What event allows air to escape from the pleural space, breaking the vacuum?

• A. Chest wall opened by surgery or chest injury
• B. Submersion in water
• C. Increased atmospheric humidity
• D. Deep inspiration

Answer: (A)

The pleural space normally stays under negative pressure, like a suction that keeps the lung expanded. When the chest wall is opened by surgery or a chest injury, a direct path is created between the atmosphere and the pleural space. Air can move freely in and out, quickly equalizing the pressure with the outside air and eliminating that suction. With the vacuum gone, the lung cannot stay fully inflated and may collapse, which is the situation described by an open pneumothorax. The other scenarios don’t create a doorway between atmosphere and the pleural space, so they don’t break the suction in the same way.