Hemodynamics of progressive pneumopericardium in the dog.

The hemodynamics of progressive pneumopericardium were studied in 6 anesthetized healthy dogs (with intact thorax). Heart rate, cardiac output, and pericardial and intravascular pressures were recorded. Pressures were measured in the pericardial space by means of a percutaneously introduced, air-filled catheter, and in the right atrium, right ventricle, left atrium, left ventricle, pulmonary artery, and aorta by means of fluid-filled catheters. The gradual increase in mean pericardial pressure up to 11 +/- 2 mm of Hg was associated with increases in heart rate and mean right atrial, mean left atrial, right ventricular end-diastolic, and left ventricular end-diastolic pressures and with decreases in cardiac output and stroke volume, with no change in left ventricular systolic and mean aortic pressures. Critical cardiac tamponade occurred at a pericardial pressure of 12.2 +/- 2.8 mm of Hg, which was produced by 8.7 +/- 1.9 cm3 air/kg of body weight. This was characterized by a sudden marked decrease in heart rate, cardiac output, stroke volume, left ventricular systolic pressure, and mean aortic pressure, and equilibration of mean right atrial, mean left atrial, right ventricular end-diastolic, left ventricular end-diastolic, and pulmonary artery diastolic pressures. These hemodynamic changes were similar to those of experimental pericardial effusion.