Left ventricular ejection before and after autonomic blockade at rest and during exercise

Left ventricular ejection and filling rates were studied in the normal heart and after pharmacologic denervation with metoprolol and atropine in 8 healthy subjects at rest and during 50% submaximal exercise. Time-activity relations throughout the cardiac cycle were generated by multigated radionuclide cardiography. From rest to exercise, relative ejection time increased by 25% in the normal heart (p < 0.05). After autonomic blockade, time to peak emptying of the left ventricle remained unchanged at rest, but the average ejection rate was reduced at expense of the filling rate. During exercise and blockade, time to peak emptying was slightly prolonged, and the average ejection rate was shortened. Autonomic blockade increased relative ejection time at rest by 25% (p < 0.05) and during exercise by 11% (p < 0.05). These findings indicate that absolute and relative ejection rates of the left ventricle are dependent on an intact autonomic nervous function that serves to shorten the systole and prolong the diastole of the cardiac cycle.