Effects of halothane on the intramyocardial pressure of the canine left ventricle.

Abstract

In the intact canine heart a gradient of systolic intramyocardial pressure from a minimum at the epicardial region to a maximum at the endocardial region is well established. No information is, however, available regarding the effects of various anaesthetic agents on this gradient. In the present study the effects of halothane on intramyocardial pressure recorded from subendocardial and subepicardial layers of the canine left ventricular free wall were assessed. Experiments were performed on seven anaesthetised mongrel dogs ventilated with 100% oxygen. Intramyocardial pressure was recorded simultaneously from the inner and outer regions of the myocardium using two Mikro-tip pressure transducers. Halothane concentration in the inspired gas varied from 0% to 2%. In the pentobarbital anaesthetised dog halothane does not significantly change the heart rate. With increasing concentrations of halothane in inspired gas systolic intramyocardial pressure at both endocardium and epicardium decreased significantly from control values. As the halothane concentration increased, the normal differential between systolic left ventricular pressure and endocardial intramyocardial pressure was abolished. The intramyocardial pressure gradient from endocardium to epicardium, however, persisted during systole. During diastole the pressure gradient was reversed, becoming maximum in the epicardial region and minimum in the endocardial region in both control and halothane treated animals. Over the range of 0-2% halothane concentration there was no significant effect on the diastolic intramyocardial pressure gradient. These results suggest that halothane affects the myocardial tissue pressure non-uniformly across the left ventricular free wall and therefore influence sth e transmural distribution of coronary blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)