The following experiences and observations concern the effect of variations in mediastinal pressure in the experimental animal. Particular attention has been paid to some of the consequences of mediastinal emphysema.
We use the term "increased mediastinal pressure," as did Jehn and Nissen,1 in the same sense as "increased intracranial pressure."
Irrespective of the mechanism, any serious encroachment on the mediastinum must of necessity produce changes which are either local or general. Such changes may vary and may be dependent on the normal arrangement of the anatomic structures in the region concerned and their resistance to stresses and strains. It is certain that in a closed thorax one structure cannot expand to any great extent except at the expense of another. Air can, of course, escape into the subcutaneous tissues through the jugulum or dissect along fascial planes.
Graham2 has shown that the presence of a liquid, gas or