Juxtacardiac pressure in closed-chest dogs

We studied pressure (Ppc)-volume (Vpc) relationships of the pericardial sac by inserting air into it at constant end-diastolic heart volume in six dogs. The lungs were inflated by positive alveolar pressure while pleural pressure was monitored using the esophageal balloon technique. Ppc-Vpc relationships were measured at transpulmonary pressures (PL) of 30, 10, and 5 cmH2O in each of three states: closed chest, open chest with lung separation, and open chest with the pericardium dissected free of its mediastinal attachment. Ppc in the closed-chest condition was more positive than Ppc in the open chest with lung separation, with increase of Vpc and PL, which suggests that the lungs compress the pericardium. Ppc in the open-chest condition with lung separation was also more positive than Ppc in the pericardium after it was dissected free, which suggests that mediastinal attachment compresses the pericardium. It is suggested that lungs in the closed-chest condition as well as mediastinal attachment reduce the heart expansion by a similar magnitude.