Lung Overexpansion Injury

Lung damage caused by expanding air that cannot escape during ascent, usually from breath-holding; the reason for scuba's first rule, never hold your breath.

A lung overexpansion injury is pulmonary barotrauma: damage to the lungs caused by gas expanding on ascent faster than it can be exhaled. A scuba diver breathes air at ambient pressure, so a lungful taken at depth contains far more gas molecules than the same volume at the surface. Ascend with a closed glottis and Boyle's law does the rest, the air stretches and ruptures alveoli. It takes surprisingly little: a breath-hold ascent from just 1 to 2 m can be enough.

The escaping gas goes one of several ways, and each is its own injury. Into the arterial blood, it becomes an arterial gas embolism, the most feared outcome. Into the space between lung and chest wall, it collapses the lung as a pneumothorax. Into the middle of the chest or under the skin of the neck, it causes mediastinal or subcutaneous emphysema, felt as voice change or crackling under the skin. Symptoms after any rapid or breath-held ascent, chest pain, breathing difficulty, or neurological signs, mean oxygen, a call to DAN, and evaluation, with hyperbaric treatment if an embolism is involved.

Prevention is the rule drilled into every student from the first pool session: breathe continuously and never hold your breath. It is also why the CESA is taught with a continuous exhale, and why panicked breath-held ascents turn an out-of-air problem into a life-threatening one. Skip diving with respiratory infections too, since congestion can trap air locally in the lungs and produce the same injury even in a diver who is breathing normally.