How come lungs do not collapse when descending or burst on the way up to the surface?
When a freediver takes a breath at the surface the lungs fill to the ambient pressure at the surface. When the freediver goes underwater, the pressure of the water increases as the freediver goes deeper. This increasing pressure squeezes several air spaces of the freediver. The largest of those air spaces is the lungs. The lungs can compress to a remarkably small size, and due to a “blood shift”, the lungs compress equally instead of flattening, thus preventing them from collapsing. As the diver ascends, the water pressure decreases allowing the air spaces to expand back to their original size upon reaching the surface. If a freediver were to take a breath of air at depth, for example from a scuba tank or a pocket of air, upon ascent that freediver could suffer a fatal lung overexpansion injury. This takes place due to the air in the lungs expanding more than the original volume inhaled at the surface, which could lead to air rupturing the lungs. See Freediving Safety for more informat
