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  • 1
    ISSN: 1435-1803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Nach Embolisation des terminalen Strombettes einer Koronararterie ist es möglich, einen peripheren koronaren Druck Ppc und den gesamten Kollateralfluß zu messen. Unter der Voraussetzung, daß Ppc dem Druck am Abgang der Kollateralen entspricht, können die Widerstände folgender Abschnitte des koronaren Gefäßsystems bestimmt werden: Der Widerstand der präkollateralen Gefäße (R1), der Widerstand der Gefäße nach Abgang der Kollateralen (R2) und der Kollateralwiderstand (R3). Die vorliegende Arbeit zeigt, daß dieses einfache Modell aus 3 Widerstände aus einem anatomisch genaueren Netzwerk von Widerständen abgeleitet werden kann. Das Netzwerk setzt sich wie folgt zusammen: Das versorgende Gefäß wird in Abschnitte vor und zwischen dem Abgang von Kollateralen mit den Widerständer r1 und r1i eingeteilt und in den Gefäßabschnitt nach Abgang der letzten Kollateralen mit dem Widerstand r2. Die Abschnitte des von Kollateralen versorgten Gefäßes werden durch entsprechende Widerstände beschrieben. Die Widerstände der verbindenden Kollateralen werden durch n parallel geschaltete Widerstände r3j wiedergegeben. Berechnungen zeigen, daß R3 hauptsächlich durch die Widerstände r3j bestimmt wird, während der Einfluß von r1i von geringerer Wichtigkeit ist. Eine Ânderung von R1 um 50% führt zu einer Ânderung von R3 um weniger als 2%. Ppc stellt den mittleren Druck am Abgang aller Kollateralen dar. Die Kollateraldurchblutung ist abhängig vom Aortendruck, dem kollateralen Widerstand und den Widerständen der Gefäßabschnitte vor und nach dem Abgang von Kollateralen. Ein Vergleich mit Ergebnissen aus Tierexperimenten zeigt, daß das Modell aus 3 Widerständen das Verhalten der erwähnten Gefäßregionen richtig wiedergibt.
    Notes: Summary After embolising the terminal bed of a coronary artery, a peripheral coronary pressure Ppc and the total collateral blood flow can be measured. Assuming that Ppc represents the pressure at the branching off of collaterals, the resistances of the following sections of the coronary vascular bed can be determined: the resistance of the precollateral arteries (R1), the resistance of the vessels behind the start of collaterals (R2), and the collateral resistance (R3). The present study demonstrates that this simple 3-resistances model can be derived from an anatomically more adequate model which consists of a network of vascular resistances. The network model was constructed as follows. The sections of the support vessel before and between the start of collaterals are represented by a resistance r1 and resistances r1i, followed by r2, the resistance of the section after the last collateral. The sections of the ischemic vessel are represented by another series of resistances. Both vessels are connected by collaterals represented by n parallel resistances r3j. Calculations made on this base revealed that R3 is mainly determined by the resistances r3j, whereas the influence of the resistance r1i is of minor importance. A change in R1 of 50% leads to a change in R3 of less than 2%. It is shown that Ppc represents the average pressure at the branching off of all collaterals. Collateral blood flow depends on the aortic pressure, on the collateral resistance, and on the resistances of the vascular regions before and behind the start of collaterals. A comparison with results from experiments on animals showed that the 3-resistances model satisfactorily reflects the behaviour of the mentioned vascular regions.
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  • 2
    ISSN: 1432-1912
    Keywords: Vasodilator agents ; Vascular resistance ; Coronary circulation ; Collateral circulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A method was applied in anesthetized dogs enabling the measurement of regional resistances up to and behind the start of collaterals and the collateral resistance. The studies show that peripheral coronary pressure, i.e. perfusion pressure of the collaterals, can change when the ratio of pre- and post-collateral resistance alters. Drugs can influence collateral blood flow not only by directly effecting the collaterals but also by altering collateral perfusion pressure. Glyceryl trinitrate given in minor doses improved collateral blood flow by directly dilating the collaterals and also by increasing collateral perfusion pressure. Higher doses did not improve collateral flow due to a decrease of collateral perfusion pressure. A stealphenomenon occurred in some cases. Adenosine and verapamil had no direct influence on the collateral resistance. Verapamil given in small doses increased perfusion pressure slightly but not enough to improve collateral blood flow. High doses of verapamil, like low doses of adenosine, had no significant influence on collateral perfusion pressure and collateral blood flow. Adenosine given in high dosage led to a diminution of collateral flow by decreasing collateral perfusion pressure, i.e. a steal-phenomenon.
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  • 3
    ISSN: 1432-1084
    Keywords: Nuclear magnetic resonance ; Magnetic resonance imaging ; Diagnostic imaging ; Trends
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 4
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