Influence of the mediastinum on the measurement of esophageal pressure and lung compliance in man.

Abstract

The influence of mediastinal organs on esophageal pressure was estimated in man from the variations of esophageal elastance and amplitude of the cardiac oscillations. From the simultaneous measurements of both parameters and of esophageal pressure at different lung volumes and levels in the esophagus, in the sitting and supine positions, using a 3 and 10 cm long ballon, at rest and during exercise, it was concluded: 1. The difference in measured pulmonary compliance with posture is mainly due to a mediastinal artifact, acting primarily at high lung volumes in the sitting position. In the supine position mediastinal loading is more pronounced but does not vary with lung volume (between 10 and 90% of vital capacity). 2. The vertical esophageal pressure gradient is more pronounced in the lower half of the esophagus. It is probably estimated correctly at that level but underestimated at higher levels. Pressure irregularities observed along the esophagus in the supine position are due to local actions of mediastinal organs. 3. The difference in pressure obtained with balloons of different size can be attributed to the influence of the elastic properties of the esophageal wall, provided one takes into account the vertical pressure gradient, and to shifts in the site of pressure recording in the longer balloon. 4. The increase in pressure without change of pulmonary compliance observed during exercise is also a mediastinal artifact. 5. Extrapolation of esophageal pressure towards zero balloon volume successfully corrects for the influence of posture on pulmonary compliance. However, this procedure does not allow for an estimation of intrathoracic pressure in the presence of a marked mediastinal compression effect.