Wedge Pressure Measurement in Obstructive Pulmonary Disease

Mean pulmonary capillary wedge absolute pressures relative to atmosphere were compared with effective wedge pressures in 19 patients with respiratory failure secondary to chronic obstructive pulmonary disease to determine whether a mean wedge or effective wedge pressure provided the most useful diagnostic information when intrathoracic pressure changes were great. The effective wedge pressure was determined by subtraction of the esophageal pressure from the measured wedge pressure. In 16 of 19 patients the actual or estimated difference between the mean wedge and effective wedge pressure ranged within ±3 mm Hg. In three patients, however, all with intrathoracic pressure changes of greater than 20 mm Hg, the mean wedge elevated (range=+6 to +17 mm Hg) in relation to the effective wedge pressure. In patients with chronic obstructive pulmonary disease with loss of lung recoil and airways obstruction, a simple mean of the wedge pressure can be elevated secondary to positive intrathorack pressures which are generated during expiration and influence the recorded absolute wedge pressure. However, in most patients, the use of the electrical mean appears to be a useful method to compensate for respiratory fluctuations in wedge pressure.