than 0.005) were found and decreased values for mean corpuscular hemoglobin concentration (MCHC) (p less than 0.025) and HDL cholesterol (p less than 0.005). Plasma viscosity, white cell deformability, white cell count, mean corpuscular volume (MCV), and plasma fibrinogen concentration did not significantly differ from the values found in the control group. It is concluded that patients with PPH have impaired blood rheology. The hemorheologic abnormalities in these patients may be of hemodynamic significance.     

Abnormalities of blood rheology in familial hypercholesterolaemia: effects of treatment

Whole blood and plasma viscosity, red cell aggregability and deformability, and plasma fibrinogen have been compared between 20 patients with heterozygous familial hypercholesterolaemia (FH), without clinical arterial disease, and 20 age- and sex-matched controls. Plasma fibrinogen was elevated in FH, associated with increased whole blood viscosity at low shear rate, plasma viscosity and red cell aggregation. At high shear rate blood viscosity was not elevated, and red cell deformability was normal. The effect of 12 weeks double blind treatment with cholestyramine 16-24 g/day, pravastatin 20 mg b.i.d. or placebo on blood rheology was studied in 17 FH patients. Mean plasma cholesterol fell significantly by 24.7% with pravastatin and 21.5% with cholestyramine, the latter also causing a significant 42% rise in triglyceride. Pravastatin, but not cholestyramine, caused a significant fall in plasma viscosity and fibrinogen, but no change was seen in whole blood rheology. This suggests that the rheological abnormalities in FH are at least partly related to the plasma lipid levels and hence reversible with treatment.     

Hypothyroidism and the influence on human blood rheology

Viscoelastic properties of human whole blood were measured in 338 subjects: 110 persons (75 F, 35 M) following total thyroidectomy but without substitution therapy over three weeks as well as 228 healthy control subjects (124 F, 104 M) were investigated in this study. Subjects with other variable factors were excluded. The viscous and the elastic portion of apparent whole blood viscosity -the latter subdivided into red cell aggregation and red cell rigidity were determined by using a newly developed oscillating capillary rheometer and densitymeter at the real hematocrit value and at a computed hematocrit of 40%. Serum viscosity, hematocrit (Hct), hemoglobin (Hb), mean corpuscular volume of red blood cells (MCV), free triiodothyronine (fT3), free thyroxine (fT4) and serum-thyrotropin (bTSH) were evaluated as well. In a further subgroup of 80 subjects (40 patients with hypothyroidism, 40 healthy control persons) additional plasma viscosity and sedimentation rate were determined. Red cell aggregation and blood viscosity especially at shear-rates below 10/sec increased significantly in hypothyroid patients. There was no significant difference of red cell rigidity, serum viscosity, plasma viscosity and sedimentation rate as against euthyroids. So new aspects of thyroid dysfunction could be described probably with consequences for therapy and for considerations about the development of atherosclerosis and ischemic disorders.     

Viscosity of blood and plasma in patients with single- and multi-vascular coronary heart disease

The aim of this study was to establish a connection between rheological disturbances and extensiveness of atherosclerotic changes in coronary angiogram. Patients were classified into two groups: group I--with multivascular atherosclerotic lesions (45 subjects at age of 58 +/- 11 years), group II--with univascular atherosclerotic lesions (18 subjects at age of 55 +/- 9 years). Blood samples were drawn from the cubital vein prior to the angiogram. Blood viscosity measurements were performed using low-shear Contraves viscometer-100 at 0.116; 1.0; 4.59 s-1 shear rates and Brokfield Cone/Plate Viscometer at 150 s-1. The plasma viscosity was measured by means of Ubbelohde's capilary viscometer. Besides the viscometric examinations the total cholesterol. LDL-cholesterol, HDL-cholesterol, triglycerides, glucose and fibrinogen as well as blood morphology and ESR were determined. All rheological measurements were carried out at the temperature of 37 degrees C immediately after blood drawing. The results of studies indicate that in patients with multivascular coronary disease whole blood viscosity at all examined shear rates was significantly greater then in univascular patients. It was found that the LDL-lipoproteins concentration was significantly elevated in the I group. Other examined parameters did not differ significantly. The examinations indicate that there exists the connection between hemorheological disturbances and the extensiveness of coronary heart disease.     

Red blood cell deformability and aggregation behaviour in different animal species

Comparative animal studies showed the wide variation of whole blood and plasma viscosity, and erythrocyte aggregation among mammalian species. Whole blood viscosity and red blood cell aggregation is influenced by red cell fluidity. To evaluate differences in erythrocyte deformability in mammals, three species were investigated, whose erythrocytes have a different aggregation property: horse, as a species with high, dog with medium, and sheep with almost unmeasurable aggregation tendency. Erythrocyte deformability was tested ektacytometrically (Elongation Index [EI], LORCA, Mechatronics, Hoorn, Netherlands) at shear stresses from 0.30 to 53.06 Pa. Equine erythrocytes showed EI-values from 0.047 at low shear stress to 0.541 at high shear stress. The EI from dog's erythrocytes ranged from 0.035 to 0.595. Sheep's erythrocytes had an EI of 0.005 at low and 0.400 at high shear stress. Although it might be presumed from the aggregation property that horse had the highest EI among the three species, the EI of canine erythrocytes exceeded the value in horses by 10% at high shear stress. Further, equine erythrocytes started to deform at higher shear stresses (1.69 Pa) than did canine and ovine cells, whose EI increased continuously with increasing shear stress. At moderate shear stress (1-5 Pa) deformability was even higher in the sheep than in the horse. However, at shear stresses higher than 5.34 Pa, equine red cell elongation clearly exceeded the values of sheep. We conclude that erythrocyte elongation is different between the animal species, not clearly linked with the aggregation property, and that the degree of deformability at various shear stresses is species-specific.     

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 prestorage leucocyte depletion and storage time on rheologic properties of erythrocyte concentrates

BACKGROUND AND OBJECTIVES: Rheological blood properties were studied during storage. MATERIALS AND METHODS: Blood viscosity, erythrocyte morphology and ATP levels were determined in filtered samples (Leukotrap WB filter system) and their unfiltered counterparts during storage with saline-adenine-glucose-mannitol (SAG-M) for 42 days. RESULTS: Prestorage leucocyte depletion decreased blood viscosity at a high shear rate and reduced the degree of anisocytosis of erythrocytes. During storage, erythrocytes underwent a time-dependent echinocytic shape transformation, which increased the suspension viscosity at high and low shear rates. On day 42, high shear viscosity in filtered units remained lower than in unfiltered counterparts, the mean cellular volume and red blood cell distribution width (RDW) were lower and erythrocytic ATP levels were higher. CONCLUSIONS: Prestorage leucocyte depletion by Leukotrap WB filters improves biophysical properties of erythrocyte concentrates throughout storage, which is, however, outweighed by a time-dependent echinocytic shape transformation and deterioration of these properties.     

Predicting human blood viscosity in silico

The viscosity of blood has long been used as an indicator in the understanding and treatment of disease, and the advent of modern viscometers allows its measurement with ever-improving clinical convenience. However, these advances have not been matched by theoretical developments that can yield a quantitative understanding of blood's microrheology and its possible connection to relevant biomolecules (e.g., fibrinogen). Using coarse-grained molecular dynamics and two different red blood cell models, we accurately predict the dependence of blood viscosity on shear rate and hematocrit. We explicitly represent cell-cell interactions and identify the types and sizes of reversible rouleaux structures that yield a tremendous increase of blood viscosity at low shear rates. We also present the first quantitative estimates of the magnitude of adhesive forces between red cells. In addition, our simulations support the hypothesis, previously deduced from experiments, of yield stress as an indicator of cell aggregation. This non-Newtonian behavior is analyzed and related to the suspension's microstructure, deformation, and dynamics of single red blood cells. The most complex cell dynamics occurs in the intermediate shear rate regime, where individual cells experience severe deformation and transient folded conformations. The generality of these cell models together with single-cell measurements points to the future prediction of blood-viscosity anomalies and the corresponding microstructures associated with various diseases (e.g., malaria, AIDS, and diabetes mellitus). The models can easily be adapted to tune the properties of a much wider class of complex fluids including capsule and vesicle suspensions.     

Effect of chronic kidney disease on red blood cell rheology

BACKGROUND: Anemia of renal failure is primarily a problem of decreased RBC production due to erythropoietin deficiency. RBC survival is also reduced, perhaps due to decreased RBC deformability. This study measured blood viscosity over a range of shear rates in erythropoietin-treated patients on hemodialysis (HD), and compared the findings to matched patients with chronic renal insufficiency (CRI) and healthy controls. METHODS: Four groups (control, CRI, non-diabetic HD, and diabetic HD) of 9 matched subjects were recruited. Blood viscosity was measured using a cone-plate viscometer over a variety of shear rates (11 to 225 s(-1)). RESULTS: Control subjects had lower viscosity values throughout all shear rates when compared to the 3 renal disease groups (P value=0.039). A trend was observed to higher levels of renal function being associated with decreased blood viscosity in patients with CRI. CONCLUSIONS: Patients with kidney disease have increased blood viscosity at all shear rates. This may be related to changes in RBC shape and decreased deformability in patients with kidney disease, independent of HD- or DM-status. This may have implications for strategies to treat anemia in these patients.