Brandi, a female from the Internet asks on February 7, 2005,
Can air in the pleural cavity cause the lungs to expand more fully than they normally would?
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Air in the pleural cavity has a name, pneumothorax. It results in the lungs becoming smaller, not larger. If the amount of air is large, it is known as a "tension pneumothorax" and it can be life threatening. Paramedics these days carry a special needle device to release the pressure in tension pneumothorax cases. Doctors use what is called a "chest tube", which is basically a plastic tube about the diameter of your thumb which is inserted (after appropriate local anesthesia) between two ribs into the pleural space. Gentle suction is applied to re-expand the collapsed lungs.
Lungs are normally expanded when breathing in by the diaphragm and the intercostal muscles that move the ribs. There is normally a negative pressure of about 5 centimeters of water in the pleural cavity. The negative pressure in the pleural cavity means that the volume of the lungs increases as the diaphragm goes down and the rib cage moves up. When the diaphragm and intercostals relax, the natural tendency of the lungs to shrink makes the lungs get smaller. They are like a big, springy sponge that was stretched apart and they recoil to their smaller size.
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