Regular established commercial airlines now fly at a constant minimum altitude of 2,000 feet over the passing terrain. To get over the Rocky Mountains they have to rise to at least 15,000 feet. These high altitudes produce definite and prompt physiologic changes which may profoundly affect any patient with artificial pneumothorax.
In the normal person the pleural cavity between the chest wall and the outer sac of the lung is only a potential cavity; that is, the two surfaces are everywhere in close contact with each other and no actual space exists. The reason for this is evident, as in this potential cavity the pressure is normally negative, that is, less than one atmosphere, while the pressure within the lungs is always the pressure of the outer atmosphere. As the interior of the lungs communicates freely with the outside air through the trachea, glottis and other structures, the two surfaces