Biorheology最新文献

Background: Red blood cell aggregation is largely influenced by hematocrit and plasma protein content with aggregation increasing as hematocrit and fibrinogen increase. Aggregation measurement techniques include light-transmission or laser-backscatter, and the impact of measurement technique on aggregation measurements with respect to changes in hematocrit and plasma protein is not well understood.

Objective: The objective of this study was to evaluate aggregation measurement techniques with respect to common effectors of red blood cell aggregation.

Methods: We obtained whole blood samples from 10 healthy participants and varied hematocrit, plasma albumin, and plasma fibrinogen concentration in a sample of healthy male and female participants. We then measured red blood cell aggregation using a Myrenne Aggregometer (light-transmission aggregometer) and a Laser Optical Rotational Red Cell Analyzer (laser-backscatter aggregometer).

Results: For Myrenne, aggregation increased from 30% to 40% hematocrit, then declined at 50% hematocrit. Measurement in the LORRCA demonstrated an increase as hematocrit increased from 30% to 40%, and again increased at 50%, which differed from the light transmission method. Red blood cell aggregation increased with increased fibrinogen concentration, but did not change significantly as albumin concentration increased.

Conclusions: Red blood cell aggregation is expected to increase as hematocrit increases, but when light transmission aggregometry is used, aggregation decreases as hematocrit increases past 40%. Each measurement technique has its own set of methodological strengths and weaknesses.

Background: Cardiovascular system is known to be affected in acromegaly. However, it was not reported to date if hemorheology was also altered and there is limited data regarding systemic oxidative status in patients with acromegaly.

Objective: To investigate alterations in hemorheology and systemic oxidative stress in patients with acromegaly.

Methods: The study comprised 19 active (AA) and 15 controlled (CA) acromegaly patients (n = 34, mean age 48.85 ± 1.69 years) and 29 controls (mean age 52.83 ± 1.37 years). Erythrocyte aggregation index (AI), aggregation half time (t½), amplitude (Amp) and erythrocyte elongation index (EI) were determined by an ektacytometer. Commercial kits were used for measuring serum total oxidant status (TOS) and total antioxidant status (TAS), and oxidative stress index (OSI) was calculated.

Results: There were statistically significant differences regarding EI at shear stresses of 16.87 ve 30.00 Pa (p = 0.034, p = 0.0001, respectively) and AI (p = 0.050, p = 0.035, respectively) values among the control, AA and CA groups. Decrement of t½ was in line with increment of AI and indicated increased erythrocyte aggregation. Serum TOS, TAS and OSI values were similar between the control, AA and CA groups (p > 0.05).

Conclusions: This pilot study demonstrated reduced erythrocyte deformability and increased erythrocyte aggregation in patients with AA and CA.

Background: Okra is a vegetable that is widely grown around the world. Okra mucilage contains a high mucus concentration that can be useful for supporting the swallowing process. Although the extensional rheology of okra mucilage is essential to its flow, its extensional viscosity has not received much attention.

Objective: Using a filament stretching rheometer, the extensional viscosity of the mucilage in okra was examined. The Giesekus model was used to predict this parameter.

Methods: The okra mucilage with different concentrations was extracted from fresh okra. The extensional viscosity was measured using a filament breakup apparatus. The diameter of the liquid bridge was measured by a laser micrometer and it was also observed by a high-speed camera. A rotational rheometer was used to measure the shear viscosity. In addition, the master curves for the shear viscosity were plotted to eliminate the influence of solvent and shear rate and evaluate the influence of concentration on the elasticity of okra mucilage. The okra mucilage shear and extensional viscosity were predicted using the Giesekus model.

Results: Every sample of okra mucilage exhibited shear thinning behavior. In addition to having a high extensional viscosity that is hundreds of times higher than its shear viscosity, okra mucilage also exhibited stretching phenomena. The master curves demonstrated that the pseudoplasticity of the okra mucilage increased along with the concentration. The rheological behavior of the mucilage in okra can be explained by the Giesekus model.

Conclusions: Okra mucilage's shear viscosity exhibited shear thinning behavior and a strong extensional viscosity that was significantly higher than its shear viscosity. The shear and extensional viscosity of okra mucilage can be described and predicted using the Giesekus model.

Background: Saliva is a complex fluid that lubricates the oropharynx and facilitates chewing, swallowing, and vocalization. Viscoelasticity is critical for the ability of saliva to fulfill these functions. Xerostomia, or a sensation of dry mouth, occurs in 17-26% of the population. Although many equate xerostomia with hyposalivation, high-risk patients frequently report oral dryness in the absence of decreased salivary flow.

Objective: This study aims to determine if xerostomia is associated with alterations in the rheological properties of saliva in addition to decreased salivary production.

Methods: The study population included patients with post-radiation xerostomia, patients with anticholinergic-induced xerostomia and healthy controls. Salivary volumetric flow rate was measured, shear viscosity was measured using oscillatory rheometry, and extensional viscosity was measured using capillary thinning methods. Groups were compared using descriptive statistics and univariate analysis.

Results: A total of 36 subjects were included: 15 with post-radiation xerostomia, 9 with anticholinergic-induced xerostomia and 12 controls. Salivary volumetric flow was significantly decreased in post-radiation and anticholinergic-induced patients compared to controls. On capillary thinning testing, saliva from xerostomia patients had significantly greater extensional viscosity compared to controls. However, saliva from the three groups showed no significant difference in the complex viscosity or the storage or loss modulus of saliva with oscillatory rheology.

Conclusions: Xerostomia is associated with decreased salivary volumetric flow and quantitative changes in the rheologic properties of saliva.

Background: Microparticles (MPs) have activity in thrombus promotion and generation. Erythrocyte microparticles (ErMPs) have been reported to accelerate fibrinolysis in the absence of permeation. We hypothesized that shear induced ErMPs would affect fibrin structure of clots and change flow with implications for fibrinolysis.

Objective: To determine the effect of ErMPs on clot structure and fibrinolysis.

Methods: Plasma with elevated ErMPs was isolated from whole blood or from washed red blood cells (RBCs) resuspended in platelet free plasma (PFP) after high shear. Dynamic light scattering (DLS) provided size distribution of ErMPs from sheared samples and unsheared PFP controls. Clots were formed by recalcification for flow/lysis experiments and examined by confocal microscopy and SEM. Flow rates through clots and time-to-lysis were recorded. A cellular automata model showed the effect of ErMPs on fibrin polymerization and clot structure.

Results: Coverage of fibrin increased by 41% in clots formed from plasma of sheared RBCs in PFP over controls. Flow rate decreased by 46.7% under a pressure gradient of 10 mmHg/cm with reduction in time to lysis from 5.7 ± 0.7 min to 12.2 ± 1.1 min (p < 0.01). Particle size of ErMPs from sheared samples (200 nm) was comparable to endogenous microparticles.

Conclusions: ErMPs alter the fibrin network in a thrombus and affect hydraulic permeability resulting in decelerated delivery of fibrinolytic drugs.