Biorheology - Volume 50, issue 1-2

Authors: Goldsmith, Harry

Article Type: Other

DOI: 10.3233/BIR-130633

Citation: Biorheology, vol. 50, no. 1-2, pp. 1-2, 2013

Authors: Lipowsky, Herbert H.

Article Type: Research Article

DOI: 10.3233/BIR-130625

Citation: Biorheology, vol. 50, no. 1-2, pp. 3-16, 2013

Authors: Down, Linden A. | Papavassiliou, Dimitrios V. | O'Rear, Edgar A.

Article Type: Research Article

Abstract: The goal of this work is to better understand the association between renal artery aneurysms and secondary hypertension through modeling the blood flow and the mechanics of diseased arteries. A large number of patients with renal artery aneurysms exhibit hypertension. Following surgical intervention, some patients experience improvement in their hypertension while others do not. This indicates that for some patients, the aneurysm is directly related to their hypertension, possibly through a hemodynamic effect on hormonal blood pressure control. In previous work, we proposed a possible mechanism for this – that high pressure inside an aneurysm may cause the arterial wall …to deform and constrict the artery, creating a “pseudostenosis”. Here, we use fluid structure interaction simulations to investigate the deformation of the renal artery in the presence of an aneurysm. Aneurysms on the superior surface and at the main bifurcation of the artery have been modeled, and the effect of changes in mechanical properties and geometry were investigated. For some cases, it was found that an aneurysm could cause flow distortions that led to higher than normal pressure losses without significant vessel wall deformation. For other cases, conditions were determined that induced movement of the arterial wall with constriction of the underlying artery. The maximum occlusion observed was 54% for a symmetric aneurysm at the main bifurcation with a severely weakened wall with a Young's modulus of 1×103 Pa. Show more

Keywords: Renin-dependent hypertension, hemodynamics, fluid structure interaction, arterial mechanics

DOI: 10.3233/BIR-130623

Citation: Biorheology, vol. 50, no. 1-2, pp. 17-31, 2013

Authors: Xu, Yingqian | Wang, Bochu | Deng, Jia | Liu, Zerong | Zhu, Liancai

Article Type: Research Article

Abstract: The purpose of this paper was to research the potential of a dynamic cell model in drug screening by studying the influence of microvascular wall shear stress on the drug absorption of endothelial cells compared to that in the static state. The cells were grown and seeded on gelatin-coated glass slides and were pretreated with extracts of Salviae miltiorrhizae (200 μg/ml) for 1 h. Then oxidative stress damage was produced by H2 O2 (300 μmol/l) for 0.5 h under the 1.5 dyn/cm2 shear stress incorporated in a parallel plate flow chamber. Morphological analysis was conducted with an inverted …microscope and image analysis software, and high performance liquid chromatography-mass spectrometry was used for the detection of active compounds. We compared the drug absorption in the dynamic group with that in the static group. In the dynamic model, five compounds and two new metabolite peaks were detected. However, in the static model, four compounds were absorbed by cells, and one metabolite peak was found. This study indicated that there were some effects on the absorption and metabolism of drugs under the microvascular shear stress compared to that under stasis. We infer that shear stress in the microcirculation situation in vivo played a role in causing the differences between drug screening in vitro and in vivo. Show more

Keywords: Dynamic screening model, antioxidant activity, HPLC-MS, Radix Salviae miltiorrhizae, bioactive compounds

DOI: 10.3233/BIR-130624

Citation: Biorheology, vol. 50, no. 1-2, pp. 33-43, 2013

Authors: Arwatz, G. | Smits, A.J.

Article Type: Research Article

Abstract: We present measurements of human blood hemolysis caused by laminar shear stresses ranging from 50 to 500 Pa for exposure times extending from 60 to 300 s using a Taylor–Couette device. A viscoelastic model is proposed that captures the response of the red blood cells to shear stress. The model is based on well-established mechanical properties of the red blood cell membrane, and shows good agreement with data from the experiments presented here, as well as data from the existing literature. Two characteristic time scales are identified: a fast time scale corresponding to the relaxation time of the red blood …cell membrane and a slow time scale that represents the onset of plasticity and is related to hemoglobin release from a damaged cell. The model proposed here collapses the available data over almost five orders of magnitude in exposure time and shear stresses up to 500 Pa. Show more

Keywords: Hemolysis, Kelvin–Voigt, Couette flow, blood experiment, erythrocyte

DOI: 10.3233/BIR-130626

Citation: Biorheology, vol. 50, no. 1-2, pp. 45-55, 2013

Authors: Deng, Wenni | Iannetta, Pietro P.M. | Hallett, Paul D. | Toorop, Peter E. | Squire, Geoffrey R. | Jeng, Dong-Sheng

Article Type: Research Article

Abstract: The outer surface of myxospermous seed coats contains mucilage which absorbs large amounts of water relative to its dry weight. Ecologically, the seed mucilage can affect seed germination and dormancy. Upon hydration, a large proportion of the seed mucilage is lost to the soil and the physics of soil-seed mucilage interactions has not been assessed. Towards that end, the dynamic rheological properties of mucilage extracted from Capsella bursa-pastoris L. Medik. (shepherd's purse) seeds were assessed as a function of mucilage concentration (1–10% [w/w]), temperature (0–80°C) and shear frequency (0.1–100 rad s−1 ). The seed mucilage was shear thinning and was …classified as a highly viscous “weak gel”. The relationship between the viscoelastic parameters (viscosity, η* , storage and loss modulus, G′ and G″, yield and flow stresses, τy and τf ) and mucilage concentration were well fitted by power law models. The values of η* , G′ and G″ increased as temperature increased above 40°C and were also slightly frequency dependent. The shepherd's purse seed mucilage is more viscous than that from other plant parts, such as fruits and roots. These properties highlight the possibility that seed mucilage may affect soil conditions and therefore present an additional facilitative ecological role (beyond that already reported, which directly affect seed biology); and this is discussed. Show more

Keywords: Myxospermy, viscosity, shear modulus, gel

DOI: 10.3233/BIR-130627

Citation: Biorheology, vol. 50, no. 1-2, pp. 57-67, 2013

Authors: Hsiu, Hsin | Hsu, Chia-Liang | Chen, Chao-Tsung | Hsu, Wei-Chen | Lin, Fong-Cheng

Article Type: Research Article

Abstract: MOTIVATION: Stroke induces abnormal microcirculatory blood flow perfusion resistance in cerebral vascular beds, which may in turn alter the arterial pulse transmission. This study aimed to determine if the frequency-domain harmonic index for the blood-pressure waveform is useful in monitoring the microcirculatory blood flow perfusion response in cerebral vascular beds of stroke patients following acupuncture stimulation. METHODS: Bilateral radial arterial blood-pressure waveform and laser-Doppler flowmetry signals were obtained noninvasively before and after acupuncture in 17 stroke patients. The amplitude proportion (Cn ) for all the acquired pulses and the coefficient of variance (CVn ) for harmonics 1–10 were calculated …to evaluate the blood-pressure harmonic variability. RESULTS: The laser-Doppler flowmetry parameters showed that the cerebral microvascular blood flow supply could be improved following acupuncture. For the blood pressure waveform harmonic index, there were significant increases in C5 and C6 and decreases in CV5 and CV7 on the stroke-affected side, but no significant changes on the contralateral side. CONCLUSION: Cn values might reflect changes in arterial pulse transmission, and the blood-pressure-harmonic-variability response might be partly attributable to cardiovascular regulatory activities caused by acupuncture-induced changes in the cerebral microvascular blood flow perfusion. The present findings of blood pressure waveform harmonic analysis may be useful to the development of a noninvasive and real-time technique for evaluating treatment efficacy in stroke patients. Show more

Keywords: Harmonic analysis, blood pressure waveform, stroke, acupuncture

DOI: 10.3233/BIR-130629

Citation: Biorheology, vol. 50, no. 1-2, pp. 69-81, 2013

Authors: Kumar, Bipin | Das, Apurba | Alagirusamy, R.

Article Type: Research Article

Abstract: BACKGROUND: Internal stress in a compression bandage wrapped over a limb in vitro is expected to reduce over time because of fatigue which may occur due to repetitive and prolonged variations in the extension of the bandage during posture change and exercise. This phenomenon may cause significant variation in the sub-bandage pressure over time. OBJECTIVE: To examine the effect of composition and construction of material on the sub-bandage pressure variation over time in the dynamic state of a limb in the laboratory. METHODS: Yarns comprising fibers of polyester, viscose, cotton and elastomeric yarn were used to prepare different …knitted bandage samples having varying thread densities in the structure. A leg-segment prototype was used for the measurement of the interface pressure over a mannequin limb to analyse different bandages under similar dynamic conditions. RESULTS: The pressure drop in the dynamic state of the mannequin limb was greater than that in the static state. The mean pressure drop in 2 h in the dynamic state was greater by >30% for bandages made of pure cotton or viscose yarns than for bandages having elastomeric yarns in their structure. At the same applied tension, increasing the number of yarns per unit length in the bandage structure resulted in a smaller drop in pressure in the dynamic mode. CONCLUSION: Elastomeric yarn improves the elasticity and fatigue resistance of the bandage. Therefore, these yarns should be used in bandages to obtain sustained compression effects under dynamic conditions. Show more

Keywords: Compression bandage, composition, mannequin limb, interface pressure, fatigue

DOI: 10.3233/BIR-130628

Citation: Biorheology, vol. 50, no. 1-2, pp. 83-94, 2013