Hemodynamic Effects of Pericardial Tamponade. ∗

Abstract

Discussion and conclusions

The increase in pericardial and central venous pressures is sufficient to impede venous return to the right atrium and thereby produces a striking drop in cardiac output (Fig. 2). In addition there is a moderate reduction in heart rate during the first 15 minutes of the tamponade (Fig. 2), which also contributes to the reduction in cardiac output. Despite the increase in total peripheral resistance, the reduced blood flow results in an immediate and marked drop in arterial pressure. This decrease activates the baroreceptor mechanisms producing an increase in heart rate which eventually exceeds the control values. The oxygen consumption drops initially because of the reduced blood flow but recovers during the course of the experiment almost to the control value. Since the recovery of oxygen consumption was greater than that of the cardiac output, the oxygen extraction from the blood must have increased, especially in the constant pressure experiments. Coincident with the onset of the tamponade there is an increase in respiratory rate and minute volume. A comparison of the two series of experiments shows that in the CV experiments, the pericardial and central venous pressures continuously and gradually decline during tamponade, allowing recovery of the reduced cardiac output by approximately 40%. As the cardiac output and arterial pressure recover, the total peripheral resistance also decreases progressively in the CV experiments. By contrast, in the CP experiments the pericardial and central venous pressures remain elevated and the reduced cardiac output and the elevated total peripheral resistance do not change throughout the course of the experiment. The arterial pressure also recovers to a lesser extent in the CP experiments. The decrease in both pericardial and central venous pressures during tamponade may be explained by two possible causes.