Guidelines for measurement of blood viscosity and erythrocyte deformability

In silico modeling of patient-specific blood rheology in type 2 diabetes mellitus

Increased blood viscosity in type 2 diabetes mellitus (T2DM) is a risk factor for the development of insulin resistance and diabetes-related vascular complications; however, individuals with T2DM exhibit heterogeneous hemorheological properties, including cell deformation and aggregation. Using a multiscale red blood cell (RBC) model with key parameters derived from patient-specific data, we present a computational study of the rheological properties of blood from individual patients with T2DM. Specifically, one key model parameter, which determines the shear stiffness of the RBC membrane (μ) is informed by the high-shear-rate blood viscosity of patients with T2DM. At the same time, the other, which contributes to the strength of the RBC aggregation interaction (D0), is derived from the low-shear-rate blood viscosity of patients with T2DM. The T2DM RBC suspensions are simulated at different shear rates, and the predicted blood viscosity is compared with clinical laboratory-measured data. The results show that the blood viscosity obtained from clinical laboratories and computational simulations are in agreement at both low and high shear rates. These quantitative simulation results demonstrate that the patient-specific model has truly learned the rheological behavior of T2DM blood by unifying the mechanical and aggregation factors of the RBCs, which provides an effective way to extract quantitative predictions of the rheological properties of the blood of individual patients with T2DM.

Hemorheological profiles and chronic inflammation markers in transfusion-dependent and non-transfusion- dependent thalassemia

The rheological properties of blood play an important role in regulating blood flow in micro and macro circulation. In thalassemia syndromes red blood cells exhibit altered hemodynamic properties that facilitate microcirculatory diseases: increased aggregation and reduced deformability, as well as a marked increase in adherence to the vascular endothelial cells. A personalized approach to treating thalassemia patients (transfusions, iron chelation, and splenectomy), has increased patients' life expectancy, however they generally present many complications and several studies have demonstrated the presence of high incidence of thromboembolic events. In this study the hemorheological profiles of thalassemia patients have been characterized to point out new indices of vascular impairment in thalassemia. Plasma viscosity, blood viscosities at low and high shear rates (η1 and η200, respectively), erythrocyte aggregation index (η1/η200), and the erythrocyte viscoelastic profile (elastic modulus G', and viscous modulus G") have been studied in transfusion-dependent and non-transfusion-dependent thalassemia patients. Moreover, the levels of inflammation biomarkers in thalassemia have been evaluated to investigate a relationship between the biomarkers, the disease severity and the rheological parameters. The biomarkers studied are the main components of the immune and endothelial systems or are related to vascular inflammation: cytokines (IL-2, IL-6, IL-10, IL-17A, TNF-alpha), chemokines (IL-8, MIP-1alpha), adipocytokines (leptin and adiponectin), growth factors (VEGF, angiopoietin-1), adhesion molecules (ICAM-1, VCAM-1, E-selectin, L-selectin), and a monocyte/macrophage activation marker (CD163). This study shows that transfusion-dependent thalassemia patients, both major and intermedia, have blood viscosities comparable to those of healthy subjects. Non-transfusion-dependent thalassemia intermedia patients show high blood viscosities at low shear rates (η1), corresponding to the flow conditions of the microcirculation, an increase in erythrocyte aggregation, and high values of the elastic G' and viscous G" modules that reflect a reduced erythrocyte deformability and an increase in blood viscosity. Levels of cytokines, chemokines and adhesion molecules are different in transfusion- and non-transfusion dependent patients and positive correlations between η1 or η1/η200 and the cytokines IL-6 and IL-10 have been observed. The evaluation of the hemorheological profiles in thalassemia can provide new indicators of vascular impairment and disease severity in thalassemia in order to prevent the onset of thromboembolic events.

Blood Viscosity in Subjects With Type 2 Diabetes Mellitus: Roles of Hyperglycemia and Elevated Plasma Fibrinogen

The viscosity of blood is an indicator in the understanding and treatment of disease. An elevated blood viscosity has been demonstrated in patients with Type 2 Diabetes Mellitus (T2DM), which might represent a risk factor for cardiovascular complications. However, the roles of glycated hemoglobin (HbA_1c) and plasma fibrinogen levels on the elevated blood viscosity in subjects with T2DM at different chronic glycemic conditions are still not clear. Here, we evaluate the relationship between the blood viscosity and HbA_1c as well as plasma fibrinogen levels in patients with T2DM. The experimental data show that the mean values of the T2DM blood viscosity are higher in groups with higher HbA_1c levels, but the correlation between the T2DM blood viscosity and the HbA_1c level is not obvious. Instead, when we investigate the influence of plasma fibrinogen level on the blood viscosity in T2DM subjects, we find that the T2DM blood viscosity is significantly and positively correlated with the plasma fibrinogen level. Further, to probe the combined effects of multiple factors (including the HbA_1c and plasma fibrinogen levels) on the altered blood viscosity in T2DM, we regroup the experimental data based on the T2DM blood viscosity values at both the low and high shear rates, and our results suggest that the influence of the elevated HbA_1c level on blood viscosity is quite limited, although it is an important indicator of glycemic control in T2DM patients. Instead, the elevated blood hematocrit, the enhanced red blood cell (RBC) aggregation induced by the increased plasma fibrinogen level, and the reduced RBC deformation play key roles in the determination of blood viscosity in T2DM. Together, these experimental results are helpful in identifying the key determinants for the altered T2DM blood viscosity, which can be used in future studies of the hemorheological disturbances of T2DM patients.

An experimental erythrocyte rigidity index (Ri) and its correlations with Transcranial Doppler velocities (TAMMV), Gosling Pulsatility Index PI, hematocrit, hemoglobin concentration and red cell distribution width (RDW)

Brain artery velocities (Time-Averaged Maximum Mean Velocity, TAMMV) by Transcranial Doppler (TCD), hematocrit, hemoglobin, Red blood cell (RBC) Distribution Width (RDW) and RBC rigidity index (Ri), when reported together with their correlations, provide a accurate and useful diagnostic picture than blood viscosity measurements alone. Additionally, our study included a sixth parameter provided by TCD, the Gosling Pulsatility Index PI, which is an indicator of CBF (Cerebral Blood Flow) resistance. All these parameters are routine in Hematology except for values of Ri. The rigidity (Ri) of the RBC is the main rheological characteristic of the blood of Sickle Cell Anemia (SCA) patients and several pathologies. However, its quantification depends on many commercial and experimental techniques, none disseminated and predominant around the World. The difference in absorbance values of the blood, during the process of sedimentation in a microwell of a Microplate Reader, is a straightforward way of semi-quantifying the RBC rigidity Ri, since the fraction of irreversibly sickled red blood cells does not form rouleaux. Erythrocyte Rigidity Index (Ri) was calculated using initial absorbance A_initial (6 s) and final A_final (540 s), Ri = 1 / (Ai-Af). The Ri of 119 patients (2–17 y / o, M & F) SCA, SCC (Sickle Cell/hemoglobin C), SCD (Sickle Cell/hemoglobin D), Sβ0thal (Sickle Cell/hemoglobin Beta Zero Thalassemia) and 71 blood donors (20–65 y / o, M & F) were measured in our laboratory while the five parameters (TAMMV and PI by TCD, Hct, Hb and RDW) were obtained from medical records. The in vitro addition of hydroxyurea (HU, 50mg /dl, n = 51 patients, and n = 8 healthy donors) in the samples decreased the rouleaux adhesion strength of both donor and patients’ blood samples, leading to extraordinarily high Ri values. The correlation between the studied parameters was especially significant for the direct relationships between Ri, TAMMV, and PI.

Amlodipine alters hemorheological parameters: Increased efficacy at the cost of edema?

Background

Despite several decades of use of calcium channel blockers, the side effect of edema persists as a class effect, and its mechanism is unresolved. Amlodipine has effects on hemorheology (HR), and its hemodilutory property may partly contribute to its antihypertensive action. This aspect is not well studied, and the literature is sparse in this regard.

Objective

This experiment was planned to determine effect of a single-dose administration of amlodipine on HR parameters in normal human volunteers.

Methods and results

Amlodipine (5 mg) or S (-) amlodipine (2.5 mg) was administered to 27 normal human volunteers. Whole-blood viscosity (WBV) at different shear rates, plasma viscosity (PV), red cell rigidity (RCR), red cell aggregation (RCA), hematocrit (Hct), plasma hemoglobin, along with plasma drug concentration were determined at time intervals, t = 0, 4, 8, 12, and 24 h. Statistically significant reductions were observed at t_max = 4 h in WBV at shear rates of 0.512 s^–1 (p < 0.005), WBV at shear rates of 5.26 s^–1 (p < 0.01), PV (p < 0.05), and Hct (p < 0.01). At t = 8 h, as drug concentration reduced, some of the changes persisted and later slowly decreased with the decreasing drug concentration till t = 24 h. Red blood cell–related parameters such as RCA and RCR remained unaltered. WBV values at all shear rates, when corrected for Hct = 0.45, did not show deviation from their original values at any time.

Conclusions

Amlodipine causes a reduction in Hct and blood viscosity, along with hemodilution. These effects persist as long as the drug remains in plasma. Edema resulting from chronic dosing may be explained by the aforementioned effects. It is possible that antihypertensive action of the drug may be due to a combination of vasodilatation and an improvement in the HR properties.

The Influence of Glicated Hemoglobine on Whole Blood Visosity in Patients with Diabetic Nephropathy

The complications, especially those affecting microcirculation, exhibit great importance in the assessment and follow-up of patients with diabetes mellitus. Blood viscosity plays its most important role in the microcirculation where it contributes significantly to peripheral resistance and may cause sludging in the post capillary venules. The effect of whole blood viscosity in patients whit diabetic nephropaty is still unclear.

The aim of this study was to examine the influence of glicaemic control measured by glicated hemoglobin on rheological parameters, and especially on whole blood and plasma viscosity in patients with diabetic nephropaty. Blood viscosity is an important determinant of local flow characteristics. Blood exhibits shear thinning behavior: its viscosity decreases exponentially with increasing shear rates.

Estimation of whole blood and plasma viscosity was made on 42 patients, comparing different stages of diabetic nephropathy and with different values of glicated hemoglobin.

Depression of the regulatory mechanisms of microvascular blood flow as well as decreased tissue perfusion indicated the restricted blood flow in microcirculatory network in diabetic nephropathy. In conclusion blood viscosity was elevated in the patients with major organ complications and not in the patients without or with early complications, in correlation with poor glicaemic control.

Oxygen transport capacity in the air-breathing fish, Megalops cyprinoides: compensations for strenuous exercise

Tarpon have high resting or routine hematocrits (Hct) (37.6+/-3.4%) and hemoglobin concentrations (120.6+/-7.3 gl(-1)) that increased significantly following bouts of angling-induced exercise (51.9+/-3.7% and 142.8+/-13.5 gl(-1), respectively). Strenuous exercise was accompanied by an approximately tenfold increase in blood lactate and a muscle metabolite profile indicative of a high energy demand teleost. Routine blood values were quickly restored only when this facultative air-breathing fish was given access to atmospheric air. In vitro studies of oxygen transport capacity, a function of carrying capacity and viscosity, revealed that the optimal Hct range corresponded to that observed in fish under routine behaviour. During strenuous exercise however, further increase in viscosity was largely offset by a pronounced reduction in the shear-dependence of blood which conformed closely to an ideal Newtonian fluid. The mechanism for this behaviour of the erythrocytes appears to involve the activation of surface adrenergic receptors because pre-treatment with propranolol abolished the response. High levels of activity in tarpon living in hypoxic habitats are therefore supported by an elevated Hct with adrenergically mediated viscosity reduction, and air-breathing behaviour that enables rapid metabolic recovery.

Theoretical and experimental aspects of erythrocyte filterability testing; flow acceleration and systemic resistance

Blood cell filterability is an established method in blood rheology. The dynamics at flow onset and its relevance to the data interpretation is, however, not fully known. This paper aims to investigate what controls the length and slope of flow acceleration as the medium accelerates to reach the steady state, and how this phenomenon may interfere with the data output. The acceleration time was not constant. With buffer the steady-state flow showed a logarithmic correlation (p<0.05) versus acceleration time and a linear correlation (p<0.001) versus acceleration slope. With 5% erythrocyte resuspension the steady-state flow instead demonstrated a linear relationship versus acceleration time (p<0.001) and no correlation versus acceleration slope. A cut-off timing of 0.6s is suggested to avoid artifacts associated with flow acceleration. The possible influence on data interpretation from the flow channel systemic resistance was also addressed, and found to significantly underestimate measurable changes in erythrocyte properties from unprocessed flow curves. This was despite the traditional correction for blank filtration flow. Both acceleration and effects from systemic resistance do probably have minor influence on the historic data interpretation but could perhaps be considered in the methodology to sharpen the data output.

Cerebral blood flow velocity and systemic vascular resistance after acute reduction of low-density lipoprotein in familial hypercholesterolemia

BACKGROUND AND PURPOSE

Low-density lipoprotein apheresis is currently used for the treatment of familial hypercholesterolemia, an inherited disorder of metabolism associated with premature development of cardiovascular disease. We wanted to evaluate cerebral blood flow velocity, cardiac output, and systemic vascular resistance in patients with familial hypercholesterolemia before and after low-density lipoprotein apheresis.

METHODS

Ten patients (age range, 14 to 46 years; 4 males, 6 females) with familial hypercholesterolemia (8 homozygotes, 2 heterozygotes) and 10 healthy control subjects of comparable age and sex distribution participated in the study. Low-density lipoprotein apheresis by dextran sulfate was performed in 8 patients (7 homozygotes, 1 heterozygote). Six patients (4 homozygotes, 2 heterozygotes) underwent a procedure of extracorporeal erythrocyte filtration with the same extracorporeal volume as for low-density lipoprotein apheresis, but with the exclusion of the passage of plasma through the dextran sulfate column. Cerebral blood flow velocity (transcranial Doppler), cardiac output, and systemic vascular resistance (electric bioimpedance cardiography) were determined by noninvasive techniques before and 1 day and 7 days after low-density lipoprotein apheresis or extracorporeal erythrocyte filtration. Plasma and blood viscosities were measured at the same time.

RESULTS

Before apheresis, mean and diastolic cerebral flow velocities were abnormally low in hypercholesterolemic patients (P < .01 and P < .02 vs healthy control subjects, respectively). After apheresis, low-density lipoprotein cholesterol was lowered by 40% to 60% from baseline, and cerebral blood flow velocities (mean, systolic, and diastolic velocities) were increased (P < .01). Cardiac output, systemic vascular resistance, and viscosity values were not significantly modified. Extracorporeal erythrocyte filtration (without passage of plasma through the dextran sulfate column) did not modify serum lipids, hemodynamic parameters, or viscosity values.

CONCLUSIONS

Low-density lipoprotein apheresis produces potentially useful hemodynamic effects. They are not adequately explained by changes in blood viscosity alone and might reflect a restoration of endothelium-mediated vasodilation, which is inhibited by high concentrations of low-density lipoprotein.

Plasma, serum and whole-blood viscosity variations with age, sex, and smoking habits

To study the influence of age, sex, and smoking habits on rheology, the authors measured plasma (PV), serum (SV), native (NBV), and corrected (CBV) blood viscosity with a computerized rotational viscometer in 152 blood donors (86 men and 66 women) and in 20 healthy persons (4 men and 16 women) attending smoke aversion treatment. None of the viscosity measures or erythrocyte sedimentation rate changed significantly with age, whereas hematocrit (HC) and fibrinogen concentration (FC) both increased with ageing (p < 0.05 and p < 0.001, respectively). Higher (p < 0.001) values of NBV and HC were found in men than in women, whereas higher values were found in women than in men for FC (p < 0.01) and ESR (p < 0.001). In blood donors, moderate smoking (mean twelve cigarettes/day) significantly influenced only ESR, which was higher (p < 0.001) in smokers than in nonsmokers. In heavy smokers (mean twenty-one cigarettes/day), however, higher (p < 0.001) PV, SV, and NBV were found, as well as higher (p < 0.01) FC and HC as compared with nonsmoking blood donors.