Fibrinogen-erythrocyte binding and hemorheology measurements in the assessment of essential arterial hypertension patients.

Some studies have reported a positive association between plasma fibrinogen levels, erythrocyte aggregation and essential arterial hypertension (EAH). The aim of this study was to understand how the interaction between fibrinogen and its erythrocyte membrane receptor is altered in EAH. EAH patients (n = 31) and healthy blood donors (n = 65) were enrolled in the study. EAH patients were therapeutically controlled for the disease, presenting a systolic blood pressure between 108 and 180 mmHg and a diastolic blood pressure between 66 and 123 mmHg. Clinical evaluation included blood pressure monitoring, electrocardiography, echocardiography and blood cell count. The hemorheological parameters were also analyzed. Fibrinogen-erythrocyte binding force and frequency were evaluated quantitatively, at the single-molecule level, using atomic force microscopy (AFM). Changes in erythrocyte elasticity were also evaluated. Force spectroscopy data showed that the average fibrinogen-erythrocyte binding forces increase from 40.4 ± 3.0 pN in healthy donors to 73.8 ± 8.1 pN in patients with EAH, despite a lower binding frequency for patients compared to the control group (7.9 ± 1.6% vs. 27.6 ± 4.2%, respectively). Elasticity studies revealed an increase of erythrocyte stiffness in the patients. The stronger fibrinogen binding to erythrocytes from EAH patients and alteration in cell elasticity may lead to changes in the whole blood flow. The patients' altered hemorheological parameters may also contribute to these blood flow perturbations. The transient bridging of two erythrocytes, by the simultaneous binding of fibrinogen to both of them, promoting erythrocyte aggregation, could represent an important cardiovascular risk factor.

In vivo venous assessment of red blood cell aggregate sizes in diabetic patients with a quantitative cellular ultrasound imaging method: proof of concept.

BACKGROUND: Diabetic patients present higher level of red blood cell (RBC) aggregation contributing to the development of vascular complications. While it has been suggested that this hematology/rheology parameter could bring additional prognostic information for the management of those patients, RBC aggregation screening is not included as a clinical practice. Most medical centers are not equipped to measure properly this parameter, although sedimentation tests can bring some indication. Here, we aimed at evaluating the feasibility of using ultrasound to assess in-vivo hyper-aggregation in type 2 diabetic patients. RESEARCH DESIGN AND METHODS: Seventeen diabetic patients and 15 control subjects underwent ultrasound measurements of RBC aggregation in both cephalic and great saphenous veins. Non-invasive in-vivo ultrasound measurements were performed using a newly developed cellular imaging technique, the structure factor size and attenuation estimator (SFSAE). Comparisons with an ex-vivo gold standard rheometry technique were done, along with measurements of pro-aggregating plasma molecule concentrations. RESULTS: In-vivo RBC aggregation was significantly higher in diabetic patients compared with controls for cephalic vein measurements, while a trend (p = 0.055) was noticed in the great saphenous vein. SFSAE measurements were correlated with gold standard in-vitro measures, fibrinogen and C-reactive protein plasma concentrations. CONCLUSION: RBC aggregation can be measured in-vivo in diabetic patients using ultrasound. Prospective studies are needed to determine whether the SFSAE method could help clinicians in the early management of vascular complications in this patient population.

[Non-invasive methods for the assessment of platelet, leukocyte, erythrocyte aggregation and coagulation hemostasis].

A non-invasive method for the study of platelet aggregation and formation of leukocyte-erythrocyte-platelet aggregates as well as certain hemostatic parameters is proposed. The method is based on the speckle-analysis of coherent light scattering from the surface of erythrocytes moving in an artificially isolated vessel segment. It was shown that light scattering index significantly correlated with ADP-, adrenalin-, or collagen-induced platelet aggregation, with the formation of leukocyte-erythrocyte or platelet-erythrocyte aggregates, and with the levels of fibrinogen, soluble fibrin-monomer complexes and related parameters. It is concluded that the proposed method for the study of hemostatic system can be used to roughly evaluate intensity of intravascular blood coagulation and probability of thrombosis.

Development of red blood cell-photon simulator for optical propagation analysis in blood using Monte Carlo method.

We have developed a "red blood cell (RBC)-photon simulator" to reveal optical propagation in prethrombus blood for various levels of RBC density and aggregation. The simulator investigates optical propagation in the prethrombus blood and will be applied to detect it noninvasively for thrombosis prevention in an earlier stage. In our simulator, Lambert-Beer's law is employed to simulate the absorption of RBCs with hemoglobin, while the Monte Carlo method is applied to simulate scattering through iterative calculations. One advantage of our simulator is that concentrations and distributions of RBCs can be arbitrarily chosen to exhibit the prethrombus, while conventional models cannot. Using the simulator, we found that various levels of RBC density and aggregation have different effects on the optical propagation of near-infrared response light in blood. The same different effects were acquired in in vitro experiments with 12 bovine blood samples, which were performed to evaluate the simulator. We measured RBC density using the clinical hematocrit index and RBC aggregation using activated whole blood clotting time. The experimental results correspond to the simulator results well. Therefore, we could show that our simulator exhibits the correct optical propagation for prethrombus blood and is applicable for the prethrombus detection using multiple detectors.

Evaluation of optical propagation in blood for noninvasive detection of prethrombus blood condition.

This article evaluates the optical propagation to detect a "prethrombus" blood noninvasively. Thrombosis is still an inevitable issue in use of blood pumps, and it is required to predict thrombus formation as early as possible. We focused on the red blood cell (RBC) aggregation that is one of the features of thrombogenic process. First, by using a computer simulation, we calculated the optical propagations in blood for the RBC aggregation and nonaggregation blood. This simulation is based on the Monte-Carlo method and attempts to calculate the optical characteristics of the blood stochastically. In our simulation, the optical propagation with the RBC aggregation showed a different characteristic from that of the nonaggregation. Next, we examined the optical propagation in bovine blood with various activated whole blood clotting time (ACT). The blood mixed with sodium citrate was circulated by a blood pump. The ACT was adjusted between 1,000 and 50 seconds by controlling the ratio of calcium chloride solution to sodium citrate. We confirmed the RBC aggregation by using microscopic images and microthromboses in the pump directly. As a result, we evaluated that the change of the optical propagation has a correlation with thrombogenic process just as it was observed in our computer simulation. Our data indicate that the measurement of optical propagation can detect a prethrombous blood condition with RBC aggregation. Our study will help to establish optical technologies to detect prethrombous continuously and noninvasively.

Monte Carlo study on ultrasound backscattering by three-dimensional distributions of red blood cells.

A Monte Carlo study on ultrasound backscattering by red blood cells (RBCs) is presented for three-dimensional (3D) distributions of particles. The cells were treated as classical spherical particles and accordingly, the Boltzmann distribution was considered to describe probability distribution of energy states of a system composed of such particles. The well-known Metropolis algorithm can generate configurations according to that probability distribution and therefore, was employed in this study to simulate some realizations of both nonaggregating and aggregating RBCs. The study of nonaggregating particles was motivated to compare simulations with existing experimental results and consequently, to validate the model. In the case of aggregating RBCs, the interaction potential between cells was modeled with the Morse potential and the frequency-dependent backscattering coefficient (BSC) was investigated at different hematocrits (H, particle volume fractions). The impact of aggregation potential on the spectral slope (SS) was also evaluated. It is shown that BSC increased as the magnitude of aggregating potential was raised and the effect was more pronounced at higher hematocrits. Moreover, spectral slopes at nonaggregating and low aggregating conditions were found to be around 4, which is consistent with the Rayleigh scattering theory. However, it had diminished significantly, particularly at higher hematocrits as the magnitude of the attractive potential energy was raised. For instance, at H=40% SS dropped from 4.04 for nonaggregating particles to 3.62 at the highest aggregating potential considered in this study. Our results suggest that this 3D model is capable of reflecting the effects of RBC aggregation on BSC and SS.

Syllectometry: the effect of aggregometer geometry in the assessment of red blood cell shape recovery and aggregation.

Syllectometry is a measuring method that is commonly used to assess red blood cell (RBC) aggregability. In syllectometry, light is incident on a layer of whole blood initially exposed to shear flow. The backscattered light is measured after abruptly stopping the driving mechanism. The resultant time-dependent intensity plot is called the syllectogram. Parameters that quantify RBC aggregability are obtained by analyzing the syllectogram. As we will show in this paper, the upstroke in the initial part of the syllectogram contains the information for measurement of RBC-shape recovery in whole blood as well. To estimate RBC-shape recovery, we extended the existing two-exponential mathematical representation of the syllectogram by a third exponent that describes the upstroke. To investigate the feasibility of RBC-shape recovery measurement from the upstroke, we derived an analytical model of the flow decay that follows after abruptly stopping the driving mechanism. The model reveals that for large gaps the flow decay may interfere with the true RBC-shape recovery process. These theoretical findings were confirmed by velocity measurements in a Couette-type aggregometer. Syllectograms obtained using large gaps differ in many respects from those obtained using small gaps. As predicted by our model large gaps show a prolonged apparent shape-recovery time-constant. Moreover, a delayed intensity peak, a reduced upstroke of the intensity peak and a considerable increase of the half-life parameter are observed. The aggregation indices for large gaps are lower than for small gaps. This paper yields a better understanding of the velocity and shear-rate decay following upon abruptly stopping the driving mechanism. A better mathematical representation of the syllectogram and recommendations for a maximum gap width enables both RBC-shape recovery and aggregation measurements in whole blood using syllectometry.