Biorheology - Volume 41, issue 1

Authors: Yamamoto, Ei | Iwanaga, Wataru | Yamamoto, Noritaka | Hayashi, Kozaburo

Article Type: Research Article

Abstract: Growth‐related changes in the mechanical properties of collagen fascicles (approximately 300 μm in diameter) were studied using patellar tendons obtained from skeletally immature 1 and 2 months old and matured 6 months old rabbits. Tensile properties were determined using a specially designed micro‐tensile tester. In each age group, there were no significant differences in the properties among cross‐sectional locations in the tendon. Tangent modulus and tensile strength significantly increased with age; the rates of their increases between 1 and 2 months were higher than those between 2 and 6 months. The tangent modulus and tensile strength were positively correlated with …the body weight of animals. However, growth‐related changes in the mechanical properties were different between collagen fascicles and bulk patellar tendons, which may be attributable to such non‐collagenous components as ground substances and also to mechanical interactions between collagen fascicles. Show more

Citation: Biorheology, vol. 41, no. 1, pp. 1-11, 2004

Authors: Pribush, A. | Meyerstein, D. | Meyerstein, N.

Article Type: Research Article

Abstract: The conductance and capacitance of flowing and quiescent red blood cell (RBC) suspensions were measured at a frequency of 0.2 MHz. The results demonstrate that the time‐dependent changes in the conductance recorded during the aggregation process differ in nature for suspensions of short linear rouleaux, branched aggregates and RBC networks. It is shown that the conductance of RBC suspensions measured during the aggregation and disaggregation processes follows the morphological transformations of the RBC aggregates. Thus, this method enables characterization of the morphology of RBC aggregates formed in whole blood and in suspensions with physiological hematocrits both under flow conditions and …in stasis. These results in combination with previous ones suggest that this technique can be used for studies of dynamic RBC aggregation and probably for diagnostic use. Show more

Keywords: Red blood cell, aggregation, morphology, conductance

Citation: Biorheology, vol. 41, no. 1, pp. 13-28, 2004

Authors: Pribush, A. | Meyerstein, D. | Meiselman, H.J. | Meyerstein, N.

Article Type: Research Article

Abstract: A novel experimental approach based on electrical properties of red blood cell (RBC) suspensions was applied to study the effects of the size and morphology of RBC aggregates on the transient cross‐stream hematocrit distribution in suspensions flowing through a square cross‐section flow channel. The information about the effective size of RBC aggregates and their morphology is extracted from the capacitance (C) and conductance (G) recorded during RBC aggregation, whereas a slower process of particle migration is manifested by delayed long‐term changes in the conductance. Migration‐induced changes in the conductance measured at low shear rates (≤3.1 s−1 ) for suspensions of …RBCs in a strongly aggregating medium reveal an increase to a maximum followed by a decrease to the stationary level. The ascending branch of G(t) curves reflects the aggregate migration in the direction of decreasing shear rate. A further RBC aggregation in the region of lower shear stresses leads to the formation of RBC networks and results in the transformation of the rheological behavior of suspensions from the thinning to the thickening. It is suggested that the descending branches of the G(t) curves recorded at low shear rates reflect an adjustment of the Hct distribution to a new state caused by a partial dispersion of RBC networks. For suspensions of non‐aggregating RBCs it is found that depending on whether the shear rate is higher or lower compared with the prior value, individual RBCs migrate either toward the centerline of the flow or in the opposite direction. Show more

Keywords: RBC migration, aggregate morphology, conductivity

Citation: Biorheology, vol. 41, no. 1, pp. 29-43, 2004

Authors: Seki, J. | Satomura, Y. | Ooi, Y.

Article Type: Research Article

Abstract: In order to clarify the phase relationship between velocity pulse and pressure pulse propagating along microvessels, the red cell velocity and intravascular pressure were simultaneously measured in the rat pial arterioles of 41–53 μm in diameter with a high temporal resolution by a laser‐Doppler anemometer and a servo‐null micropressure system. It was found that the velocity pulse preceded the pressure pulse in all the measured arterioles by 18.7–35.6 ms. The corresponding phase difference was 43.6±6.9° (mean ± SD), which is not statistically different from 45°. The value is consistent with the phase difference predicted for the blood flow in microvessels …with a small reflection coefficient at frequencies as low as the heart rate of the rats. The present results suggest that the upstream changes in blood flow are transmitted by the velocity pulse faster than by the pressure pulse in the microvasculature. Show more

Keywords: Pulse wave propagation, phase lag, red cell velocity, micropressure, laser‐Doppler anemometer

Citation: Biorheology, vol. 41, no. 1, pp. 45-52, 2004

Authors: Kameneva, Marina V. | Wu, Zhongjun J. | Uraysh, Arkady | Repko, Brandon | Litwak, Kenneth N. | Billiar, Timothy R. | Fink, Mitchell P. | Simmons, Richard L. | Griffith, Bartley P. | Borovetz, Harvey S.

Article Type: Research Article

Abstract: Over the past several decades, blood‐soluble drag reducing polymers (DRPs) have been shown to significantly enhance hemodynamics in various animal models when added to blood at nanomolar concentrations. In the present study, the effects of the DRPs on blood circulation were tested in anesthetized rats exposed to acute hemorrhagic shock. The animals were acutely resuscitated either with a 2.5% dextran solution (Control) or using the same solution containing 0.0005% or 5 parts per million (ppm) concentration of one of two blood soluble DRPs: high molecular weight (MW=3500 kDa) polyethylene glycol (PEG‐3500) or a DRP extracted from Aloe vera (AVP). An …additional group of animals was resuscitated with 0.0075% (75 ppm) polyethylene glycol of molecular weight of 200 kDa (PEG‐200), which possesses no drag‐reducing ability. All of the animals were observed for two hours following the initiation of fluid resuscitation or until they expired. We found that infusion of the DRP solutions significantly improved tissue perfusion, tissue oxygenation, and two‐hour survival rate, the latter from 19% (Control) and 14% (PEG‐200) to 100% (AVP) and 100% (PEG‐3500). Furthermore, the Control and PEG‐200 animals that survived required three times more fluid to maintain their blood pressure than the AVP and PEG‐3500 animals. Several hypotheses regarding the mechanisms underlying these observed beneficial hemodynamic effects of DRPs are discussed. Our findings suggest that the drag‐reducing polymers warrant further investigation as a potential clinical treatment for hemorrhagic shock and possibly other microcirculatory disorders. Show more

Keywords: Drag‐reducing polymers, hemorrhage, rats, survival, microcirculation, microchannel flow, viscosity

Citation: Biorheology, vol. 41, no. 1, pp. 53-64, 2004