The lungs and chest wall are connected within the chest cavity in such a way that there is tension between the two. Without the lungs, the ribcage would naturally expand. Without the connective tissue between the lungs and chest wall, the lungs would naturally contract or deflate like a balloon. When both are strong enough and healthy enough, the two forces balance each other.
A collapsed lung occurs when the lung separates from the chest wall and contracts. This results in the pleural lining around the lung to fill with air. The air pocket then puts pressure on the lung causing a great deal of pain.
The dark black region on the right side of this CT image clearly shows where the lung has separated from the chest wall. Note the difference between the two lungs. One is fully expanded and fills up the chest cavity, the other is shrunken (i.e. collapsed) and only fills up part of the chest cavity.
In the picture below, the lung on the left has separated from the chest wall. This is confirmed by a CT scan and/or chest X-ray.
In patients with cystic fibrosis, there comes a time when the elasticity and strength of the lungs has deteriorated. The connective tissue has become weakened by frequent lung infections and pneumonia. This typically happens as the disease progresses from moderate to severe.
Symptoms of a collapsed lung:
"Blebs" are a leading cause of collapsed lungs in cystic fibrosis patients. A bleb is a particularly weak or abnormal section of the lining of the lungs that may burst. When this happens, the lung deflates rapidly.
Depending on the severity of the collapse (as determined by CT scan or X-ray) there are different treatments. Although some degree of collapse can resolve itself with the help of supplemental oxygen, there are times when a chest tube must be placed. A chest tube is inserted to allow the air that is accumulating between the lung and the chest wall to flow out. Once the air in the chest cavity is out of the way, the lung can then begin to re-inflate on its own.
The photograph below is of a chest tube that has been inserted to promote re-inflation of the lung.
For more information about pneumothorax, please visit the following site:
Medline Plus Medical Encyclopedia "Pneumothorax"