Intrathoracic pressures and left ventricular configuration with respiratory maneuvers

In 12 dogs, we examined the correspondence between esophageal (Pes) and pericardial pressures over the anterior, lateral, and inferior left ventricular (LV) surfaces. Pleural pressure was decreased by spontaneous inspiration, Mueller maneuver, and phrenic stimulation and increased by intermittent positive pressure ventilation (IPPV) and positive end-expiratory pressure (PEEP). To separate effects due to blood flow, we analyzed beating and nonbeating hearts. In beating hearts, there were no significant differences between changes in Pes and pericardial pressures. In arrested hearts, increasing LV pressure by 8 Torr increased pericardial pressures by only 3.6 Torr. With IPPV and PEEP, increases in Pes and pericardial pressures were equal in live hearts and in low-volume arrested hearts (LV pressure = 4 Torr). In high-volume arrested hearts (LV pressure = 12 Torr), the increase in pericardial pressure over the anterior LV surface was less than Pes, whereas that over the lateral and inferior LV surfaces was the same as Pes. At high LV volume, in arrested hearts pericardial pressures decreased less than Pes during negative pressure maneuvers. In another six dogs, external LV configuration and volume were measured. In beating hearts during spontaneous inspiration, Mueller maneuver, and phrenic stimulation (endotracheal tube open), septal-lateral dimension and LV volume decreased by approximately 3% (P less than 0.05). This was also true for PEEP. In arrested hearts, septal-lateral dimension and LV volume decreased only with PEEP. We conclude that 1) the relationship between Pes and pericardial pressures is complex and depends on LV volume, local pericardial compliance, and the means by which Pes is changed, 2) changes in measured pericardial pressures did not completely explain changes in LV configuration, and 3) during different respiratory maneuvers, different forces account for the same observed changes in LV volume and configuration.