Influence of mediastinal structures on the esophageal pressure gradient in dogs.

Abstract

The esophageal pressure gradient has been studied in curarized dogs in different body positions. In the upright position, a mean gradient of 0.28 cm H2O/cm is observed. The gradient completely disappears following thoracotomy and collapse of the lungs. Still, in the supine and prone positions, discontinuous pressure variations, already observed in the intact animals, persist after pulmonary collapse. In the various body positions, before as well as after thoracotomy, a positive correlation is observed between pressure in the esophagus and esophageal elastance. This points to an intervention of the mediastinum in the observed positional pressure variations. Fraction or pressure exerted by the mediastinal structure simultaneously modifies esophageal pressure and elastance. Therefore, the esophageal pressure gradient in the upright position seems to be the result primarily of those mediastinal effects. Only in the middle third of the esophagus are the observed positional pressure variations possibly a reflection of the pleural pressure gradient.