Biorheology - Volume 48, issue 3-4

Authors: Hu, Feng | Zha, Daogang | Du, Rongsheng | Chen, Xianghui | Zhou, Bingjie | Xiu, Jiancheng | Bin, Jianping | Liu, Yili

Article Type: Research Article

Abstract: Drag-reducing polymers (DRPs) are blood-soluble macromolecules that can increase blood flow and reduce vascular resistance. The purpose of the present study is to examine the effects of DRPs on microcirculation in rat hind limb during acute femoral artery occlusion. Two groups of 20 male Wistar rats were subjected to either hemodynamic measurement or contrast enhanced ultrasound (CEU) imaging during peripheral ischemia. Both groups were further subdivided into a DRP-treated group or a saline-treated group. Polyethylene oxide (PEO) was chosen as the test DRP, and rats were injected with either 10 ppm PEO solution or saline through the caudal vein at …a constant rate of 5 ml/h for 20 min. Abdominal aortic flow, iliac artery pressure, iliac vein pressure, heart rate, carotid artery pressure and central venous pressure (CVP) were monitored, and vascular resistance was calculated by (iliac artery pressure−iliac vein pressure)/abdominal aortic blood flow. Flow perfusion and capillary volume of skeletal muscle were measured by CEU. During PEO infusion, abdominal aortic blood flow increased (p<0.001) and vascular resistance decreased (p<0.001) compared to rats that received saline during peripheral ischemia. There was no significant change in ischemic skeletal capillary volume (A) with DRP treatment (p>0.05), but red blood cell velocity (β) and capillary blood flow (A×β) increased significantly (p<0.05) during PEO infusion. In addition, A, β and A×β all increased (p<0.05) in the contralateral hind limb muscle. In contrast, PEO had no significant influence on heart rate, mean carotid artery blood pressure or CVP. Intravenous infusion of drag reducing polymers may offer a novel hydrodynamic approach for improving microcirculation during acute peripheral ischemia. Show more

Keywords: Drag-reducing polymers, microcirculation, acute limb ischemia, contrast-enhanced ultrasound

DOI: 10.3233/BIR-2011-0592

Citation: Biorheology, vol. 48, no. 3-4, pp. 149-159, 2011

Authors: Peng, Yiyan | Turng, Lih-Sheng | Cui, Zhixiang | Woodson, Robert D. | Li, Haimei | Wang, Xiaofeng

Article Type: Research Article

Abstract: Piezoresistance describes the change of electrical resistance in a material undergoing deformation. Heterogeneous materials having different resistivities of dispersed and continuous matrix phases, such as blood (comprised of red and white blood cells and platelets suspended in plasma), can exhibit the piezoresistance effect. For an initially isotropic material, two independent intrinsic material coefficients, λ1 and λ2 , would uniquely describe the piezoresistance phenomenon. Materials undergoing deformation affect a material's resistivity in two ways: (a) by introducing anisotropy in the material, which is characterized by λ1 and (b) by changing the volume density of the inclusions, which is associated …with (1/3 λ1 +λ2 ). In this paper, the piezoresistance effect in bovine blood samples is studied under oscillatory shear flow with a planar sensor rosette. The first piezoresistance coefficient, λ1 , was measured at various frequencies and shear rates in the blood flow and compared with cos δ (equal to G′/G* , where G′ and G* are the storage and complex moduli, respectively), which reflects the degree of elasticity. The coefficient λ1 was found to have a trend similar to that of cos δ under all conditions tested. Thus λ1 might potentially be used to characterize the viscoelastic properties of blood and the deformability of red blood cells, thus clarifying pathophysiology and facilitating diagnosis. Show more

Keywords: Piezoresistance measurement, piezoresistance coefficients, blood viscoelasticity, blood elasticity, red blood cell deformability

DOI: 10.3233/BIR-2011-0594

Citation: Biorheology, vol. 48, no. 3-4, pp. 161-172, 2011

Authors: Alexy, Tamas | Baskurt, Oguz K. | Nemeth, Norbert | Uyuklu, Mehmet | Wenby, Rosalinda B. | Meiselman, Herbert J.

Article Type: Research Article

Abstract: Prior studies exploring the effects of lanthanides (Ln) on red blood cells (RBC) have primarily focused on ion transport, cell fusion, and membrane protein structure. Our previous report [Biorheology 44 (2007), 361–373] dealt only with lanthanum (La) and cell rigidity; the present study extends these observations to other lanthanides (Nd, Sm, Eu, Dy, Er) and to RBC response to mechanical shear. Deformation-shear stress behavior of normal human RBC was measured at Ln concentrations up to 200 μM. In another series of experiments, RBC were exposed to mechanical stress (190 Pa, 300 s) at 50 μM Ln and deformation-stress data obtained …prior to and after this stress. Data were fitted to a Lineweaver–Burke model to obtain the shear stress at one-half maximum deformation (SS1/2 ). Our results include: (1) lanthanides cause decreased cell deformability with the magnitude of the decrease dependent on concentration and shear stress; (2) this decrease of deformability is affected by Ln ionic radius such that La>Nd>Sm>Eu>Dy>Er and is reversible for cells in Ln-free media; (3) mechanical stress decreases deformability (i.e., increases SS1/2 ) such that compared to control, La and Sm reduce and Dy and Er enhance the mechanical stress effect; (4) the decrease of deformability consequent to mechanical stress scales inversely with Ln ionic radius. These results indicate a reciprocal relation between cell rigidity and sensitivity to mechanical stress that is mediated by Ln ionic radius. Additional studies are clearly warranted, particularly those that explore membrane-glycocalyx and intracellular mechanisms. Show more

Keywords: Lanthanides, red blood cell, deformability, mechanical stress, ionic radius

DOI: 10.3233/BIR-2011-0589

Citation: Biorheology, vol. 48, no. 3-4, pp. 173-183, 2011

Authors: Cristea, Artur | Neagu, Adrian | Sofonea, Victor

Article Type: Research Article

Abstract: Embryonic tissues and multicellular aggregates of adult cells mimic the behavior of highly viscous liquids. The liquid analogy helps to understand morphogenetic phenomena, such as cell sorting and tissue fusion, observed in developmental biology and tissue engineering. Tissue fusion is vital in tissue printing, an emergent technique based on computer-controlled deposition of tissue fragments and biocompatible materials. Computer simulations proved useful in predicting post-printing shape changes of tissue constructs. The simulation methods available to date, however, are unable to describe the time evolution of living systems made of millions of cells. The Lattice Boltzmann (LB) approach allows the implementation of …interaction forces between the constituents of the system and yields time evolution in terms of distribution functions. With tissue engineering applications in mind, we have developed a finite difference Lattice Boltzmann model of a multicellular system and applied it to simulate the sidewise fusion of two contiguous cylinders made of cohesive cells and embedded in a medium (hydrogel). We have identified a biologically relevant range of model parameters. The proposed LB model may be extended to describe the time evolution of more complex multicellular structures such as sheets or tubes produced by tissue printing. Show more

Keywords: Tissue engineering, tissue printing, Differential Adhesion Hypothesis, Boltzmann equation

DOI: 10.3233/BIR-2011-0595

Citation: Biorheology, vol. 48, no. 3-4, pp. 185-197, 2011

Authors: Brereton, G.J.

Article Type: Research Article

Abstract: Analytical solutions to the model problem of unsteady Newtonian fluid flow in straight, elastic-walled vessels can provide: theoretical insights into the flow of blood in arteries; a theoretical basis for clinical measurements in diagnoses of arterial flow rates; and guidance for boundary conditions in numerical simulations of flow in finite computational domains. However, while Womersley's analyses of blood flow assume solution forms that treat the flow as periodic and continuously unsteady, many flow variables in the smaller arteries are not continuously unsteady at all. They are characterized more accurately as rapid transient motions followed by a period of recovery to …a stationary state, repeated in successive cycles. These flows are not continually unsteady ones described by Womersley's solutions but unsteady flows restarted from rest in each cycle, characterized as initial-boundary value problems. In this paper, we compare the Womersley and initial-boundary value solutions for model transients that stop then restart, explain these previously unreported limitations of Womersley's solutions, and demonstrate how the initial-boundary value solutions provide excellent agreement with measurements of blood flow in the anterior tibial and popliteal arteries of patients. Some consequences of these findings for understanding and interpreting measurements of blood flow, and for prescribing boundary conditions in computer simulations of arterial blood flow are discussed. Show more

Keywords: Womersley, unsteady flow, blood flow, arterial flow, mathematical models, boundary conditions

DOI: 10.3233/BIR-2011-0591

Citation: Biorheology, vol. 48, no. 3-4, pp. 199-217, 2011

Authors: Chen, Chao-Tsung | Huang, Shih-Min | Hsiu, Hsin | Hsu, Wei-Chen | Lin, Feng-Cheng | Lin, Hung-Wen

Article Type: Research Article

Abstract: Objective: Beat-to-beat cardiovascular variability analysis provides important information on the autonomic control. Bilateral radial arterial blood pressure waveforms (BPW) in stroke patients were compared to explore the efficacy of frequency-domain variability index in evaluating bilateral differences in the cerebral blood-flow condition. Methods: Five-minute BPW signals were obtained in 22 stroke patients (Group S) and 21 healthy volunteers (control Group C). Amplitude proportions of the acquired pulses and their coefficient of variance (CVn ) were calculated for 1st–10th harmonics to evaluate the blood pressure harmonic variability (BPHV). Results: In Group S, CV1 –CV7 were significantly larger on the …stroke side than on the contralateral side. CV1 , CV3 –CV5 and CV7 were significantly larger on the stroke side in Group S than on either side in Group C. Conclusions: We first demonstrate the feasibility of using BPHV index to noninvasively detect the bilateral difference in cerebral vascular resistance in stroke patients. Two main indexes could be developed based on the present results: (1) bilateral differences in BPHV in stroke patients; (2) BPHV differences between normal and stroke subjects. It might have meaning in developing an easy-to-perform, noninvasive and continuous monitoring technique to improve the early detection and disease progress monitoring for stroke. Show more

Keywords: Blood pressure waveform, stroke, variability, harmonic analysis

DOI: 10.3233/BIR-2011-0593

Citation: Biorheology, vol. 48, no. 3-4, pp. 219-228, 2011

Authors: Geerligs, Marion | Oomens, Cees | Ackermans, Paul | Baaijens, Frank | Peters, Gerrit

Article Type: Research Article

Abstract: This study presents an in vitro experimental method to determine shear properties of the epidermis. Shear tests were performed with a parallel plate rheometer on samples of stratum corneum and the viable epidermis. The method was validated on very thin silicon sheets. Preliminary test were performed to determine the linear viscoelastic range, the effect of normal loading on the sample and the time to reach equilibrium after changes of temperature and relative humidity. The study shows that reproducible results can be obtained for the shear properties of epidermis in an in vitro set up. The dynamic shear modulus for stratum …corneum ranges from about 4–12 kPa, decreasing with increasing relative humidity. The values are considerably lower than the shear modulus value based on tensile Young's moduli in the literature, indicating a considerable anisotropic material behavior. Results for the epidermis were of the same order of magnitude, but were less consistent possibly due to a less well-defined tissue composition. Show more

Keywords: Stratum corneum, epidermis, mechanical properties, in vitro

DOI: 10.3233/BIR-2011-0590

Citation: Biorheology, vol. 48, no. 3-4, pp. 229-245, 2011