A collapsed lung is often the result of pressure on an airway from outside - a swollen lymph node or fluid between the lining of the lungs and the chest wall, for example - can also cause a lung to collapse.
When the airway is blocked, the blood absorbs the air inside the air sacs (alveoli). Without more air, the sac shrinks. The space where the lung was before the collapse fills up with blood cells, fluids and mucus. It may then become infected.
Other factors can lead to a collapsed lung include:
A plug of mucus, a tumor or something breathed into the lungs.
Abdominal swelling
Experiencing high speeds, such as being a fighter jet pilot
Injuries, such as from a car accident, a fall or a stabbing
Lack of the liquid (surfactant) that coats the lining of the alveoli, which helps keep it from collapsing. This can happen in premature babies or in adults who have had too much oxygen therapy or mechanical ventilation.
Large doses of opioids or sedatives
Lying immobilized in bed
Scarring and shrinking of the membranes that cover the lungs and line the inside of the chest, which can occur as a result of exposure to asbestos
Smoking
Surgery, especially involving the chest or abdomen
Tight bandages
Diagnosis