Physiology: Lung over expansion

Physiology: Lung over expansion

Today we are going to talk about lung over expansion injuries and how to treat them. The trend these days is to disregard the issue and believe it only happens to others going deep. Unfortunately, this is a myth. DCS and DCI can occur from only ten meters depth and you, as a going to be Scuba Instructor or Divemaster, need to know how to identify them and how to treat them.

Let’s have a look at the lungs. In general, the divers’ lungs inflate to normal volume when using scuba. If the diver ascends while holding a breath or has a blockage, during ascent expanding air can rupture the lungs. This can cause different lung over expansion injuries. They either occur alone or, in a very serious case, all 4 of them together.

Arterial gas embolism or air embolism

This is the most serious form of lung over expansion injuries. It occurs when the alveoli and pulmonary capillaries rupture, allowing air to enter the bloodstream. This results into Arterial blockage as air bubbles block anywhere in your bloodstream. Once those bubbles travel up your the carotid arteries they cause Cerebral Air embolism and result in dizziness, unconsciousness, paralysis and death. This is one of the most serious diving injuries possible.


A collapsed lung results from air forcing itself in-between the chest wall and the lung (pleural cavity), deflating the lung while air bubbles are escaping. Symptoms include chest pain, coughing up blood and painful breathing.

Mediastinal Emphysema:

Air from a ruptured lung can form in the centre of the chest on the top of the heart pressing against it. This can result in symptoms like fainting, shortness of breath due to the pressure on the heart.

Subcutaneous Emphysema:

This occurs when air from the lung rupture accumulates in soft tissues around the neck and armpits. This results in a feeling of fullness around those areas, change in voice and colour of the skin that crackles when touched. It can occur together with mediastinal emphysema.

Practical approach first aid:

All forms of lung over expansion injuries are categorised as DCI. Use First aid techniques as you already learned in your EFR and rescue course. Basically get the injured diver as fast as possible out of the water, call Emergency Medical services and/or DAN and provide emergency oxygen. Treat the patient for shock, and try to get to the next hospital or medical professional as quick as possible as time is critical with these types of injuries. Even if you are not sure which of the four it is, always treat a patient like it is the worst scenario.

Like for DCS it will require some recompression, so it would be handy to have dive profiles and a small accident report ready for medical professionals to arrange further treatment.

Thanks for reading and stay tuned for our next topic on Physiology in Joe’s Gone Diving’s Classroom for IDC and Divemasters: Decompression Sickness.

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