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Pneumothorax. How does it happen?

Updated: May 27, 2021

The lungs are found within the thoracic cavity. This is the cavity of organs found underneath the ribcage and comprises of the heart, lungs, trachea and greater blood vessels. The pulmonary system is further divided into 2 sub-cavities to understand its function. Each lung (left & right) is suspended within a sealed compartment in the left and right of the chest. The lungs is within a bag-like membrane called the pleural membrane. The pleural membrane is a double folded membrane, the visceral pleura lies against the lung and the parietal pleura against the chest wall. There is a fluid between the visceral and parietal pleural membranes that allows frictionless movement as the chest moves up and out and the diaphragm moves down. The drop in pressure pulls the fluid, the pleural membrane and lung outwards increasing its volume. This in-turn causes the lung to expand inside the chest and air to rush down the trachea.

A pneumothorax occurs when trauma to the chest allows air between the visceral and parietal pleural membranes. This means that when patient’s chest expands under the normal cycle of inhalation, air is drawn in via the site of trauma and collects in the gap. This reduces the volume of the chest and the lung cannot inflate. With each breath this becomes progressively significant. If the trauma site forms a one way valve and air cannot escape during the relaxing of the chest muscles/diaphragm then air builds up forming tension in the pleural cavity. This tension puts pressure on the internal organs. If the pressure is not released and the cavity decompressed then damage to the major organs is likely.

Pneumothorax is a medical emergency. Some individual’s especially tall males can develop spontaneous pneumothorax; others with genetic conditions affecting the connective tissues can also develop pneumothorax.


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