Lung Overexpansion Injury

The fundamental cause of Lung Overexpansion Injury (LOI) is Boyle's Law, which states that for a fixed amount of gas at constant temperature, pressure and volume are inversely proportional. As a diver ascends, the ambient pressure decreases, causing the air in their lungs to expand. If a diver holds their breath or has an obstructed airway, this expanding air cannot escape. The resultant pressure buildup within the lungs can lead to the rupture of delicate lung tissues.

Even a seemingly small pressure difference can cause significant damage. For instance, ascending just a few metres from 10 metres (33 feet) to the surface causes the air volume in the lungs to double. This rapid expansion, if not adequately exhaled, can tear alveoli and other lung structures, allowing air to escape into surrounding body spaces or into the bloodstream, leading to various forms of barotrauma.

LOI manifests in several distinct ways, each with its own set of symptoms and severity. The most critical is Arterial Gas Embolism (AGE), where air bubbles enter the bloodstream and travel to the brain, causing stroke-like symptoms such as confusion, paralysis, or unconsciousness, often appearing within minutes of surfacing. This is a medical emergency.

Other forms include Pneumothorax, where air escapes into the space between the lung and chest wall, potentially causing lung collapse; Mediastinal Emphysema, where air collects around the heart and trachea, leading to chest pain or difficulty breathing; and Subcutaneous Emphysema, where air collects under the skin, often around the neck or collarbone, causing swelling and a crackling sensation when touched. Early recognition of any of these symptoms is vital for effective treatment.

Preventing Lung Overexpansion Injury on a liveaboard is crucial for a safe and enjoyable dive safari. The primary preventative measure is to always breathe continuously during ascent and never hold your breath. Maintain a slow, controlled ascent rate, no faster than your smallest bubbles, and always perform a safety stop at 5 metres (15 feet) for 3 minutes to allow for off-gassing and controlled ascent.

Furthermore, ensure your dive gear, particularly your regulator, is well-maintained and functioning correctly to avoid free-flowing or hard-breathing issues that might tempt you to hold your breath. On a liveaboard, where multiple dives are common, staying hydrated and well-rested helps maintain overall health, reducing the likelihood of fatigue-induced errors. Should an incident occur, immediately alert the dive crew; they are trained in emergency protocols and can provide initial first aid, including administering 100% oxygen, and coordinating evacuation to the nearest medical facility.

Myth: LOI only happens to beginners or divers who panic. Fact: While holding your breath due to panic or inexperience is a significant risk factor, LOI can affect any diver, regardless of experience level. Equipment malfunctions (e.g., free-flowing regulator), medical conditions (e.g., asthma, mucus plug), or even minor ascents from shallow depths without exhaling can lead to LOI.

Myth: You have to ascend very quickly for LOI to occur. Fact: A rapid ascent significantly increases the risk, but LOI can occur even with a relatively slow ascent if the diver holds their breath. As little as 1-2 metres (3-6 feet) of ascent without exhaling from shallow depths (e.g., 5 metres/15 feet) can be enough to cause lung overexpansion due to the largest proportional change in ambient pressure near the surface.

Myth: If you feel a mild chest pain after a dive, it's probably just muscle strain. Fact: Any unusual chest pain, shortness of breath, or discomfort after a dive, no matter how mild, should be taken seriously as a potential symptom of LOI. It's crucial to seek medical evaluation immediately and inform them you've been diving, as early diagnosis and treatment are critical for positive outcomes.