Mediastinal emphysema following stab wounds or other trauma of the chest has long been recognized. It has also been described as occurring secondary to violent coughing, bronchial asthma, artificial pneumothorax, pneumonia, difficult labor, straining at stool and other forms of extreme effort. McGuire and Bean1 point out that Laennec2 described grating sounds and bubbling rales during respiration as diagnostic of subpleural and interlobar emphysema. Skoda3 subsequently confirmed these signs, and von Rokitansky4 described the pathologic aspects of the condition. Müller5 noted the presence of bubbling crepitations that occurred with the heart beat and the occasional disappearance of cardiac dulness. He observed that the presence of subcutaneous emphysema aided in making the diagnosis of mediastinal emphysema.
Rees and Hughes6 in a report on wounds of the chest encountered during World War I noted loud "tapping" sounds over the cardiac area in 9 cases of wounds of the left