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Biomedical subjects

G V Seaman

Publications and source records attributed to G V Seaman.

At least 19 recordsLinked to original sources
PubMed1991

Chronic blood hyperviscosity in subjects with acute stroke, transient ischemic attack, and risk factors for stroke.

The origin and significance of blood hyperviscosity in subjects with acute stroke has been controversial. It has been argued that viscous abnormalities simply reflect either elevated hematocrit or an acute-phase response to the stroke itself. To address these issues, we measured the factors that determine blood viscosity in a cross-sectional study of 430 subjects, including 135 with acute stroke, 89 with acute transient ischemic attacks of the brain, 115 with recognized risk factors for stroke, and 91 healthy controls. The at-risk group was balanced with the acute stroke group for types of risk factors and medication usage, and all four groups were balanced for age. The viscosity of whole blood at low rates of shear and the plasma viscosity were significantly elevated in both groups with cerebrovascular symptoms and in the at-risk group compared with the healthy controls. The severity of hyperviscosity was stroke group greater than transient ischemic attack group greater than at-risk group greater than healthy controls. Increased viscosity of whole blood was associated with an elevated plasma fibrinogen concentration and with a decreased albumin/globulin ratio. This study provides evidence that blood hyperviscosity is present not only in subjects with acute brain infarction, but also in those with risk factors for stroke, and that these abnormalities are, to a considerable degree, chronic.

Acute Disease↗
PubMed1990

Membrane active plasma factor in multiple sclerosis: characterization and isolation by recycling isoelectric focusing.

Recycling isoelectric focusing is a rapid, high resolution technique that has the capability of fractionating complex mixtures of proteins on a preparative scale on the basis of their isoelectric points (pIs). For this reason, it appeared to be an ideal tool to further characterize and isolate the surface active plasma component(s) which is abnormal in multiple sclerosis (MS). The normal control and the abnormal MS plasma components, or factors, proved to be stable under the conditions used in this technique, including deionization by electrodialysis, dialysis against distilled water, lyophilization and the presence of 3M urea and carrier distilled water, lyophilization and the presence of 3M urea and carrier ampholytes. The presence or absence of plasma factor activity was determined by incubating red blood cells in a test plasma, or plasma fraction, followed by the determination of the red blood cell electrophoretic mobility in the presence and absence of linoleic acid. Both the normal and MS factor had a pI of 4.0 +/- 0.1 under the conditions used. A high degree of purification was achieved and albumin was eliminated as a possible candidate for the factor(s).

Dialysis↗
PubMed1989

The importance of formaldehyde purity in studies on the electrokinetic charge of human red cells.

Electrokinetic measurements and rheological studies conducted in parallel have previously shown red cell surface charge to play a role in governing aggregative behavior and bulk flow properties of red cell suspensions. For these and other types of model investigations, aldehyde stabilized cells have been widely used. In this communication, the influence of the purity of formaldehyde was investigated. It was found that (a) the direct dissolution of commercially available paraformaldehyde in water or suitably buffered saline results in impure solutions which, if utilized in the fixation of human erythrocytes, produces cells which have significantly different electrophoretic properties from native cells; (b) the basis for the differences is the presence of metallic impurities in some commercially available paraformaldehyde preparations; (c) the impurities and thus the anomalous electrokinetic properties of the fixed cells may be eliminated by generating formaldehyde gas from paraformaldehyde by heating the latter to 203-210 degrees C; (d) alternatively, the impurities may be eliminated by addition of disodium ethylenediamine tetraacetate dihydrate to fixative solutions prepared directly from paraformaldehyde.

Adult↗
PubMed1989

Blood modeling using polystyrene microspheres.

The steady flow viscosity at shear rates 0 to 120 sec-1 and dynamic viscoelasticity at frequencies 0.02 to 0.8 Hz were determined for aqueous suspensions of uniform polystyrene microspheres of 1.0 micron diameter. Rheological properties of the microsphere suspensions were Newtonian for particle concentrations up to 32%. By introducing dextran and calcium chloride into the particle suspensions, non-Newtonian behavior was produced similar to that observed for human blood. The cooperative effects of dextran and calcium ions promoted aggregation of particles at a concentration as low as 12%. Thus, a suspension of uniform sized spherical polystyrene particles in aqueous solution of dextran may be made to mimic blood by controlling the surface charge on the polystyrene spheres using addition of calcium ions to the medium.

Blood↗
PubMed1988

Increased vascular resistance due to a reduction in red cell deformability in the isolated hind limb of swine.

This study investigated whether red cells with reduced deformability impeded flow through the microcirculation. Red cells were made less deformable in their normal biconcave disc shape by incubation with 2% formaldehyde (fRBCs). The blood supply to the right hind limb was isolated in 26 swine and the femoral artery was instrumented with two fine catheters, a flow probe, and an inflatable occluder. Flow was measured over a range of different perfusion pressures during adenosine-induced vasodilation under control conditions (C) and during an infusion of fRBCs at 1 ml/kg per minute (not to exceed 20 ml) into the femoral artery. At the same perfusion pressure (P), flow was significantly reduced 5 min after the fRBC infusion: Flow at P = 20 mm Hg, C = 41 ml/min vs fRBC = 10 ml/min; at P = 40, C = 160 ml/min vs fRBC = 79 ml/min; and at P = 60, C = 278 ml/min vs fRBC = 147 ml/min, with P less than 0.02 for all comparisons. Flow was still significantly reduced 15 min after the fRBCs, but by 30 min, it had returned to the control value. Chromium-51-labeling of red cells revealed that about one-third of fRBCs was trapped in the microcirculation compared to less than 3% of normal cells. This reduction in flow with fRBC infusion was not altered by alpha blockade, indicating that adrenergically mediated spasm was not responsible for the reduced flow. Aspirin 35 mg/kg iv completely prevented the reduction in flow despite an absence of change in the percentage of fRBCs trapped. Thus, red cells with reduced deformability infused into the circulation caused a significant, but transient, reduction in flow. The reduction in flow was not primarily related to entrapment of the abnormal RBCs, but may be mediated through platelet aggregation or release of potent vasoconstrictor substances from platelets or endothelial cells.

Adenosine↗
PubMed1987

Fractionation of K-562 cells on the basis of their surface properties by partitioning in two-polymer aqueous-phase systems.

The K-562 cell line is a culture of human leukemia stem cells originally derived from a patient with chronic myelogenous leukemia in blast crisis. We have subjected such cells, in the log phase of growth, to countercurrent distribution in a charge-sensitive dextran-polyethylene glycol aqueous-phase system, a method that fractionates cells on the basis of subtle differences in their surface properties, and found that: (1) The cell population is heterogeneous since it is composed of cells with different partition ratios. (2) There is a correlation between increasing cell partition ratios and increasing cell electrophoretic mobilities. (3) Cells under different parts of the distribution curve have dissimilar ratios of cells in different parts of the cell cycle, a phenomenon that may, at least partially, be the basis for the subfractionation of these cells. There is a clear tendency for cells in G0 + G1 + early S to decrease and for those in late S + G2 + M to increase with increasing partition ratios. (4) Sialic acid is a major surface charge component of the cells as evidenced by a dramatic drop in their partition ratios after treatment with neuraminidase.

Cell Cycle↗
PubMed1986

Effect of surface modification of rat erythrocytes of different ages on their partitioning behavior in charge-sensitive two-polymer aqueous phases.

Partitioning differences between cells in two-polymer aqueous phase systems originate from subtle differences between the surface properties of cells. Because of the exponential relation between the parameters affecting the partition ratio (P) and the P itself, differences in membrane components suspected of effecting the differential partitioning of closely related cell populations cannot be directly established by conventional chemical assay techniques. In order to study the chemical nature of the components responsible for the age-related changes in surface properties of rat red cells we have devised an approach which uses a combination of isotopic labeling of erythrocyte subpopulations of distinct cell age with different enzyme and/or chemical treatments followed by countercurrent distribution in charge-sensitive two-polymer aqueous phase systems. These studies show that: neuraminidase-susceptible sialic acid is not responsible for the cell age-related surface differences detected by partitioning; the component(s) responsible for the cell age-related surface differences can be extracted (from aldehyde-fixed red cells) with ethanol or cleaved with dilute sulfuric acid. Our data are consistent with the hypothesis that ganglioside-linked sialic acid is the chemical moiety responsible for the cell charge-associated surface differences among rat red blood cells of different ages.

Age Factors↗
PubMed1978

Red cell aging. II. Anomalous electrophoretic properties of neuraminidase treated human erythrocytes.

Desialylation of human red blood cells (RBC) by Vibrio cholerae neuraminidase (VCN) was found to produce cells with electrophoretic properties which were inconsistent with the view of simple loss of N-acetylneuraminic acid (NANA) as the sole effect of VCN treatment. Modification of human RBC with 50--350 U VCN/10(10) RBC for one hour at 37 degrees C releases 90-100% of the NANA and produces a progressive decrease towards zero in their electrophoretic mobilities when measured in 0.15 M NaCl (pH 7.2) at 25 degrees C. The appearance of positive groups on the desialylated cells was indicated by the VCN-treated cells displaying positive mobilities below approximately pH 5.5 and increased negative mobilities at approximately pH 9 as well as substantial increases in their mobility at neutral pH following treatment with formaldehyde. Adsorption of about 95% of the VCN activity at 0 degrees C to the RBC did not produce any significant change in their electrophoretic mobilities thus indicating that the observed changes in the electrophoretic properties of the RBC following VCN treatment could not be attributable to adsorption of VCN. These studies indicate that the cationic charge groups which appear at the electrophoretic surface of the RBC after VCN treatment are probably of endogenous origin. It is suggested that this alteration rather than simple NANA release may operate to shorten the in vivo survival time of desialylated red cells.

Adult↗
PubMed1978

Absence of particle and fiber release from commercial transfusion blood microfilters.

The objective of this study was to evaluate the level of particle or fiber shedding by the five types of commercially available transfusion microfilters (Bentley, Fenwal, Johnson & Johnson, Pall and Pioneer Filters). The study was performed in a class 100 laminar flow clean bench in order to minimize particulate contamination from extraneous sources. Particle-free phosphate buffered saline was flushed through each of 12 filters of each type. The effluent particles or fibers were collected on clean Millipore filters, and their number and size determined by light microscopy and by examination of photographs of the whole Millipore filters. In addition in the case of selected representative particles identification was sought by means of scanning electron microscopy. Small particles in the effluent media were electronically counted. The microfilters did not release significant quantities of particles of fibers greater than 10 micrometer at filtration rates of 300--600 cc/min. No release of any characteristic particles or fibers was observed for any of the filter types. The present study indicates that insignificant levels of particulate matter would be introduced into blood by any of the five types of blood microfilter.

Blood Transfusion↗
PubMed1978

Analytical particle electrophoresis applied to immunologic research.

The technique of analytical particle electrophoresis has been applied to the study of membrane phenomena associated with lectin stimulation of lymphocytes. It has been observed that such treatment results in a significant increase in the electrophoretic mobility of murine T-cells. Moreover, it has been demonstrated that the mobility changes in most cells are attributable to the release of a factor from relatively few cells. Preliminary evidence suggests that the murine factor has a comparatively low relative molecular mass, is heat-labile, and will alter the mobility of cultured human T-cells.

Animals↗