This was asked of me at a recent beach dive meeting. I think it is important to consider lung injury from overexpansion (from uncontrolled ascent) and secondary pulmonary embolism (air in the bloodstream from the insulted lung tissue).
Lung overexpansion injury occurs when a diver holds their breath when ascending underwater. This can be as little as a 1.5 meter ascent near the surface.
How it happens (the technical reason)
When using underwater diving equipment, the diver is breathing compressed air at a pressure equal to that of the water around him. This means that the air entering your lungs is at the same pressure as water. When the diver ascends, according to Boyle’s Law, the air expands due to the reduction in hydrostatic pressure (the shallower the depth, the lower the pressure), causing the lungs to over-inflate.
The lung does not explode like a balloon when over-inflated, but rather ruptures. However, the tear itself is not so much a problem as the resulting air that enters the tissues and bloodstream. The result of such a rupture causes the pulmonary capillaries and alveoli to rupture mixing blood and air in the lungs, which generally causes the diver to cough up blood. (A definite red flag) The rupture can also cause one of four injuries: air embolism, pneumothorax, mediastinal emphysema, and subcutaneous emphysema.
Why it happens (The human factor)
The most common causes of lung overexpansion injury are panic and ignorance. Other less common causes are choking, nausea, carelessness, and even smoking. Smoking can destroy the surfactant that keeps the lungs from closing when they are ventilated. This can cause parts of the lungs to get stuck and appear to hold their breath.
How to avoid
Never hold your breath while wearing scuba gear.
- Never Give a free diver a “puff” of air when using SCUBA gear underwater. The free diver may be unaware of the problem of the lung overexpansion injury and ascend without releasing their breath.
- Avoid diving while you have chest congestion problems (eg colds, flu, etc.).
- Smokers should not smoke for several hours before a dive. (Good luck convincing them of that! NO dive if you are a heavy smoker and have recently had a cold or flu).
- Consult an experienced diving physician before learning to dive, and if you have any injury to your lungs or chest, see the doctor again. What to do The most common and biggest warning sign of a lung overexpansion injury is coughing up blood. Other indications include chest pains and shortness of breath. If you suspect such an injury, see an emergency medical specialist immediately. If you want to know the nitty-gritty more, please message me at a local dive meeting. All that medical school must be used in some way! Tevis
