Whole Blood Viscoelasticity Research Articles

Detection of clot formation & lysis In-Vitro using high frequency photoacoustic imaging & frequency analysis

Clotting is a physiological process that prevents blood loss after injury. An imbalance in clotting factors can lead to lethal consequences such as exsanguination or inappropriate thrombosis. Clinical methods to monitor clotting and fibrinolysis typically measure the viscoelasticity of whole blood or optical density of plasma over time. Though these methods provide insights into clotting and fibrinolysis, they require milliliters of blood which can worsen anemia or only provide partial information. To overcome these limitations, a high-frequency photoacoustic (HFPA) imaging system was developed to detect clotting and lysis in blood. Clotting was initiated in vitro in reconstituted blood using thrombin and lysed with urokinase plasminogen activator. Frequency spectra measured using HFPA signals (10–40 MHz) between non-clotted blood and clotted blood differed markedly, allowing tracking of clot initiation and lysis in volumes of blood as low as 25 µL/test. HFPA imaging shows potential as a point-of-care examination of coagulation and fibrinolysis.

Characterization of the hemorrhagic syndrome in the New Zealand white rabbit model following total body irradiation

Purpose The hemorrhagic syndrome is a major cause of morbidity and mortality associated with the acute radiation syndrome (ARS). We previously characterized the dose–response relationship for total body irradiation (TBI)-induced ARS in the New Zealand White (NZW) rabbit. Thrombocytopenia, hemorrhage, and anemia were strongly associated with morbidity/mortality during the first three weeks post-TBI. The objective of the current study was to further characterize the natural history of thrombocytopenia, hemostatic dysfunction and hemorrhage in the rabbit model at a TBI dose range to induce ARS. Methods Fifty male NZW rabbits were randomized to receive 7.0 or 7.5 Gy of 6 MV-derived TBI. Sham-irradiated controls (n = 6) were included as a comparator. Animals were treated with minimal supportive care including pain medication, antibiotics, antipyretics for temperature >104.8 °F, and fluids for signs of dehydration. Animals were culled at pre-determined timepoints post-TBI, or for signs of imminent mortality based on pre-defined euthanasia criteria. Hematology parameters, serum chemistry, viscoelasticity of whole blood, coagulation tests, and coagulation factor activities were measured. A gross exam of vital organs was performed at necropsy. Results Findings in this study include severe neutropenia during the first week post-TBI followed by thrombocytopenia and severe acute anemia with petechial hemorrhages of the skin and hemorrhage of the vital organs during the second to third weeks post-TBI. Abnormalities in whole blood viscoelastometry were observed concurrent with thrombocytopenia and hemorrhage. Antithrombin activity was significantly elevated in animals after exposure to 7.5 Gy, but not 7.0 Gy TBI. Conclusions The hemorrhagic syndrome in the rabbit model of TBI recapitulates the pathogenesis described in humans following accidental or deliberate exposures. The rabbit may present an alternative to the rodent model as a small animal species for characterization of the full spectrum of multiorgan injury following TBI and early testing of promising medical countermeasures.

Correlation and agreement between the TEG® 5000 and the TEG® 6s during liver transplant surgery.

The TEG® 5000 and novel TEG® 6s measure the viscoelasticity of whole blood during in vitro clot formation. The two devices measure similar coagulation variables but utilize distinctly different technologies. This study aimed to determine the correlation and agreement between the thrombelastographic parameters obtained by the two devices during liver transplant surgery. We obtained blood samples at six predefined intervals during the surgery of 10 consecutive patients. Two operators proficient in the use of the TEG® 6s and TEG® 5000 systems performed thrombelastographic measurements on each sample: non-citrated TEG® 5000, citrated TEG® 5000 and citrated TEG® 6s. Agreement and correlation were assessed using Bland Altman plots and Lin's concordance correlation. There was considerable inter-device variability for the different parameters measured by the TEG® 5000 and TEG® 6s devices. Acceptable agreement was observed when results were within the normal reference ranges. However, with increasing coagulopathy, agreement was poor and results could not be considered interchangeable. Although each of the three tests appeared reliable for qualitative detection of abnormalities of clot formation during liver transplant surgery, we found their quantitative results were not interchangeable.

Viscoelasticity of whole blood as a function of age, gender, cigarette smoking and intake of oral contraceptives

To assess whether the viscoelastic properties of whole blood might be influenced by age gender cigarette smoking and oral contraceptives (OCs) the authors measured viscoelasticity of whole blood and plasma at different shear rates in healthy adult subjects. 35 male and 40 female subjects were classified into 10 groups and their viscoelastic data were evaluated. Viscoelasticity of whole blood (shear rates 10/s and 50/s) viscosity of plasma (shear rate 10/s) aggregation index shear resistance and flexibility index of erythrocytes and density hematocrit were measured with an oscillating capillary rheometer and densitymeter. Age was found to increase whole blood elasticity significantly at low shear rates when young male nonsmokers were compared with old nonsmokers of both sexes. OC intake was found to increase whole blood elasticity at higher shear rates when young nonsmoking men were compared with young nonsmoking women who had taken OCs for at least 1 year. Concerning shear resistance of aggregated erythrocytes the values of young nonsmoking men were significantly lower than the values of all other groups except the group of young smoking women who had not taken OCs. Density hematocrit was higher in men than in women. Whole blood and plasma viscosities as well as aggregation and flexibility indices were not significantly different when 10 groups were compared by analysis of variance. (authors)

Viscoelasticity of whole blood and its dependence on laboratory parameters

The viscous component of viscoelasticity depends mainly on hematocrit and to a small degree on plasma viscosity. The elastic component of viscoelasticity is influenced by plasma viscosity and by the plasma proteins and platelets. Thus, 81% of the variation found for the viscous and 75% for the elastic component of normal donors could be explained

Development of standard tests to examine viscoelastic properties of blood of experimental animals for pediatric mechanical support device evaluation.

We investigated the applicability of measuring the viscoelasticity of bovine, ovine, and porcine whole blood for the evaluation of sublethal damage to red blood cells (RBCs). An increase in blood viscosity and elasticity without changes in hematocrit and plasma viscosity would signify a decrease in RBC deformability. Blood viscoelasticity was assessed using a Vilastic Scientific viscoelastometer. Due to the natural absence of RBC aggregation and small RBC size in normal bovine and ovine blood, viscoelastic properties are less readily detected. However, we found that adjustment of blood hematocrit to a standard level of 40-50% allows for sensitive assessment of viscoelasticity in these blood types demonstrating a marked non-Newtonian behavior mostly related to RBC deformability. Porcine blood showed a pronounced non-Newtonian behavior at all tested hematocrit values, which makes it rheologically comparable to human blood. Both viscosity and elasticity were elevated after blood exposure to a uniform mechanical stress. RBCs rigidified by heat exposure demonstrated a loss of viscoelasticity dependence on shear rate. Measurements of blood viscoelasticity can be meaningful in bovine, ovine, and, especially, porcine blood, and can be used for evaluation of sublethal blood damage during in vitro and animal trials of heart-assist devices.

Alteration in viscoelasticity of whole blood from dogs with experimental acute necrotizing pancreatitis

Alteration in viscoelasticity of whole blood from dogs with experimental acute necrotizing pancreatitis

Importance of blood viscoelasticity in arteriosclerosis.

Corpuscular and biochemical components of blood create the viscoelastic nature of blood flow, which varies because of changes in flow velocity. The flow properties of blood are of special interest in arteriosclerotic diseases for vasoregulatory mechanisms are often disturbed in these states. The authors compared the rheologic properties of blood in patients with arteriosclerotic lesions (coronary heart disease: n = 56; cerebrovascular disease: n = 37; peripheral arterial occlusive disease: n = 29 and healthy controls: n = 42). With a new oscillating capillary rheometer imitating the physiologic pulsations of blood flow in an unbranched artery, the viscosity (eta') and elasticity (eta") of whole blood and plasma were measured (diameter of the capillary: 0.9928 mm; pulse rate: 2/s; shear rate: gamma = 0.03-200/s; temperature: 37 degrees C). In arteriosclerotic patients a statistically significant elevation of the viscoelasticity of whole blood and plasma was found. In addition, plasma fibrinogen levels were augmented in the patients' groups. Clotting parameters (Quick, partial thromboplastin time, platelet count) and total serum protein levels were in the normal range in all patients investigated. In conclusion the question arises whether the increase of blood viscoelasticity is an additional risk factor for patients with arteriosclerotic disease or if it is just a consequence of the underlying disease. The authors' observations concerning blood viscoelasticity support the clinical importance of improving blood rheology by appropriate therapeutic measures.