Biorheology - Volume 29, issue 4

Authors: Verdugo, Pedro | Silberberg, Alex

Article Type: Announcement

DOI: 10.3233/BIR-1992-29401

Citation: Biorheology, vol. 29, no. 4, pp. iii-iii, 1992

Authors: Chiarelli, P. | Basser, P.J. | DeRossi, D. | Goldstein, S.

Article Type: Research Article

Abstract: A hydrogel strip relaxes when it is stretched. The decay in tensile stress can be ascribed primarily to strain-induced swelling of the polymer network—a result that follows from a continuum model of the gel-solvent system. An equation of motion and a linear constitutive law of the polymer network, Darcy’s law, and the conservation of mass of the network and interstitial fluid are solved with boundary and initial conditions appropriate for a stress-relaxation experiment. This model predicts that the time constant of decay depends inversely upon the square of the thickness of the sample. This result is confirmed by experiments. In …addition, the network shear modulus, μ , bulk modulus, k, and hydraulic permeability, 1/f, which are estimated by non-linear regression, all agree with measurements obtained using other methods. Show more

Keywords: Continuum model, poroelasticity, viscoelasticity, material properties, hydrogel, estimation

DOI: 10.3233/BIR-1992-29402

Citation: Biorheology, vol. 29, no. 4, pp. 383-398, 1992

Authors: Papenfuss, H.D. | Gross, J.F. | Yokota, S.D.

Article Type: Research Article

Abstract: The present work is a mathematical model of the fluid filtration in the glomerular network occurring in snakes. The model is based on the differential form of Starling’s hypothesis and takes into account the angioarchitecture of the network and the behaviour on the microrheology of blood with nucleated red cells. The model predicts the hemodynamics and the transvascular fluxes in each vascular segment within the network. The model is applied to a vascular network of the glomerulus of the garter snake. A value of 0.593 μ m/(s·mmHg) was determined for the hydraulic conductivity of the glomerular capillaries using the geometrical …data of the network together with experimental data for the pressures and the blood flow rate reported in the literature. The analysis shows that the local filtration rates cover a wide range. In some of the vascular segments, the filtration leads to such a high increase in colloid-osmotic pressure that the level of the transvascular hydrostatic pressure difference is reached. Mathematical simulations of the variation of the glomerular blood flow rate due to vasoactivity of preglomerular arterioles show the effect on the filtration rate and the hemorheologic parameters. Show more

Keywords: Filtration, glomerulus, network model, snake, microhemorheology

DOI: 10.3233/BIR-1992-29403

Citation: Biorheology, vol. 29, no. 4, pp. 399-410, 1992

Authors: Matsumoto, Takayoshi | Kawai, Masahiro | Masuda, Toshiro

Article Type: Research Article

Abstract: Steady flow properties were measured at various concentrations for aqueous systems of alginates with different mannuronate/gluronate (M/G) ratios using a cone-plate type rheometer. The flow curve (a plot of shear stress vs . shear rate) shows a plateau region, which is ascribed to a heterogeneous structure, at low shear rate. This plateau region is more noticeable in the G-rich systems than in the M-rich systems. On the other hand, the flow curves for the systems with the same molecular weight but different M/G ratios are congruent in the high shear rate region. The zero shear viscosity can be reduced by …the segment contact parameter, cMw , for the alginates with the same M/G ratio but different molecular weights. The zero shear viscosity is proportional to cMw in a low concentration region and is proportional to (cMw )3.4 at relatively high concentrations. The critical value of cMw for which the zero shear viscosity changes from proportionality with cMw to proportionality with (cMw )3.4 is ca. 900. Show more

Keywords: Alginate, polysaccharide, steady flow property, heterogeneous system, zero shear viscosity

DOI: 10.3233/BIR-1992-29404

Citation: Biorheology, vol. 29, no. 4, pp. 411-417, 1992

Authors: Liepsch, Dieter | Singh, Megha | Lee, Martin

Article Type: Research Article

Abstract: We studied the flow behavior under steady flow conditions in four models of cylindrical stenoses at Reynolds numbers from 150 to 920. The flow upstream of the constrictions was always fully developed. The constriction ratios of the rigid tubes (D) to the stenoses (d) were d/D = 0.273; 0.505; 0.548; 0.786. The pressure drop at various locations in the stenotic models was measured with water manometers. The flow was visualized with a photoelasticity apparatus using an aqueous birefringent solution. We also studied the flow behavior at pulsatile flow in a dog aorta with a constriction of 71%. The flow …through stenotic geometries depends on the Reynolds number of the flow generated in the tube and the constriction ratio d/D. At low d/D ratios, (with the increased constriction), the flow separation zones (recirculation zones, so-called reattachment length) and flow disturbances increased with larger Reynolds numbers. At lower values, eddies were generated. At high Re, eddies were observed in the pre-stenotic regions. The pressure drop is a function of the length and internal diameter of the stenosis, respective ratio of stenosis to the main vessel and the Reynolds numbers. At low Re-numbers and low d/D, distinct recirculation zones were found close to the stenosis. The flow is laminar in the distal areas. Further experiments under steady and unsteady flow conditions in a dog aorta model with a constriction of 71% showed similar effects. High velocity fluctuations downstream of the stenosis were found in the dog aorta. A videotape demonstrates these results. Show more

Keywords: Flow visualization, stenoses, arterial model, birefringent solution, constriction

DOI: 10.3233/BIR-1992-29405

Citation: Biorheology, vol. 29, no. 4, pp. 419-431, 1992

Authors: Lorenzi, G. | Böhm, G.M. | Guimarães, E.T. | Costa Vaz, M.A. | King, M. | Saldiva, P.H.N.

Article Type: Research Article

Abstract: The relationship between mucus rheologic variables and in vitro ciliary transport was investigated in mucus samples collected from the upper airways of 30 Wistar rats. In vitro mucus transportability was determined by means of the frog palate preparation. Rheologic evaluation was done by measuring the rigidity modulus (log G ∗ , representing the vectorial sum of viscosity and elasticity) and the loss tangent (tan δ , i.e. the ratio between viscosity and elasticity) at 1 and 100 radian/s using a magnetic microrheometer. The correlation between the rheologic variables and in vitro …mucus transportability was made by stepwise multiple linear regression analysis, with frog palate transport rate considered as the dependent variable. A significant relationship was obtained between the rheologic parameters (log G* and tan δ ) measured at 1 radian/s and the frog palate transport ratio. The relative speed of mucus samples was related to rheology according to the following relationship: rat / frog speed ratio = 1.666 − 0.434 log G ∗ − 0.331 tan δ , for G* and δ determined at 1 radian/s (multiple r = 0.666, p < 0.001). Transport rates predicted from the above formula gave a satisfactory fit to those observed in a second set of 30 rats. The present results indicate that the overall mucus impedance, as well as the ratio between viscosity and elasticity, are important in determining the efficiency of clearance. In addition, it was shown that measurements performed by applying relatively low frequency deformations are preferable for predicting ciliary transport. Show more

Keywords: Mucociliary clearance, mucus viscoelasticity, biorheologic matching

DOI: 10.3233/BIR-1992-29406

Citation: Biorheology, vol. 29, no. 4, pp. 433-440, 1992

Article Type: Other

DOI: 10.3233/BIR-1992-29407

Citation: Biorheology, vol. 29, no. 4, pp. 441-442, 1992