Intracoronary propofol does not decrease myocardial contractile function in the dog
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The intravenous administration of propofol is associated with a considerable decrease in arterial blood pressure. The present study was undertaken to test the hypothesis that myocardial function is not affected by propofol and therefore does not contribute to the hypotensive effect of this anaesthetic agent. Propofol was administered in anaesthetized, open-chest dogs by direct arterial infusion into the left anterior descending coronary artery (LAD). Mean arterial blood pressure, heart rate, left ventricular pressure, dP/dt, regional lactate and oxygen extraction, as well as coronary blood flow were measured. Diastolic function was determined by calculation of the time constant of isovolumetric relaxation from the left ventricular pressure measurement and dP/dt. Contractility was evaluated by measuring regional systolic shortening in an area of the myocardium supplied by the LAD. This was compared with systolic shortening in the distribution of the circumflex (CIRC) artery and with the effects obtained with the intracoronary administration of thiopentone. Intracoronary infusions of propofol and thiopentone did not produce any change in systemic arterial blood pressure, heart rate, or left ventricular end diastolic pressure. Propofol, at a concentration of 5 or 10 micrograms.ml-1 did not decrease systolic shortening in the area perfused by the LAD while thiopentone (40 micrograms.ml-1) reduced systolic shortening by 33% (P < or = 0.05). Neither drug had an effect on systolic shortening in the CIRC area, LAD blood flow or diastolic function. The results of this study suggest that propofol does not have an effect on myocardial contractility. The hypotension associated with the intravascular administration of propofol is more likely due to either a direct vascular or a central effect.
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