Chest
Volume 66, Issue 6, November 1974, Pages 628-632
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Wedge Pressure Measurement in Obstructive Pulmonary Disease

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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.

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MATERIALS AND METHODS

The 19 patients studied had been admitted to the Jefferson Davis Hospital intensive care unit because of acute exacerbations of chronic obstructive pulmonary disease with respiratory failure. All patients fulfilled the American Thoracic Society criteria5 for obstructive pulmonary disease and had airways obstruction on pulmonary function testing with the percent of forced vital capacity expired within the first second (FEV1 percent) of 20 percent to 60 percent. Their ages were from 42 to 77

RESULTS

Respiratory fluctuation in wedge pressure tracings could be minimized and in some cases eliminated by electrical subtraction of the esophageal pressure (Fig 1). The magnitude of the total change in esophageal pressure and the total change in wedge pressure correlated well (Fig 2). The intrathoracic pressure changes of groups 1 and 2 are shown in Table 1. Four patients were able to produce marked intrathoracic pressure changes by voluntary hyperventilation, and despite great fluctuations of the

DISCUSSION

In patients with severe obstructive pulmonary disease intrathoracic pressure can influence the recording of intracardiac and wedge pressures. Experimentally, pulmonary artery and vein pressures have been shown to parallel changes in intrathoracic pressure when there are positive pressures and within limits negative pressures.8 If marked, we feel these intrathoracic changes may result in elevated mean wedge values relative to atmosphere. Since the pressures in the heart and pulmonary veins are

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The opinions expressed herein are those of the authors and cannot be construed as reflecting the views of the Navy Department or of the Naval Service at large.

Manuscript received March 8; revision accepted May 10.

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