Biorheology - Volume 23, issue 4

Article Type: Editorial

DOI: 10.3233/BIR-1986-23409

Citation: Biorheology, vol. 23, no. 4, pp. I-III, 1986

Authors: Silberberg, Alex | Copley, Alfred L.

Article Type: Editorial

DOI: 10.3233/BIR-1986-23401

Citation: Biorheology, vol. 23, no. 4, pp. 307-309, 1986

Authors: Mizrahi, J. | Maroudas, A. | Lanir, Y. | Ziv, I. | Webber, T.J.

Article Type: Research Article

Abstract: The present study was undertaken with two objectives in view. The first was to distinguish between the “instantaneous” deformation and creep of articular cartilage when subjected to a step loading in unconfined compression. This was done by observing changes in the specimen’s diameter rather than its thickness. The second objective was to investigate experimentally the anisotropic behaviour of cartilage in a compressive loading mode, corresponding to the physiological situation. An apparatus was thus developed and constructed which enabled us to follow the “instantaneous” changes of the surface area of the sample as the latter was being loaded in unconfined compression. …Specimens of human articular cartilage from normal femoral heads and condyles were tested. Full thickness specimens were tested with and without the underlying bone, as well as partial thickness specimens, characterizing the different zones of cartilage. Solutions of different ionic strength were used to vary the osmotic stress and specimens covering a considerable range of proteoglycan concentrations were selected. The effects of hydration and proteoglycan removal on the “instantaneous” deformation were also studied. The “instantaneous” deformation was found to be of a strongly anisotropic nature in all zones. The deformation was always smaller along the Indian-ink prick pattern than at 90° to it, and this effect was most pronounced in the superficial zone of cartilage. The results reveal an analogy with the tensile properties of cartilage and indicate that the collagen network is mainly responsible for controlling the “instantaneous” deformation. The proteoglycans play an indirect role by modulating the stiffness of the collagen network through their osmotic pressure. Show more

Keywords: anisotropy, articular cartilage, instantaneous deformation, unconfined compression

DOI: 10.3233/BIR-1986-23402

Citation: Biorheology, vol. 23, no. 4, pp. 311-330, 1986

Authors: Dintenfass, L.

Article Type: Research Article

Abstract: A project on “Aggregation of Red Cells” has been accepted by NASA in 1977. An automated slit-capillary photo-viscometer has been designed during 1979–1984, and its last version met NASA’s space hazards requirements. The ‘heart’ of instrument is a set of two highly polished glass plates, spaced by a gap of 12.5 micrometers. An original drum-like infusion pump allows utilization of up to eight blood samples. During a sequential process, blood flows through the slit, and then stops to allow formation of aggregates. Micro- and macro-photography is carried out, and 500 photographs are obtained. Blood from normal donors and patients with …history of ischaemic heart disease, colon cancer, juvenile-onset diabetes, hyperlipidaemia, etc., is anticoagulated and adjusted to haematocrit of 0.30 using native plasma. Samples are divided, and infused into the ‘flight’ and ‘ground’ instruments. Prior to experiment temp. is 5°C; temp. during experiment is 25°C. Experiments took place on 24–25 January 1985, on the middeck of space shuttle ‘Discovery’. Subsequent results showed that red blood cells do not change shape under zero gravity; that aggregation of red cells does take place; that aggregates in pathologic blood show morphology of normal rouleaux under zero gravity, while identical blood shows clumps of red cells on the ground. The latter observation suggests that zero gravity might affect cell-to-cell interaction, and perhaps microstructure of the cell membrane. These aspects must remain however tentative till a confirmation by subsequent experiments can be obtained. Show more

Keywords: zero gravity, aggregation of red cells in disease, NASA Space Shuttle, slit-capillary photo-viscometer, rouleaux and clumps of red cells, morphology under zero gravity

DOI: 10.3233/BIR-1986-23403

Citation: Biorheology, vol. 23, no. 4, pp. 331-347, 1986

Authors: Rudraiah, N. | Pal, Dulal | Siddheshwar, Pradeep G.

Article Type: Research Article

Abstract: A generalized dispersion model is used to obtain exact solution for unsteady convective diffusion in the presence of couple stresses. The effect of the couple stress parameter ‘a ’ on the most dominant dispersion coefficient is clearly depicted. The dimensionless mean concentration distribution is obtained as a function of dimensionless axial distance, time and ‘a ’. The results for ‘pure convection’ are also reported. It is shown that the effect of couple stress is predominant only for small values of ‘a ’ and when a → ∞ the flow characteristics tend to their equivalents in Newtonian theory. …The results of Taylor’s dispersion model are recovered as a particular case in the limit τ → ∞ . Show more

Keywords: Couple Stress, Biomechanics, Dispersion, Blood flow

DOI: 10.3233/BIR-1986-23404

Citation: Biorheology, vol. 23, no. 4, pp. 349-358, 1986

Authors: Ku, D.N. | Liepsch, D.

Article Type: Research Article

Abstract: To study the fundamentals of hemodynamics in arteries, the flow parameters: pulsatility, elasticity and non-Newtonian viscoelasticity were considered in detail in a 90°-T-bifurcation of a rigid and elastic model. The velocity distribution 2.5 mm behind the bifurcation in the straight tube was measured with a laser-Doppler-anemometer. The fluid used was an aqueous glycerine solution and a viscoelastic Separan mixture. Flow visualzation studies were done with a sheet of laser light in the plane of the bifurcation. The velocity distribution was measured for both steady and pulsatile flows with a laser-Doppler-anemometer in a backward scattered way. From the velocity measurements the …shear gradients were calculated. Substantial differences were found in the flow behavior of Newtonian and non-Newtonian fluids, especially behind the bifurcation in the main tube, where secondary flows and flow separation started. Also, differences due to the elastic and rigid wall could be seen. Very high shear gradients were found in the flow between main flow and the separation zone which can lead to a damage of the blood cells. Show more

Keywords: 90°-T-junction, elastic models, Newtonian, non-Newtonian fluids, steady and pulsatile flow, laser-Doppler-anemometer, viscoelasticity

DOI: 10.3233/BIR-1986-23405

Citation: Biorheology, vol. 23, no. 4, pp. 359-370, 1986

Authors: Mak, Arthur F.

Article Type: Research Article

Abstract: A biphasic poroviscoelastic theory was used to analyze the unconfined compression creep and stress relaxation of a hydrated viscoelastic tissue. The intrinsic shear properties of the tissue matrix was described by an integral-type viscoelastic constitutive law while the intrinsic bulk property of the matrix was assumed to be linearly elastic. Parametric data were presented to show how the two major energy dissipative mechanisms, namely the interstitial fluid flow and the intrinsic matrix viscoelasticity, may each contribute to the apparent viscoelastic behavior of the whole tissue under unconfined compression. The hydraulic permeability of the tissue was found to enter in only …as a scaling factor for time. Show more

Keywords: Soft Tissues, Hydration, Biphasic Theory, Poroviscoelasticity

DOI: 10.3233/BIR-1986-23406

Citation: Biorheology, vol. 23, no. 4, pp. 371-383, 1986

Authors: Mchedlishvili, George | Varazashvili, Manana

Article Type: Research Article

Abstract: We assessed the red blood cell concentration (by estimating the cell number and hematocrit) in blood samples taken from the rabbit common carotid artery. This parameter was found to be dependent upon the blood flow velocity in the artery: reduction of the velocity to mean 62% of the initial value (100%), produced by partial obstruction of the artery, resulted in the decrease of red cell concentration by 1/4 to 1/7, despite the same systemic arterial pressure level and absence of appreciable changes in the blood taken from the control (contralateral) carotid artery. The relationship of the red cell number and …hematocrit in the carotid artery was linear (r = 0.76). We conclude therefore, that changes in the local blood flow: hematocrit relationship induced by separation of red cells and plasma in vascular bifurcations occur not only in the microvascular beds, but in the entire arterial branching sequence, including the largest arteries. Show more

Keywords: local hematocrit changes, blood flow: hematocrit relationship, red cell separation from plasma in flowing blood, distribution of blood in arterial bifurcations, cerebral blood flow

DOI: 10.3233/BIR-1986-23407

Citation: Biorheology, vol. 23, no. 4, pp. 385-393, 1986

Authors: Liepsch, D.W.

Article Type: Review Article

Abstract: The cardiovascular circulatory system of the human body can be compared with a network of tubes. It consists of a pump and a system of branched vessels. The arteries transport the blood to the periphery in a manner similar to that of a water supply network. It is important to know what kind of forces act upon “fittings”, bends and bifurcations. It is also essential to assess whether the flow is laminar or turbulent, attached or separated. The flow should be optimized in such a manner as to minimize the drop in pressure. This means that no additional pressure loss …due to separation or turbulence should occur, since such losses increase the pump power requirements. The loss appears in heating and acoustic energy. The necessary understanding of blood flow in human vessels is also of great interest to physicians since it is believed that the local flow behavior of blood determines the formation of atherosclerotic plaques. As in tubing systems, deposits in blood vessels are found close to bends and bifurcations. These deposits lead to impaired cerebral circulation and to myocardial infarction. A partial review of recent research into the details of flow behavior (like separation, stagnation and reattachment points) in bends and bifurcations of arterial models is presented. Studies involving steady and pulsatile flow conditions in rigid and elastic models with Newtonian and non-Newtonian fluids are shown here. The most important differences between blood vessels and tubes are discussed. This modern biofluidmechanical approach of detailed flow examination is compared with the more classical hemodynamic approach considering only gross features such as pressure loss coefficients. Show more

Keywords: Biofluidmechanics, laser-Doppler-anemometer, birefringent solution, bifurcation, 90°-T-junction, Newtonian- non-Newtonian fluid, rigid and elastic models, steady and pulsatile flow, arterial blood flow

DOI: 10.3233/BIR-1986-23408

Citation: Biorheology, vol. 23, no. 4, pp. 395-433, 1986