Power Doppler ultrasound scan imaging of the level of red blood cell aggregation: an in vitro study.
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PURPOSE: The purpose of this study was to evaluate the effect of the shear rate on red blood cell (RBC) aggregation with power Doppler ultrasound scanning (PDU), pulsed-wave Doppler scanning, and color Doppler flow imaging. METHODS: Equine and porcine blood were circulated with a steady flow in a phantom with a diameter of 9.52 mm. The color Doppler flow imaging mode was used to estimate the velocity profile and the shear rate across the tube. A transfer function that related the Doppler scan power, measured in gray level with the PDU method, to the power, measured in decibels with the pulsed-wave Doppler scan technique, was used to estimate the echogenicity of blood and the level of aggregation. RESULTS: For the four experiments reported, the power peaked at low shear rates probably because of increased RBC collisions and aggregation and then decreased thereafter because of disaggregation. The largest power variations were measured at shear rates of less than 40 seconds -1. At flow rates that varied between 75 and 500 mL/min, the echogenicity was low near the wall of the tube, increased toward the middle, and decreased at the tube center. The Doppler scan power was uniform across the tube at flow rates of 750 and 1000 mL/min. CONCLUSION: PDU is reliable to quantify the echogenicity of blood and the level of RBC aggregation. In comparison with other methods proposed to measure RBC aggregation, ultrasound scanning is applicable in vivo and may help to improve our basic understanding of the relationship between the hemodynamic of the circulation and RBC aggregation in human vessels. (+info)
The African relapsing fever spirochete Borrelia crocidurae forms aggregates with erythrocytes, resulting in a delayed immune response. Mice were infected with B. crocidurae and monitored during 50 days after infection. Spirochetes were observed extravascularly at day 2 after infection. Two days later, inflammatory responses, cell death, and tissue damage were evident. The pathologic responses in lungs and kidneys were similar, whereas the symptoms in the brains were delayed, with a less pronounced inflammatory response. Microemboli were found in the blood vessels, possibly a result of the erythrocyte aggregation. The B. crocidurae invasion emerged more rapidly than has been described for Lyme disease-causing Borrelia species. In addition to erythrocyte rosetting, the presence of extravascular B. crocidurae indicates a novel route for these bacteria to propagate and cause damage in the mammalian host. The histopathologic findings in this study may explain the clinical manifestations of human relapsing fever. (+info)
Hemorheologic variables in critical limb ischemia before and after infrainguinal reconstruction.
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PURPOSE: Plasma and whole blood viscosity are elevated in patients with intermittent claudication. The objectives of this study were to investigate whether critical limb ischemia influences hemorheologic variables and whether the rheologic variables in blood from the affected limb differ from the general circulation. We also intended to study whether successful infrainguinal reconstruction improved hemorheologic variables. METHODS: Ten consecutive patients with critical limb ischemia (CLI) underwent arterial reconstruction, one patient with profundaplasty and nine patients with bypass procedures. Venous blood was sampled from the antecubital vein (arm) and the femoral vein (leg) of the affected limb 1 day before and 1 month after surgery. Ten control subjects (matched according to age, sex, diabetic status, and renal insufficiency) were also sampled. Whole blood viscosity, plasma viscosity, erythrocyte aggregation tendency, and erythrocyte fluidity (the latter variable describing the deformability of the erythrocytes) were measured by means of rotational viscometry. Erythrocyte volume fraction was also determined. Fibrinogen was measured in the patients with CLI. RESULTS: Erythrocyte fluidity, blood viscosity, and erythrocyte volume fraction were lower in patients with CLI than in control subjects (P <.01, P <.01, and P <.05, respectively). No major differences between cubital and femoral vein blood were seen before or after the operation in patients with CLI or in control subjects. Successful revascularization did not influence the hemorheologic variables, except for a decrease in blood viscosity in femoral vein blood (P <.05). CONCLUSION: Hemorheologic properties was impaired in patients with CLI. Because no differences were seen between the systemic and local circulation and because no major improvement occurred 1 month after arterial reconstruction, other mechanisms besides local tissue ischemia may play a role. (+info)
Kinetics of linear rouleaux formation studied by visual monitoring of red cell dynamic organization.
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Red blood cells (RBCs) in the presence of plasma proteins or other macromolecules may form aggregates, normally in rouleaux formations, which are dispersed with increasing blood flow. Experimental observations have suggested that the spontaneous aggregation process involves the formation of linear rouleaux (FLR) followed by formation of branched rouleaux networks. Theoretical models for the spontaneous rouleaux formation were formulated, taking into consideration that FLR may involve both "polymerization," i.e., interaction between two single RBCs (e + e) and the addition of a single RBC to the end of an existing rouleau (e + r), as well as "condensation" between two rouleaux by end-to-end addition (r + r). The present study was undertaken to experimentally examine the theoretical models and their assumptions, by visual monitoring of the spontaneous FLR (from singly dispersed RBC) in plasma, in a narrow gap flow chamber. The results validate the theoretical model, showing that FLR involves both polymerization and condensation, and that the kinetic constants for the above three types of intercellular interactions are the same, i.e., k(ee) = k(er) = k(rr) = k, and for all tested hematocrits (0.625-6%) k < 0.13 +/- 0.03 s(-1). (+info)
Effects of swimming exercise on red blood cell rheology in trained and untrained rats.
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Red blood cell (RBC) mechanical properties were investigated after swimming exercise in trained and untrained rats. A group of rats was trained for 6 wk (60 min swimming, daily), and another group was kept sedentary. Blood samples were obtained either within 5 min or 24 h after 60 min swimming in both groups. In the untrained rats, the RBC aggregation index decreased to 2.60 +/- 0.4 immediately after exercise from a control value of 6.73 +/- 0.18 (P < 0.01), whereas it increased to 13.13 +/- 0.66 after 24 h (P < 0.01). RBC transit time through 5-microm pores increased to 3.53 +/- 0.16 ms within 5 min after the exercise from a control value of 2.19 +/- 0. 07 ms (P < 0.005). A very significant enhancement (166%) in RBC lipid peroxidation was detected only after 24 h. In the trained group, the alterations in all these parameters were attenuated; there was a slight, transient impairment in RBC deformability (transit time = 2.64 +/- 0.13 ms), and lipid peroxidation was found to be unchanged. These findings suggest that training can significantly limit the hemorheological alterations related to a given bout of exercise. Whether this effect is secondary to the training-induced reduction in the degree of metabolic and/or hormonal perturbation remains to be determined. (+info)
Diameter changes in skeletal muscle venules during arterial pressure reduction.
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Previous studies in skeletal muscle have shown a substantial (>100%) increase in venous vascular resistance with arterial pressure reduction to 40 mmHg, but a microcirculatory study showed no significant venular diameter changes in the horizontal direction during this procedure. To examine the possibility of venular collapse in the vertical direction, a microscope was placed horizontally to view a vertically mounted rat spinotrapezius muscle preparation. We monitored the diameters of venules (mean diameter 73. 8 +/- 37.0 microm, range 13-185 microm) oriented horizontally and vertically with a video system during acute arterial pressure reduction by hemorrhage. Our analysis showed small but significant (P < 0.0001) diameter reductions of 1.0 +/- 2.5 microm and 1.8 +/- 3. 1 microm in horizontally and vertically oriented venules, respectively, upon reduction of arterial pressure from 115.0 +/- 26. 3 to 39.8 +/- 12.3 mmHg. The venular responses were not different after red blood cell aggregation was induced by Dextran 500 infusion. We conclude that diameter changes in venules over this range of arterial pressure reduction are isotropic and would likely increase venous resistance by <10%. (+info)
Influence of erythrocyte aggregation on leukocyte margination in postcapillary venules of rat mesentery.
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The role of erythrocyte (red blood cell; RBC) aggregation in affecting leukocyte (white blood cell; WBC) margination in postcapillary venules of the mesentery (rat) was explored by direct intravital microscopy. Optical techniques were refined and applied to relate the light-scattering properties of RBCs to obtain a quantitative index of aggregate size (G), which, under idealized conditions, represents the number of RBCs per aggregate. WBC margination, defined as the radial migration of WBCs to the venular wall and their subsequent rolling along the endothelium, was measured as the percentage of the potentially maximal WBC volumetric flux within the microvessel lumen (F(WBC)(*)). In normal blood, F(WBC)(*) increased exponentially fourfold, and G increased from 1 to 1.15 as wall shear rates () were reduced from a steady-state value of approximately 600 to <100 s(-1) by proximal occlusion with a blunt microprobe. Enhancement of aggregation by infusion (iv) of dextran 500 (428 kDa), to attain a systemic concentration of 3 g/100 ml, resulted in a four- and sevenfold increase in G and F(WBC)(*), respectively, as was reduced below 100 s(-1). Inhibition of RBC aggregation by infusion of dextran 40 (37.5 kDa) caused F(WBC)(*) to fall to one-half of its steady-state level for < 100 s(-1). Thus it appears that the well-known increase of WBC margination with reductions in is strongly dependent on the occurrence of RBC aggregation. Increasing the extent of RBC aggregation during reductions in also increased the firm adhesion of WBCs to the endothelium because of an enhanced probability of contact between leukocytes and the postcapillary venular wall. (+info)
Tk, a new colon tumor-associated antigen resulting from altered O-glycosylation.
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Erythrocyte polyagglutination antigens T and Tn are truncated O-glycan chains that are also carcinoma-associated antigens. We investigated whether Tk polyagglutination antigen could similarly be a carcinoma-associated marker and a target of immunotherapy. Monoclonal antibody LM389 was raised against Tk erythrocytes and tested by immunohistochemistry. LM389 strongly reacted with 48% human colorectal carcinomas. Labeling of normal tissues was visible on epithelial cells, mainly digestive, but was confined at a supranuclear level. Expression of the antigen on cloned human carcinoma cells correlated with sialosyl-Tn expression. O-Sialoglycoprotein endopeptidase treatment revealed that on carcinomas and cell lines, the epitope was present on O-glycans. Antibody specificity was determined using synthetic carbohydrates. Direct binding and inhibition studies indicated that LM389 best ligands were terminated by two branched N-acetylglucosamine units. Screening of murine cellular cell lines with LM389 allowed development of an experimental model with Tk-positive and -negative cells in syngeneic BDIX rats. Vaccination of rats with Tk erythrocytes provided a protection against growth of rat Tk-positive, but not of Tk-negative, tumor cells in association with the development of antibodies. Taken together, the results indicate that Tk polyagglutination antigen is a new colorectal carcinoma-associated antigen, absent from the normal cell surface, resulting from alteration of O-glycans biosynthesis and with potential as a target of immunotherapy. (+info)