Cardiac Function and Coronary Flow in Chronic Endotoxemic Pigs

Abstract

Abstract

We have reported that myocardial inotropism was depressed in acute and chronic endotoxemia. One possible mechanism for this observation is that endotoxemia reduces myocardial perfusion and indeed, we observed reduced myocardial perfusion in acute endotoxemia. This study tested the hypothesis that reduced inotropism of chronic endotoxemia was accompanied by reduced coronary artery blood flow. Fifteen pigs were equipped with left atrial and ventricular catheters, circumflex coronary and pulmonary artery flow meters, left ventricular pressure transducer, and ultrasonic crystals in the anterior-posterior axis to measure internal short axis diameter by sonomicrometry. The pigs recuperated for 3 days before basal data were collected over the next 3–5 days. After at least 7 postoperative days, an osmotic pump containing Salmonella enteriditis endotoxin was implanted in 12 pigs. Endotoxin was delivered at 10 μg/hr/kg for 2 days, at which time the animals were sacrificed. Osmotic pumps containing sterile saline were implanted in 3 pigs. Eight of the 12 endotoxemic pigs survived; 4 died before the morning of the second day. The survivors exhibited elevated heart rate, peak left ventricular systolic pressure, and cardiac output. Inotropism was evaluated by calculating the slope of the end-systolic pressure-diameter relationship (ESPDR) and % diameter-shortening. ESPDR was significantly depressed on the second endotoxemic day, while % diameter-shortening was depressed on both endotoxemic days. Coronary artery blood flow was significantly elevated on both endotoxemic days, while cross-sectional stroke work was unchanged. Therefore, the ratio of coronary blood flow to stroke work increased on both endotoxemic days. Nonsurvivors exhibited reduced heart rate, cardiac output, peak left ventricular systolic pressure, ESPDR, and % diameter-shortening. Neither coronary artery blood flow nor flow-to-work ratios increased in this group. Sham endotoxemic pigs demonstrated no cardiac or hemodynamic changes over 3 days. These results indicate that depressed inotropism during chronic endotoxemia was not caused by reduced coronary blood flow; rather, the myocardium was relatively overperfused.