Your lungs are sponge-like organs that transfer air molecules to and from blood cells. They expand as you inhale, and contract as you exhale. A normal person inhales a few pints of air with every breath, and this is why your buoyancy shifts as you breathe.
As you breathe, the air is pulled into millions of tiny air sacs called alveoli. These microscopic sacs are thin enough to allow air to pass to and from the blood cells that circulate through the lungs.
As you can see, your lungs are a major air space in your body. Fortunately, this air space equalizes automatically as you breathe. However, your lungs are delicate and can easily rupture if they become a closed air space. For this reason, you must never hold your breath when scuba diving. But even taking this precaution, injuries are possible.
This page describes the various type of overexpansion injuries, how they occur, and first-aid treatment to follow.
Causes of Lung Overexpansion Injuries
If the airflow inside your lungs becomes restricted as you ascend, the expanding air can rupture the delicate alveoli inside your lungs. This happens without any warning or sensation, and can occur in as little as 4 feet of water.
The best prevention against lung overexpansion injuries is to never hold your breath. This is why you must exhale small bubbles whenever your regulator is out of your mouth, and the reason you must exhale continuously during an emergency swimming ascent.
Holding your breath isn't the only cause of lung injuries. Chest congestion, scar tissue, lung disease, and damage from smoking can create airflow restrictions that trap air and lead to overexpansion injuries.
Types of Lung Overexpansion Injuries
There are four major types of lung overexpansion injuries, and the type that develops depends on where the expanding air escapes to.
Arterial Gas Embolism
The most serious lung injury is an arterial gas embolism. This occurs when air from the lungs escapes into the bloodstream. As the air expands and forms bubbles, it interferes with blood flow. Without immediate treatment, this injury can lead to death.
A pneumothorax occurs when air enters the space between the lung's two outer linings. As the air expands, it causes the lung to collapse, making breathing very difficult.
Mediastinal emphysema occurs when air escapes the lung and enters the space between your chest and lung. As the air expands, pressure is placed against your lungs, making breathing difficult. The air may also press against the heart or blood vessels and interfere with the circulatory system.
Subcutaneous emphysema begins much like a mediastinal emphysema, but the escaped air travels underneath the skin. This usually occurs around the neck, and results in voice changes, crackling sounds underneath the skin, and difficulty swallowing.
Treating Lung Overexpansion Injuries
Symptoms of lung overexpansion injuries occur immediately, and can include difficulty breathing, chest pain, crackling under the skin, unconsciousness, or death. First aid must begin immediately while transportation to a medical facility is arranged.
First aid for lung injuries includes delivery of 100% oxygen and CPR if necessary. Reputable dive operators keep a supply of oxygen on their boats, and you can receive training for oxygen delivery by enrolling in a rescue diver or oxygen administrator course.
The victim will need treatment in a hyperbaric chamber as soon as possible. During this treatment, the victim is placed in a pressurized chamber to shrink the air bubbles, then slowly decompressed to allow the air to pass out of the body before it expands and interferes with respiration and circulation.