Biorheology - Volume 59, issue 1-2

Authors: Good, Bryan C.

Article Type: Research Article

Abstract: BACKGROUND: Computational fluid dynamics (CFD) is an important tool for predicting cardiovascular device performance. The FDA developed a benchmark nozzle model in which experimental and CFD data were compared, however, the studies were limited by steady flows and Newtonian models. OBJECTIVE: Newtonian and non-Newtonian blood models will be compared under steady and pulsatile flows to evaluate their influence on hemodynamics in the FDA nozzle. METHODS: CFD simulations were validated against the FDA data for steady flow with a Newtonian model. Further simulations were performed using Newtonian and non-Newtonian models under both steady and pulsatile flows. …RESULTS: CFD results were within the experimental standard deviations at nearly all locations and Reynolds numbers. The model differences were most evident at Re = 500, in the recirculation regions, and during diastole. The non-Newtonian model predicted blunter upstream velocity profiles, higher velocities in the throat, and differences in the recirculation flow patterns. The non-Newtonian model also predicted a greater pressure drop at Re = 500 with minimal differences observed at higher Reynolds numbers. CONCLUSIONS: An improved modeling framework and validation procedure were used to further investigate hemodynamics in geometries relevant to cardiovascular devices and found that accounting for blood’s non-Newtonian and pulsatile behavior can lead to large differences in predictions in hemodynamic parameters. Show more

Keywords: FDA, computational fluid dynamics, non-Newtonian, pulsatility, benchmark

DOI: 10.3233/BIR-201019

Citation: Biorheology, vol. 59, no. 1-2, pp. 1-18, 2023

Authors: Rereddy, S.K. | Cao, A.C. | Blackwell, B. | Poling-Skutvik, R. | Arratia, P.E. | Mirza, N.

Article Type: Research Article

Abstract: 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. Show more

Keywords: Xerostomia, saliva viscosity, salivary volumetric flow, extensional viscosity, anticholinergic effects, radiation effects

DOI: 10.3233/BIR-210014

Citation: Biorheology, vol. 59, no. 1-2, pp. 19-27, 2023

Authors: Minh, Nguyen Ngoc

Article Type: Research Article

Abstract: 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. Show more

Keywords: Okra, extensional viscosity, shear viscosity, Giesekus model

DOI: 10.3233/BIR-220006

Citation: Biorheology, vol. 59, no. 1-2, pp. 29-42, 2023

Authors: Buerck, James P. | Foster, Kylie M. | Larson, Preston R. | O’Rear, Edgar A.

Article Type: Research Article

Abstract: 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. Show more

Keywords: Erythrocyte, microvesicle, thrombus, ventricular assist device

DOI: 10.3233/BIR-220012

Citation: Biorheology, vol. 59, no. 1-2, pp. 43-59, 2023