Biorheology - Volume 24, issue 6

Authors: Liepsch, D.W. | Steiger, H.J. | Poll, A. | Reulen, H.-J.

Article Type: Research Article

Abstract: The flow velocities in glass and silastic lateral aneurysm models were quantitatively measured with the non-invasive laser Doppler method. The influences of the elasticity of the wall, the pulse wave and the properties of the perfusion medium on the intra-aneurysmal circulation were investigated. As shown previously, the inflow into the aneurysm arose from the downstream lip and was directed toward the center of the fundus. Backflow to the parent vessel took place along the walls of the fundus. with non-pulsatile perfusion, flow velocities in the center of the standardized aneurysms varied between 0.4 and 2% of the maximum velocity in …the parent vessel. with pulsatile perfusion, flow velocities in the center of the fundus ranged between 8 and 13% of the flow velocity in the axis of the parent vessel. Flow velocities in the aneurysms were slower with a polymer suspension with blood-like properties compared to a glycerol/water solution. Flow velocity measurements near the aneurysmal wall allowed the estimation of the shear stresses at critical locations. The maximum shear stresses at the downstream lip of the aneurysm were in the range of the stresses measured at the flow divider of an arterial bifurcation. The present results suggest that in human saccular aneurysms intra-aneurysmal flow and shear stress on the wall are directly related to the pulsatility of perfusion, i.e. the systolic/diastolic pressure difference and that the tendency to spontaneous thrombosis depends on the viscoelastic properties of the blood, namely the hematocrit. Show more

Keywords: Cerebral aneurysm, laser-Doppler-anemometer, hemodynamics, wall shear stress, viscoelastic fluid, steady and pulsatile flow

DOI: 10.3233/BIR-1987-24621

Citation: Biorheology, vol. 24, no. 6, pp. 689-710, 1987

Authors: Shu, Mark C.S. | Noon, George P. | Hwang, Ned H.C.

Article Type: Research Article

Abstract: A phase-by-phase analysis of local flow patterns at the venous anastomosis of an arteriovenous hemodialysis angioaccess loop graft (AVLG) was made. The study was carried out in an elastic, transparent Silastic in vitro flow model, which duplicates the detail geometry of the AVLG obtained from an animal model (30+ kg dogs with 12 weeks bilateral femoral AVLG implantation). The flow model was installed in a mock pulsatile flow loop system designed to simulate physiological conditions. Flow visualization was made in laser-illuminated flow fields using a high-speed cine camera. Analysis of the high-speed cine indicates there is a distinct separation region …downstream of the anastomotic toe in the median plane and a stagnation region that oscillates along the opposite wall. During inward motion of the vessel wall, accumulation of particles in the separation region and the nearby stagnation region is observed. A large swirl appears in the distal vein during end-systolic period. A double-helical flow pattern occurs further down in the distal vein. Retrograde flow in the distal vein occurs in an “oscillating” manner following each cardiac cycle. Show more

Keywords: arterial-venous loop graft, angioaccess, venous anastomosis, phasic flow patterns, stagnation region, flow separation, swirl, retrograde flow

DOI: 10.3233/BIR-1987-24622

Citation: Biorheology, vol. 24, no. 6, pp. 711-722, 1987

Authors: Shu, Mark C.S. | Noon, George P. | Hwang, Ned H.C.

Article Type: Research Article

Abstract: The phasic velocity field in the vicinity of the venous anastomosis In a hemodialysis angioaccess arteriovenous fistula loop graft (AVLG) is investigated employing a laser Doppler anemometer (LDA) system. Detailed LDA velocity profiles are obtained by sectional survey performed in a transparent, elastic flow model which was fabricated to represent the geometry of the AVLG system under physiological pressure and flow waveforms. The geometry of the flow model was based on a silicone rubber cast obtained from an experimental dog model. In the present study, detailed distribution of velocity profiles is obtained. The distribution of wall shear stress in the …model is computed from the slope of the local velocity profiles near the wall. The relationship between the results obtained by flow visualization and the LDA measurement is discussed. Show more

Keywords: Venous anastomosis, laser Doppler anemometer (LDA), phasic velocity profile, wall shear stress

DOI: 10.3233/BIR-1987-24623

Citation: Biorheology, vol. 24, no. 6, pp. 723-735, 1987

Authors: Oka, Syoten | Nakai, Masatsugu

Article Type: Research Article

Abstract: The optimal geometry of the vascular bifurcation is interpreted on the basis of the principle of minimum work. We consider the energy expenditure due to the viscosity of blood, and that for maintaining the metabolic states of the blood cells and of the vessel wall. It is shown that the optimal radii of the stern and branch vessels and the optimal branching angle are related to two parameters which represent the morphologic and metabolic states of the blood and the vessel wall. In the special case of symmetrical bifurcation, it was found that as the metabolic demand of the vessel …wall becomes more apparent when compared with that of the blood, the branch radius relative to that of the stern takes values of from 0.794 down to 0.758 minimally, and the angle from 37.5° up to 48.7° maximally with respect to the direction of the stern. Show more

Keywords: vascular bifurcation, vessel wall, vessel caliber, branching angle, optimality principle

DOI: 10.3233/BIR-1987-24624

Citation: Biorheology, vol. 24, no. 6, pp. 737-751, 1987

Authors: Yamaguchi, T. | Hanai, S.

Article Type: Research Article

Abstract: An electrochemical surface shear stress measurement was applied to a model of unilateral arterial stenosis. The unilateral stenosis model was made up of a removable stenosis plug, in an electrochemical shear stress measurement test section with 100 cathodes. Three dimensional wall shear stress distribution was measured under steady flow field. At a relatively low Reynolds number, Re=270, there was a characteristic high and low wall shear distribution pattern downstream of the unilateral stenosis. There were also remarkable high shear stress areas on the opposite wall up- and downstream, and both side walls of the stenosis upstream. It was clearly shown …that detailed three dimensional structure of the flow field must be studied in order to correlate it to pathological findings. Show more

Keywords: arterial blood flow, wall shear stress, electrochemical method, stenosis, atherosclerosis

DOI: 10.3233/BIR-1987-24625

Citation: Biorheology, vol. 24, no. 6, pp. 753-762, 1987

Authors: Rakow, A.L. | Chappell, M.L.

Article Type: Research Article

Abstract: A dilute suspension of Spirulina Microalgae is found to exhibit radial migration in laminar flow in a 650 micron vertical tube. As the tube Reynolds number increases, the particles concentrate in a narrower region around the tube axis. When the turbulent regime is approached, the particles disperse as expected.

Keywords: Spirulina, Microalgae, Radial migration, Laminar flow, Tubular pinch

DOI: 10.3233/BIR-1987-24626

Citation: Biorheology, vol. 24, no. 6, pp. 763-768, 1987

Authors: Kössler, A. | Hagmüller, K. | Winkler, R.

Article Type: Research Article

Abstract: Three groups of male Sprague Dawley rats received methimazole without or with Na-thyroxine in drinking water (3 and 0.33 mg T4 /l, respectively) to induce characteristic alterations of their thyroid status (hypothyroid, hyperthyroid, euthyroid). A fourth group served as an untreated control without any additive to the drinking water. With respect to the different thyroid status, the following changes in the blood parameters were found: increasing plasma-T3 -levels caused a reduction in plasma viscosity, in total plasma protein and in α 1 -globulin, but an increase in hematocrit, whole blood viscosity, the number of erythrocytes …and leukocytes, α 2 -globulin and β -globulin. It was concluded that the increase in the plasma viscosity in the hypothyroid status is mainly due to an alteration of the plasma protein pattern, and that the increase in whole blood viscosity in the hyperthyroid rat is a consequence of increased hematocrit. Show more

Keywords: Blood viscosity, blood parameters, hemorheology, hyperthyroidism, hypothyroidism, plasma viscosity, rat

DOI: 10.3233/BIR-1987-24627

Citation: Biorheology, vol. 24, no. 6, pp. 769-774, 1987

Authors: Koyama, T. | Araiso, T. | Ishikawa, M. | Okada, F. | Kobayashi, H.

Article Type: Research Article

Abstract: In an effort to find a method to intensify the rheological destruction of tumor cells, rat fibrosarcoma KMT 17 cells in ascitic form were exposed to rheological stresses in test solutions; modified Eagle medium with EDTA, and phosphate buffer solution without divalent cations or with verapamil. KMT 17 cells were exposed to a uniform shear stress produced by the rotation of a rotating cone plate viscometer for 1 to 2 hours and to the strong deformation by the passage through Nuclepores of 10, 8 and 5 micrometer. KMT 17 cells suspended in the test solutions were more effectively destroyed by …the stresses than those suspended in normal solutions containing divalent cations without any other calcium-suppressing agents. These results suggest that the elimination of divalent cations and/or the block of calcium ion channels of cell membranes intensify the rheological destruction of tumor cells migrating in the circulatory system. Show more

Keywords: Cancer cells, Rheological destruction, divalent cations, EDTA

DOI: 10.3233/BIR-1987-24628

Citation: Biorheology, vol. 24, no. 6, pp. 775-782, 1987

Authors: Winlove, C.P. | Parker, K.H.

Article Type: Research Article

Abstract: The influence on fluid flow of the fixed charge on the surface of capillaries is calculated using the linearised Poisson-Boltzmann equations. The results depend strongly upon the ratio of the capillary radius to the Debye length. At physiological ionic strength, the Debye length is less than 1 nm and electrostatic effects are negligible. In particular, they can not explain the Copley-Scott Blair phenomenon in artificial capillaries. Electrostatic effects can be significant in smaller channels and it is calculated that in intercellular clefts in the capillary endothelium the apparent viscosity of the fluid may increase more than 50%. These effects can …also be important in the flow in the narrow gap between a red cell and the blood capillary wall. Using the Fitzgerald-Lighthill model of this flow and parameters typical of the human microcirculation, the theory predicts that the apparent viscosity in the gap will be increased by about 5%. Show more

Keywords: Capillary blood flow, Streaming potential, Apparent viscosity

DOI: 10.3233/BIR-1987-24629

Citation: Biorheology, vol. 24, no. 6, pp. 783-793, 1987

Authors: Huang, C.R. | Pan, W.D. | Chen, H.Q. | Copley, A.L.

Article Type: Research Article

Abstract: The steady state non-Newtonian viscosity of whole human blood has been widely studied as a function of the shear rate; and used to characterize the blood in various pathological disorders. In our previous studies, we demonstrated that blood is a thixotropic fluid. Its time-dependency and shear rate dependency of rheological behavior can be represented by an equation developed by Huang. Parameters of the equation can be used for the characterization of an individual’s blood. They provide information, such as the kinetic rate constant of breakdown of RBC rouleaux to individual erythrocytes and the relative amount of rouleau formation in the …dynamic equilibrium between rouleaux and individual erythrocytes. In this communication, the thixotropic parameters from blood samples of fifteen apparently healthy human subjects were investigated. When compared to the use of apparent viscosity values for the correlation with a pathological disorder, thixotropic parameters are preferable. The mean values of thixotropic parameters obtained from apparently healthy human subjects provide a base for comparison with the same parameters as obtained from blood samples of patients with certain pathological disorders involving the circulation. Show more

Keywords: Blood thixotropy, erythrocyte rouleaux, hemorheology, Huang thixotropy equation, pathological conditions

DOI: 10.3233/BIR-1987-24630

Citation: Biorheology, vol. 24, no. 6, pp. 795-801, 1987