Biorheology - Volume 34, issue 6

Article Type: Other

DOI: 10.3233/BIR-1997-34608

Citation: Biorheology, vol. 34, no. 6, pp. I-VII, 1997

Authors: Goldsmith, Harry

Article Type: Editorial

DOI: 10.3233/BIR-1997-34601

Citation: Biorheology, vol. 34, no. 6, pp. iii-iv, 1997

Article Type: Obituary

DOI: 10.3233/BIR-1997-34602

Citation: Biorheology, vol. 34, no. 6, pp. v-x, 1997

Authors: Bilston, Lynne E. | Liu, Zizhen | Phan-Thien, Nhan

Article Type: Research Article

Abstract: We report the results from a series of rheological tests of fresh bovine brain tissue. Using a standard Bohlin VOR shear rheometer, shear relaxation and oscillating strain sweep experiments were performed on disks of brain tissue 30 mm in diameter, with a thickness of 1.5–2 mm. The strain sweep experiment showed that the viscoelastic strain limit is of the order of 0.1% strain. Shear relaxation data do not indicate the presence of a long-term elastic modulus, indicating fluid-like behavior. A relaxation spectrum was calculated by inverting the experimental data and used to predict oscillatory response, which agreed well with measured …data. Show more

Keywords: Biomechanics, rheology, tissue mechanics, viscoelasticity

DOI: 10.3233/BIR-1997-34603

Citation: Biorheology, vol. 34, no. 6, pp. 377-385, 1997

Authors: Craelius, W. | Huang, C.-J. | Guber, H. | Palant, C.E.

Article Type: Research Article

Abstract: The response of cells to mechanical forces depends on the rheological properties of their membranes and cytoplasm. To characterize those properties, mechanical and electrical responses to swelling were measured in rat mesangial cells (MC) using electrophysiologic and video microscopic techniques. Ion transport rates during hyposmotic exposures were measured with whole-cell recording electrodes. Results showed that cell swelling varied nonlinearly with positive internal pressure, consistent with a viscoelastic cytoplasm. The extrapolated area expansivity modulus for small deformations was estimated to be 450 dyne/cm. Cell swelling, caused either by positive pipet pressure or hyposmotic exposure (40–60 mOsm Kg-l ), rapidly induced an …outwardly rectifying membrane conductance with an outward magnitude 4–5 times the baseline conductance of 0.9 ± 0.5 nS (p < .01). Swelling-induced (SI) current was weakly selective for K+ over Na+, partially reversed upon return to isotonicity, and was antagonized by 0.5 mM GdCl3 (p < 0.02; n = 6). Isolated cells treated with GdCl3 rapidly lysed after hypotonic exposure, in contrast to untreated cells that exhibited regulatory volume decrease (RVD). Our results indicate that volume regulation by MC depends upon a large swelling-induced K+ efflux, and suggest that swelling in MC is a viscoelastic process, with a viscosity dependent on the degree of swelling. Show more

Keywords: Cell swelling, kidney, membrane stiffness, stretch-activated channels

DOI: 10.3233/BIR-1997-34604

Citation: Biorheology, vol. 34, no. 6, pp. 387-403, 1997

Authors: Poflee, Narendra M. | Rakow, Allen L. | Dandy, David S. | Chappell, Micheal L. | Pons, Marie-Noelle

Article Type: Research Article

Abstract: When a dilute suspension flows in the laminar regime through a tube, under certain conditions the suspended particles migrate radially to an equilibrium radial position. Branched tubes can use this radial concentration distribution to concentrate dilute suspensions. Suspensions of micro algae , Chlorella vulgaris, were pumped through tubes of various diameters for tube Reynolds number ranging from 47-1839 and photographed. Upstream particle concentration profiles were obtained by image analysis of the photographs. The dividing stream surfaces in branched tubes were obtained from the three- dimensional numerical solutions of the Navier-Stokes equations for steady, laminar, and homogeneous flow through tubes having …one and two orthogonal branches. Concentration factors for Chlorella suspensions in branched tubes, predicted by a general method, fall in the range of 1.0–1.3 Show more

Keywords: Inertial particle migration, suspension concentration technique, branched tube separators, dividing stream surfaces

DOI: 10.3233/BIR-1997-34605

Citation: Biorheology, vol. 34, no. 6, pp. 405-421, 1997

Authors: Lim, Brian | Bascom, Peter A.J. | Cobbold, Richard S.C.

Article Type: Research Article

Abstract: A simulation model has been developed for red blood cell (RBC) aggregation in shear flow. It is based on a description of the collision rates of RBC, the probability of particles sticking together, and the breakage of aggregates by shear forces. The influence of shear rate, hematocrit, aggregate fractal dimension, and binding strength on aggregation kinetics were investigated and compared to other theoretical and experimental results. The model was used to simulate blood flow in a long large diameter tube under steady flow conditions at low Reynolds numbers. The time and spatial distribution of the state of aggregation are shown …to be in qualitative agreement with previous B-mode ultrasound studies in which a central region of low echogenicity was noted. It is suggested that the model can provide a basis for interpreting prior measurements of ultrasound echogenicity and may help relate them to the local state of aggregation. Show more

Keywords: RBC aggregation, simulation, aggregate size, shear rate

DOI: 10.3233/BIR-1997-34606

Citation: Biorheology, vol. 34, no. 6, pp. 423-441, 1997

Authors: Cloutier, Guy | Qin, Zhao

Article Type: Review Article

Abstract: The objective of the present paper is to provide a detailed review of theoretical, experimental and clinical works aimed at understanding the scattering of ultrasound by red blood cells (RBC). The paper focuses on the role of biofluid mechanics and blood biorheology on the scattering mechanisms. The influence of RBC aggregation on the ultrasound backscattered power is specifically addressed. After a short introduction, the paper presents the theory of Rayleigh scattering and summarizes theoretical models on ultrasound backscattering by RBC. The particle, continuum and hybrid models are presented along with reported packing factors used to consider the orderliness in the …spatial arrangement of RBC. Computer models of ultrasound backscattering by RBC are also presented in this section. In the second section, experimental factors affecting the ultrasound backscattered power from blood are presented. The influence of the volume of the scatterers, ultrasound frequency, hematocrit, orientation of the scatterers, flow turbulence, flow pulsatility, and concentration of fibrinogen and dextran is discussed. The third section focuses on the use of ultrasound to characterize RBC aggregation. Three aspects are reported: the shear rate dependence of the backscattered power, the “black hole” phenomenon, and the kinetics of RBC rouleau formation. The fourth section reports in vivo observations of the “smoke like” echo in mitral valve disease, and blood echogenicity and backscattered power in veins and arteries. In the last section, new areas of research, clinical applications of ultrasound backscattering, and areas of potential future developments are presented. Show more

Keywords: Acoustic backscattering, blood echogenicity, spontaneous echo contrast, red blood cell aggregation, turbulence, power Doppler ultrasound

DOI: 10.3233/BIR-1997-34607

Citation: Biorheology, vol. 34, no. 6, pp. 443-470, 1997