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ZusammenfassungMonoextrakte aus den Blättern des Ginkgobaumes (Ginkgo biloba L.) werden zur Behandlung von peripheren und zentralen Durchblutungsstörungen sowie bei nachlassender intellektueller Leistungsfähigkeit eingesetzt. Der Spezialextrakt EGb 761 wird in einem standardisierten, vielstufigen Produktionsverfahren gewonnen. Ziel des Herstellungsprozesses ist neben der Anreicherung aktiver Inhaltsstoffe die weitgehende Entfernung von Substanzen mit unerwünschten Eigenschaften. Die experimentellen Befunde zeigen, daß dieser Extrakt pharmakologische Effekte auf alle wesentlichen, an der Blutversorgung beteiligten Komponenten ausübt. Auf der Gefäßebene bewirkt EGb 761 eine Steigerung der lokalen Durchblutung, beeinflußt den Arterienund Venentonus, vermindert eine erhöhte Kapillarpermeabilität und stimuliert die endotheliale Prostazyklinsynthese. Die Wirkungen auf das Blut umfassen unter anderem eine Verbesserung der rheologischen Eigenschaften, eine Stabilisierung der Erythrozytenmembran und die Hemmung PAF-vermittelter Reaktionen. Im Gewebe erhöht EGb 761 die Hypoxietoleranz, besitzt antiischämische Eigenschaften, verbessert den Energiemetabolismus und schützt vor Radikalinduzierten Schädigungen durch Hemmung und Neutralisierung von freien Radikalen.
ZusammenfassungMonoextrakte aus den Blättern des Ginkgobaumes (Ginkgo biloba L.) werden zur Behandlung von peripheren und zentralen Durchblutungsstörungen sowie bei nachlassender intellektueller Leistungsfähigkeit eingesetzt. Der Spezialextrakt EGb 761 wird in einem standardisierten, vielstufigen Produktionsverfahren gewonnen. Ziel des Herstellungsprozesses ist neben der Anreicherung aktiver Inhaltsstoffe die weitgehende Entfernung von Substanzen mit unerwünschten Eigenschaften. Die experimentellen Befunde zeigen, daß dieser Extrakt pharmakologische Effekte auf alle wesentlichen, an der Blutversorgung beteiligten Komponenten ausübt. Auf der Gefäßebene bewirkt EGb 761 eine Steigerung der lokalen Durchblutung, beeinflußt den Arterienund Venentonus, vermindert eine erhöhte Kapillarpermeabilität und stimuliert die endotheliale Prostazyklinsynthese. Die Wirkungen auf das Blut umfassen unter anderem eine Verbesserung der rheologischen Eigenschaften, eine Stabilisierung der Erythrozytenmembran und die Hemmung PAF-vermittelter Reaktionen. Im Gewebe erhöht EGb 761 die Hypoxietoleranz, besitzt antiischämische Eigenschaften, verbessert den Energiemetabolismus und schützt vor Radikalinduzierten Schädigungen durch Hemmung und Neutralisierung von freien Radikalen.
Blood flow in microvessels differs significantly from that of red blood cells (RBC) flowing through long, straight glass tubes in vitro. The in vivo situation is characterized by the presence of plasma favoring aggregation, by the irregular geometry of vessel segments, and by frequent branching points. Here, a method is presented to characterize flow patterns in microvascular blood flow during intravital microscopy based on Fourier analysis of recorded light intensity patterns. The interpretation of the resulting power spectra in terms of pattern size distribution was validated by model experiments employing artificial textures and by reverse transformation of idealized spectra. The determined size of RBC flow patterns in microvessels ranged from approximately 8 microm in capillaries to approximately 14 microm in vessels of >30 microm. With increasing shear rate above approximately 100 s(-1) pattern size increased, possibly reflecting formation of short-lived flow clusters. Below approximately 100 s(-1) an increase of pattern size with decreasing shear rate was found in experiments using local occlusion and treatment with high-molecular-weight dextran, suggesting the formation of aggregates. The dynamic process of generation and destruction of RBC flow patterns could well contribute to flow resistance in vivo in peripheral vascular beds.
Resistance to blood flow through peripheral vascular beds strongly influences cardiovascular function and transport to tissue. For a given vascular architecture, flow resistance is determined by the rheological behavior of blood flowing through microvessels. A new approach for calculating the contribution of blood rheology to microvascular flow resistance is presented. Morphology (diameter and length), flow velocity, hematocrit, and topological position were determined for all vessel segments (up to 913) of terminal microcirculatory networks in the rat mesentery by intravital microscopy. Flow velocity and hematocrit were also predicted from mathematical flow simulations, in which the assumed dependence of flow resistance on diameter, hematocrit, and shear rate was optimized to minimize the deviation between measured and predicted values. For microvessels with diameters below %z40 ,um, the resulting flow resistances are markedly higher and show a stronger dependence on hematocrit than previously estimated from measurements of blood flow in narrow glass tubes. For example, flow resistance in 10-am microvessels at normal hematocrit is found to exceed that of a corresponding glass tube by a factor of =4. In separate experiments, flow resistance of microvascular networks was estimated from direct measurements of total pressure drop and volume flow, at systemic hematocrits intentionally varied from 0.08 to 0.68. The results agree closely with predictions based on the above-optimized resistance but not with predictions based on glass-tube data. The unexpectedly high flow resistance in small microvessels may be related to interactions between blood components and the inner vessel surface that do not occur in smooth-walled tubes. (Circ Res. 1994;75: 904-915.) Key Words * blood viscosity * peripheral resistancemicrovascular networks * pressure drop * hematocrit E arly in the 19th century direct measurements of arterial and venous blood pressure by Jean Leonard Marie Poiseuille12 revealed that the pressure drop in the circulation occurs mainly in the peripheral vascular bed (the microcirculation), which consists of large numbers of tiny vessels. The microcirculation is therefore the site of most of the resistance to flow, which depends on the architecture of the microvascular network and on the rheological behavior of blood flowing through it. Information about bulk rheological properties of blood has been obtained using rotational viscometers. The findings of such studies, including the nonlinear increase of viscosity with increasing hematocrit and with decreasing shear rate,3-5 have strongly influenced the interpretation of physiological and pathophysiological behavior of the peripheral circulation.However, knowledge of the bulk material properties of blood does not provide a sufficient basis for understanding blood flow through narrow cylindrical tubes. In tubes with diameters >1 mm, the measured apparent viscosities correspond to bulk values from rotational viscometry, but a marked reduction of viscosity is...
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