Regional and global myocardial function in the dog when nitrous oxide is added to halothane in the presence of critical coronary artery constriction

The effect of substituting 66% nitrous oxide for nitrogen on global and regional myocardial function before and after critical constriction of the left anterior descending coronary artery (LAD) was studied in six open-chested dogs anesthetized with 1% halothane (inspired). Regional myocardial function was measured in the region of the LAD and in the region of the left circumflex artery using sonomicrometry, and LAD blood flow was measured. Administration of nitrous oxide produced moderate depression of global performance. Regional shortening in both myocardial segments was reduced, and dysfunction also appeared in the LAD segment. This dysfunction was observed in the presence of both normal coronary blood flow, and after critical constriction. The appearance of dysfunction when coronary blood flow was unimpaired suggests that ischemia may not be the only cause of regional myocardial dysfunction.