BackgroundResidual strains in the unloaded human aorta are fundamental for understanding the in vivo stress and strain distribution across the aortic wall, including the intima, media, and adventitia, which is crucial for aortic function.ObjectiveTo report the detailed pattern of axial variation in layer-specific residual stretches and its relationship to age, gender, and circumferential location.MethodsCircumferential and axial strips from the anterior and posterior quadrants of nine aortic levels from twenty-one autopsy subjects were photographed before and after dissection into layers to determine layer-specific zero-stress states. Image analysis was used to assess variations in opening angles, residual stretches, and thickness at each level and direction.ResultsAge-related changes included a significant decline in the axial opening angle of the intact wall, driven by the adventitia. Its axial external residual stretch declined strikingly with age in the descending thoracic and abdominal aorta, outweighing the smaller increase in intact wall external residual stretch. Similarly, the slight age-related increase in intact wall internal residual stretch was more than offset by the significant decrease in circumferential internal residual stretch of the intima in the arch and descending thoracic aorta. The posterior quadrant was thicker and experienced lower external residual strains than the anterior. Gender-related differences were minimal, aside from greater wall thickness in males.ConclusionsThe age-related differences identified, distinguished by direction and layer, are consistent with previous observations on the orientation and age-related depletion of elastin across aortic layers, reinforcing its role as the primary determinant of residual strains.
Background The viscosity of blood analog fluid (BAF) influences the hemodynamics during testing of medical devices and implants in cardiovascular systems mimicking physiologic flow conditions. BAF, typically composed of water, glycerin, and Xanthan gum, is used to simulate blood's non-Newtonian shear-thinning behavior. Additionally, BAF may include microsphere particles for flow visualization in Laser Doppler Velocimetry (LDV) experiments, though their impact on viscosity remained an under-investigated area. Hypothesis: Addition of particles in the form of polymer microspheres in a BAF solution influences the rheological properties of the fluid.Methods Three different test fluids comprising of 16 ml BAF solution with the varying concentrations of polymer microspheres were created: 1% (weight/volume; w/v) and 2% w/v represent test samples, whereas 0% w/v (no microsphere) represents a control sample. The viscosities of BAF for with and without polymer microspheres were measured using a concentric cylinder viscometer. Recorded viscosity data was then optimized by fitting the Carreau model.Results Seeding of polymer microspheres in BAF results in significant changes in shear-thinning properties, such as zero- and infinite-viscosity ( mu 0 and mu infinity , respectively), in relation to viscosity of real blood or BAF without microspheres. It is evident that effect of microsphere seeding in BAF is relatively more pronounced on mu 0 as compared to mu infinity .Conclusion Polymer microspheres in BAF significantly alters its shear-thinning properties and must be considered for better hemodynamic evaluations in medical device testing.
BackgroundPrevious studies characterizing the tensile strength of abdominal aortic aneurysms (AAAs) have disregarded the post-failure phase during which rupture propagates.ObjectiveTo identify aneurysm-induced changes in the post-failure phase of the intact infra-renal aortic wall, examining its three layers.MethodsWe analyzed ex vivo tensile tests on tissues from 27 AAA patients and 27 age-matched autopsy subjects.ResultsThe failure stress of the intact wall circumferentially and the intimal failure stress in both circumferential and longitudinal directions were significantly lower (p < 0.05) in AAAs than in non-aneurysmal aortas (NAAs). Failure stretch showed no significant changes. However, the pre-failure stretches of the intact wall and media circumferentially were higher (p < 0.05) in AAAs, as were the post-failure stretches of the intact wall and media in both directions and the adventitia circumferentially. The pre-extensions of the media and adventitia were also higher (p < 0.05) when coupled to the intact wall.ConclusionsThe study demonstrates an earlier onset of damage in AAAs and a strength decrease, indicating weakening. The medial and adventitial layers contribute more in determining AAA intact-wall properties. Their greater capacity for post-failure stretch may delay rupture progression outward, preserving the integrity of the entire aortic thickness despite initiation in the weakened intima.
Background Obesity can result in increased visceral adipose tissue, insulin resistance, and impaired fasting glucose. Objective The aim of the study was to investigate the acute and chronic effects of WBVE on erythrocyte deformability, plasma viscosity, total oxidant/antioxidant status (TOS/TAS), oxidative stress index (OSI) and serum exerkine levels in obese women. Methods The study comprised 13 obese women (mean age 41.32 +/- 5.26 years, BMI 34.18 +/- 1.67 kg/m2). Participants performed exercises using a vibration device for 12 sessions. Erythrocyte deformability (ektacytometry), plasma viscosity (rotational viscometry), plasma TOS/TAS, OSI and serum irisin, visfatin and resistin concentrations (ELISA) were evaluated. Blood samples were collected before and after the exercise at the first and fourth weeks. Results Erythrocyte deformability values were increased after single session of WBVE at shear stress of 0.30 and 9.49 Pa and decreased after single session of WBVE at shear stress of 16.87 and 30 Pa (p < 0.05) at the first week. However, after 4 weeks of WBVE, erythrocyte deformability at 0.30 and 0.53 Pa increased; TOS, OSI and plasma viscosity were all decreased (p < 0.05). Serum irisin and resistin levels significantly increased after 4 weeks of WBVE (p < 0.05), whereas visfatin did not show statistically significant changes (p > 0.05). Conclusions Four weeks of WBVE significantly improved the erythrocyte deformability, oxidative stress, plasma viscosity, and serum levels of irisin and resistin in obese women.
BackgroundThe plant stem is composed of epidermal and inner tissues that are under tension and compression, respectively. Therefore, the adhesion of both tissues is considered to be involved in the structural integrity of the stem. However, the role of tissue adhesion in stem structure is unclear.ObjectiveThis study aimed to develop a method for quantitatively measuring the adhesive strength between the epidermal and inner tissues using a tensile tester to determine the possible role of tissue adhesion in stem integrity.MethodsThe epidermal tissue was partially peeled from the segment of pea epicotyls using forceps to create a peeling arm. The peeling arm and the segment region of the partially removed epidermal tissue were fixed to the upper and lower clamps, respectively. By raising the upper clamp at various speeds, the epidermal tissue was peeled from the segment, and the peeling force was recorded.ResultsAdhesive strength was defined as the peeling force normalized by the width of the peeled epidermal tissue. The peeling rate was determined as 100 mm/min. The adhesive strength in the elongation region of the stem was substantially smaller than in the non-elongation region.ConclusionsA method for quantitatively measuring the adhesive strength between the epidermal and inner tissues was developed. Analysis using this method suggests that adhesive strength may be involved in regulating stem growth.
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 (t 1/2), 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 t 1/2 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: A challenge for coaches and athletes is to find the best combination of exercises during training. Considering its favorable effects, HIIT has been very popular recently. OBJECTIVE: The goal of this study was to investigate anthropometric features, performance, erythrocyte deformability, plasma viscosity (PV) and oxidative stress in response to acute and long-term (6 weeks) HIIT in adolescent basketball players. METHODS: 22 sportsmen between the ages of 14-16 were included. Tabata protocol was applied to the HIIT group in addition to their routine training program 3 days/week, for 6 weeks. Erythrocyte deformability was determined using an ectacytometer (LORCA), PV with a rotational viscometer. Total oxidant status (TOS), total antioxidant status (TAS) were measured by kits. RESULTS: HIIT for 6 weeks induced an improvement in performance tests and waist circumference. 6 weeks of HIIT resulted in a decrement, while the last exercise session yielded an increment in RBC deformability. PV and TOS of HIIT groups were decreased on the 6th week. CONCLUSIONS: Our results demonstrate that, HIIT in addition to the routine exercise program is beneficial for improving performance and blood fluidity as well as decreasing oxidative stress in basketball players. Therefore, HIIT seems as an efficient training strategy for highly-trained individuals.
Leukocytes and platelets must adhere to the wall of blood vessels to carry out their protective functions in inflammation and haemostasis. Recruitment is critically dependent on rheological variables (wall shear rate and stress, red cell aggregation and haematocrit) which affect delivery to the vessel wall as well as velocities and forces experienced there. Leukocyte recruitment is efficient only up to wall shear rates of about 300 s−1 and usually restricted to low-shear post-capillary venules in inflammation. Being smaller, platelets experience lower velocities and shear forces adjacent to the wall and can adhere at much higher shear rates for haemostasis in arteries. In addition, we found quite different effects of variations in haematocrit or red cell aggregation on attachment of neutrophils or platelets, which also assist their separate recruitment in venules or arteries. However, it has become increasingly evident that inflammatory and thrombotic responses may occur together, with platelets promoting the adhesion and activation of neutrophils and monocytes. Indeed, it is 30 years since we demonstrated that platelets could cause neutrophils to aggregate in suspension and, when attached to a surface, could support selectin-mediated rolling of all leukocytes. Thrombin-activated platelets could further induce neutrophil activation and immobilisation. In some conditions, platelets could bind to intact endothelial monolayers and capture neutrophils or monocytes. Subsequently, we found that extracellular vesicles released by activated platelets (PEV) fulfilled similar functions when deposited on surfaces or bound to endothelial cells. In murine models, platelets or PEV could act as bridges for monocytes in inflamed vessels. Thus, leukocytes and platelets are rheologically adapted for their separate functions, while novel thrombo-inflammatory pathways using platelets or PEV may underlie pathogenic leukocyte recruitment.
The International Society for Biorheology has selected Professor Gerard Nash as recipient of the Poiseuille Medal for his seminal work on the role of leukocytes, platelets and the vessel wall in thrombosis and inflammation.After studying engineering and physics as an undergraduate in Manchester, Gerard pursued a research career in the biophysical sciences and received a Ph.D. in London that focused on the development of flowbased instrumentation for automated cell characterization.These studies led to an interest in blood cell mechanics, which he pursued in post-doctoral studies at Guy's hospital and subsequently with Professor Herbert Meiselman at the University of Southern California.His post-doctoral studies centered on analysis of the physical properties of red cells and leukocytes, that influence their circulation.On returning to UK to work with
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.
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: 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.
