Biorheology - Volume 32, issue 4

Authors: Yamamoto, R.

Article Type: Research Article

Abstract: The effects of pressure and temperature on water conductivity were examined in okra stem segments. Segments were incubated in various concentrations of sorbitol solution at various temperatures. Water was found to pass mainly through the lateral side of the segments. The shrinkage rate was found to be proportional to the difference in the water potential between the inside of the cells and the ambient solution, while the rate was inversely proportional to the viscosity of water, which is a function of temperature. The nature of the media for water conductivity was found to be consistent with Darcy’s law and with …Hagen-Poiseuille’s law with a rough approximation. An attempt was made to estimate the size of the water path. Okra stem segments were incubated with and without the plant hormone auxin before transference to sorbitol solution. Shrinkage rates of segments showed that auxin caused an increase in water conductivity and thus the size of the water path. Show more

Keywords: Auxin, cell wall, okra hypocotyls, pressure, temperature

DOI: 10.3233/BIR-1995-32401

Citation: Biorheology, vol. 32, no. 4, pp. 421-430, 1995

Authors: Marquart, M. | Jamieson, A.M. | Blackwell, J. | Gerken, T.

Article Type: Research Article

Abstract: Rheological methods have been used to investigate the intermolecular interactions of porcine submaxillary mucins (PSM) in solution. PSM is a high molecular weight glycoprotein consisting of a linear, semi-flexible protein backbone to which a large number of oligosaccharides (1–5 saccharide units) are attached as side chains. Concentrated aqueous solutions of PSM containing different amounts of guanidine hydrochloride (GdnHCl) were subjected to both controlled stress and controlled strain rheological analyses. In the absence of GdnHCl, PSM solutions exhibit viscoelastic properties characteristic of a gel: the storage modulus, G ′ , is much larger than the loss …modulus, G ″ , at all deformation frequencies, and the compliance is 100% recoverable at small stresses, indicative of strong intermolecular interactions. In 3.0 M aqueous GdnHCl, PSM forms a viscoelastic solution, with G ″ > G ′ at all frequencies and a relatively small recoverable compliance, pointing to disruption of the intermolecular interactions by the chaotropic salt. Intermediate behavior is observed in 1.5 M GdnHCl, characteristic of a marginal gel: G ′ ≈ G ″ and greater than 50% recoverable compliance. In dilute solution, PSM behaves viscoelastically as a typical polyelectrolyte. However, concentrated solutions are turbid, the turbidity decreasing as GdnHCl is added, indicating that extensive intermolecular association accompanies the gelation process. The results show that although PSM is secreted in nature as a viscous solution, it can form gels that are similar to those of tracheobronchial and gastric mucins, and suggest common features to the gelation mechanism, with the strength of the gel correlated with the length of the oligosaccharide side chains. Show more

Keywords: Gel, mucin, viscoelasticity

DOI: 10.3233/BIR-1995-32402

Citation: Biorheology, vol. 32, no. 4, pp. 431-446, 1995

Authors: He, X. | Ku, D.N.

Article Type: Research Article

Abstract: The local geometry of a bifurcation has been hypothesized to be a potential geometrical risk factor for the development of atherosclerosis. While flow division and branch area ratios clearly affect the flow field, the importance of the flow divider shape is not as clear. A fast spectral element computational fluid mechanics (CFD) solver was used to simulate flow through 900° T-bifurcations with three different flow divider shapes. Other factors, such as flow partition, area ratio, and bifurcation angle, were kept constant. A Reynolds number range of 15 to 350 was studied to bracket experimental results in the literature. The variation in …the sharpness of the corners had a dramatic effect on both the flow field and wall shear stress distribution in the side branch, but little effect on the flow in the main tube. The magnitude of reverse velocities and wall shear stress in the side branch increased linearly over a physiological range of Reynolds number and corner shape. This paper verifies the accuracy and usefulness of spectral element CFD in studying three-dimensional hemodynamics. Show more

Keywords: Bifurcation flow, shear stress, bifurcation corner, flow divider, sharpness, hemodynamics

DOI: 10.3233/BIR-1995-32403

Citation: Biorheology, vol. 32, no. 4, pp. 447-458, 1995

Authors: Cohen, M.I. | Wang, D.-M. | Tarbell, J.M.

Article Type: Research Article

Abstract: In vitro experiments were conducted to measure the oscillatory flow pressure gradient along an elastic tube in order to assess the recent nonlinear theory of Wang and Tarbell. According to this theory, in an elastic tube with oscillatory flow, the mean (time-averaged) pressure gradient cannot be calculated using Poiseuille’s law. The effect of wall motion creates a nonlinear convective acceleration, and an induced mean pressure gradient is required to balance the convective acceleration. The induced mean pressure gradient depends on the diameter variation over a cycle, the pulsatility and unsteadiness of the flow, and the phase difference between the …pressure wave form and the flow wave form. The amplitude of the pressure gradient also depends on these parameters and may deviate significantly from Womersley’s rigid tube theory. A flow loop was constructed to produce oscillatory flow in an elastic tube. Flow wave forms were measured with an ultrasonic flow probe, and ultrasonic diameter crystals were used to measure wall movement. A special device for pressure drop measurement was constructed using Millar catheter tip transducers to obtain both forward and backward pressure drops that were then averaged. This averaging method eliminated the static error of the pressure transducers. The pressure-flow phase angle was varied by clamping a distal elastic section at various locations. Pressure gradients were obtained for a range of phase angles between -55° and +49°. The mean and amplitude of the measured pressure gradient were compared to theoretical values. Both positive and negative induced mean pressure gradients were measured over the range of phase angles. The measured pressure gradient amplitudes were always lower than predicted by Womersley’s rigid tube theory. The experimental means and amplitudes are in good agreement with the elastic tube theoretical values. Thus, the experiments verify the theory of Wang and Tarbell. Show more

Keywords: Blood flow, pressure gradient, elastic artery, wall motion, phase angle, wave reflection

DOI: 10.3233/BIR-1995-32404

Citation: Biorheology, vol. 32, no. 4, pp. 459-471, 1995

Authors: Rachev, A. | Greenwald, S.E. | Kane, T.P.C. | Moore Jr., J.E. | Meister, J.J.

Article Type: Research Article

Abstract: The variation of wall stress distribution with age in the thoracic and abdominal aortas of normotensive rats was studied. Dimensions of the zero-stress configurations were measured at the ages of 4, 8, 12, 20, and 52 weeks. Using data from previously published inflation tests, the circumferential stress-strain relationship was obtained in each age group. The calculated stress distribution showed that the average circumferential stress remained practically constant after the age of 20 weeks. The circumferential stress at the innermost part of the arterial wall was greater than the stress at the outermost part, but the difference was maintained at a …moderate level with adjustments in the zero-stress configuration. It is speculated that, after the age of 20 weeks, changes in arterial geometry and rheological properties tend to maintain a constant stress distribution under varying conditions of loading. This distribution was achieved by enhanced growth at the inner part of the media in comparison with the growth at its outer margins and suggests that during development and maturity, the growth of the aorta is modulated by circumferential stress. Show more

Keywords: Aging, zero stress state, stress distribution

DOI: 10.3233/BIR-1995-32405

Citation: Biorheology, vol. 32, no. 4, pp. 473-485, 1995

Authors: Chen, S. | Gavish, B. | Zhang, S. | Mahler, Y. | Yedgar, S.

Article Type: Research Article

Abstract: The morphology of red blood cell (RBC) aggregates was studied by direct visualization of RBC aggregation at different flow conditions in a computerized image analyzer. The aggregate morphology is expressed by an Aggregate Shape Parameter (ASP), defined as the ratio of the aggregate projected area to its square perimeter. Aggregation was induced by either dextran-70 (m.w. 70,000) or dextran-500 (m.w. 500,000), and compared to that in plasma. It was found that the aggregate morphology is a characteristic of the aggregating agent—in dextran-500, the RBC form rouleau aggregates as in plasma, while in dextran-70, they form clusters. In each system, while …maintaining the overall typical morphology, the ASP decreases (i.e. , the aggregate becomes longer) as the aggregate size is increased. The distribution of the ASP as a function of the aggregate size remains unchanged when the aggregate size is changed by modulation of the dextran concentration or the shear stress. Stretching of a rouleau aggregate by application of shear stress is reflected by a corresponding change in the ASP. It is suggested that the ASP is a characteristic of intercellular interactions. A theoretical model is proposed for evaluation of the deviation of aggregate shape from that of rouleau structure. Show more

Keywords: Erythrocyte rheology, computerized image analysis, aggregate morphology, aggregate size distribution

DOI: 10.3233/BIR-1995-32406

Citation: Biorheology, vol. 32, no. 4, pp. 487-496, 1995

Article Type: Correction

DOI: 10.3233/BIR-1995-32407

Citation: Biorheology, vol. 32, no. 4, pp. 497-497, 1995

Article Type: Announcement

DOI: 10.3233/BIR-1995-32408

Citation: Biorheology, vol. 32, no. 4, pp. 499-499, 1995

Article Type: Other

DOI: 10.3233/BIR-1995-32409

Citation: Biorheology, vol. 32, no. 4, pp. 501-502, 1995