Closing volumes with variations in pulmonary capillary wedge pressure

Increased closing volumes have been documented in patients in whom there was suspected to be early pulmonary edema due to increased pulmonary capillary wedge pressure. However, the relationship between the actual pulmonary capillary wedge pressure and closing volume has not been established. To attempt to define this relationship and to determine whether the closing volume might be a useful indicator of the onset of pulmonary edema, we measured the closing volume in dogs while sequentially increasing the pulmonary capillary wedge pressure by way of a left atrial balloon. We found a small but significant increase in closing volume (p less than 0.01) when a pulmonary capillary wedge pressure of 25 mm Hg was achieved, and it was at this pressure that pulmonary edema would hypothetically be expected to begin.