Biorheology - Volume 31, issue 5

Authors: Tomkiewicz, R.P. | Biviji, A. | King, M.

Article Type: Research Article

Abstract: This in vitro study addressed the question of clearance-related changes in the physical properties of mucous gel simulants (MGS) subjected to oscillating air flow. Delineating some of the possible mechanisms of action for the reported beneficial effects of high-frequency chest compression (HFCC) therapy constituted the rationale. The rheological variables measured were spinnability by filancemeter and viscoelasticity (mechanical impedance, G*, and loss tangent, tan δ ) by magnetic microrheometry. Two derivative parameters, mucociliary clearability index (MCI) and cough clearability index (CCI), were computed from the rheological variables, based on relationships established from model studies of clearance. Two ranges of …air flow oscillation frequencies used previously in animal and clinical studies, i.e. , 12–13 Hz or 22–23 Hz, were applied. The measurements were made after application of oscillating air flow for 15, 30 and 60 minutes, and compared with those at baseline and negative control. A significant decrease in log G* with administration of oscillations was observed (p = 0.06 at 30 minutes, p < 0.01 at 60 minutes, for G* measured at 1 rad/s). Spinnability also decreased by 19.3% and 30.7% after 15 minutes; 32.9% and 41.1% after 30 minutes; 36.4% and 50.5% after 60 minutes, for 12 Hz and 22 Hz, respectively (all significantly different from baseline). There was a positive correlation between viscoelasticity and spinnability, and a negative correlation between spinnability and CCI, but no correlation between spinnability and MCI. Oscillating air flow seemed to act as a physical “mucolytic” that affected mostly the cough clear ability of the mucus simulant. Show more

Keywords: High-frequency oscillation, mucus clearance, rheology

DOI: 10.3233/BIR-1994-31501

Citation: Biorheology, vol. 31, no. 5, pp. 511-520, 1994

Authors: Hashimoto, S.

Article Type: Research Article

Abstract: To control the morphology of a clot formed on an artificial flow path in pulsatile blood flow, the hydrodynamic effect of periodically fluctuating shear rate on clot growth has been quantitatively investigated in vitro . Uniform shear rates were applied to a sample of beagle blood in the concave-convex cones system. These shear rates were sinusoidally fluctuated between a maximum and a minimum in one direction at frequencies between 0.1 and 0.6 Hz. Evaluation of clot growth was derived from a clot ratio, which was experimentally determined from the rate of increase of frictional torque between the two cones. The …results show that clot growth is controlled so as not to occupy a large space when the minimum shear rate is higher than 100 s−1 , or when the time of application of lower (<100 s−1 ) shear rates is modified by the intermittent application of higher (> 500 s−1 ) shear rates as long as the frequency is less than 0.6 Hz. Show more

Keywords: Blood, clot, shear, Couette flow, torque, pulsatile flow

DOI: 10.3233/BIR-1994-31502

Citation: Biorheology, vol. 31, no. 5, pp. 521-532, 1994

Authors: Delfino, A. | Moore Jr., J.E. | Meister, J.-J.

Article Type: Research Article

Abstract: The fluid flow through a tube with an oscillating elliptical cross-section was analyzed in order to understand better the effects of lateral deformation and movement on flow patterns in large and medium-sized blood vessels. Time-dependent elliptical deformation may be caused by external forces, as is the case for the large vessels near the heart, or by lateral movement of the entire compliant vessel, as in the coronary arteries. An analytic, perturbation-type solution was found for the case of fully developed flow in a tube where the cross-section oscillated periodically from an ellipse to a circle. Analytic expressions were found for …all three components of the velocity vector. The effects of the deformation on the axial velocity profile included near-wall fluctuations in velocity that depended on the local wall motion. At higher values of the Womersley parameter, these effects were more pronounced. Secondary flow patterns were established that swirled fluid from the center of the vessel to the walls, then back to the center. It was concluded that these phenomena could be important to flow in the largest vessels, but may not be so important in determining flow patterns in the coronary arteries. Show more

Keywords: Blood flow, deformable tubes, perturbation method

DOI: 10.3233/BIR-1994-31503

Citation: Biorheology, vol. 31, no. 5, pp. 533-547, 1994

Authors: Wang, S.K. | Hwang, N.H.C.

Article Type: Research Article

Abstract: The motion of a single, spherical particle, released at different radial positions at the inlet of the entrance region of a straight circular laminar flow tube (Re = 260), was studied theoretically. Radial migration of the particle, either toward the tube center or toward the tube wall, was predicted. Based on the hypothesis that the particle experienced a lift force which was produced by the vorticity in the boundary layer and a velocity difference between the center of the suspended particle and the fluid medium, an inertia-vorticity fluid dynamic model was formulated to analyze the particle radial motions. Computational flow …dynamics (CFD) solutions obtained from a 9.8 mm diameter tube model included the resulting particle loci for three particle radii (a = 0.1 cm, 0.085 cm, 0.050 cm), with the particle entry at various radial positions. The computation also covered a range of different particle entry speeds. The results showed that the particle migrates toward the tube center if it lags behind the medium in the core region; otherwise, it migrates toward the tube wall. Additional flow experiments were conducted in a circular (2R = 10.2 mm), 300 mm long straight tube. A small polystyrene sphere (2a = 1.72 mm, density ρ p = 1.014 g · cm − 3 ) was released at the inlet (X = 0, η / R = 0.48 ) with two dimensionless release velocities (ω p = 0 , and ω p > 1.0 ). The recorded particle traces agree well with the computational model. Show more

Keywords: Laminar tube flow, entrance region, single particle, radial migration, inertia-vorticity effect, numerical model

DOI: 10.3233/BIR-1994-31504

Citation: Biorheology, vol. 31, no. 5, pp. 549-563, 1994

Authors: Ballyk, P.D. | Steinman, D.A. | Ethier, C.R.

Article Type: Research Article

Abstract: In order to quantify the importance of non-Newtonian blood rheology on anastomotic flow patterns, the characteristics of Newtonian and non-Newtonian blood flows were compared in a 2-D, 45° end-to-side anastomosis model under both steady and unsteady flow conditions. All flows were assumed to be two-dimensional, and were simulated numerically using parameters consistent with blood flow in the femoral artery. A novel, purely viscous constitutive relation, based on a generalized form of the power law relation, was developed to model the non-Newtonian rheology of blood. The resulting wall shear stress patterns indicate that for the parameter values under consideration, non-Newtonian blood rheology …has a significant effect on steady flow wall shear stresses, but no significant effect on unsteady flow wall shear stresses. Based on these and other simulations, a parameter is formulated that gives an indication of the importance of non-Newtonian blood rheology under a given set of flow conditions. In addition, an argument is presented for allowing the conclusions from this two-dimensional study to be extended to three-dimensional blood flow. Show more

Keywords: Blood, end-to-side anastomosis, non-Newtonian, generalized power law model, numerical simulation, finite elements

DOI: 10.3233/BIR-1994-31505

Citation: Biorheology, vol. 31, no. 5, pp. 565-586, 1994

Authors: Muralidharan, E.

Article Type: Research Article

Abstract: A method has been developed to study erythrocyte aggregation parameters based on He-Ne laser light scattering. Laser light is passed through a well mixed sample of blood and the forward scattered light intensity is recorded continuously. The orientation of erythrocytes, formation of aggregates and their sedimentation under the gravitational field produces a variation in scattered light intensity. The amplitude and frequency of light signal fluctuations depend on the size of aggregates and their sedimentation velocity. From the recorded light signal, the different erythrocyte aggregation parameters of interest are simultaneously obtained.

Keywords: Erythrocyte aggregation, laser scattering, aggregate size, sedimentation velocity, aggregation kinetics

DOI: 10.3233/BIR-1994-31506

Citation: Biorheology, vol. 31, no. 5, pp. 587-599, 1994

Article Type: Other

DOI: 10.3233/BIR-1994-31507

Citation: Biorheology, vol. 31, no. 5, pp. 601-602, 1994