Assessment of left ventricular end-systolic pressure-volume relations with an impedance catheter and transient inferior vena cava occlusion: use of this system in the evaluation of the cardiotonic effects of dobutamine, milrinone, Posicor and epinephrine

The end-systolic pressure-volume relation has been postulated as a load-independent measure of cardiac contractility, but has been difficult to measure because of technical problems associated with the serial measurement of intracardiac volume over a physiologic range of ventricular loading conditions. Utilizing a multielectrode impedance catheter to assess continuous, on-line left ventricular relative volume during transient inferior vena cava occlusion, a method is described for determining the end-systolic pressure-volume relation and for assessing changes in this relation secondary to inotropic modulation. In particular, using this method, the relative inotropic properties were determined of four drugs: dobutamine, milrinone, epinephrine and an experimental cardiotonic agent (Ro 13-6438, Posicor). Left ventricular micromanometer pressure and impedance catheter volume were measured continuously in 10 open chest, anesthetized dogs and 14 pigs. Arterial pressure was altered over a range of 20 to 60 mm Hg by brief inferior vena cava constriction. A linear end-systolic pressure-volume relation was observed in pressure-volume diagrams constructed from on-line pressure and impedance catheter recordings. Administration of dobutamine, milrinone and epinephrine resulted in a leftward shift and an increase in the slope of the end-systolic pressure-volume relation as compared with baseline; Posicor did not alter the slope over a range of doses, despite an increase in the cardiac output secondary to arterial vasodilation. Volume changes as measured by the impedance method closely paralleled simultaneous changes in the ultrasonic crystal-determined segment length, and the impedance end-systolic pressure-volume relation slope was reproducible with repeated load-altering maneuvers.(ABSTRACT TRUNCATED AT 250 WORDS)

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