In a previous study1 it was noted that in the dog an increased intrapulmonic pressure would result in interstitial emphysema, acute pneumothorax, pneumoperitoneum and air embolism. It was found that air injected intrabronchially under increased pressure had little or no effect if a good outlet for it was supplied. If, on the other hand, there was an insufficient outlet or a complete blocking of the outflow of air, the lung expanded when the intrabronchial pressure was raised between 20 and 35 mm. of mercury. When the pressure reached a point between 60 and 100 mm. of mercury, invariably, the dogs showed the syndrome of interstitial emphysema, pneumothorax, pneumoperitoneum and air embolism. These results were obtained in dogs with normal and also with pneumonic lungs.
We have repeatedly noticed that the pulmonary vessels can be emptied easily by increasing the alveolar pressure. In fact, after severing the heart from its connections