A pneumothorax is commonly known as a collapsed lung. Normally, the outer surface of the lung sits next to the inner surface of the chest wall. The lung and the chest wall are covered by thin membranes called pleura. A collapsed lung occurs when air escapes from the lungs or leaks through the chest wall and enters the space between the two membranes (pleural cavity). As air builds up, it causes the nearby lung to collapse.

A collapsed lung is usually caused by an injury to the lungs or chest wall, such as:

A penetrating injury, such as a knife or gunshot wound
Blunt trauma from a fall or car accident
Medical procedures, such as removal of fluid from the pleural cavity with a needle (thoracentesis) or a lung biopsy

Occasionally, a lung will collapse without any direct injury to the lung or chest. This happens when the lung is damaged by diseases such as asthma, cystic fibrosis and pnuemonia. It is particularly common in emphysema, which causes air-filled sacs, called blebs, to form. When one of these sacs bursts, air is released into the pleural cavity, causing the lung to collapse. A spontaneous pneumothorax also can develop in people who don't have any obvious lung disease. It's most common in tall, thin men between the ages of 20 and 40 and is much more common in smokers. Some people who don't have any obvious lung disease have blebs that can rupture and cause this type of spontaneous pneumothorax.

In most cases of pneumothorax, some air can move in and out through the tear in the lung or chest wall. If air can only move into the chest cavity, but not out, a condition called a tension pneumothorax can occur. A growing air pocket causes increased pressure within the pleural cavity. This can cause complete collapse of the nearby lung and can push the heart and major blood vessels to the other side of the chest. This movement, called a mediastinal shift, can cause a life-threatening drop in blood pressure. Tension pneumothorax most commonly occurs in people with penetrating chest injuries. It also occurs in people on ventilators or those who have undergone cardiopulmonary resuscitation.

About 9 of every 100,000 people each year have a lung collapse.

What is a hole in the tyre as compared to five holes in the lungs? =( =(