Biorheology - Volume 32, issue 5

Authors: Thurston, C.B. | Henderson, N.M.

Article Type: Research Article

Abstract: By use of an impedance to quantify the pressure-to-flow relation for a clot-filled tube, a simple model is developed that encompasses both viscoelastic and porous properties of the clot. Measurements over a range of frequencies are used to separate the role of clot permeability from clot matrix elasticity. The theoretical impedance model consists of a series resistance and capacitance (representing structural flow) in parallel with a resistance (representing permeating flow). The viscoelasticity of the matrix, permeability and effective pore size are related to these three impedance elements. The validity of the model has been verified for a range of vessel …sizes approximating small arteries (1 to 3 mm in diameter). The presence of dextran T40 in clotted fibrinogen solutions changes the clot impedance by increasing clot permeability and decreasing clot viscoelasticity. Because the flow contains two components, the behavior of a clot in vivo under pulsatile pressure cannot be predicted from the viscoelastic properties obtained from non-tube flow instruments nor from steady flow permeation measurements; a combination of the two as provided by oscillatory tube-flow measurements is required. Show more

Keywords: Fibrin clots, impedance, permeability, viscoelasticity, rigidity

DOI: 10.3233/BIR-1995-32501

Citation: Biorheology, vol. 32, no. 5, pp. 503-520, 1995

Authors: Kawakami, S. | Kaibara, M. | Kawamoto, Y. | Yamanaka, K.

Article Type: Research Article

Abstract: Coagulation of blood in cultured endothelial cell-coated tubes was examined using a rheological technique. Coagulation of recalcified, platelet-free plasma in contact with an endothelial cell monolayer did not occur within the experimental time period (more than 150 min). The endothelial cell surface did not activate the intrinsic coagulation reaction or the extrinsic coagulation reaction initiated by tissue factor. The time of onset of coagulation in platelet-free plasma supplemented with erythrocytes was nearly the same as that of whole blood (31.2 ± 5.5 min), which was shorter than that for platelet-rich plasma (54.3 ± 14.3 min) and platelet-free plasma supplemented with …granulocytes (58.3 ± 6.3 min). In factor VII-, XI- or XII- deficient, platelet-free plasma supplemented with erythrocytes, the time of onset of coagulation was about 30 min. The coagulation of factor IX-deficient, platelet-free plasma supplemented with erythrocytes, however, did not occur within the experimental time period. These data suggest that activation of factor IX on the erythrocyte surface is capable of activating the intrinsic coagulation system. Show more

Keywords: Blood coagulation, endothelial cell, erythrocyte factor IX, rheometer

DOI: 10.3233/BIR-1995-32502

Citation: Biorheology, vol. 32, no. 5, pp. 521-536, 1995

Authors: Goldsmith, H.L. | Kaufer, E.S. | McIntosh, F.A.

Article Type: Research Article

Abstract: Both chemical and physical effects of red cells are known to play a role in the adenosine diphosphate (ADP)-induced aggregation of human platelets in sheared blood. Using a previously described double infusion technique (Bell et al ., 1989a), we studied the effect of increasing hematocrit from 10 to 60% on the rate and extent of platelet aggregation with 0.2 µM ADP in citrated whole blood undergoing tube flow. Blood and agonist were rapidly mixed in a small chamber and the suspensions flowed through lengths of 1.19 mm-diameter polyethylene tubing at mean transit times <t> from 0.2 to 42.8 s at …a mean tube shear rate <G> = 335 s-l . Effluent was collected into 0.5% glutaraldehyde, the red cells removed by centrifugation through Percoll, and all single platelets and aggregates in the volume range 1–105 µm3 counted and sized using an aperture impedance counter. Both the initial rate (over the first 8.6 s) and the extent of aggregation with time increased with increasing mean hematocrit up to 35.8%, being significantly greater than in citrated plasma (cPRP). However, at 61.5% hematocrit, the extent of aggregation decreased markedly to a level close to that in cPRP. We also studied the effect of washed red cells at 39% hematocrit on the aggregation of washed platelets in Tyrodes-albumin fibrinogen-free suspensions. It had previously been shown that, at <G> ⩾ 335 s-l , washed platelets in platelet-rich Tyrodes (PRT) aggregated with 0.7 µM ADP. We found that red cells markedly increased the extent of aggegation from that in PRT, and promoted the formation of large aggregates, absent in PRT. Spontaneous aggregation in whole blood or washed cell suspensions in the absence of added ADP at <t> = 42.8 s was < 10% of that in the presence of ADP. The results indicate that a physical effect of red cells, likely manifested as an increase in the efficiency of aggregate formation (Goldsmith et al. , 1995), plays an important role at low and normal hematocrits; however, at high hematocrits, particle crowding impedes the formation of aggregates. Show more

Keywords: Platelet aggregation, ADP, tube flow, red cells, hematocrit, fibrinogen

DOI: 10.3233/BIR-1995-32503

Citation: Biorheology, vol. 32, no. 5, pp. 537-552, 1995

Authors: Artmann, C.M.

Article Type: Research Article

Abstract: The Microscopic Photometric Monolayer Technique provides a tool to measure red blood cell (RBC) stiffness (resistance to elongation) and relaxation time. It combines many of the advantages of flow channel studies of point-attached RBCs with the simplicity, sensitivity and accuracy of photometric light transmission measurement. This technique allows the study of the effects of physicochemical factors on the elongation and relaxation time of the same cells within an average of four to five thousand cells adhered as a monolayer to glass. Further, the time course of physicochemical effects on cell membrane and wash-in/wash-out kinetics of interactions can be followed. An …automated version of this technique was developed. A dense monolayer of point-attached RBCs was prepared at the bottom of a flow-chamber. A steady-state flow, with stepwise increases of flow rate, induced the RBC elongation. The light transmission perpendicular through the monolayer plane was measured photometrically. Photomicrographs compared with photometric results showed that the flow-induced bending and curvature change of RBC membrane was associated with the increase of light transmission. There was a linear correlation between the photometric index of elongation and the elongation taken from photomicrographs for shear stresses up to 0.75 Pa. A stiffness parameter, S (in Pa), was defined as the ratio of shear stress and elongation at a shear stress of 0.25 Pa. Following a sudden flow stoppage, the RBCs returned to their resting shape and the RBC relaxation time was measured. The stiffness-relaxation time product, V (in mPas), was calculated to provide an estimate of viscosity. Diamide treatment, known to stiffen RBCs, did result in dose-dependent decreases of elongation and relaxation time. With increasing temperature, the relaxation time decreased at a rate of -2.96 ms/K; the stiffness increased significantly at a rate of 0.0038 Pa/K, and the stiffness-relaxation time product decreased with -2.95 mPas/K, reflecting an inverse relationship between RBC viscosity and temperature. Using the automated version of this technique (Elias-c-) to test RBCs of 36 healthy subjects, we found the inter-individual coefficients of variation to be 8.6% for stiffness, 7.9% for relaxation time and 12.4% for stiffness-relaxation time product. Show more

Keywords: Erythrocytes, membrane, method, deformability, relaxation time, drug

DOI: 10.3233/BIR-1995-32504

Citation: Biorheology, vol. 32, no. 5, pp. 553-570, 1995

Authors: Godin, C. | Violleau, M. | Caprani, A.

Article Type: Research Article

Abstract: Interactions of blood cells (RBCs) with a microelectrode of 50 µm diameter have been examined under flow conditions using impedance measurements at high frequencies. At such frequencies, the electrolyte resistance (Re ) is assimilated to the real part of impedance, and interactions are associated with transient fluctuations of Re , Sedimentation experiments suggest that one erythrocyte contributes to a 1.1% Re increase. Effects of wall shear rate (from 25 to 140 s-1 ) and RBC concentration (from 8.4 × 105 to 2.7 × 106 cells/ml) have been investigated; the number of interactions rapidly decreases with wall shear rate. …Event frequency is proportional to RBC concentration ranging from 3.1 × 106 cells/ml to 1.3 × 107 cells/ml. At high concentrations of RBCs, some transient events overlap. Videotaped images help to determine how many RBCs interact with the microelectrode at the same time on separate surface areas. Under flow conditions, the contribution of one RBC on the Re increase is similar to the mathematical value obtained by sedimentation and decreases slightly with wall shear rate. Show more

Keywords: Blood cells, erythrocyte, shear rate, interactions, electrical impedance

DOI: 10.3233/BIR-1995-32505

Citation: Biorheology, vol. 32, no. 5, pp. 571-587, 1995

Article Type: Correction

DOI: 10.3233/BIR-1995-32506

Citation: Biorheology, vol. 32, no. 5, pp. 589-589, 1995

Article Type: Other

DOI: 10.3233/BIR-1995-32507

Citation: Biorheology, vol. 32, no. 5, pp. 591-592, 1995