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  • 1
    Digitale Medien
    Digitale Medien
    Microrheology and light transmission of blood (1975)
    Springer
    Pflügers Archiv 354 (1975), S. 319-337 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Red Cell Aggregation ; Rouleaux ; Photometry of Blood ; Viscometry of Blood ; High Molecular Weight Dextrans ; Low Molecular Weight Dextrans
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Employing both microscopic and photometric methods the rheology of pathological red cell aggregation was studied in model experiments. Suspensions of washed human red blood cells in dextran solutions containing rising concentrations of dextrans (M.W. 40000, 70000, 110000, 250000, 500000) were used. At low concentrations (〈500 mg-%) of high molecular weight dextrans (〉70000)red cell suspensions formed aggregates similar to the ones found in normal human blood. At higher concentrations, the aggregates were similar to those observed in pathological human blood. The aggregates were studied under the condition of stasis, slow flow and at shear rate of their hydrodynamic dispersion. Besides, the flow behavior of the dispersed cells at high shear rates was studied. We found: 1. In all samples the rate of spontaneous aggregate re-formation in stasis (following hydrodynamic desaggregation) rose with rising dextran concentration up to 5.0 g-%. 2. The shear resistance of the aggregates, as measured by the shear stress necessary to keep them dispersed, rose up to concentrations of 2.5 g-%, but fell at higher concentrations. 3. Only with dextran of a molecular weight above 110000 coarse agglomerates could be produced at high concentrations. Loose elastic meshes were rapidly produced at high concentrations of Dx 70. 4. When subjected to steady state low shear (7 sec−1) only the agglomerates, but not the meshes rapidly grew in size. Most of the aggregation kinetics recorded by photometry and microscopy evaded detection by viscometry.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00587850
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  • 2
    Digitale Medien
    Digitale Medien
    Red cell aggregation in blood flow (1976)
    Springer
    Journal of molecular medicine 54 (1976), S. 149-157 
    Details
    ISSN: 1432-1440
    Schlagwort(e): Blutrheologie ; arterielle Verschlußkrankheiten ; Diabetes mellitus ; Myelom ; photometrische Aggregometrie ; Rouleaux-Bildung ; Rouleaux-Klumpen ; Rouleaux-Netzwerke ; scheinbare Blutviskosität ; Schwangerschaft ; Apparent blood viscosity ; arterial vascular disease ; blood rheology ; diabetes mellitus ; myeloma ; photometric aggregometry ; pregnancy ; rouleaux clumps ; rouleaux formation ; rouleaux networks
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Summary The rheological behavior of normal and pathological red cell aggregates in viscometric flow (artificial flow in cone plate chamber) is studied by direct microscopy, (rheoscopy) viscometry and photometry. Marked differences between normal and pathological blood are measured in the microrheological properties of red cell aggregates; only discreet differences are measured by blood viscometry (macrorheology). Both in normal and abnormal blood, red cell aggregation is a reversible process in the presence of adequate shear forces; their respective influences on apparent blood viscosity at low rates of shear are complex functions of shear rate, shear time, hematocrit and plasma viscosities. Pathological red cell aggregation (RCA) forms more rapidly and extensively than normal RCA. The pathological aggregates frequently have a tendency to grow at low rates of shear and they are highly shear resistant.
    Notizen: Zusammenfassung Das rheologische Verhalten von normalen und pathologischen Erythrocytenaggregaten in viskometrischer Strömung (künstliche Strömung in Platte-Kegel-Kammer) wird mittels direkter mikroskopischer Beobachtung (im „Rheoskop“), Viskometrie und Photometrie untersucht. Erhebliche Unterschiede finden sich bei dem mikrorheologischen Verhalten, während im makrorheologischen Verhalten (Blut-Viskometrie) nur diskrete und oft komplexe Differenzen zwischen normalen und pathologischem Blut gemessen werden. Sowohl im normalen wie im pathologischen Blut ist die Erythrocytenaggregation ein reversibler Prozeß, vorausgesetzt, daß ausreichende Scherkräfte vorhanden sind. Der Einfluß der normalen und pathologischen Aggregate ist eine komplexe Funktion des Schergrades, der Scherzeit, des Hämatokritwertes und der Plasmaviskosität. Pathologische Erythrocytenaggregate bilden sich schneller und extensiver aus als normale Aggregate. Sie haben oft eine Tendenz, bei langsamer Strömung zu wachsen und sind hochgradig scherungsresistent:
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01468879
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  • 3
    Digitale Medien
    Digitale Medien
    Red cell aggregation in blood flow (1976)
    Springer
    Journal of molecular medicine 54 (1976), S. 159-167 
    Details
    ISSN: 1432-1440
    Schlagwort(e): Blutrheologie ; Fahraeus-Effekt ; Rouleaux-Klumpen ; Rouleaux-Netzwerke ; scheinbare Blutviskosität ; scheinbare relative Blutviskosität ; Viscosimetrie ; Apparent blood viscosity ; blood rheology ; Fahraeus-effect ; relative apparent blood viscosity ; rouleaux clumps ; rouleaux networks ; viscometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Summary The apparent viscosity of blood strongly increases at low shear in rotational viscometers, this phenomenon is based on the reversible formation of red cell aggregates. The magnitude of this increase strongly depends on the hematocrit value, on plasma viscosity and lastly on the microrheological properties of the aggregates. The independent measurement of the microrheological behavior and the effects on viscosity allows a detailed analysis of the hemodynamic effects of red cell aggregates under defined flow conditions in vivo. The comparative analysis shows that the conventional viscometry strongly underestimates the rheological differences between normal and pathologically intensified aggregation. Based on detailed analysis under defined flow conditions in vitro, the biological significance of viscometric results and the hemodynamic relevance of red cell aggregates are discussed.
    Notizen: Zusammenfassung Die scheinbare Viskosität des Blutes steigt bei langsamer Scherung in Rotationsviskosimetern durch die reversible Bildung von Erythrocytenaggregaten sehr stark an. Das Ausmaß des Viskositätsanstiegs hängt jedoch wesentlich von dem Hämatokritwert, daneben von der Plasmaviskosität und schließlich von den mikrorheologischen Eigenschaften der Aggregate ab. Die unabhängige Messung der mikrorheologischen Eigenschaften und des Viskositätsverhaltens erlaubt die detaillierte Analyse des hämodynamischen Effektes von Erythrocytenaggregaten unter definierten Fließbedingungen in vitro. Die vergleichende Analyse zeigt, daß die konventionelle Viskosimetrie die rheologischen Unterschiede zwischen normaler und pathologisch gesteigerter Aggregation eindeutig unterschätzt. Basierend auf der detaillierten Analyse unter definierten Bedingungen in vitro werden die biologische Bedeutung von viskometrischen Befunden und die hämodynamische Relevanz von Erythrocytenaggregaten abgehandelt.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01468880
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  • 4
    Digitale Medien
    Digitale Medien
    Microrheology and light transmission of blood (1972)
    Springer
    Pflügers Archiv 333 (1972), S. 126-139 
    Details
    ISSN: 1432-2013
    Schlagwort(e): Blood Photometry ; Blood Viscosity ; Red Cell Aggregation ; Red Cell Deformation ; Red Cell Orientation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The well known flow dependence of the optical density of whole blood was studied by measuring light transmission of blood in viscometric flow. A cone-plate chamber (3° cone angle) was transilluminated (λ=500–800 nm) while under shear (0–460 sec−1). The transmitted light was monitored with a selenium barrier layer photocell and was continuously recorded. In an identical chamber, the microrheological behaviour of the cells in flow was monitored by microphotography and then correlated to photometric events. Light transmission of human blood showed a biphasic behaviour when plotted as a function of shear rate: between 0 and about 60 sec−1, the light transmission decreases with shear, corresponding to aggregate dispersion. Above 60 sec−1, an increase of light transmission with shear occurs, corresponding to red cell deformation, alignment, and orientation. Bovine blood, which does not form aggregates, shows minimum light transmission at rest. Light transmission then rises progressively with shear from the very onset of slow flow. Equine blood (equus zebra) which has very strong aggregation shows a progressive decrease of light transmission with shear due to aggregate persistence up to 460 sec−1. Amphibia blood (rana esculanta) shows very pronounced increase in light transmission at low shear rates, but no progression with shear. The nucleated amphibia erythrocytes are oriented but not deformed in flow. Rigidified cells which neither aggregate nor become oriented in flow show no flow dependent changes in light transmission. It became evident that in all blood samples minimum light transmission was recorded when the cells were dispersed and randomly oriented; both aggregation and orientation produced increased light transmission. These results explain earlier controversies in the literature, they shed doubt on the existence of a “tubular pinch effect” in whole blood rheology.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00586912
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