Mediastinal emphysema occurs when air escapes the lung and enters the space between your chest and lung. As the air expands, pressure is placed against your lungs, making breathing difficult. The air may also press against the heart or blood vessels and interfere with the circulatory system.

Subcutaneous emphysema begins much like a mediastinal emphysema, but the escaped air travels underneath the skin. This usually occurs around the neck, and results in voice changes, crackling sounds underneath the skin, and difficulty swallowing.