Biorheology - Volume 45, issue 6

Authors: Baskurt, Oguz K.

Article Type: Review Article

Abstract: It is has been known for more than 80 years that compared to in vitro determinations, blood behaves as a less viscous fluid under in vivo flow conditions. The experiments of Whittaker and Winton were among the first dealing with the in vivo effects of altered blood rheology, and experimental studies during the second half of 20th century have provided additional evidence for the complexity of in vivo hemodynamics–hemorheology relationships. Careful studies indicate that the impact of a given blood rheology alteration is determined by the properties of the experimental model (e.g., organ or tissue under investigation), experimental approach (e.g., …intravital microscopy, whole organ perfusion) and method used to modify blood rheology. In addition, vascular control mechanisms may play a major role in the resulting hemodynamic effects of a hemorheological alteration: (1) a response simply related to metabolic autoregulation in which there is a compensatory vasodilation due to altered in vivo blood flow and organ/tissue hypoxia; (2) modulation of endothelial function (e.g., NO production) via altering wall shear stress, thereby leading to changes of vascular hindrance. The in vivo effects of altered red blood cell (RBC) aggregation have been investigated in various experimental models. A novel technique for modifying RBC aggregability (i.e., intrinsic tendency of RBC to aggregate) by covalent attachment of specific co-polymers has been used in some studies, and has provided data reflecting the specific effects of RBC aggregation without the influence of altered suspending phase properties. These data indicate that both the magnitude of the hemodynamic effect and the direction of the alteration depend on the intensity of RBC aggregation. Using the same novel technique, RBC aggregation has been shown to be an important determinant of endothelial function through its effects on RBC axial distribution and wall shear stress. These somewhat diverse findings can be explained by considering the contribution of various in vivo hemorheological mechanisms that have opposite effects on in vivo flow resistance. Show more

Keywords: Hemorheology, erythrocyte aggregation, erythrocyte deformability, in vivo blood flow, hemodynamics

DOI: 10.3233/BIR-2008-0515

Citation: Biorheology, vol. 45, no. 6, pp. 629-638, 2008

Authors: Kaliviotis, E. | Yianneskis, M.

Article Type: Research Article

Abstract: The present work reports on an important feature of the fast response dynamics of blood flow observed after abrupt changes of the shearing conditions: distinctive peak values in conductance and light reflection/transmission have been observed at short times after the abrupt changes in the shearing conditions and have been attributed to red blood cell (RBC) disorientation and shape changes. Optical shearing microscopy results from the present study show that this peak is directly related to the inter-cellular or inter-aggregate spacing, quantified as the plasma gaps present in the captured images. In order to provide a more in-depth understanding of the …structural characteristics of blood subjected to abrupt changes in the flow conditions, normal human blood samples at hematocrits of 45, 35, 25 and 10% were sheared at 100 s−1 and the shear then suddenly reduced to values decreasing from 60 to 0 s−1 . Results from the present study agree qualitatively and quantitatively with results previously reported in the literature: the hematocrit and the magnitude of the final shear rate affect the magnitude of the peak values. The characteristic peak time was mostly influenced by the cell concentration. It is suggested that aggregation forces may play a part in the process of the fast response structural and spatial rearrangements of RBC. Show more

Keywords: Aggregation dynamics, image analysis, inter-cellular spacing, deformation

DOI: 10.3233/BIR-2008-0514

Citation: Biorheology, vol. 45, no. 6, pp. 639-649, 2008

Authors: van den Broek, Chantal N. | Pullens, Rolf A.A. | Frøbert, Ole | Rutten, Marcel C.M. | den Hartog, Wilfred F. | van de Vosse, Frans N.

Article Type: Research Article

Abstract: Physiological wall shear rates and stresses in vessel culture or tissue engineering are relevant for maintaining endothelial cell (EC) integrity. To this end, the culture medium should have an appropriate viscosity. The viscosity of a standard culture medium was increased using xanthan gum (XG) and compared with literature data on whole blood, resulting in a medium with blood-analog shear-thinning behavior (XG-medium). The measured osmolality of the XG-medium was 285±2 mOsm kg−1 , which is within a physiologically acceptable range. The XG-medium was compared to standard medium to verify whether XG alters vascular cell function. First, the effect of XG on …the growth of human EC monolayers was determined. In addition, to study whether XG changes drug-induced vasoconstriction or endothelium-dependent vasodilation, different drugs were administered to porcine coronary artery rings in a solution with or without XG, measuring the isometric force developed. XG did not influence EC growth, nor did it change drug-induced vascular tone. Moreover, the ECs aligned in the direction of flow after 24 h of physiological shearing with XG-medium. We conclude that, unlike standard culture media, XG-medium as a blood-analog culture medium has rheological properties suitable for use in vessel culture and tissue engineering to induce physiological wall shear stresses at physiological flow rates. Show more

Keywords: Xanthan gum, wall shear stress, viscosity, coronary artery, tissue engineering

DOI: 10.3233/BIR-2008-0513

Citation: Biorheology, vol. 45, no. 6, pp. 651-661, 2008

Authors: Hrapko, M. | van Dommelen, J.A.W. | Peters, G.W.M. | Wismans, J.S.H.M.

Article Type: Research Article

Abstract: No validated, generally accepted data set on the mechanical properties of brain tissue exists, not even for small strains. Most of the experimental and methodological issues have previously been addressed for linear shear loading. The objective of this work was to obtain a consistent data set for the mechanical response of brain tissue to either compression or shear. Results for these two deformation modes were obtained from the same samples to reduce the effect of inter-sample variation. Since compression tests are not very common, the influence of several experimental conditions for the compression measurements was analysed in detail. Results with …and without initial contact of the sample with the loading plate were compared. The influence of a fluid layer surrounding the sample and the effect of friction were examined and were found to play an important role during compression measurements. To validate the non-linear viscoelastic constitutive model of brain tissue that was developed in Hrapko et al. (Biorheology 43 (2006), 623–636) and has shown to provide a good prediction of the shear response, the model has been implemented in the explicit Finite Element code MADYMO. The model predictions were compared to compression relaxation results up to 15% strain of porcine brain tissue samples. Model simulations with boundary conditions varying within the physical ranges of friction, initial contact and compression rate are used to interpret the compression results. Show more

Keywords: Brain tissue, compression, constitutive model, friction, mechanical properties

DOI: 10.3233/BIR-2008-0512

Citation: Biorheology, vol. 45, no. 6, pp. 663-676, 2008

Authors: Geerligs, Marion | Peters, Gerrit W.M. | Ackermans, Paul A.J. | Oomens, Cees W.J. | Baaijens, Frank P.T.

Article Type: Research Article

Abstract: Subcutaneous adipose tissue contributes to the overall mechanical behavior of the skin. Until today, however, no thorough constitutive model is available for this layer of tissue. As a start to the development of such a model, the objective of this study was to measure and describe the linear viscoelastic behavior of subcutaneous adipose tissue. Although large strains occur in vivo, this work only focuses on the linear behavior to show the applicability of the described methods to adipose tissue. Shear experiments are performed on porcine samples on a rotational rheometer using parallel plate geometry. In the linear viscoelastic regime, up …to 0.1% strain, the storage and loss modulus showed a frequency- and temperature-dependent behavior. The ratio between the two moduli, the phase angle, did not show any dependency on temperature and frequency. The shear modulus was found to be 7.5 kPa at 10 rad/s and 37°C. Time–temperature superposition was applicable through shifting the shear modulus horizontally. A power-law function model was introduced to describe both the frequency dependent behavior at constant temperature and the stress relaxation behavior. In addition, the effect of snap freezing as a preservation method was analyzed. Histological examination demonstrated possible tissue damage after freezing, but the mechanical properties did not change. Since results were reproducible, it is concluded that the methods we used are most probably suited to explore the non-linear behavior of subcutaneous adipose tissue. Show more

Keywords: Mechanical properties, rheometry, hypodermis, time–temperature superposition, power–law model, snap freezing

DOI: 10.3233/BIR-2008-0517

Citation: Biorheology, vol. 45, no. 6, pp. 677-688, 2008

Authors: Samukawa, Keiichi | Suzuki, Yoji | Ohkubo, Nobutaka | Aoto, Mamoru | Sakanaka, Masahiro | Mitsuda, Noriaki

Article Type: Research Article

Abstract: The extract from Panax ginseng has been reported to improve the microcirculation in various organs. However, the mechanisms underlying this phenomenon are still poorly understood. In the present study, using the rheological properties of erythrocytes as an index, we have screened the components of Panax ginseng extract and identified Rg2 and Rh1 as the active ingredients. These two ginsenosides prevented the oxidative stress-induced elevation of erythrocyte suspension viscosity and the impairment of erythrocyte elongation in response to shear stress. Rg2 and Rh1 ginsenosides did not have antioxidant activity in an aqueous phase and did not inhibit …the peroxidation of membrane lipids, either. However, they inhibited the oxidation-induced decrease of SH-groups in band 3 (anion exchanger-1), one of the important structural proteins of the erythrocyte membrane, but not in other structural proteins: bands 1 and 2 (spectrins), band 4.2 or band 5 (actin). These results suggest that ginsenosides Rg2 and Rh1 protect the rheological functions of erythrocytes against oxidative stress by preventing the oxidation of SH-groups in band 3 protein. Show more

Keywords: Ginsenoside Rg_2, ginsenoside Rh_1, thiol group, band 3, oxidative stress, erythrocyte

DOI: 10.3233/BIR-2008-0516

Citation: Biorheology, vol. 45, no. 6, pp. 689-700, 2008

Article Type: Abstract

DOI: 10.3233/BIR-2008-0518

Citation: Biorheology, vol. 45, no. 6, pp. 701-705, 2008

Article Type: Other

Citation: Biorheology, vol. 45, no. 6, pp. 707-712, 2008