REGIONAL VASODILATING PROPERTIES OF ISOFLURANE IN STUNNED SWINE MYOCARDIUM

Studies about the coronary vasodilating properties of isoflurane indic ate that this drug induces coronary vasodilation. No work has examined isoflurane-induced vasodilation in known stunned myocardium. This stu dy was conducted to determine isoflurane's coronary vasodilation poten cy in stunned myocardium and to compare the results obtained with norm al myocardium. We determined the vasodilating properties of isoflurane in regionally perfused swine myocardium. Six domestic swine were anes thetized with pentobarbital and fentanyl. The left anterior descending artery (LAD) was cannulated and perfused with blood drawn from the ca rotid artery and passed thorough a membrane oxygenator. LAD arterial f low was controlled by a calibrated roller pump with continuous digital readout, and LAD arterial pressure was measured directly. The anterio r interventricular vein was cannulated and dimension crystals placed i n the LAD-perfused myocardium. Myocardial stunning was induced by redu ction of coronary blood flow (CBF) to 30% of control flow for 20 minut es. One hour after reperfusion, the vasodilatory response to 0%, 1%, a nd 2% isoflurane administered via the membrane oxygenator was determin ed and compared to maximum vasodilatation produced by regional intraco ronary administration of adenosine. Systemic blood pressure and heart rate remained constant throughout the experiment. At 2% isoflurane, sy stolic shortening and regional myocardial oxygen consumption decreased 53% and 17%, respectively. The same concentration increased CBF by 33 % and reduced coronary vascular resistance (CVR) by 25%. One percent i soflurane affected neither CBF nor CVR. Regional coronary administrati on of adenosine produced much greater changes in CBF (+509) and CVR (- 89.5%). We conclude that isoflurane is a mild dose dependent coronary vasodilator in the stunned myocardium. At 1% isoflurane concentration the coronary vasodilating properties of isoflurane are minimal.