Über die Abhängigkeit der Strophanthinwirkung auf den myokardialen Sauerstoffverbrauch vom Funktionszustand des Herzens
On the basis of some divergent observations concerning the action of cardiac glycosides on the myocardial oxygen consumption, it was suggested that the direction and the magnitude of this effect might be dependent on the experimental conditions and on the functional state of the hearts. Further characterization of this dependence was expected from measurements of the oxygen consumption of isolated guinea pig hearts working under different, well defined hemodynamic conditions. The hearts were perfused with Tyrode solution (37° C, carbogen saturated) and the mean aortic pressure (30 mm Hg) and the stimulation frequency (180/min) were kept constant.
In one series of experiments the venous filling pressure was fixed at 10 cm H2O and the end-diastolic pressure, the cardiac output, the coronary flow, and the oxygen consumption were measured. Ouabain (5 × 10−8 g/ml) caused an increase in cardiac output and a decrease in end-diastolic pressure, but did not significantly influence the coronary flow and the oxygen consumption. This result, however, is not conclusive because of the simultaneous and opposite change of two parameters (cardiac output, end-diastolic pressure) known to be involved in the regulation of the myocardial oxygen consumption.
In another series of experiments the cardiac output was kept constant (30 ml/ min), in addition to frequency and mean aortic pressure, and the changes in the aforementioned parameters were studied. Under these conditions the external cardiac work remained unchanged, only the end-diastolic pressure varied depending on the contractile ability of the particular heart muscle preparation. In both groups the oxygen consumption was increased with increasing end-diastolic pressure but the values for the ouabain-treated preparations were consistently higher than the corresponding control values at the same end-diastolic pressure. The maximum rate of rise in pressure development (dp/dt) showed an analogue dependence on the end-diastolic pressure. A combined analysis of all these data indicated that the myocardial oxygen consumption under all conditions studied was determined only by the magnitude of the maximum rate of rise of pressure development.
Because of the dependence of this parameter on the end-diastolic pressure (besides the direct influence of ouabain) it is conceivable that the effect of ouabain on the myocardial oxygen consumption is dependent on the hemodynamic conditions that is on the degree of sufficiency. Therefore, different effects of ouabain on myocardial oxygen consumption (increase, reduction, no change) may result at different functional states of the myocardium. The possible involvement of other factors determining the myocardial oxygen consumption under the influence of cardiac glycosides is briefly discussed.
Key-WordsHeart Muscle Ouabain Oxygen Consumption Hemodynamic Parameters kg]De|Schlüsselwörter Herzmuskel Strophanthin Sauerstoffverbrauch Hämodynamische Parameter
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