Biorheology最新文献

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.

BackgroundThe 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.MethodsThree 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.ResultsSeeding of polymer microspheres in BAF results in significant changes in shear-thinning properties, such as zero- and infinite-viscosity (${\mu }_0$ and ${\mu }_{\infty }$, 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 ${\mu }_{\infty }$.ConclusionPolymer microspheres in BAF significantly alters its shear-thinning properties and must be considered for better hemodynamic evaluations in medical device testing.

BackgroundCardiovascular 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.ObjectiveTo investigate alterations in hemorheology and systemic oxidative stress in patients with acromegaly.MethodsThe 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_½), 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.ResultsThere 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_½ 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).ConclusionsThis pilot study demonstrated reduced erythrocyte deformability and increased erythrocyte aggregation in patients with AA and CA.

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.

BackgroundRed 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.ObjectiveThe objective of this study was to evaluate aggregation measurement techniques with respect to common effectors of red blood cell aggregation.MethodsWe 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).ResultsFor 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.ConclusionsRed 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.

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 whole body vibration exercise (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 included 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.