Lung Overexpansion — What It Is and Why It Matters
Lung overexpansion injury occurs when a diver ascends while holding their breath, causing the expanding air in the lungs to rupture lung tissue. Per Boyle's law, a lungful of air at 10 meters doubles in volume by the surface — if the airway is closed, this expansion has nowhere to go and tears the delicate alveolar tissue.
The consequences can include pneumothorax (collapsed lung), mediastinal emphysema (air in the chest cavity), subcutaneous emphysema (air under the skin), and arterial gas embolism (AGE) — the most serious, where air bubbles enter the bloodstream and can cause stroke-like symptoms. This is the primary reason for the cardinal rule of scuba: breathe continuously and never hold your breath.
Frequently Asked Questions
Can lung overexpansion happen in shallow water?
Yes — in fact, the greatest relative pressure change occurs in the first 10 meters (from 2 ATA to 1 ATA, a 50% volume increase). A diver who takes a breath at 5 meters and holds it to the surface can suffer lung overexpansion. The injury can occur in as little as 1 to 2 meters of depth change.
How do I prevent lung overexpansion?
Breathe continuously and never hold your breath during ascent. Even during emergency ascents like a CESA (controlled emergency swimming ascent), you must continuously exhale during the entire ascent. This allows expanding air to escape safely from the lungs.
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