The degree of red blood cell aggregation on peripheral blood glass slides corresponds to inter-erythrocyte cohesive forces in laminar flow

Microfluidic-based speckle analysis for sensitive measurement of erythrocyte aggregation: A comparison of four methods for detection of elevated erythrocyte aggregation in diabetic rat blood

Biochemical alterations in the plasma and red blood cell (RBC) membrane of diabetic blood lead to excessive erythrocyte aggregation (EA). EA would significantly impede the blood flow and increase the vascular flow resistance contributing to peripheral vascular diseases. In this study, a simple microfluidic-based method is proposed to achieve sensitive detection of hyperaggregation. When a blood sample is delivered into the device, images of blood flows are obtained with a short exposure time for a relatively long measuring time. A micro-particle image velocimetry technique was employed to monitor variation of the flow rate of blood as a function of time. Given that EA formation in the channel creates clear speckle patterns, the EA extent can be estimated by calculating a speckle area (ASpeckle) through a normalized autocovariance function. The hematocrit effect is assessed by comparing optical images transmitted through blood samples. EA variations caused by dextran treatment are quantitatively evaluated using characteristic time (λSpeckle) obtained by fitting the variations of ASpeckle. Other indices including number of RBCs in an aggregate (NRBC), characteristic time of erythrocyte sedimentation rate (λESR), and aggregation index estimated from ultrasound signals (AIEcho) are determined under different EA conditions using conventional techniques. The four different methods are applied to diabetic blood samples to compare their indices under hyperaggregation conditions. It is found that the proposed method can detect variation of EA reasonably, compared with conventional measurement techniques. These experimental demonstrations support the notion that the proposed method is capable of effectively monitoring the biophysical properties of diabetic blood.

Structural analysis of red blood cell aggregates under shear flow

A set of measures of red blood cell (RBC) aggregates are developed and applied to examine the aggregate structure under plane shear and channel flows. Some of these measures are based on averages over the set of red blood cells which are in contact with each other at a given time. Other measures are developed by first fitting an ellipse to the planar projection of the aggregate, and then examining the area and aspect ratio of the fit ellipse as well as the orientations of constituent RBCs with respect to the fit ellipse axes. The aggregate structural measures are illustrated using a new mesoscale computational model for blood cell transport, collision and adhesion. The sensitivity of this model to change in adhesive surface energy density and shear rate on the aggregate structure is examined. It is found that the mesoscale model predictions exhibit reasonable agreement with experimental and theoretical data for blood flow in plane shear and channel flows. The new structural measures are used to examine the differences between predictions of two- and three-dimensional computations of the aggregate formation, showing that two-dimensional computations retain some of the important aspects of three-dimensional computations.

On the effect of dynamic flow conditions on blood microstructure investigated with optical shearing microscopy and rheometry

Red blood cell (RBC) aggregation affects significantly the flow of blood at low shear rates. Increased RBC aggregation is associated with various pathological conditions; hence an accurate quantification and better understanding of the phenomenon is important. The present study aims to improve understanding of the effect of dynamic flow conditions on aggregate formation; whole blood samples from healthy volunteers, adjusted at 0.45 haematocrit were tested in different flow conditions with a plate-plate optical shearing system, image analysis, and a double-walled Couette rheometric cell. Results are presented in terms of aggregation index Aa, aggregate size index As and number of aggregates, which are shown to vary with shear rate γ and with different shear rate variations with time γ. The aggregation index Aa was observed to increase as the shear rate decreased between 10 and 3 s−1. Above 10 s−1, Aa was found to have a minimum value indicating minimal aggregation while, at approximately 3 s−1, Aa reaches a maximum. The aggregation size index As, the number of aggregates, and the blood viscosity were found to vary considerably when the same sample was examined over the same shear rate range, but for different variations of shear rate with time, γ.

Increased erythrocyte adhesiveness and aggregation in obstructive sleep apnea syndrome

BACKGROUND

Obstructive sleep apnea (OSA) is associated with an increased incidence of stroke and myocardial infarction as well as increased prothrombotic and inflammatory processes. Although erythrocyte adhesiveness/aggregation is known to be elevated in cardiovascular diseases, it has never been evaluated in OSA. The aim of this study was to examine the possible association of OSA and erythrocyte adhesiveness/aggregation.

METHODS

The study was conducted in the Sleep Laboratory of a tertiary university-affiliated medical center in 79 patients (age 57.1+/-12.9 years) with a diagnosis of OSA (apnea hypopnea index 41.2+/-25.9). Findings were compared with data on 1079 controls without clinical symptoms of OSA, matched for sex, age, and body mass index. Overnight polysomnography and blood sampling for erythrocyte sedimentation rate, levels of fibrinogen, high-sensitivity C-reactive protein, and erythrocyte adhesion/aggregation test consisting of measures of erythrocyte percentage and vacuum range on image analysis.

RESULTS

The study group had significantly higher values than controls of all three markers of inflammation (p<0.001 for erythrocyte sedimentation rate and fibrinogen; p=0.037 for C-reactive protein). Erythrocyte percentage was significantly lower in the sleep apnea group (84.05+/-15.97 vs. 90.79+/-11.23%, p<0.001), and vacuum range was significantly higher (8.22+/-7.98 vs. 4.63+/-4.05 microm, p<0.001), indicating stronger erythrocyte adhesion/aggregation. Both these factors were significantly correlated with erythrocyte sedimentation rate and to hs-CRP (percentage: r=-0.630; 0.258, p=0.005; 0.031; vacuum range: r=0.494; -0.328, p=0.001; 0.005 respectively).

CONCLUSION

OSA is associated with increased erythrocyte aggregation/adhesion, which is correlated with an increase in inflammation markers. These findings might help explain the increased cardiovascular morbidity in OSA.

Plasma dependent reduction in red blood cell aggregation after dextran sulfate low-density lipoprotein apheresis--implications for rheological studies

Red blood cell (RBC) aggregation is increased in familial hypercholesterolemia, and is reduced significantly after low density lipoprotein (LDL) apheresis. The purpose of the present study was to clarify whether this reduction depends on changes in plasma composition, RBC membrane properties, or both. RBC aggregation was determined in a computerized cell flow-properties analyzer, before and after LDL apheresis. We compared RBC aggregation in autologous plasma with aggregation in a plasma-free standard solution (0.5% of dextran 500 kDa) to define the separate contributions of plasma and cellular properties to the observed RBC aggregation. RBC aggregation in autologous plasma was reduced by 35.5% after LDL apheresis (P=0.01) but was not significantly affected when measured in dextran 500. This suggests that LDL apheresis attenuated RBC aggregation by altering plasma composition rather than RBC membrane properties. These results are relevant to the understanding of hemorheological changes which follow therapeutic apheresis in hypercholesterolemic patients.

Association of components of the metabolic syndrome with the appearance of aggregated red blood cells in the peripheral blood. An unfavorable hemorheological finding

BACKGROUND

Components of the metabolic syndrome are associated with low-grade inflammation. This can be accompanied by the synthesis of sticky proteins and erythrocyte aggregation.

METHODS

The degree of erythrocyte aggregation was evaluated by a simple slide test and image analysis along with other markers of the acute-phase response, including the white blood cell count (WBCC), erythrocyte sedimentation rate (ESR), fibrinogen and high sensitivity C-reactive protein (hs-CRP) concentrations. Patients were categorized in four groups according to the absence or presence of 1, 2 and 3 or more components of the metabolic syndrome.

RESULTS

We examined a total of 1447 individuals (576 women and 871 men) who gave their informed consent for participation. A significant cardiovascular risk factors, age and hemoglobin adjusted correlation was noted between the degree of erythrocyte aggregation and the number of components of the metabolic syndrome (r = 0.17, p < 0.0005). This correlation was better than that observed for clottable fibrinogen (r = 0.13 p < 0.0005), for ESR (r = 0.11 p < 0.0005) or WBCC (r = 0.13 p < 0.0005). A somewhat better correlation was noted for hs-CRP (r = 0.26 p < 0.0005).

CONCLUSIONS

The multiplicity of components of the metabolic syndrome is associated with enhanced erythrocyte aggregation, probably related to the presence of multiple adhesive macromolecules in the peripheral blood. The enhanced aggregation might contribute to capillary slow flow, tissue deoxygenation as well as vasomotor tone changes in the presence of multiple components of this syndrome.