Coronary vascular resistance during halothane anesthesia

To study the effect of halothane on the coronary circulation, the circumflex diastolic coronary vascular resistance was measured in the working heart and total mean coronary resistance (TCR) in the isolated nonworking heart of the dog during administration of 100 per cent oxygen and during administration of 2--3 per cent halothane in oxygen. In the working heart, when the diastolic aortic pressure was kept at a nearly control level, halothane induced decreases of 12 per cent in circumflex diastolic coronary vascular resistance and 18 per cent in left ventricular arteriovenous oxygen content difference and no significant change in diastolic coronary blood flow. This effect occurred in spite of the absence of any significant change of myocardial oxygen consumption. In the nonworking beating, arrested or fibrillating heart, halothane induced a decrease of 24 per cent in total mean coronary resistance. Since the decrease in circumflex diastolic coronary vascular resistance in the working heart connot be attributed to myocardial hypoxia and since the results in the isolated nonworking heart eliminate the influences of mechanical and neurohumoral factors on coronary resistance, it is concluded that the observed decrease in resistance is probably due to vasodilation produced by a direct action of halothane on the coronary vessels. This effect was not modified by beta-adrenergic blockade.